Monday, October 31, 2011

Well Motivated Particles By Intrinsic Spin, Particularly Glueballs

All known fundamental particles have intrinsic spins of 1/2 (fermions) or 1 (bosons), although a hypothetical graviton would have an intrinsic spin of 2 (making it a boson), and a hypothetical Higgs boson would have an intrinsic spin of 0.

All known hadrons (composite particles made of quarks) have two quarks (mesons) or three quarks (baryons). Mesons are bosons which come in pseudoscalar (spin 0), or vector (spin 1) varieties. Baryons come in spin 1/2 and spin 3/2 varieties. The only stable hadrons are protons and bound neutrons, both of which have spin 1/2.

There is some evidence of pairs of mesons bound into a "molecule" although it isn't entirely clear if the concept of intrinsic spin applies to this system. Unitary tetraquarks and pentaquarks (as opposed to "molecules" of two mesons, or of baryons and mesons) have been theorized but not observed.

There is also a theoretical variant on a hydrogen atom in which a antimatter version of a charged lepton takes the place of a proton, such as muonium. A number of other "exotic atoms" have been conceived.

This leaves some hypothetical loose ends.

I've discussed before the possibilty of a particle made of two neutrinos of different flavors and opposite matter/antimatter status bound by the Z boson mediated weak force into a "molecule". If this functioned as a composite particle, these would be pseudoscalar spin 0 particles (and like kind neutrinos would repel each other rather than bind, preventing the formation of the analog to spin 1 mesons), but it isn't clear that intrinsic spin would apply to this kind of bound system.

Another interesting possibility that is well motivated theoretically is the possibility of glueballs. These strong force bound particles should be capable of existing as free particles, like other hadrons, and should have well defined intrinsic spin, which could be either spin-0 (scalar or pseudoscalar), or spin-2 (tensor) (presumably each made of two gluons). Presumably, there could be either two gluon or three gluon states that would be color charge neutral. Conceptually, spin 1 (vector) and spin 3 glueballs (made of three gluons) are possible.

In particle physics, a glueball is a hypothetical composite particle. It consists solely of gluon particles, without valence quarks. Such a state is possible because gluons carry color charge and experience the strong interaction. Glueballs are extremely difficult to identify in particle accelerators, because they mix with ordinary meson states.

There have been hints of direct glueball detection as far back as 2005 (see also here), but even now, there is not a definitive detection.

As a 2008 review explained:

Many different experiments exploiting a large variety of production mechanisms have presented results in recent years on light mesons with J(PC) = 0(++), 0(-+), and 2(++) quantum numbers. This review looks at the experimental status of glueballs. Good evidence exists for a scalar glueball which is mixed with nearby mesons, but a full understanding is still missing. Evidence for tensor and pseudoscalar glueballs are weak at best.

Since some glueballs appear in lattice simulations to be massive (on the order of 1-2 GeV/c^2) and scalar, a scalar glueball would look very much like the hypothetical Higgs boson, but lighter.

As recently as 2011, published physics papers have contemplated what sort of experimental signature a pseudoscalar glueball would have and compared it to the high energy physics evidence.

While some particles of spin 0 (scalar and pseudoscalar mesons and perhaps glueballs and hypothetically Higgs bosons), 1/2 (fermions and some baryons), 1 (fundamental bosons and some mesons and hypothetically some three gluon glueballs) and 3/2 (some baryons) have been observed; no particles of spin 2 (hypothetically gravitons or two gluon tensor glueballs, some candidates for which has been identified, and also here) or 3 (hypothetically some three gluon glueballs) have been observed.

There are questions, however, about whether gluons are even a meaningful way to describe the low energy limits of QCD. For example, there are doubts about whether intrinsic gluon spin or gluon helicity is the proper concept to use to theoretically model glueballs. Theoretical challenges to even the existence of three gluon glueballs are particularly daunting, although some progress has been made in modeling them in lattice QCD models.

Then, there are gluelumps (also here) which are "one-gluon states, allowed because of the static colour octet source.", in more elaborate models such as SUSY ("These are another hypothetical type of gluonic hadrons, where a spinless, static, color-octet source is added to the gauge field. Gluelumps have actually been a first attempt to model gluino-gluon bound states.") Another of the references talks about a gluelump made of a charm-anti-charm and gluon triplet.

Given the fact that all of the fundamental bosons and at least one kind of meson act as force carriers phenomenologically, and the fact that all glueballs are bosons composed themselves entirely of bosons, the possibility that glueballs might act as force carriers of some type is fascinating. We know that it is conceptually possible for a spin-2 particle to reproduce gravity (and indeed that one can understand QCD through a correspondence between its gauge theory and five dimensional classical gravity in anti-deSitter space), but what kind of force might be carried by a spin-3 glueball if one existed?

Some consideration has been given to this question, and spin-3 bosons present fewer theoretical challenges than high spin bosons (see also here). This has some application in condensed matter physics and might matter in SUSY theories.

Thursday, October 27, 2011

Seven Thousand Years Too Young Neanderthal Tools Found

The consensus had been that Neanderthals were beginning to experience a serious decline in range and numbers by 40,000 years ago, and went extinct around 29,000 years ago. I recited that "fact" in a post just yesterday.

But, today, I learn via Maju that carbon dates from new find "in the valley of Liébana (Cantabria, Spain)," shows evidence of Mousterian industries strongly associated with Neanderthals as recently as 22,000 years ago (after calibrating the date), give or take a century or two, in continuity with similar industries from tens of thousands of years before modern humans were present anywhere in Europe.

The dates are "contemporary with local Gravettian (c. 20,700 BP, uncalibrated, at Morín) and Solutrean cultures (c. 19,000 BP at Las Caldas), almost shoulder with shoulder geographically." Both of these tool industries are completely associated with modern humans, and modern humans tend to be very good at picking up superior technology from the next valley over eventually over a period of centuries.

While this may have been simply one more relict population in a region that has a long history of successful resistance to demographic change that has affected its neighbors, it has also drawn attention to other recent Neanderthal dates that were widely viewed as experimental error in that past that now have greater credibility.

Higgs Numerology And Other Unbounded Musings

Time for fun with fundamental constants, and in particular, potential Higgs boson mass and Higgs v.e.v. formulas. All of this, as the post title suggests, is nothing more than numerology with no real solid theoretical framework upon which is rests. But, it is interesting nonetheless.

A Higgs Boson Mass From Boson Mass Formula

It is interesting to note that within the range of Higgs boson masses not excluded by experiment is H^2=W+^2 + W-^2 + Z0^2 (i.e. a Higgs boson rest mass equal to the sum of the squares of the rest masses of the three weak force bosons). The Higgs mass under that formula would be 115.5 GeV about plus or minus 1%, just above the LEP exclusion range.

If one takes charge to come in units of plus or minus the imaginary number i, then this same equation also holds. Of course, color charge, baryon number and lepton number are zero for each term of these equations as well. This would also seem to imply some sort of special relationship between the Higgs boson the the triple W+ boson, W- boson and Z0 boson triple coupling which is indeed one of the permitted weak force couplings.

Indeed, all of this would also be true if the Higgs boson rest mass were taken to be the sum of the square of the rest masses of all four of the electroweak bosons (the W+, W-, Z0 and photon). Indeed, that relationship would suggest the square of the Higgs boson rest mass is the dot product of the electroweak boson rest mass matrix with itself, an interesting operation in and of itself, since the dot product of vectors (here we are taking the dot product of four vector boson rest masses) produces a scalar, which is notable because the Higgs boson is a scalar boson.

The dot product ansatz also has the curious suggestion that fundamental particle mass is deeply and fundamentally intertwined with the electroweak force, while continuing to set apart the gluon mediated strong force - whose massless bosons don't interact with any of the electroweak forces, which is not renormalizable while the electroweak forces are renormalizable, and whose color charge is seemingly totally independent of electroweak charges.

Higgs Boson Mass From Boson and Fermion Masses

Suppose you want to get even bigger picture and are worried that 115.5 GeV is bit too light to be a good bet. You can make H^2=(sum of squares of each of the spin 1/2 fermion masses)^1/2+(sum of squares of each of the spin-1 boson masses)^1, omitting only the top quark mass, which does not hadronize and is the only massive particle heavier than the Higgs boson, from the total. Voila! One gets a Higgs boson mass of 120.3 GeV, just perfect for a possible to detect value from the LHC. For extra cleverness, you can put the (H^2)^0 since it is a spin zero particle, which is equivalent to making the Higgs boson mass the fundamental unit of rest mass, and throw in a term for the graviton on the right hand size (or the left hand side, for that matter) of (G*2)^2, since gravitons have zero rest mass. The down side is that maybe you should be triple counting quarks as you do when you do weak force decay percentage calculations. Also, it would be wonderful to be able to relate the Higgs boson mass of 120.3 GeV (or perhaps 115.5 GeV) to the Higgs field vacuum expectation value of 246 GeV, which is not quite double the Higgs boson mass by this formula, by some trivial formula.

Higgs v.e.v. from fermion and boson masses counted correctly

There is an interesting formula for the Higgs v.e.v. from first principles that is even nicer than the 120.3 GeV Higgs boson mass formula above (the 115.5 GeV Higgs boson mass formula is prettier and more natural). In this formula the Higgs v.e.v. of 246 GeV is equal to, to within experimental measurement uncertainty, double: (the sum of squares of spin 1/2 fermion masses (except top quarks), counting each quark mass three times, one for each color)^1/2+(sum of squares of spin 1 boson masses)^1+(sum of squares of spin 2 boson masses)^2. One can justify leaving out the top quark mass, again, on all sorts of grounds, such as, for example, the fact that a top-antiquark mass pair is energetically prohibited at the Higgs v.e.v. (yes, I realize that this is somewhat circular, but the formula is also quite beautiful as formulas go, so the anomaly may be worth it if it can save the formula).

