Vacuum Decay Is Not Coming Soon To A Place Near You

I have a short piece at Quanta Magazine this week, about a physics-y end of the world as we know it called vacuum decay. . . .

Gamma () here is the decay rate, its inverse gives the time it takes for a cubic gigaparsec of space to experience vacuum decay. The three uncertainties are from experiments, the uncertainties of our current knowledge of the Higgs mass, top quark mass, and the strength of the strong force. . . . Vacuum decay might happen in as few as years or as many as years, and that’s the result of an actual, reasonable calculation! 

From 4gravitons.

This is yet another circumstance in which precise measurements of these particular physical constants matter a lot. 

The relative uncertainty in the Higgs boson mass is about 0.08%. The relative uncertainty in the top quark mass is about 0.17%. The relative uncertainty in the strong force coupling constant is about 0.76%. The observable universe is about 10^10.15 years old.

Atri's Eclipse

This paper on ancient astronomy is relevant to dating the Rig Veda itself, and by association, the timing of the Indo-Aryan migration to India. 

The dates that are proposed are very early compared to estimates of the timing of the Rig Veda from other sources, which could reflect an oral tradition from either the pre-existing Indo-Iranian (which is associated with the the early Andronovo culture of ca. 2000 BCE) or Harappan cultures. 

It could reflect misanalysis by the authors of the "legendary history" described in the Rig Veda, which could correspond to knowledge of the existence of solar ellipses and a fictional invention with religiously or symbolically important dates (at a time when nobody could confirm the account), and not to a particular actual solar ellipse in India with the timing relative to the equinoxes described.

The earliest written reference in Indian astronomy to a total solar eclipse is in the Rig Veda where Rishi Atri is said to have demolished the asura Swarbhanu to liberate the Sun from a total solar eclipse. 

The Rig Veda describes the occurrence of the eclipse, how the Sun suddenly disappeared in the daytime under the spell of the Asura. The people and gods were scared but the Great Sage Atri saved the Sun and restored his full glory. While discussing the eclipse, Tilak refers to the eclipse as having occurred when the Vernal Equinox was in Orion and three days before the Autumnal Equinox. 

Based on these data, we identify Atris eclipse as the one that occurred on 22 October 4202 BC or on 19 October 3811 BC.

Mayank Vahia, Misturu Soma, "An examination of "Atri's Eclipse" as described in the Rig Veda" arXiv:2407.19733 (July 29, 2024). This is a post-print of 26 (2) Journal of Astronomical History and Heritage 405-410 (2023).

The introduction in the body text notes that:

The Rig Veda is one of the oldest known documents. It dates from 1500 BC, when its contents were assimilated and formalised on the basis of traditions of different schools of thought. It was essentially a summary of various religious ideas and philosophies, as well as their image of the world and its working as understood at that time. It comprises a set of 10 books associated with 10 different groups of priests who assimilated different aspects of the prevailing belief systems (see Dalal, 2014; Donigar, 1984). The writing style in the Rig Veda is highly poetic and abstract, and sometimes it is difficult to understand. It also requires some experience in order to interpret it.

While the Rig Veda dates from 1500 BC, there is a significant amount of evidence that it incorporates memories of events that were much further back in time. For example, it discusses events when the Vernal Equinox was in Orion, which occurred around 4500 BC, while the final reference to the Vernal Equinox in the Rig Veda relates to its being in the Pleiades, which happened in 2230 BC.

There are various other astronomical references in the Rig Veda, and one of these refers to a solar eclipse, which is the subject of this paper.

For the sake of argument, assuming that the Rig Veda is indeed referring to real historical events when it talks about where the equinoxes are (and that the means of determining which constellation is associated with an equinox), it could also help determine which part of of the hybrid culture that produced Hinduism in India, i.e. the Indo-Iranian tradition or the Harappan tradition, is the predominant source for the Rig Veda.

The dates suggested for Atri's Eclipse coincide roughly with the time at which the Proto-Indo-European language emerged. But this seems like a better fit to more sedentary and agricultural early Indus Valley civilization (the strict sense IVC dates to 3300 BCE, but agricultural societies in continuity with it were present there from 6500 BCE), which would have been expected to have better astronomy in that time frame. The more pastoral initial Proto-Indo-European society would be expected to have less advanced astronomy at that time. So, the Rig Veda could recount Harappan oral traditions (it had some writing, but the Harappan script was probably not a full written language) translated from the Harappan language into Sanskrit.

