Thursday, June 29, 2017

Constrictor Snakes Kill By Ending Blood Circulation

According to new research in the Journal of Experimental Biology, the constrictor part of boa constrictor actually refers to the snake’s squeeze cutting off its prey’s blood supply—not its breath.

Despite sounding worse, it actually ends things for the poor little critter about to be lunch much faster: While most animals can survive short periods without breathing, once the snake begins to squeeze, it cuts off the victim’s circulation, causing the animal to pass out within seconds. . . . the prey soon dies from heart failure, not shortness of breath.
From here.

Armenia's mtDNA Gene Pool Basically Unchanged Since The Mesolithic

A new review of ancient mtDNA in the Southern Caucasus mountains region reveals that the make up of this gene pool has changed little over the last 10,000 years despite the introduction of agriculture and the appearance of multiple archaeological cultures over that time period.

On one hand, this isn't terribly surprising, since the mtDNA mix in a region tends to be more stable over long periods of time than the Y-DNA mix and autosomal genetics of the same region. On the other hand, most of Europe saw a dramatic shift in mtDNA frequencies with the arrival of the Neolithic revolution, and another in the late Neolithic/early to middle Bronze Age period when there were mass migrations from the steppe.

The Caucasus, in contrast, have not seen a major mtDNA turnover which is consistent with the perception that it is a refugium in which direct ancestors of ancient populations have more staying power than they do elsewhere.

mtDNA is inherited by children solely from their mothers, so this mtDNA continuity implies that any changes in the gene pool in the Southern Caucasus mountain region over the last 10,000 years must have derived mostly from male dominated migrations (which the Y-DNA pool of the region suggest did indeed take place on at least a few occasions in some locations).

The fact that this mtDNA pool is not dominated almost entirely by a few clades of mtDNA haplogroup U is also notable, because this clade is dominant among most hunter-gather populations of Europe during the Mesolithic, probably because these populations were derived from a small number of refuges that weathered the Last Glacial Maximum period. Apparently, the refuge from which the repopulation of Europe took place was not the one in the Caucasus.

UPDATE July 10, 2017:

Davidski identifies some serious methodological flaws that detract from this conclusion. Basically, all ancient DNA samples are lumped into one group despite the fact that the 52 samples span 8,000 years of time. He sees shifts in the gene pool in the early Bronze Age looking at the raw data.


Wednesday, June 21, 2017

Explaining Matter-Antimatter Asymmetry

I've long been an advocate of an approach to explaining the matter-antimatter asymmetry of the universe in which antimatter predominantly in a partner universe whose boundary with our own is at a shared Big Bang. A brief new paper explores the idea more formally, although the use of multiverse terminology is somewhat unfortunate for a proposal that lacks many of the flaws more commonly found in multiverse arguments.
In the multiverse, the universes can be created in entangled pairs with spacetimes that are both expanding in terms of the time variables experienced by internal observers in their particle physics experiments. The time variables of the two universes are related by an antipodal-like symmetry that might explain why there is no antimatter in our universe: at the origin, antimatter is created, by definition and for any observer, in the observer's partner universe. The Euclidean region of the spacetime that separates the two universes acts as a quantum barrier that prevents matter-antimatter from collapse.
Salvador J. Robles-Perez, "Restoration of matter-antimatter symmetry in the multiverse" (June 20, 2017).

An earlier version of the proposal from 2013 can be found here.

Why Are Hyaenas Smart?

Behavioural data indicate that there has been considerable convergence between primates and hyaenas with respect to their social cognitive abilities.
From here (hat tip to Razib Khan).

I have long attributed the exceptional intelligence of hyaenas, one of the most intelligent and successful African megafauna, to the fact that unlike most other mammals, the reproductive organs of hyaenas require both the male and female to be simultaneous aroused to reproduce. This has the effect of giving female hyaenas much more control of their reproductive decisions than comparable felines and canines. 

Hyaenas are the poster children for Planned Parenthood of the animal world.

Cosmopolitan Scandinavians Of Old And Y1K

In the Middle Ages in Europe it is commonly said that most people never traveled more than thirty miles from where they were born. But, then there were the Vikings:
In the centuries around and before 1000 A.D. there was a “Viking international” of sorts. Harald Hardrada may have died in England trying to become king of that nation, but he served for a time in the Varangian Guards in Constantinople. His connections to Kievan Rus were such that priests in the Eastern Christian tradition were brought in to aid in the conversion of Norway.
N.B. The time period that I call Y1K was a fascinating one all over the world. For example, Viking Lief Erikson makes it to the New World, the Gypsies start their migration from India, the Brahui migrate from the Deccan Peninsula to the Indus River Valley, the Crusades start one of the first very distant foreign wars in history, and more.