Since this Higgs v.e.v. has no dependence whatsoever on the Higgs boson mass, and three of the Higgs bosons are gobbled by the W and Z bosons that are included in the formula, maybe the Higgs boson mass doesn't even matter, and one can build a Higgsless model on that coincidence.

A Higgs Boson Mass From Hardon Interacting Particle Mass Formula

A Higgs boson mass of exactly half of the 246 GeV Higgs v.e.v. value (i.e. 123 GeV) isn't yet ruled out by LHC, but it isn't a favorite either. A few GeV less is more strongly suggested.

If we want a Higgs boson mass of above 115 GeV, the thing to do might be to take half of the Higgs v.e.v. calculated as above, and to find some legitimate reason to omit a term that accounts for about 4 GeV. For example, if you include non-top quarks, but not leptons in the calculation above, you get about 119 GeV, which is the sweet spot for Higgs boson mass if there is one.

Thus, in this bit of numerology, while all particle masses would contribute proportionate to their fermion or boson status to the Higgs v.e.v. up to the v.e.v. scale, only particles that are part of, or are emitted or absorbed directly by hadrons would contribute to the Higgs boson rest mass formula. After all, the Higgs field, like the strong force, would be a self-interacting one since Higgs bosons themselves have the mass that a Higgs field creates, so it might make sense that only self-interacting particles contribute to its mass. This would also ground the fundamental concept of mass in fundamental particles more closely to the concept of mass in hadrons that account for the vast majority of the non-dark mass in the universe. Thus, this distinction between the Higgs v.e.v. and the Higgs boson mass would have the added bonus of suggesting some mysterious connection between the strong force and the electroweak force that could point towards a way towards a GUT.

Phenomenological Formulas For The Lonely Top Quark Mass

It is also interesting to observe that there are a variety of formulas to which one can appeal as a special case to find the top quark mass, many of which, of course, have no real good theoretical motivation. For example, the square root of the top quark mass less the square root of the W boson mass equals the bottom quark mass, which suggests that formula t+W-2(tW)^1/2=b^2 is correct to within the limits of experimental accuracy. One can imagine this kind of equation popping out in some way as the leading order derived somehow from the Feynman diagram for a top quark decaying into a bottom quark, with the diagrams weighed somehow by their transition probabilities, since top to bottom quark decay via W boson emission from the top quark is the dominant mode of decay for top quarks to the near exclusion of all other terms (Only 0.02% of top quark decays are to charm or up rather than bottom quarks quarks, while 5.2% of bottom quarks transition to top or up quarks rather than charm quarks, energy permitting).

Incidentally, the natural next iterations of this equation (at least at the leading order term values) not true or even close for b+W-2(bW)^1/2=c^2, and for c+W-2(cW)^1/2=s^2, so this is special pleading to some extent.

What would the Higgs v.e.v. be if you did the sum of squares of masses of a type to the power of spin? You'd get a bit less than 600 GeV.

But, one can also imagine some sort of weighting of mass matrix values with CKM and PMNS matrix values, with top quark mass being virtually removed from the equation because its amplitude to remain as a top quark rather than a bottom quark is so trivally low, while the other particles far more regularly transition into each other.

The Weak Sector and Strong Sector Compared

If the Higgs v.e.v. and Higgs boson mass are in some sense superpositions of the masses of all of the fundamental particles using rules similar to those involved in weak force calculations, then this suggsts that quark-lepton complementarity is related in some deep way to the electroweak force from whose CKM and PMNS matrixes it is gleaned, while having little or nothing to do with the strong force (although the weak force does recognize different colored quarks as equal and distinct fundamental particles on a par with each other probability-wise, rather than mere versions of the same single thing).

Indeed, one way to think about quark-lepton complementarity is to see the four parameters of the CKM matrix whose three theta angles correspond to the three dimensions of space and whose CP violation phase corresponds to the dimension of time, which can be express as a four dimensional unit vector with a complentary PMNS unit vector to it. This notion has the happy feature of representing the relationship of the CKM matrix and PMNS matrix to each other in the background independent way preferred by general relativity, and since the CKM/PMNS matrixes appear to have some deep relationships to rest mass, and since rest mass is one of the core elements of general relativity (indeed, the Newtonian formulation of gravity that ignores all non-rest mass terms in the stress-energy matrix is an extremely good approximation of reality over a broad range of circumstances), this suggests an avenue of attack to linking the two.

It also heightens the intuition that the three generations of fermions are a weak force thing (as transitions between generations are mediated by the weak force), rather than a strong force thing - since the strong force treats all quarks of the same color essentially the same.

Less impressively, there are both four electroweak bosons (apart from the Higgs) and four kinds of fermions, each with a different electromagnetic charge. But, it would, again, provide a distinction between a correspondence that the electroweak force seems to play a part in, and one that doesn't obviously relate to the strong force.

And, of course, there are no demonstrated circumstances in which the strong force is observed to be CP violating, even though there are natural terms in the QCD equations to permit this to happen. The obliviousness of the strong force to electromagnetic charge could be at play here and it is worth remarking that hadrons and anti-hadrons appear to have the same masses, even though most of their masses arise from the strong force in the conventional account, rather than the rest mass of the component fermions.

Musings On Realistic Four Color QCD Models

Query if there is some sort of Color Charge-Parity near symmetry relationship analogous to the electroweak charge-parity relationship that is broken in a similar way in chiral strong force interactions. After all, there are, for example, red and anti-red colors for quarks and gluons that can be reversed with a reversal of parity.

It is also worth noting that one way to see the eight gluons is as a 2*2*2 toggle of three orthogonal unit vectors in space, but not time. Indeed, this heuristic is one of the better ways to understand why there are eight rather than nine (RGB*RGB) kinds of gluons. Viewed this way, the necessity that a hardron or gluon be color neutral is another way of saying that the vector sum of its color charges, which can be expressed in a space-like background independent way, must sum to zero. But, why in a general relativistic world are there not sixteen gluons with a color charge toggle forward and backward in time as well?

Indeed, it isn't obvious to me that color charge has to be anything other than polarization, because I'm not aware of any way yet devised to directly measure gluon polarization, since gluons are always confined and can't be measured directly so far, although experiments to measure gluon polarization have been proposed.

Given that the natural scale of time-like distances is so much greater than the natural scale of space-like distances for human beings, and that gluons like photons are massless, one can imagine that the time-like fourth component of color charge is suppressed in much the same way that the time-like polarity components of photons are suppressed even though QED equations consider 4-part rather than the day to day functional 2-part polarizations of photons, with two components cancelling out (see, e.g. Richard P. Feynnman, QED at pages 120-123), but might have some physical implications in extreme conditions or another class of interactions.

In the QED equation, the extra two components of polarization are particular relevant to virtual photons, for example, between electrons and protons in atoms), so one might imagine by crude analogy, that a missing fourth color charge might be mostly pertinent to the exchange of virtual gluons, for example, between quarks within hadrons, that we tweak by using an effective coupling constant of the strong force when we should be using a bare value perhaps.

It might be easier to reconile a four color strong force with the time-like color strongly suppressed with background invariant general relativity.

It also might very well be that if one used the running of the bare coupling constant of four color strong force with the timelike color suppressed, rather than the effective coupling constant of the three color strong force, that one might be able to achieve the holy grail of GUT theorists, a GUT scale energy level where the strong, weak and electroweak running coupling constants converge to exactly the same value, which, by hypothesis, would be precisely the same as the energy level where the electromagnetic and weak force running coupling constants coincide (without the nuisance of a menagerie of supersymmetric particles - we'd have the same old six quark (but in four colors each instead of three), the same old six leptons, the same old four electroweak bosons, and sixteen rather than eight kinds of gluons that are otherwise the same in all respects.

Anyway, it is a nifty idea that would be simply in principle to check out even if it might be harder to actually do once one got down to really cruncking equations and putting numbers into lattice models and beta functions for the strong force coupling constant.

Wednesday, October 26, 2011

A Work In Progress Out of Africa Model Part II: Hominins To Humans


This is the first part of a three post blog discussion.

Part I provided the Preface and Disclaimers that apply to this post and the next one.

This Part II provides a work in progress narrative of the Out of Africa story of hominins from the first hominins to leave Africa until the extinctions of archaic hominins outside of Africa (as noted in the first part, the discussion of archaic hominin populations in Africa is mostly beyond the scope of this post.

Part III will provide a work in progress narrative of the Out of Africa story following the extinction of archaic hominins. A link to that post will be provided here when the third part is posted.

From Hominins To Humans

Hominins Before The Genus Homo

Starting around 7 million years ago, a new kind of primate, for which the chimpanzee and bonobo are the most closely related species that survive today, started to evolve as a distinct species. From about 7 million years ago until about 2.5 million years ago, multiple species of these primates arose. Modern humans are directly descended from some of these species, while others species in this clade of the primate evolutionary tree evolved in parallel to our ancestor species, possibly with some admixture with the species from which we are descended, before going extinct. There are perhaps a dozen named hominin species in this time period, but this partially flows from the tendency to identify each net set of fragmentary hominin remains at a new location or time frame as a new species without rigorous efforts to confirm or deny the possibility that some may belong to the same species.