Another hint could be derived from comparing the Avesta, in the Avestan language, with the Rig Veda, written in Sanskrit. Where something is present in both, like the drug soma, it is likely to derive from a shared Indo-Iranian tradition. Where  something is only found in the Rig Veda with no parallel in the Avesta it is more likely to have Harappan origins. But, the Avesta was compiled much later than the Rig Veda so a great deal of the Indo-Iranian tradition might have been lost or deliberately omitted by Zoroaster (who by tradition is its author) at that point in the 500s BCE. The oldest part of the Avesta, the 17 hymns called the Gathas written in Old Avestan comprise only about 6,000 words in 238 stanzas and have linguistic and cultural similarities to the Rig Veda, which has 1,028 hymns with 10,600 verses.

The Rig Veda and the historic religion of the Indo-Europeans were both polytheistic, while Zoroastrianism is usually characterized as dualistic. We know, however, that significant parts of what became the Hindu religious tradition deviated for the common Indo-European source of the religious traditions of the Norse, the Greeks, and the Romans, for example, and also have no source in Egyptian mythology. These deviations are plausibly attributed to Harappan sources.

The Wikipedia article on the Rig Veda is suggestive of a more Indo-Iranian than Harappan society, and states that:

The Rigveda offers no direct evidence of social or political systems in the Vedic era, whether ordinary or elite. Only hints such as cattle raising and horse racing are discernible, and the text offers very general ideas about the ancient Indian society. There is no evidence, state Jamison and Brereton, of any elaborate, pervasive or structured caste system. Social stratification seems embryonic, then and later a social ideal rather than a social reality.  

The society was semi-nomadic and pastoral with evidence of agriculture since hymns mention plow and celebrate agricultural divinities. There was division of labor and a complementary relationship between kings and poet-priests but no discussion of a relative status of social classes.  

Women in the Rigveda appear disproportionately as speakers in dialogue hymns, both as mythical or divine Indrani, Apsaras Urvasi, or Yami, as well as Apāla Ātreyī (RV 8.91), Godhā (RV 10.134.6), Ghoṣā Kākṣīvatī (RV 10.39.40), Romaśā (RV 1.126.7), Lopāmudrā (RV 1.179.1–2), Viśvavārā Ātreyī (RV 5.28), Śacī Paulomī (RV 10.159), Śaśvatī Āṅgirasī (RV 8.1.34). The women of the Rigveda are quite outspoken and appear more sexually confident than men, in the text. Elaborate and aesthetic hymns on wedding suggest rites of passage had developed during the Rigvedic period. There is little evidence of dowry and no evidence of sati in it or related Vedic texts.

The Rigvedic hymns mention rice and porridge, in hymns such as 8.83, 8.70, 8.77 and 1.61 in some versions of the text; however, there is no discussion of rice cultivation.  

The term áyas (metal) occurs in the Rigveda, but it is unclear which metal it was. Iron is not mentioned in Rigveda, something scholars have used to help date Rigveda to have been composed before 1000 BCE. Hymn 5.63 mentions "metal cloaked in gold", suggesting that metalworking had progressed in the Vedic culture.

Some of the names of gods and goddesses found in the Rigveda are found amongst other belief systems based on Proto-Indo-European religion, while most of the words used share common roots with words from other Indo-European languages. However, about 300 words in the Rigveda are neither Indo-Aryan nor Indo-European, states the Sanskrit and Vedic literature scholar Frits Staal. Of these 300, many – such as kapardin, kumara, kumari, kikata – come from Munda or proto-Munda languages found in the eastern and northeastern (Assamese) region of India, with roots in Austroasiatic languages. The others in the list of 300 – such as mleccha and nir – have Dravidian roots found in the southern region of India, or are of Tibeto-Burman origins. A few non-Indo-European words in the Rigveda – such as for camel, mustard and donkey – belong to a possibly lost Central Asian language. The linguistic sharing provides clear indications, states Michael Witzel, that the people who spoke Rigvedic Sanskrit already knew and interacted with Munda and Dravidian speakers.

Witzel, however, was late to recognize that there was a distinct Harappan language which was neither Munda nor Dravidian.

As an aside, the Harappans did trade with the Sumerians who had a full written language and not just a set of symbols like the Harappan and Vinca scripts. Neither the Sumerian written language, nor the entire concept of it, however, seems to have been borrowed by the Harappans. Perhaps this was because Sumerian writing was largely confined to a small class of priest-clerks and perhaps some aristocrats, and perhaps because Sumerian-Harappan trade was thin and the Harappan maritime merchants may not have been all that influential in Harappan society. The Harappan script seems to have been used largely by merchants.