Even before the Vikings, the Bronze Age Scandinavians got around as well. There is evidence of trade of amber for Egyptian jewelry that brought goods, and probably people with them, from the Baltic Sea to Egypt.

Monday, June 19, 2017

Physics Is Culturally Neutral

Lubos Motl should know better than to make the ad hominem argument that a physics concept is discredited just because a Nobel Prize winning physicist who also became a Nazi at some point in his life toyed with the idea.

In this case he is attacking the loop quantum gravity approach to quantum gravity (he prefers the approach to quantum gravity based upon gravitons in 10-11 dimensional string theory), because the physicist who invented the cathode ray tube (which was at the heart of all video screens for half a century) toyed with a somewhat similar aether theory.

Loop quantum gravity (LQG) is a really a class of theories of quantum gravity that argues that, as in general relativity, gravity involves a background independent deformation of space-time, rather than a force mediated by a boson in the special relativistic space-time background of quantum-mechanics. Thus, in loop quantum gravity, there is quantization of space-time at the Planck scale, rather than quantization of a force acting between particles.

It is certainly fair game to criticize potential flaws in one of the two major approaches to quantum gravity, which is one of the great unsolved problems of physics, and eventually he does address some of his concerns on that score.

But, it is not fair game to field as an argument against LQG the politics of an admittedly technically accomplished physicist who explored a distant predecessor of the idea, any more than it is to denounce half a century of television screens as "Nazi Science". This is the kind of criticism that confuses people who don't know better while not informing or persuading anyone who does know better. It is particularly unseemly coming from someone whose own distasteful politics and poor social skills appear to have cost him a position in the physics department at Harvard, despite his clearly solid command of the discipline of physics itself, however, opinionated he might be in that regard towards rival approaches in his discipline.

Motl's offhand accusations of plagiarism directed at an academic rival (which having read many of the academic rival's papers, I can confidently tell you is hog wash), and his failure to engage in the real issues by offering up straw man versions of LQG, are likewise unworthy of a serious and sincere academic.

Wednesday, June 14, 2017

Social v. Solo Spider Genetics

Social spiders have a homogenized, less diverse gene pool than solo spiders.

Chesapeake Bay Conceals A 35 Million Year Old Impact Crater

There is a 35 million year old impact crater from an extraterrestrial impact in Chesapeake Bay (which is in the vicinity of Washington D.C.). 

This particular impact isn't associated with any major extinction event extreme enough to find in the paleological record, although it surely had lesser climate and impact effects, but it is a good illustration of how a body of water can conceal an impact crater.

Parsi Genetics

I have seen the new paper on the genetics of the contemporary Parsi (i.e. Zoroastrian) population of South Asia, but I didn't blog it, except in passing as a link to a post that mentions it in another post. Here is the abstract and citation to the paper (emphasis mine).
The Parsis are one of the smallest religious communities in the world. To understand the population structure and demographic history of this group in detail, we analyzed Indian and Pakistani Parsi populations using high-resolution genetic variation data on autosomal and uniparental loci (Y-chromosomal and mitochondrial DNA). Additionally, we also assayed mitochondrial DNA polymorphisms among ancient Parsi DNA samples excavated from Sanjan, in present day Gujarat, the place of their original settlement in India. 
Among present-day populations, the Parsis are genetically closest to Iranian and the Caucasus populations rather than their South Asian neighbors. They also share the highest number of haplotypes with present-day Iranians and we estimate that the admixture of the Parsis with Indian populations occurred ~1,200 years ago. Enriched homozygosity in the Parsi reflects their recent isolation and inbreeding. We also observed 48% South-Asian-specific mitochondrial lineages among the ancient samples, which might have resulted from the assimilation of local females during the initial settlement. Finally, we show that Parsis are genetically closer to Neolithic Iranians than to modern Iranians, who have witnessed a more recent wave of admixture from the Near East. 
Our results are consistent with the historically-recorded migration of the Parsi populations to South Asia in the 7th century and in agreement with their assimilation into the Indian sub-continent's population and cultural milieu "like sugar in milk". Moreover, in a wider context our results support a major demographic transition in West Asia due to the Islamic conquest.
Gyaneshwer Chaubey, et al., "'Like sugar in milk': reconstructing the genetic history of the Parsi population"(June 14, 2017)

Tuesday, June 13, 2017

Baryon Effects Can't Save Cold Dark Matter Models

The New Result

Simulations that include only Cold Dark Matter (CDM) don't reproduce something close to reality at the galaxy scale. One argument that this doesn't invalidate CDM models is that interactions between ordinary matter and dark matter (baryon effects) cure this problem and bring CDM models more closely into line with observed reality. CDM models can include baryon effects that can solve the problem, but they have to be highly unrealistic to accomplish this goal.