Modern humans descend from some of the more gracile, rather than from some of the more robust of these species. These transitional species apparently did not manufacture stone tools or any other kinds of tools that left traces in the archaeological record.

Some of the most famous representatives of these "missing link" species between Great Apes and members of the primate genus Homo, are "Ardi" a.k.a. Ardipithecus ca. 5 million years ago in Kenya, and "Lucy" a.ka. Australopithecus afarensis, ca. 3.2 million years ago in Ethiopia.

Homo Erectus and Homo Ergaster

Around 2.5 million years ago in Africa, most characteristically in savanna and water's edge environments, the first hominins that we classify in our own genus, Homo called Homo Habilis, which are the first hominins know to have made tools became distinct. By around 1.9 million years ago in Africa, a species called Homo Ergaster for which begins to appear in the fossil record outside of Africa around the same time as the physically similar the archaic hominin species Homo Erectus appears in Asia, arose. I will describe both H. Erectus and H. Ergaster as "Homo Erectus" in this narrative, eschewing the distinction between H. Erectus and H. Ergaster, as it seems most likely to me that they were probably really only subspecies of a single species of hominin.

By around 1.9 million years ago in Africa, Homo Erectus lived a lifestyle somewhat similar to contemporary modern human hunters and gatherers (although not as sophisticated), using primitive stone tools to secure and process food by hunting small game and larger herbivores, scavenging meat, and gathering plants and sessile animals (like shellfish). They walked on two legs, lacked the tails and heavy fur covering of the Great Apes, has some sort of language skills although those language skills may have been primitive, were recognizably humanoid, were smaller than modern humans although not tiny, were smarter than all or most of the hominin species that arose before them, and ultimately some of them developed more advanced stone tools (Achuelean industry ca. 1,500,000-1,600,000 years before present) and used fire in a controlled manner to keep themselves warm and cook food (ca. 500,000 years ago in Europe, 750,000 years ago in the Levant, and perhaps earlier in Africa). They lived in semi-nomadic groups of about twelve to twenty individuals with very few of them living long enough to be alive at the same time as their grandchildren for any meaningful length of time. They had a range far greater than that of any previous hominin species both within Africa and outside it. They had little that we would call "art" and don't appear to have initially crafted tools out of bone or wood (which is not to stay that they might not have used an entire bone or tusk as a club or spear or fire prod, for example). Many popular stereotypes of the life of "cave men" are a better fit to Homo Erectus than to the Neanderthals or earliest modern humans that evolved later.

Homo Erectus (including Homo Ergaster) was the first hominin species to leave Africa and did so no later than 1.8 million years ago, by which time Homo Erectus remains prove they were present in Java, Indonesia. In Southeast Asia and East Asia, Homo Erectus managed with the more primitive Oldowan stone tools invented by Homo Habilis in Africa and continued to use this tool set until at least about 200,000-300,000 years ago when they disappear from the fossil record.

In South Asia, Homo Erectus had begun to use more sophisticated Achuelean stone tools by somewhere in the time frame of 1 million to 1.5 million years ago, and a perhaps as early as 1.6 million years ago in Africa. Archaic hominins called Homo Antecessor, sometimes called a new species, are found in Spain 870,000 years ago, and by 400,000 years ago or so, Homo Erectus remains and Achuelean industry are present and common in Europe.

It is reasonable to conclude that the Homo Erectus of Southeast Asia and East Asia were a population that was separate from the Homo Erectus of Western Eurasia, South Asia and Africa from their arrival in Southeast Asia from Africa around 1.9 million years ago, are at least starting some time prior to the arrival of Achuelean industry in South Asia from Africa around 1,000,000 to 1,500,000 years ago, until their extinction as a result of the arrival of modern humans in region, possibly exacerbated by other "natural" factors (e.g. climatic effects related to the Toba volcanic eruption ca. 75,000 years ago).


The island of Flores, just over the non-Eurasian side of the Wallace line in Indonesia, was inhabited by Homo Floresiensis from ca. 95,000-18,000 years ago as evidence by 12-15 sets of remains of individuals with adult heights of 3.5 feet (hobbit sized) and their material culture (including stone tools, dwarf elephant remains from their hunts and fire use) from Liang Bua cave, which they inhabited on that island. They are probably pygmy version of Homo Erectus who followed the commonly known pattern of island dwarfism. Their ancestors could have arrived in Flores as early as 800,000 years ago.


Neanderthals appear in Europe around 200,000 and ultimately have a range that skirts that includes most of Europe, Southwest Asia (i.e. Arabia and the Levant), the southern fringe of the Central Asian steppe, West Asia, and South Asia before their extinction sometime between 40,000 and 30,000 years ago. Their extinction coincides with a string of major volcanic eruptions that also led to major climate changes in their range and the arrival of modern humans in Europe.

Neanderthals were behaviorally more advanced than Homo Erectus, more robust than either Homo Erectus or modern humans, show signs of adaptation of ice age European climates, and had relatively short legs well suited to steep terrain. They are associated technologically with Mousterian industry stone tools, which are more sophisticated than Achuelean industry stone tools associated with later Homo Erectus populations in Europe, Africa and South Asia.

Mousterian tools that have been found in Europe were made by Neanderthals and date from between 300,000 BP and 30,000 BP. . . In Northern Africa and the Near East they were also produced by anatomically modern humans. In the Levant for example, assemblages produced by Neanderthals are indistinguishable from those produced by Qafzeh type modern humans. It may be an example of acculturation of modern humans by Neanderthals because the culture after 130,000 years reached the Levant from Europe (the first Mousterian industry appears there 200,000 BP) and the modern Qafzeh type humans appear in the Levant another 100,000 years later. It was superseded by the [Neanderthal] Châtelperronian industry around 35,000-29,000 BP.

They don't appear to have engaged in harpoon fishing, although they may have used unaltered bones as tools and may have simply grabbed fish out of streams to eat. There were primarily big game hunters although there is evidence that they collected shellfish on the English coast ca. 125,000 years ago. Male Neanderthals were larger than female Neanderthals to a greater extent that male and female modern humans are different in size.

Ancient Neanderthal DNA indicates that there were probably at least three regional subpopulations of Neanderthals in Europe, that their effective population size was quite small at the cusp of their extinction (perhaps 1,500-4,500 reproductive aged individuals in all of Europe).

It isn't entirely clear if they evolved from prior European Homo species, or if they evolved from prior Homo species elsewhere (e.g. Africa) and then migrated to Europe. They are genetically closer to modern humans and more distant from the Great Apes than the only other archaic human population for which we have ancient DNA, the Denisovians.

Neanderthals are not a direct ancestor of modern humans. Neanderthals diverge from the direct ancestor of modern humans around 400,000 to 500,000 years ago. In my view, the Homo Erectus who brought the Achuelean industry to Europe around 400,000 years ago were probably the population from which Neanderthals descended.

Modern Humans

Modern humans evolved in Africa around 200,000 to 160,000 years ago at a time when Neanderthals were found in Europe, West Asia, Southwest Asia and South Asia, and Homo Erectus was present in the lower latitudes of Asia.

We are familiar with modern humans, although these early Cro-Magnons would have initially been monoracial, monoethnic, hunter-gatherers, probably, although not certainly, in East Africa.

Proto-Eurasians, however, surely must have been East Africans, because modern humans did not originally leave Africa via the Strait of Gibralter into Iberia, and the only other ways out of Africa on either side of the Red Sea can only be reached via East Africa, a conclusion buttressed by the fact that the closest phylogenetic relatives of Eurasian specific Y-DNA (B* and BF) and mtDNA (L3*) haplogroups are found in East Africa today, have maximum diversity there, and show no obvious signs of relocation to there from somewhere else.

The modern human population (predominantly made up of men with Y-DNA haplogroup F* and mtDNA haplogroup L3*) undergo a fission ca. 80,000-75,000 years ago when they vanish from the Levant. One of the two branches ends up in a Persian Gulf Oasis or Iran or Pakistan and produces a community with mtDNA haplogroup N that ultimately spread both West to SW Asia and Europe, and East to South Asia and beyond to all points East by about 50,000 years ago. The other of the two branches ends up in a South Asian refugium and produces a community with mtDNA haplogroup M that becomes thoroughly admixed with members of the Western branch as it expands eastward.

A fission of the proto-Eurasian population before or at around the time that the mutations that distinguish mtDNA haplogroups M and N from L3 is necessary because only mtDNA descendants of haplogroup N are found with any frequency in West Eurasian populations (and the exceptions show the clear signatures of backmigrations), while Asia, Australia and New Zealand have both.