Now, a realistic, bottom up effort to determine that magnitude of these baryon effects has established that baryon effects don't solve the problems with cold dark matter models that are revealed in simulations using only cold dark matter.

Where Does This Leave Us?

First, dark matter phenomena are absolutely real and everyone agrees that this is the case. But, there is lack a consensus explanation of the mechanism behind these phenomena.

Warm Dark Matter Is Still Viable, But Is Tightly Constrained

This new result leaves basically one viable particle dark matter model: warm dark matter (WDM) with particles with masses of ca. 2-15 keV. There are very tight constraints on the parameter space of WDM, but those constraints still, just barely, leave a narrow mass range open. If one were looking for a theoretical framework to fit WDM into, a gravitino without other SUSY particles, a right handed neutrino, or a sterile neutrino singlet would both be plausible, yet minimal models. But, a neutrino that oscillates with ordinary neutrinos is also extremely constrained in parameter space.

Some Gravity Modification Theories Are Still Viable

There are also multiple gravity modification theories that could explain dark matter phenomena, although some gravity modification theories have been shown to be inconsistent with experiment. (Not, however, due to the Bullet Cluster which actually favors modified gravity theories over particle dark matter theories.)

Self-Interacting Dark Matter Models Are Pretty Much Ruled Out

Models with a 5th force finite but long range Yukawa force transmitted by a massive boson that acts between dark matter particles called self-interacting dark matter (SIDM) looked promising for a while. But, pretty much all plausible models of SIDM have been completely ruled out because sufficiently strong self-interactions should give rise to dark matter annihilations which are not observed. Also, while Occam's razor is pretty neutral between the WDM and gravity modification approaches discussed above, it disfavors SIDM which basically requires both.

Axion Dark Matter Isn't Definitively Ruled Out But Is Materially Constrained

It isn't entirely clear how axion dark matter models measure up - the range of axion dark matter models under consideration is great and the phenomenology seems to be all over the map, and this approach isn't subject to the limitations associated with thermal dark matter models. Most axion dark matter proposals mostly aren't a good fit to the originally proposed particle that would explain why there is no CP violation in the strong force (which I have never found compelling), however. And, this parameter space is still meaningfully constrained.

Not Clear Where Wave Dark Matter Stands

Another proposal which I haven't seen definitively ruled out is wave dark matter.

Cold Dark Matter, Including WIMPs And MACHOs Are Ruled Out

But, pretty much the entire universe of CDM (the subset of CDM called WIMPs is already pretty much ruled out by direct detection experiments which is bad news for SUSY theories which generically predict WIMP dark matter candidates) and MACHOs (such as primordial black holes) has been ruled out in an increasingly convincing way.

Any Dark Matter Candidate Must Be Basically Sterile And Stable At Low Energies

Of course, by hypothesis, any particle that interacts via the electromagnetic force or strong force was ruled out. And, experiments in the parameter range that remains viable for any kind of dark matter particle rules out any weak force interactions comparable to those of the existing Standard Model particles. So, any dark matter candidate needs to be basically completely "sterile" (i.e. without interactions other than Fermi contact interactions), at least at low energies.

Dark matter must also be either completely stable, or "metastable" with a mean lifetime on the order of the age of the universe or more.

Two Waves Of Steppe Migration?

Davidski at his Eurogenes blog, buried in a lot of technical jargon and software discussion, makes a pretty notable observation

He observes that the steppe component of the autosomal genetics of some South Asian populations shows a greater affinity to ancient Yamnaya genomes, which he attributes to an earlier Indo-Aryan wave of migration (speaking an early dialect of Sanskrit), while the steppe component of some linguistically Indo-Iranian populations (the oldest attested ancestral versions of which are Avestan a.k.a. Zend, and Old Persian) shows greater affinity to ancient Andronovo genomes, which he attributes to a later Indo-Iranian wave of migration.

Some quotes from his post (quotation updated in this post on June 14, 2017 as indicated, all emphasis mine):
My main model is also a decent statistical fit for at least a number Indian groups, like, for instance one of the Gujarati subpopulations labeled GujaratiD in the Human Origins dataset. But it fails marginally for Pathans, so it's not a robust solution for all of South Asia. Incredibly, using Andronovo instead of Yamnaya in the Pathan model makes it work. Tajiks can also be modeled in this way using Andronovo. I say incredibly, because Pathans and Tajiks are obviously Iranic speakers, and their Iranic ancestors in all likelihood arrived in South Asia from the Eurasian steppe much later than the Indo-Aryan ancestors of the Kalash and most Indians. . . .
So what we might be seeing here is substructure within the steppe-related admixture amongst South Asians, with Indo-Aryan speakers apparently showing Yamnaya-related (Catacomb?) ancestry, and Iranic speakers, as well as possibly groups with significant Iranic ancestry, showing a preference for later Andronovo-related ancestry.
Update 14/06/2017: I've now had the chance to test many more Indo-Aryan and Iranic groups with my model. Most of these groups show a slight, non-significant, preference for Yamnaya_Samara as the steppe reference population. However, those that show a slight, and again non-significant, preference for Andronovo are usually Iranic, such as the Balochi in the graphs below. I'm not claiming that this proves anything, but I do think that it hints at something, and I'll try testing a few different hypothesis in the near future[.] 
In fairness to Davidski, should this not pan out, he has made clear that this analysis is preliminary and involves some of the first times that he has used a new software tool that he is not yet fully familiar with using. Also, as an editorial note, if I recall correctly, the GujaratiD population consists of ethnically Gujarati immigrants from India in Dallas, Texas. (Similarly, one of the major reference sets of Chinese genomes, CHD, consists of Han Chinese immigrants from Denver and one of the major reference sets for Northern European CEU, consists of white people from Utah).

This is very plausible in historical context. It would also explain why it is hard to develop a good fitting model that involves just a single wave of steppe migration to South and West Asia, which has been pretty much the default assumption so far.

ANI v. ASI Puzzles That May Or May Not Be Related

It isn't clear if this has anything to do with an analysis of contemporary South Asian genomes using linkage disequilibrium dating (a methodology that is heavily biased towards the most recent date of any admixture) that appears to reveal that places in North India, which should have encountered Indo-Aryans first, shows the youngest data of most recent Ancestral North Indian (ANI) admixture, suggesting that these areas experienced two, rather than one, wave of ANI admixture. But, it is quite possible that this is unrelated and that the ANI in both waves of admixture was basically the same genetic population.

I should also note that while ASI (Ancestral South Indian) genetics are probably autochthonous and from a single source, the ANI is a component is probably composed of multiple layers: a Paleolithic North Indian layer with a clinal relationship to ASI (possible pre-dating the Last Glacial Maximum ca. 18,000 BCE given its affinity of ASI to Onge DNA), a Harappan layer from West Asian Neolithic migrants (ca. 7000 BCE given the date of the Indus River Valley Neolithic), but possibly including additional migration, for example, in connection with an Uruk expansion from Mesopotamia that occurs around the time that Harappan civilization with which it had trade ties, emerges, and at least one subsequent layer of Indo-Aryan steppe migrant contributions (ca. 2000 BCE to 1500 BCE), but quite possibly two layers.

Uruk Expansion

Razib Khan has been dropping hints in several posts that he is interested in the explanatory possibilities of the Uruk expansion from Mesopotamia ca. 3600 BCE, that could be an important genetic and cultural source for the people in the nearby highlands of Anatolia, the Caucasus and West Asia, and ultimately perhaps also cultures influenced secondarily by those cultures such as the Minoans and maybe even the Yamnaya people.

I agree and think that this could be at the root, which is perhaps too deep in time depth to be discerned definitively from linguistic data given the quality of the available linguistic data, of the ergative languages of this region and perhaps also Basque.

About Kashmiri

Another interesting aside, from a post at the Brown Pundists blog, is that the Kashmiri language is closer in many respects to Sanskrit than other Indo-Aryan languages.

Wednesday, June 7, 2017

300,000 Year Old Modern Human Bones Found In Morocco

Image from here.