Once two distinct lineages of mtDNA haplogroups are present in a population that has had even just a few generations to admix (perhaps four or five generations over a single century), it is extremely difficult to extricate one lineage from the other in a population that branches off from the mixed group unless the founding population of the branch is extremely small, or is a little bit larger and organized matrilocally. If one takes a scenario where the fully admixed proto-Eurasian source population has an effective population size of 3,000 (see, e.g., this 2007 paper estimating a proto-Eurasian effective population size of about 3,100, and a Yoruba ancestral effective population size of about 7,500) and the splinter group of proto West-Eurasians has an effective population size of 150 (which is quite a bit smaller than conventional estimates), for example, and the relative frequencies of mtDNA haplogroups M (with all descendants) and N (with all descendants) are similar to those of modern South India (which is probably the closest modern comparable without an extremely small founding population to the proto-Eurasian population in the narrative I've presented here), it is extremely difficult to get all of the women in the proto-West Eurasian population to all have mtDNA haplogroup N types by random chance. This statistical relationship is just weakly related to the size of the source population (although it is quite sensitive to structure within the source population's mtDNA such as matrilocal family patterns, or regional clines that arose due to founder effects when M and N arose), but it very strongly related to the effective population size of the founding population. It is extremely unlikely for an unstructured source population in the thousands and a splinter population in the high hundreds to randomly remove all mtDNA M individuals by random chance via founder effects in a stable or expanding population.

The effective size of the founding population of the Americas ca. 14,000 years ago, is estimated to be on the order of 70 people.

A founding population estimate of 1,000 for Papua New Guinea and Australia, respectively, would probably be significant overestimate, although firm predictions are hard to find in the literature. There are just five root mtDNA founder lineages and not more than four root Y-DNA founder lineages (perhaps as few as one) among indigeneous Australians (with a founder lineage defined as the most basal branch of lineage private to Australia and Papua New Guinea and not due to Holocene era admixture); there are four root mtDNA founder lineages and not more than three Y-DNA founder lineages (perhaps as few as one) among indigenous Melanesians. Two of the founder mtDNA lineages of Australia and Melanesia, and two of the Y-DNA founder lineages are shared, so there are no more than seven mtDNA founder lineages and five Y-DNA founder lineages in Australia and Melanesia combined (perhaps as few as two or three). This is similar to the number of founding lineages in the New World. The Australian and Melanesian genomes have deep connections to each other not shared by other populations, matched by their shared similar proportions of Denisovian ancestry and similar in time founding dates, and their founder lineages are both very close to the Eurasian basal lineages (probably within 5,200 years). Thus, it is not unreasonable to infer that they derive from a single wave founding population and to estimate that the founding effective population size for these populations that is on the same order of magnitude as that of the Native Americans, conservatively, in the hundreds for the combined Australian and Melanesian proto-population, which fissioned early on (probably in the vicinity of Flores, Indonesia) in not quite complete break isolating the two populations after that point, with Melanesia's founding population being slightly less diverse. Melanesia's founding population may have been less than one hundred, Australia's founding population may have been in the low hundreds.

In an expanding population, you generally don't lose significant percentage haplogroups of any kind, although a bottleneck, for example, post-Toba, could provide an alternate solution for this problem.

Indeed, it is easier from a modeling perspective, for some of the same reasons, unless mtDNA haplogroups M and N are not selectively neutral (and there is no reason to think that they have selective effects of their own), to imagine a scenario in which mtDNA haplogroups M and N and Y-DNA haplogroup F are simply local offshoots within East Africa of mtDNA L3* and Y-DNA BF that would have looked simply like minor variants of L3 and B at the time, that both migrate to the Levant, perhaps even separately, but close in time or fissioning almost immediately. Otherwise one has to figure out how to purge almost all of mtDNA L3 (xM,N) and Y-DNA A and B and BF (xF) from the source proto-Eurasian population(s).

There may have been a minority of men belonging to Y-DNA haplogroup DE* in the original group that fissioned, or those men may venture, unaccompanied by women, to South Asia to a community dominated by mtDNA haplogroup M that has not yet admixed with mtDNA haplogroup N women in Eastern India.

The Proto-Eurasian populations were quite homogeneous, having only two matrilines and one or two patrilines, so they too were probably monoracial and probably comprised no more than a couple of ethnicities or languages. Conventional estimates put the effective population size of the proto-Eurasian population in the low single digit thousands by more than one partially independent method (some of those methods rely on Y-DNA and mtDNA diversity, rather than autosomal DNA, and hence wouldn't be distorted by Neanderthal admixture in the autosomal genome which would exaggerate effective population size).

Given the fact that there are human remains to prove that modern humans were in the Levant ca. 100,000 years ago (although we can't definitely show that later Eurasians were actually descended from then as opposed to a later wave), and that there is pretty much no evidence whatsoever to definitely favor a Gate of Tears and Arabian coastal route migration, an Out of Africa route for modern humans up the Nile Basin (or parallel to it on the Lake Chad side in a wet sahara era), which are down hill routes with good fresh water supplies that naturally attract game and provide a fishing resource, and across the Suez to the Levant seems more plausible than the Gate of Tears route. Indeed, even today, the lack of continuity in populations on either side of the Gate of Tears is quite striking. Since we know from digs in India that produced charcteristically modern human tools in India prior to 75,000 years ago (pre-and post-Toba ash deposits), we don't need an Arabian coastal route to West Asia theory to get modern humans to South Asia and beyond in the right time frame, if we can get them from the Levant to West Asia between 100,000 and about 76,000 years ago via the Fertile Crescent, which we can just as easily as we can via the Arabian coastal route, in a matter of a few centuries. Recent discoveries from Arabian digs really do nothing to disturb that analysis decisively.

Humans Meet Archaic Hominins Outside of Africa


Neanderthals had an overlapping presence with modern humans in the Levant from about 100,000 years ago to 75,000 years ago, were the only hominin species in the Levant from about 75,000 years ago until 50,000 years ago, and after thousand years of another overlapping presence with modern humans in the Levant around 50,000 years ago, were no longer found in Southwest Asia. The last Neanderthals went extinct around 29,000 years ago.

Neanderthals were outnumbered 10:1 by the modern human hunter-gatherers that immediately followed them in residing at the same locations in Europe where adjacent layers are present. There is no convincing evidence that there were ever communities in which both pure modern humans and pure Neanderthals lived side by side, although there are a few remains that arguably suggest the presence of hybrid individuals, something that the genetic record strongly supports the existence of historically, and one interpretation of a brief period

Neanderthals admixed with the proto-Eurasians leaving a roughly 1-4% admixture percentage (average about 2.5%) of Neanderthal genes in all non-African modern humans. Neanderthal admixture in Western Eurasia overlaps only slightly and in the most common surviving types of Neanderthal DNA in modern humans with Neanderthal admixture in Eastern Eurasia. These admixture estimates are based on direct comparisons of several ancient Neanderthal DNA samples from the period shortly before Neanderthals went extinct, and are corroborated by indications from the nature of the genome sequences found there that the Neanderthal sequences are mutationally and recombinationally distant in time depth from the rest of the modern human genome.

Neanderthals did not contribute any Y-DNA patrilines or mtDNA matrilines to modern humans.

I suspect that what happened is that there was admixture in both directions in some quite specific and parallel patterns.

Neanderthal men impregnated modern human women outside lasting pair bonds, and the modern human women gave birth to hybrid children nine months later in their own modern human tribes. Those children had their mother's mtDNA and due to Haldane's law, the fertile interspecies hybrid children that were produced were overwhelmingly female. Some of the more robust arguably modern human remains may have had significant Neanderthal admixture.

Neanderthal women likewise would have been impregnated by modern human men outside lasting pair bonds and the Neanderthal women gave birth to hybrid children nine months later in their own Neanderthal tribes, the last of whose descendants died out when Neanderthals went extinct around 29,000 years ago. They hybrid children would have had Neanderthal mtDNA and due to Haldane's law, the fertile interspecies hybrid children would have been overwhelmingly female, so they would lack modern human Y-DNA.

The interspecies liaisons were probably sometimes rape and some times "flings" during seasonal periods when Neanderthal and modern human tribes were near each other. But, the great gaps between the two species probably impaired any hope of successful long term relationships. (Matrilocal long term pairings would lead to the same result, but the little evidence that we have suggests that Neanderthals were patrilocal and that patrilocality was probably more common than matrilocality for modern humans.)

The Neanderthal Châtelperronian industry around 35,000-29,000 BP, about 5,000 after a dramatic transition from Neanderthals to modern humans that reached a tipping point as a result of volcano driven climate change, is sometimes described as a crude attempt by Neanderthals to copy modern human tool making methods. But, I suspect that there was more to it than simply Neanderthal efforts to copy modern human tool making. My suspicion is that this industry was also a product of modern human admixture with late Neanderthals, after hundreds of thousands of years without innovation in tool crafting technologies. Modern human admixture may have made some level of innovation possible, but without membership in a modern human tribe, the necessary training to perfect those methods would have been absent.

The universality of Neanderthal DNA at similar levels in all non-Africans, and the apparent lack of overlap, suggest the following narrative.

Neanderthal admixture happens early once modern humans leave Africa. It may happen in the Levant in the time period from 100,000 to 75,000 years ago, or more likely in my view, given the lack of overlap, the Western group and the Eastern group admix with Neanderthals separately and in parallel admix at similar rates, with Neanderthals who are initially present in both areas, over thousands of years, until the Neanderthal go extinct locally. Two separate sources of Neanderthal genes would explain the limited overlap of specific Neanderthal source genes between Western Eurasia and Eastern Eurasia, and the processes involved in each case would probably be quite similar since they involve two parts of a recently split population with similar cultures interacting with the same species in similar environments.