Just two days after a paper analyzing 2000 year old Khoi-San DNA from South Africa and determining that the Khoi-San divergence date from other African populations was ca. 260,000 years ago, there is an announcement that an anatomically modern human bone that is 300,000 years old has been found, much older than the oldest accurately dated modern human remains previously known from about 195,000 years ago in Ethiopia.
The oldest fossil remains of Homo sapiens, dating back to 300,000 years, have been found at a site in Jebel Irhoud, Morocco. This is 100,000 years older than previously discovered fossils of Homo sapiens that have been securely dated. The discovery was presented in a study in the journal Nature on Wednesday. 
This marks the first discovery of such fossils in north Africa, and widens the "cradle of mankind" to encompass all of Africa, the researchers said. Previous finds were in south or east Africa. The fossils, including a partial skull and a lower jaw, belong to five different individuals including three young adults, an adolescent and a child estimated to be 8 years old. Stone tools, animal bones and evidence of fire were also found within the same layer at the site.
This result doesn't strongly contradict the current paradigm, but does clearly push it in the direction of older anatomically modern human speciation (Y-DNA had pointed to a date about 270,000 years ago), and a wider geographic range within Africa of early modern humans. This also brings the speciation date closer to the divergence date for other archaic hominins like Neanderthals and Denisovans.

The abstract and citation to the paper are as follows:
The timing and location of the emergence of our species and of associated behavioural changes are crucial for our understanding of human evolution. The earliest fossil attributed to a modern form of Homo sapiens comes from eastern Africa and is approximately 195 thousand years old1, 2, therefore the emergence of modern human biology is commonly placed at around 200 thousand years ago3, 4. The earliest Middle Stone Age assemblages come from eastern and southern Africa but date much earlier5, 6, 7. Here we report the ages, determined by thermoluminescence dating, of fire-heated flint artefacts obtained from new excavations at the Middle Stone Age site of Jebel Irhoud, Morocco, which are directly associated with newly discovered remains of H. sapiens8. A weighted average age places these Middle Stone Age artefacts and fossils at 315 ± 34 thousand years ago. Support is obtained through the recalculated uranium series with electron spin resonance date of 286 ± 32 thousand years ago for a tooth from the Irhoud 3 hominin mandible. These ages are also consistent with the faunal and microfaunal9 assemblages and almost double the previous age estimates for the lower part of the deposits10, 11. The north African site of Jebel Irhoud contains one of the earliest directly dated Middle Stone Age assemblages, and its associated human remains are the oldest reported for H. sapiens. The emergence of our species and of the Middle Stone Age appear to be close in time, and these data suggest a larger scale, potentially pan-African, origin for both.
Daniel Richter, et al., "The age of the hominin fossils from Jebel Irhoud, Morocco, and the origins of the Middle Stone Age" 546 Nature 293–296 (June 7, 2017).

A sister paper discusses the taxonomy of these remains and assigns them to the "early stages of the H. sapiens clade" despite a mosaic and archaic and primitive features. It may be more fair to classify these remains as transitional between archaic and anatomically modern human, rather than a completely anatomically modern human individual. John Hawks is tweeting his skepticism about the classification of these remains as Homo sapiens with a cogent and fuller explanation here.
Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure because the fossil record is scarce and the chronological age of many key specimens remains uncertain. In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315 ± 34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established. Furthermore, it shows that the evolutionary processes behind the emergence of H. sapiens involved the whole African continent.
Jean-Jacques Hublin, et al., "New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens" 546 Nature289–292 (June 7, 2017)

SUSY With Different Assumptions

As the early efforts to use the GAMBIT software that fits data to supersymmetry (SUSY) and supergravity (SUGRA) models illustrates, the targets of these beyond the Standard Model (BSM) SUSY and SUGRA models are anything but random. Some of the assumptions include the following:

* Dark matter has a particle nature and is composed primarily of the lightest stable supersymmetric particle (the LSP). Usually, this is accomplished with conservation of a supersymmetric quantum number called R-parity, although sometimes R-parity conservation is only approximate allowing for an unstable LSP with a lifetime on the order of the lifetime of the universe.

* Neutrinos are Majorana particles. Often a see-saw model and right handed neutrinos are assumed as well.

* None of the Standard Model particles are super-partners of each other.

* SUSY and SUGRA models are embedded in a larger grand unified theory (GUT) that gives rise to gauge coupling unification at a GUT scale.

* The extended boson sector of SUSY And SUGRA do not create any new fundamental forces with new fields that have additional coupling constants, and certainly not to any with phenomenological importance that is observed empirically.

* The gluons, the photon and the graviton are the only zero mass particles.

I'm sure that there are other  important assumptions that I've overlooked.