Members of the West Asian branch of modern humans, predominantly Cro-Magnons of certain subgroups of mtDNA haplogroup U, colonize much of Europe once the population barrier created by the presence of Neanderthals in Europe weakens due to volcano driven climate change opening the flood gates to a surge of more effective modern human hunters with better tools who outnumber them, admixing at low rates with the shrinking Neanderthal population as they advance and developing higher levels of Neanderthal admixture than other modern humans. But, after the first 10,000 years or so of this, Neanderthals are extinct, but the influx of modern humans from West Asia and Central Asia and Southwest Asia to Europe continues, their population is reduced and diluted as they retreat to refugia during the Last Global Maximum ca. 20,000 years ago, and further replacement and dilution takes place in the Younger Dryas repopulation of Europe and in subsequent Neolithic, dairy farming Neolithic and Indo-European migrations, diluting the elevated levels of hybrid Neanderthal admixture in Cro-Magnons from the time period when the two hominin species co-existed for long periods among people whose lines of descent stayed on the boundaries of the expansion to unmeasurably low levels.

Homo Erectus, Denisovians and Hobbits

In my view, the most plausible possibility is that Homo Erectus to the East of South Asia (separated from other hominins from ca. 1.9 million years ago until the encounter modern humans ca. 100,000 years ago) are the same species whose ancient DNA was extracted from a cave in South Siberian Denisovia from ca. 40,000 years ago - probably a representative of the Northern extreme of this population when forced by modern human population pressures to a refugium outside their comfort zone.

A first wave of modern humans arrives not earlier than 100,000 years ago, and probably not in large numbers until they are emboldened by weakness in the Homo Erectus population due to climate change caused by the Toba volcano ca. 75,000 and possibly facing push pressure that started their migration from a West Asian/South Asian start by the exile of modern humans from the Levant in favor of Neanderthals, and possibly not even until 50,000 years ago, perhaps emboldened by cultural developments within their West Asian and South Asian refugia.

Due to their superior competition for resources, larger numbers and possibly outright warfare, modern humans prevail over Homo Erectus sending them to extinction outside relict populations. Modern humans are smarter and more adaptable than Homo Erectus, are stronger, have better tools, are probably better organized as team players, and are superior hunters who also make more systemic use of fire. And, these Homo Erectus, who had not even acquired Achuelean industry to replace their more primate stone tools, perhaps because the abundance of their environment made innovation unnecessary to survive, were even more vulnerable to the modern human onslaught than archaic hominins elsewhere.

This relative weakness means that the replacement of Homo Erectus by a wave of incoming modern humans happens more rapidly than it does with Neanderthals vis-a-vis whom modern humans have less of a competitive advantage, so the admixture percentage for the most part is much lower than it was with Neanderthals to the point of being almost negligible except in rare cases like HLA complex genes that have selective advantage and survive from a very small percentage of Homo Erectus/Denisovian genes. But, in this pre-LGM, high sea level era, Indonesian islands and territory across the mountains in Siberia falls much less rapidly to incoming modern humans than the rest of the mainland, because they are not so greatly outnumbered there.

Probably over a couple of thousand years or less, a wave of modern humans including the proto-Papuans and proto-Australians, who are at that point a single founding population that will also seed Filipino Negrito populations in part, advance along the island chain somewhat haphazardly, and their very small founding population admixes with relict Homo Erectus giving rise to a fixed 8% admixture percentage, probably before possibly absorbing a small second wave of mainland modern human migrants (that is large relative to their population), and before fissioning into proto-Papuans and proto-Australians.

The exception to the pattern of rapid extinction of Homo Erectus in the face of advancing waves of modern humans is in Flores, Indonesia where the Hobbits co-exist with modern humans from about 40,000 to 18,000 years ago, possibly because they required fewer resources to survive, their small size made them seem like less of a threat, and the Hobbits may have been co-opted into a servant-master relationship with the modern humans. Hobbits probably make first contact with modern humans in the form of the proto-Papuan/Australian population. Also, the Wallace line gap insured that the number of modern humans who got this far was much smaller and less intense than it had been relative to Homo Erectus in mainland populations.

The much larger Denisovian admixture percentage in this proto-population (probably about 8%), the fact that Flores is a necessary stop on the path to Papua New Guinea and Australia, and the lack of notable Denisovian admixture percentages in mainland populations, and the 22,000 years of stable co-existence between the two species on the relatively small island, suggests that perhaps the principal source of Denisovian admixture in these populations was actually with the Hobbits of Flores and not elsewhere, as relatively long term relationships and higher levels of interaction might have been possible on Flores than elsewhere. Homo Erectus did not make it to Papua New Guinea or Australia (at least prior to modern human arrival), so Flores may well have been the very most distant refugium of Homo Erectus in the world to the South of Siberia before their extinction. Perhaps hobbit servants even accompanied modern humans to Papua New Guinea and Australia and admixed within these very small founding populations more readily as the available choice of mates was scarce.

There is even some indication that Flores, linguistically, shows the simplifying elements associated with children learning a language from non-native language speakers that could be a legacy of thousands of years of Hobbit nannies not fully equipped to learn modern human languages and of interaction with Hobbits in day to day life that influenced language development there that is not seen in neighboring islands, although the age depth of an apparent Hobbit presence looks a bit great for that hypothesis to fit.

As in the case of Neanderthals, Haldane's law would insure that most fertile interspecies hybrids (and the species distance would have been even greater for Denisovians than for Neanderthals) were female (and hence lacked Homo Erectus Y-DNA). In the case of modern human mothers, the Denisovian mtDNA would have been absent even in first generation modern humans. Hobbit mothers may not have been able to give birth to hybrid children given the impact of the immense size disparity between the mothers and fathers, perhaps instead dying in childbirth in a death that also kills the baby or having stillbirths.

The strong genetic similarity of Indonesian Homo Erectus (as evidenced by their genetic legacy in Australian aborigines and indigenous Papuans) and Denisovians suggests that the Eastern Homo Erectus population had by diffusion over a couple of million years remained a fairly coherent single genetic population. Their lack of expansion beyond Southeast Asia and Southern East Asia until the very end suggest that they were unable to cope with cold climates with the level of success that Neanderthals did and were not inclined to try absent great duress.

Millions of years of exposure to Homo Erectus helped megafauna in the region, which was in any case not as marginal in a biologically rich environment, survive and co-evolve to the point where they were able to survive the onslaught of modern humans. But, in Australia and Papua New Guinea and the Americas and Northeastern Eurasia, a lack of exposure to modern humans meant that they had not co-evolved to handle these threats and megafauna were quickly hunted to extinction when moder human arrived.

Subsequent waves of migration into Southeast Asia and East from South Asia (and eventually from further East), after Homo Erectus was extinct in almost all of its range, diluted and replaced the original modern human populations that had co-existed with Homo Erectus and thus had an opportunity to admix with them. This would greatly dilute the percentage of admixture in later populations in mainland Asia and Indonesia to the West of the Wallace line (much as later waves diluted excess Neanderthal admixture percentages in Europe).

A Work In Progress Out of Africa Model Part I: Preface and Disclaimers

We Know A Lot About Prehistory And Much Of This Knowledge Is Recent

New information on the migration of hominins out of Africa and into Eurasia and beyond emerges every few weeks. There is a great deal of evidence, from archaeology, from current population genetics, from ancient DNA, from ancient climate data, from archaeozoology data, from linguistics and more that is pertinent to piecing together what happened, and evidence in the last few years has materially advanced our knowledge.

There Is Still A Lot We Don't Know About Hominin Prehistory

What we know is incomplete. The ancient DNA evidence is sparse and grows more thin as one looks further back in time and as one wants to know about more than mtDNA that is more easily recovered than non-replicating Y-DNA or autosomal markers. Some dates and classifications of specimens may be inaccurate. Skeletal remains are quite rare in the period prior to the Upper Paleolithic and not abundant in the Upper Paleolithic. Our records of material culture are particularly sparse in places like Southeast Asia when modern humans first arrived where we would very much like to have more detail. Founder effects for current relict populations and limited preservation of ancient DNA make it had to make strong inferences about the overall genetic makeup of ancient modern human populations from what we know. Admixed populations and a lack of solid data on prehistoric demographic parameters can confound efforts to determine effective population sizes of proto-populations. The enterprise of trying to date branches of the human genetic phylogeny from genetic variation arising from mutations have inherent and probably unresolvable amounts of uncertainty and are not particularly well calibrated to the extent that they can provide insight at all. Linguistic and cultural markers that have survived to be documented or observed today don't have enough time depth to tell us all that much about people in the Upper Paleolithic and earlier eras.

Hominin prehistory is a puzzle that is missing a great many pieces.

More Data Produces Increasing Returns By Strengthening Our Capacity To Make Reasonable Inferences

This uncertainty should not, however, take away from the wealth of information that we do have and from the emergent capacity that are growing body of knowledge permits us to infer from what we do know. As we gain new information we learn not just a specific fact, but also how particular kinds of processes, in general, work. For example, ancient DNA data from Europe didn't just tell us that a person with a particular haplogroup and material culture lives in a particular place at a particular time. The collection of data points also helped refine our knowledge about how stable population genetics are over time and what kind of factors from other lines of evidence appear to be associated with (or not associated with) population genetic change.

A Work In Progress Narrative Is A Suitable Way To Describe What We Know.

Summing up what we know in a "what we know from certainty" and what inferences can we make from that data point on a case by case basis, understates the richness of that data set we have with all of its deep, logical relationships. This approach would also rival reading a Pentagon-speak mission statement for clarity, precision and ease of reading.