Suppose that you remove the assumption that there is a stable or metastable LSP because dark matter phenomena can be fully understood as arising from graviton self-interactions (as proposed, for example, by Alexandre Deur) not properly accounted for in general relativity, rather than from dark matter particles. This would make R-parity conservation unnecessary (and indeed, maybe even preferable to do without to avoid creating additional kinds of dark matter which have not been detected experimentally). The lack of the need for an LSP also reduces pressure on the need for an LSP that is fairly close to the electroweak scale in mass.

Also, suppose that supersymmetric particles exist at high energy scales far in excess of the electroweak scale, for example, with masses on the order of 1-50+ TeV, as LHC results to date strongly suggest, although relaxing the assumption that there is a stable or metastable LSP also greatly opens up the parameter space of supersymmetry. This masses might be tied not to the ordinary Higgs boson (which would be the light scalar little h Higgs boson in this scenario), but to a heavy quartet of Higgs bosons (A, H, H+ and H-) at masses of the same order of magnitude as the mass scale of the heaviest supersymmetric particles.

Naively, this would lead us to expect that it is highly likely that supersymmetric particles would have very short lifetimes, presumably far shorter  than those of the top quark, Higgs boson, W boson and Z boson which are currently the most short lived known particles (although how a particle could experience W boson weak decay in a time period of less than the W boson lifetime is problematic, perhaps a W' boson would be necessary). 

Of course, while this would make fitting experimental data easier, it isn't obvious that this achieves much in terms of explanatory power. Certainly, for example, it does little to solve the hierarchy problem in a "natural" way which was a major motivator for SUSY in the first place.

Monday, June 5, 2017

One Guy's Ideas About Links Between The Harappan And Brahmi Script

The paper is Subhajit Ganguly, "Relation Between Harappan And Brahmi Scripts" (copyright 2012 uploaded in 2017).

It is posted on the vixra site (an ungated pre-print archive mostly for non-professional researchers) which is notorious for crackpot postings, particularly in some of its forums such as those related to fundamental physics, but is not always so far off the mark in some of its other forums. Nothing on the vixra site, including this paper, should be taken as proven, but every once and a while one of its authors produce some interesting ideas like this one that deserve a little further attention. There are several other papers posted at the site by the same author on the same theme.

The abstract states:
Around 45 odd signs out of the total number of Harappan signs found make up almost 100 percent of the inscriptions, in some form or other, as said earlier. Out of these 45 signs, around 40 are readily distinguishable. These form an almost exclusive and unique set. The primary signs are seen to have many variants, as in Brahmi. Many of these provide us with quite a vivid picture of their evolution, depending upon the factors of time, place and usefulness. Even minor adjustments in such signs, depending upon these factors, are noteworthy. Many of the signs in this list are the same as or are very similar to the corresponding Brahmi signs. These are similarities that simply cannot arise from mere chance. It is also to be noted that the most frequently used signs in the Brahmi look so similar to the most frequent Harappan symbols. The Harappan script transformed naturally into the Brahmi, depending upon the factors channelizing evolution of scripts.
The Harappan script is last attested ca. 1900 BCE when that civilization collapsed and remains undeciphered with disputed theories regarding its origins and the origins of the language it describes. There are credible claims, however, that it continued to be used on a limited basis until 1500 BCE or even as late as 1100 BCE. There is serious dispute over whether the Harappan script codes a true language, or merely a proto-language made up mostly of trademarks, analogous to the Vinca script of the Neolithic Vinca culture in the Balkans. Per Wikipedia
An opposing hypothesis that has been offered by Michael Witzel and Steve Farmer, is that these [Harappan] symbols are nonlinguistic signs which symbolise families, clans, gods, and religious concepts—similar to components of coats of arms or totem poles. In a 2004 article, Farmer, Sproat, and Witzel presented a number of arguments stating that the Indus script is nonlinguistic, principal among them being the extreme brevity of the inscriptions, the existence of too many rare signs (increasing over the 700-year period of the Mature Harappan civilization), and the lack of the random-looking sign repetition typical of language.
A couple of credible academic claims have been made, however, that the script actually codes the Harappan language.

The earliest attested version of the Brahmi script is roughly the 3rd century BCE and its origins are disputed among professionals, and it wouldn't take many undiscovered inscriptions to bridge the gap in an area where there is probably a significant amount remaining to be discovered in the archaeological record. The leading view is that the Brahmi script is ultimately derived from the Phoenician script that is the source of the Roman and Greek alphabets, for example, but this is not a consensus view and the argument for an indigenous origin of the script also has credible supporters within academic linguistics.