Rather than going that route, what I propose below is a "work in progress" narrative. While stated in the positive, it isn't intended to be authoritative, definitive and final. But, it is intended to be consistent with what we know and among the more probable of the possible narratives given what we do know. To the extent that there is really no way to make any reasonable inferences at all, it is silent. At almost every point, there are reasonable arguments for somewhat different absolutely dated timelines, for material culture continuity to mask significant changes in population genetics, for material culture shifts to involve population genetic continuity, for the scale of admixture events or splitting populations to be off by orders of magnitude, and even for sequences of events to be out of order. Also, I have evaluated plausibility wholistically, rather than on a case by case basis, with an eye towards assumptions that make the overall narrative arc, rather than particular details, maximally accurate.

This is also a work in progress in the sense that conclusions are frequently based sources not referenced in this first draft and that some pieces of the puzzle that the scholarly literature elucidates reasonably well are omitted in this first draft.


This narrative also intentionally not comprehensive. It omits almost all of the evolution of hominins from the African Great Apes within Africa prior to the emergence of hominins outside Africa. It discusses pre-modern human hominins, in general, only to the extent that detail about them is necessary to tell the story of modern humans and isn't particularly interested in what their lives were like or what impact they had for their own sake. It omits almost everything about the Holocene except to the extent that it helps to link the current population genetic landscape to the Upper Paleolithic population genetic landscape.

It omits a great deal of interregional detail within Africa. This narrative is agnostic on the point in time at which hominins other than modern humans went extinct in Africa. Some genetic evidence suggests that there could have been admixture between modern humans (mostly Pygmy and Khoisan) and archaic humans in Africa (probably two separate archaic human populations, at least) as recently as sometime in the last 20,000 years, but absence of corroborating material culture or skeletal remains for archaic humans until a much more remote point in the past, and the limited reliability of relatively untested and uncalibrated genome based dating protocols make the most recent result, which has not even been independently confirmed, calls for skepticism regarding this result at this stage, although it should not be dismissed out of hand.

Tuesday, October 25, 2011

Direct Dark Matter Search Results Still Contradictory

Direct searches for dark matter are still producing contradictory results that are not easy to reconcile.

Some experiments that show some dark matter signal at the low mass end of the WIMP mass range. But the experiments showing some dark matter signals differ both from the experiments showing no dark matter signals, and from each other. The experiments that do show a dark matter signal indicate the existence WIMPs in mass ranges (on the order of 5% of a top quark or 10% of a W boson or Z boson) that particle accelerator data should have revealed if these particles were fundamental, but have instead been ruled out experimentally. Moreover, all known or even seriously hypothesized composite particles (mesons, quarks and exotic hadrons) are too heavy to fit the apparent dark matter signals.

Also disappointing from leading lights of the scientific world making conference presentations on dark matter are several omissions:

1. Failure to include the results of new baryonic matter surveys from elliptical galaxies that show that past estimates of the relative proportions of dark matter and baryonic matter profoundly underestimate the amount of baryonoic matter in the universe. The old estimates put the amount of dark matter at 3-5 times the amount of ordinary matter. The new ordinary matter census suggests that the actual value is tantalizingly close to 1:1. This data is not so new that dark matter keynote speeches in the fall of 2011 should still be using the old pie charts. Yet, it profoundly influences inferrences about dark matter candidates from baryongenesis and leptogenesis processes.

2. Failure to grapple seriously with studies that have shown that models of galactic rotation curves based upon Newtonian approximations are significantly overestimating the amount of dark matter necessary to produce the observed rotation curves, by omitting graviational effects found in general relativity but not Newtonian gravity in these systems. At the very least, any serious analysis of the issue should acknowledge that these papers are out there and evaluate them on the merits. Any result that can explain some of the observed anamolies with existing, well proven physical laws that don't need to be modified at all to reach a result need to be taken seriously. This further pushes the ordinary to dark matter ratio in the universe to 1:1 or even 1:0.5 or so, although probably not to zero.

3. Failure to engage warm dark matter theory analysis that suggests that large scale galactic structure considerations require a somewhat lighter and faster dark matter candidate than the one necessary to fit a traditional cold dark matter hypothesis. Given that most of the direct detection experiments are premised on certain assumptions about dark matter particle speed and are tuned to particular mass ranges, this matters quite a bit.

The big picture dark matter presentations also systemically tend to overstate how well motivated WIMP candidates are given the various direct detection and astronomy limitations on their mass. There are lots of weakly interacting particles predicted by extensions of the Standard Model, but almost all of the lighter ones have been ruled out experimentally by exhaustive high energy experimentation and almost all of the heavier ones are too heavy to fit the experimental limitations on dark matter.

For any particle in the hundreds of GeV mass range or less, collider data place stringent limitations on the properties of any particles that can be produced, and while direct detection experiments are contradictory in some respects, they are unanimous in ruling out heavier WIMP possiblities. Any fundamental WIMP candidate that can be produced in W or Z boson decay is pretty definitely ruled out in the entire mass range from the fraction of a eV mass associated with neutrinos to half of the W/Z boson mass, and no resonnance of unstable heavier particles has been detected either. Even one stable, fundamental heavy WIMP candidate is going to produce an immense quantity of missing traverse energy if it is produced in a decay from a very high energy W or Z (e.g. from top quark decay).

To escape those limitations, a WIMP must either be a composite particle of some sort, or be in a matter sector that has no weak force interactions, in addition to having no strong force and no electromagnetic interactions.

There is at least some emerging acknowledgment that the dark matter sector must be more complicated than a single WIMP model could fit.

The issue of particle stability is also huge. All matter with quarks in it except protons and neutrons, all charged leptons except electrons in the Standard Model, and all free bosons in the Standard Model except photons are massively unstable. Neutrinos are metastable, oscillating between types, but too light. Any realistic fundamental dark matter candidate needs to have a very narrow decay width (which is proportional to the reduced Planck's constant divided by the decay time period of the particle). The decay width of any realistic fundamental dark matter candidate needs to be on the order of that of an electron or neutrino.

A Little Introspection

It is not lost on me that most of my posts at this blog are on topics that have historically been the province of religion and metaphysics: the fundamental nature of reality, and the origins of humanity. 

Neither field, of course, has any great practical application.  We are reaching the point where any unsolved problems in physics are unlikely to have engineering applications.  And, the prehistoric ancestral roots of humanity aren't necessarily helpful and indeed have the potential to be counterproductive in dealing with the present affairs of humanity.  These fields are science for the sake of science.  One can imagine spin-off benefits arising from these studies, but they aren't terribly utilitarian pursuits.

Do I blog to satisfy some unmet psychological need that arises because I am not religious, and in particular, do not subscribe to theological doctrine regarding metaphysics and human origins?  Perhaps.  But, part of the point is that these are grand problems that address ultimate and eternal questions.  They are difficult and complex, but most of the "forest level" data needed to think seriously about them are widely accessible to members of the educated lay public like myself, via the Internet, for free or something close to free.

Monday, October 24, 2011

The (Absence of the) Acheulean In Asia

Selected Pre-Modern Human Stone Tool Cultures

The Acheulean period corresponds it a material culture made of stone tools more sophisticated than those of the previous "Clactonian or Oldowan/Abbevillian industries but lacking the sophistication of the (usually later) . . . Middle Palaeolithic technology, exemplified by the Mousterian industry."

Generally, Acheulean technology is seen as a proxy for Homo Erectus or species of hominins fairly closely related to Homo Erectus, while Mousterian industry is associated with Neanderthals as is at least one later stone tool material culture. Later stone tool material cultures are associated with modern humans.  Oldowan technology as long as 1.76 million years ago, by Homo habilis is harder to distinguish from background rocks because it is less sophisticated and less obviously crafted to the unskilled observer.

As explained here:

The earliest stone tools in the life span of the genus Homo . . . come from what has been termed the Oldowan Industry, named after the type site (many sites, actually) of Olduvai Gorge in Tanzania where they have been found in very large quantities. Oldowan tools were characterised by their simple construction, predominantly using core forms. These cores were river pebbles, or rocks similar to them, that had been struck by a spherical hammerstone to cause conchoidal fractures removing flakes from one surface, creating an edge and often a sharp tip. The blunt end is the proximal surface; the sharp, the distal. Oldowan is a percussion technology. Grasping the proximal surface, the hominid brought the distal surface down hard on an object he wished to detach or shatter, such as a bone or tuber.

The earliest known Oldowan tools yet found date from 2.6 million years ago, during the Lower Palaeolithic period, and have been uncovered at Gona in Ethiopia. After this date, the Oldowan Industry subsequently spread throughout much of Africa, although archaeologists are currently unsure which Hominan species first developed them, with some speculating that it was Australopithecus garhi, and others believing that it was in fact the more highly evolved Homo habilis. Homo habilis was the hominin who used the tools for most of the Oldowan in Africa, but at about 1.9-1.8 million years ago Homo erectus inherited them. The Industry flourished in southern and eastern Africa between 2.6 and 1.7 million years ago, but was also spread out of Africa and into Eurasia by travelling bands of H. erectus, who took it as far east as Java by 1.8 million years ago and Northern China by 1.6 million years ago.

However, it is not that simple:

In Eastern Asia, H. erectus specimens are associated not with Acheulean tools, but instead with Oldowan tools, which were retained until 200,000 to 300,000 years ago.

This pattern was first pointed out by Hallam Movius in 1948. The line dividing the Old World into Acheulean and non-Acheulean regions became known as the Movius line. Handax cultures flourished to the west and south of the line, but in the east, only choppers and flake tools were found.

The Movius Line (via Wikipedia)

This provides archaeological continuity for a long time period (1.3-1.4 million years), although not right up to the presumed time period at which modern humans and archaic hominins encounter each other in Asia, but presents its own mysteries. "Why were there no Acheulean handax cultures in the Eastern provinces of Asia?"

Theories that could answer this question include the possibility that it was due to the "quality of raw materials (fine-grained rocks rare)," "different functional requirements (related to environment and food procurement)," or "'bamboo culture' bamboo tools used in place of stone implements to perform tasks."

The early dates of hominin fossils in Java and Dmanisi can help explain the gap, since the "Acheulean developed in Africa from the preceding Oldowan Tradition only after 1.8 Myrs ago, but if people moved into eastern Asia at 1.8 million years ago or before, they would have arrived without Acheulean tools." The fact is suggestive of the absence of Neanderthals or even Western Eurasian Hominins after about 1.5 million years ago from Southeast Asia and East Asia.

Of course, resolution of this question poses yet another question, "what kept Asian hominins separated from West Eurasian, South Asian and African hominins for 1,200,000 years?"

There are examples at least 1-1.5 million years old are found in South Asia, while Homo Erectus fossils are found on the island of Java going back about 1.9 million years. There is also a deep divide genetically between South Asia and Southeast Asia, but it isn't at all clear why Burma, between them, should be so imposing to genetic exchange or cultural exchange between earlier Homo Erectus hominins.

The chronology of the Homo Erectus to Neanderthal transition and of the Neanderthal to modern human transition in Europe and to a slightly lesser extent in Southwest Asia (i.e. the Middle East), is reasonably well established. We also see in the archaeological record a break in archaeological record of Acheulean tools in Africa ca. 600,000 years ago, where they become somewhat more sophisticated, sometimes attributed to Homo heidelbergensis.

But, there is a big gap in time between the youngest definitively non-modern human skeletons in Asia (other than Homo Florensis, the "hobbits" of the island of Flores in Indonesia), and the earliest definitive example of modern humans. Basically, we have a 300,000-400,000 year gap or so between the most recent Homo Erectus skeletons and the earliest arguable modern human skeletons (100,000 years ago), and there is good circumstantial evidence to think that modern humans were not pervasive in Asia until close to 75,000-45,000 years ago in Asia, with the more recent date marking the at which point modern humans reach Papua New Guinea and Australia in a historic moment marked by megafauna extinctions, reasonably well dated modern human skeletal evidence, and a sharp uptick in evidence of vegetation fires.

In the absence of skeletons, which the prevailing temperature and moisture conditions in much of Asia don't help to preserve, the next best things are stone tools, which are much more likely to be preserved and can serve as a proxy for the people who made them. Also, since the first modern humans in Asia would presumably have had post-Mousterian tool kits, which should be in sharp contrast to the Oldowan industry that apparently prevailed there until about 200,000 years ago.

Even looking to stone tools a proxy, we have a gap of at least 100,000 years, in comparison to a European fossil record that shows a gap between stone tool industries associated with Neanderthals and those associated with modern humans that are no more than 1,000 years in some of the better resolved sites with strata containing both kinds of tools. Perhaps this is simply a product of the low density of archaeologists in Asia and will be remedied in coming years.

The presence of Denisovian DNA admixture in modern humans from Papua New Guinea, pre-European Australians and Filipino Negritos suggests that there was some sort of archaic hominin in Southeast Asia with whom they could have admixed before the Denisovians vanished, with the last Denisovian traces found in a South Siberian cave ca. 40,000 years ago, around the same time as the last of the Neanderthals.

But, between the tiny bone from which the Denisovian ancient DNA was extracted (too small and isolated to make much in the way of speculation about even which species they belonged to), and the much, much older most recent Homo Erectus skeletal remains in Asia, we really have nothing in terms of hominin remains to go on. So, we don't know much about the hominins that modern humans encountered when they first arrived in Asia.

Were Denisovians the last of the Homo Erectus, or were they something else entirely? There is no other obvious alternative. But, the direct proof is surprisingly scant.

Megafauna Extinctions In Asia

Also, helpful would be evidence to date megafauna extinctions in Asia, if any (and it is not clear that this event took place in the same kind of way there), but I'm not as familiar with this evidence as I would like to be. But, as a 2007 article on the topic which asserted that there was a megafauna extinction in Southeast Asia explained "the chronological resolution of these extinctions is poor," in contrast with quite clear timelines in Australia and the Americas where there were no prior hominin presences before modern humans. The decline in megafauna there was less dramatic than in Northern Eurasia, Australia and the Americas, however.

Indeed, according to one source (Extinctions in near time: causes, contexts, and consequences By R. D. E. MacPhee (1999) at page 257), while there were pronounced megafauna extinctions in the Americas, Australia and Northern Eurasia, sub-Saharan Africa and Southern Asia "were hardly affected." In the first set of regions "all of the animals of 1000kg (1 metric tonne) or more became extinct. In contrast, all species of 1 tonne or more present in the Late Pleistocene of sub-Saharan Africa and southern Asia survive to the present day." But, more recent researchers have claimed that while current levels of megafauna diversity do go back to the sometime around the Late Pleistocene, that immediately prior to that there was significantly greater megafauna diversity in Southern Asia.

Does Co-Evolution Explain Megafauna Extinction Patterns?

The theory that exposure to Homo Erectus with primative Oldowan tools that they could survive without evolving signficantly helped megafauna to evolve enough to survive later hominin onslaughts makes sense in the case of Africa (humans co-evolved with megafauna there), Southern Asia (Homo Erectus with Oldowan tools appeared ca. 1,900,000 years ago), Australia (modern humans arrived suddenly ca. 45,000 years ago as the first hominin encounter) and the Americas (modern humans arrived suddenly ca. 14,000 years ago as the first hominin encounter), but doesn't make much sense at all in Northern Eurasia, where megafauna had long exposure to Neanderthals with tools more sophisticated than even Acheulean tools before modern humans arrived on the scene and wiped them out, particularly in light of recent evidence suggesting that the Neanderthal range extended much further North than previously believed depriving North European megafauna of a refugium where it was too cold for Neanderthals to survive.

Advanced tools did come relatively late to Europe compared to Africa: "Acheulean methods did not reach the continent until around 400,000 years ago." Indeed, the time frame is closer to the arrival of the Neanderthals in Europe than Homo Erectus.

But still, a co-evolution theory of megafauna extinction doesn't explain why other regions fit this theory while Northern Eurasia did not. One needs to twist the theory, perhaps with a co-evolution plus additional vulnerability to advanced hominin predators as a result of living in an ecologically margial region where it took "hunting plus" to dispatch these co-evolved large animals to fit Northern Eurasia into the rubric.

Does A Plains v. Hills Factor Explain Megafauna Extinctions in Northern Eurasia?

One could also argue that modern humans, at least, although this is less clear of their predecessor species, may have been adapted to savannah and open plain environments and used fire strategically in a way that produced extinctions, something not possible in Southern Asia that was too moist for mass wildfires and to heavily wooded to give modern humans a decisive advantage. Evidence from leg bone length relative to the rest of their bodies that Neanderthals may have been particularly adapted to steep terrains could also help explain why there was less co-evolution of Northern Eurasian megafauna with hominins than there was elsewhere, even if Neanderthals could handle more cold than previously believed. Perhaps it is much harder to take down an elephant or other large mammal with primative tools in small groups on open ground than it is in hills and mountains, and so Neanderthals adapted themselves to places where they could more effectively take down their big game quarry. (But note that 125,000 years ago, Neanderthals were apparently dining on shellfish in England.)

A range that was concentrated in hills and highlands would also help to explain how Neanderthals survived so many ups and downs of climate under modern humans arrived. The big game may have had refugia in the plains and steppes, where Neanderthals may have been less prone to hunt, so the Neanderthals may have been in an ecological balance that was buffered and prevented them from overhunting when the climate conditions were poor for their prey.

This could also explain why Neanderthals apparently didn't extend their range very far into Northern Eurasia, and it is quite possible that Asian Homo Erectus, unlike Neanderthals, never evolved to survive Northern Eurasia's close weather and never ventured much further north than the Denisovians (perhaps pushed to this clime by population pressures from modern humans) ever did.

Why Care About Climate Change?

There are essentially four bad things that could result from climate change as far as typical Americans are concerned:

(1) Ice caps could melt causing sea levels to rise and causing storms in coastal areas to become more worrisome. Anybody with a topographic map can see who the winners and losers are in a rising sea level scenario, although far more elaborate reports show the same thing. Suffice it to say that South Florida, coastal property owners, people who abut salt water wetlands and estuaries (e.g. many people in Louisiana), and people on low lying islands are screwed if the sea level rises too much.

(2) Droughts could be more intense and longer, turning arid places to deserts, expanding existing major deserts, and turning places that get sufficient moisture now into arid environments. This is a really troubling possibility as it could lead to massive crop failure, famine, and large scale migration of people from arid areas that could provoke wars.

(3) Increased temperatures could allow previously tropical flora and fauna to move to higher latitudes than their conventional range, including disease carrying bugs to which local humans, flora and fauna lack resistance. This would require significant adaptations in the affected regions.

(4) Snow capped alpine areas could get less snow, destroying ski resort based economies where they currently exist. Bad news for Vail, but it probably won't utterly destroy life as we know it. The more serious piece of this development, however, would be that snow packs are a principal source of fresh water for people in the river basins that the snowpacks feed.

Note that any one of these possibilities, by itself, is a real problem, regardless of its precise cause or the mechanism of that cause, and that shrinking ice caps, retreating alpine deserts, expanding deserts, and the migration of tropical flora and fauna to higher latitudes have all independently been observed over the last few centuries and particularly intensely in the last dozen or so decades.

Even if sea levels stop rising or ski areas stay white, if a couple of the other observed trends continue, the world has a problem. Conservely, even if the predicted droughts and tropical zoology range expansions don't happen, rising sea levels or shrinking alpine snow cover present their own worries.

Maybe there are other effects as well. But, it doesn't matter much if there are or there aren't. Ice caps, sea levels, glaciers, desert area, droughts and tropical zoology ranges aren't just canaries in the mine, they are the harm causing symptoms of climate change themselves. These observed phenomena are the principal reasons that we care if climate changes. And, to the extent that man made air pollutants are linked to these particular symptoms, it really doesn't matter if every single prediction of global warming models pans out. Maybe there will be global cooling elsewhere, for example. Who cares? The results are robust enough to act upon. The data that climate change is really happening is overwhelming.

Also, there are two kinds of policy responses to climate change. One is to stop making the situation worse by controlling air pollution. The other is to prepare to respond to the symptoms of climate change whatever the reasons for it may be. Even if there is a lack of political will to address the former, because of doubts (even if never very well grounded scientifically) about the cause of climate change, that shouldn't matter when it comes to policy responses to address the latter.

Natural climate change will flood beach front properties, drown the Everglades, shrink the land area of Louisiana dramatically, devistate the Colorado ski industry, cause crop failures and civil war spawning mass migrations, and welcome tropical bugs into more Northern climes just as well as man made climate change. These traumas aren't going to get any easier to deal with if we wait for them to happen.

The point of this post is that one only needs a quite weak set of assumptions about climate change to justify some kinds of policy actions, and an even weaker set of assumptions about climate change to justify other particular sets of policy actions. So, even if one is skeptical about some versions of global climate change models or the mechanism involved in formulating them, this doesn't necessarily mean that the skepticism is about anything that really matters from a policymaker's perspective on particular issues that really matter.

In the same way, skepticism about the Higgs boson's existence doesn't imply that one should be skeptical about the accuracy of Kepler's laws in the solar system or the rules for determining the voltage at a particular point in an electrical circuit. Climate change data, like non-fundamental laws of physics, are robust enough that they can speak for themselves and be relied upon even in the absence of a perfect theory to explain them.

LHC and SUSY Models

As the chart (from here) above illustrates, the Large Hadron Collider is providing excellent confirmation of the Standard Model of Particle Physics and strong exclusions for any Beyond The Standard Model physics, including anything predicted by supersymmetry (i.e. SUSY), at the energy scales that it is capable of exploring.

Another chart (from the same source blog post) maps the exclusion range for two key SUSY parameters that determine the masses of all of the SUSY particles:

the two quantities on the axes are the universal masses of scalars (in the horizontal axis) and fermions (in the vertical axis). The filled areas contain parameter space points excluded by previous experiments; the black thin lines show the mass of gluinos and quarks that the parameter space points correspond to. The ATLAS exclusion region is the one to the left and below the thick purple curve. In green is shown the result of another ATLAS search, which considered events with smaller jet multiplicities, again containing large missing Et.

The bottom line is that SUSY theories with light superpartner particles, particularly light supersymmetric bosons (which would be the superpartners of ordinary fermions) in models which light supersymmetric fermions (which would be the superparners of ordinary bosons), are excluded.

Indeed, given that the heaviest ordinary fundamental fermion (the top quark) is about 174 GeV and the heaviest ordinary fundamental boson (the Z boson) is about 91.1 GeV, and that supersymmetry models, in general, call for exactly three generations of ordinary fermions, one can conclude, for example, from the exclusion data that:

1. All supersymmetric fermions are heavier than all ordinary fermions and bosons, and
2. All supersymmetric bosons are heavier than all ordinary fermions and bosons.

Supersymmetry suggests that almost all of the superpartners would be unstable, which isn't really a surprise and wouldn't be even if they were much lighter, as all but two Standard Model quarks, one standard model charged lepton, (arguably all three Standard Model neutrinos) and only the massless Standard Model bosons (not the W or Z bosons), are stable themselves, and eight of the nine kinds of massless Standard Model bosons (gluons) are part of sets of particles confined into hadrons and hence can't be observed directly.

In supersymmetry models where R parity must be observed (i.e. supersymmetric-ness like baryon number, lepton number, and charge must be conserved in a particular way), this leaves only a couple of stable superpartners. The much higher masses of superpartners than ordinary particles presumably also imply that they decay much more rapidly than ordinary particles when they aren't stable rest states.

Lubos cites a claim that the exclusion ranges aren't quite as tight as the chart above would suggest. One model he cites (and in fairness, he cites it simply as an example to illustrate that LHC boundaries aren't really so tight and not as a likely correct version of SUSY) claims that there could be a Higgs (a neutral scalar boson), a neutralino (a neutral fermion) and an stau (a charged boson) all with masses between that of a Z boson and a top quark that remain undiscovered. It claims that:

While basic supersymmetric constructions such as mSUGRA and the CMSSM have already suffered overwhelming reductions in viable parameterization during the LHC's initial year of operation, about 80% of the original No-Scale F-SU(5) model space remains viable after analysis of the the first 1.1 fb^-1 of integrated luminosity. This model is moreover capable of handily explaining the small excesses recently reported in the CMS multijet supersymmetry search, and also features a highly favorable "golden" subspace which may simultaneously account for the key rare process limits on the muon anomalous magnetic moment (g - 2) and the branching ratio of the flavor-changing neutral current decay b to s\gamma. In addition, the isolated mass parameter responsible for the global particle mass normalization, the gaugino boundary mass M_1/2, is dynamically determined at a secondary local minimization of the minimum of the Higgs potential V_min, in a manner which is deeply consistent with all precision measurements at the physical electroweak scale.

But, I find it extraordinarily unlikely that there are thirteen undiscovered SUSY particles with masses of less than 800 GeV out there (some fermions, some bosons (scalar and non-scalar), some charged, some electromagnetically neutral), yet somehow LHC and every other detector known to mankind has never seen a convincing whiff of even one of them.

The absence of direct detection of particles shouldn't be the only clue that SUSY is out there, if it is real. We would also expect to see some sort of phenomenology beyond direct detection of new particles.

The spectrum of superpartners, at this stage of the exclusion range, seem to be limited to what amounts of another high energy phase of particles that are never found in nature at anything other than energies seen moments after the Big Bang and have almost no influence at all on lower energy Standard Model interactions. SUSY exists mostly to keep the Standard Model equations well behaved at high (roughly TeV plus) energy scales and the evidence is overwhelming that SUSY adds no predictive experimental power to the Standard Model at early LHC run scales.

The only really strong phenomenological implication of SUSY at low energies is that it provides dark matter candidates, most probably in the form of a neutralino in the hundreds of GeV plus mass range.

The trouble is that the experimentally permitted mass ranges for neutralinos, while they would make fine dark matter candidates, would be incompatible with recent astronomy data that seem to exclude dark matter candidates that are that heavy mostly on the grounds that they would produce a different kind of large scale structure to the universe at the galactic scale. Direct dark matter detection experiments have also failed to find any dark matter candidates that heavy. Thus, the only significant low energy phenomena that one would expect from an R-parity observing SUSY theory is inconsistent with experimental data.

Experimental data from dark matter searches related to models of the large scale structure of the universe and the direct detection experiments leave only a twinkle of a change that there could be anything in the single digit GeV range (it would probably have to have different cross sections of interaction within the Earth and in open space by a factor of about 0.7), and the large scale structure data points towards dark matter particles about six orders of magnitude lighter (i.e. lighter by a factor on the order of 10^6) than the proposed neutralino mass in the toy model of SUSY that Lubos refers to in his post.

If SUSY isn't providing a dark matter candidate, and isn't explaining any sub-TeV energy scale phenomena, it becomes increasingly clear that even if SUSY is out there is some way, that it is utterly irrelevant from a technology perspective and can't add much to any other branch of science outside high energy physics. At the energy scales where it becomes relevant, conditions are too energetic to even be very useful in modeling the internal workings of stars in any way that is observable. It might conceivably help us make sense of how the pieces in the Standard Model fit together better, but that is about it.

All of this has deeper stakes than SUSY extensions of the Standard Model, of course, because all versions of M theory a.k.a. String Theory, have SUSY embedded into them as a low energy limit of the theory. The positive piece of this, of course, is that the Standard Model is the low energy limit of SUSY. The negative piece of this, however, for string theorists, is that a failure to find any evidence of SUSY casts doubt on String Theory as a whole.

If a SUSY sourced dark matter candidate consistent with other lines of evidence about dark matter mass ranges is not found, all of string theory is strongly disfavored by the available data from experiments and astronomy observations.

In the meantime, all eyes will be on what LHC can tell us about the 115 GeV-125 GeV mass range, which is for a wide variety of reasons the most plausible mass range by far for a Standard Model Higgs boson or a lightest SUSY Higgs boson, if one exists, given the data we have in hand right now.  A "medium weight" Higgs has been all but completely ruled out and the mass limitations on a very heavy Higgs (>500 GeV), which itself necessarily requires beyond the Standard Model physics, are increasingly rising as well.