Turtles All The Way Down

From this physics preprint.

Making Sense Of Cosmological Neutrino Mass Bounds

A new paper tries to make sense of the DESI results that suggest a sum of the three neutrino masses that is equal to or smaller than the minimum value suggested by neutrino oscillation experiments (which is roughly 0.06 eV).

An outlier data point in the DESI data and a known methodological issue in the Planck 18 data that a later version of the analysis of the Planck data has corrected largely resolve this issue. A non-constant "cosmological constant" would also help resolve the discrepancy and is increasingly favored by observation.

Even with relaxed bounds, however, the cosmological constraints on the sum of the three neutrino masses are still considerably tighter than those derived from direct measurements of the lightest neutrino mass. And, cosmological bounds, along with other data sources, continue to favor a "normal hierarchy" of neutrino masses over an "inverted hierarchy."

Cosmological neutrino mass bounds are becoming increasingly stringent. The latest limit within ΛCDM from Planck 2018+ACT lensing+DESI is ∑mν < 0.072eV at 95% CL, very close to the minimum possible sum of neutrino masses (∑mν > 0.06eV), hinting at vanishing or even ''negative'' cosmological neutrino masses. 

In this context, it is urgent to carefully evaluate the origin of these cosmological constraints. In this paper, we investigate the robustness of these results in three ways: i) we check the role of potential anomalies in Planck CMB and DESI BAO data; ii) we compare the results for frequentist and Bayesian techniques, as very close to physical boundaries subtleties in the derivation and interpretation of constraints can arise; iii) we investigate how deviations from ΛCDM, potentially alleviating these anomalies, can alter the constraints. 

From a profile likelihood analysis, we derive constraints in agreement at the ∼10% level with Bayesian posteriors. We find that the weak preference for negative neutrino masses is mostly present for Planck 18 data, affected by the well-known "lensing anomaly". It disappears when the new Planck 2020 HiLLiPoP is used, leading to significantly weaker constraints. Additionally, the pull towards negative masses in DESI data stems from the z=0.7 bin, which is in ∼3σ tension with Planck expectations. Without these outliers, and in combination with HiLLiPoP, the bound relaxes to ∑mν<0.11eV at 95% CL. The recent preference for dynamical dark energy alleviates this tension and further weakens the bound. As we are at the dawn of a neutrino mass discovery from cosmology, it will be very exciting to see if this trend is confirmed by future data.

Daniel Naredo-Tuero, et al., "Living at the Edge: A Critical Look at the Cosmological Neutrino Mass Bound" arXiv:2407.13831 (July 18, 2024).

Outstanding Issues In Human Evolution And Prehistory

About half of this blog's posts are devoted to developments in human evolution and our understanding of human pre-history and ancient history. Midway into 2024, what are the hot issues that are outstanding in these fields?

Archaic Hominins

What ecological pressures drove early hominin evolution from a common ancestor of, or sister clade to chimpanzees and bonobos?

When did early hominins become bipedal and why?

Why did modern humans lose most of their body hair?

Precisely which archaic hominin species were ancestral to modern humans and which were "dead ends"? 

Which archaic hominin species could produce hybrid offspring with each other? We know that there was modern human-Neanderthal admixture, modern human-Denisovan admixture, Neanderthal-Denisovan admixture, and Denisovan-super archaic admixture. Did Homo floresiensis have hybrid offspring with modern humans? Was there any archaic admixture with modern humans in Africa, and if so, in whom is a legacy of this (if any) found today?

What species is the source of super-archaic admixture in Denisovans? Did Denisovans admix with Homo erectus or with Homo floresiensis? 

What did Denisovans look like? What were their lives like? How smart were they?

What was the population structure within Denisovans like and what waves of Denisovan populations existed and replaced each other?

What archaic hominin species were present in Africa and when?

What archaic hominin species were present outside of Africa and when and how did they get there?

When and why did various archaic hominin species go extinct (especially outside of Africa)? Why did the Neanderthals go extinct? Are there any relict archaic hominin populations in the world? If not, when did the last relict population of archaic hominins go extinct? Why did the Neanderthals go extinct? Why did the Denisovans go extinct? Why did Homo floresiensis go extinct? Are our legends of human-like fairies, elves, dwarves, Yeti, trolls, etc. oral history recollections of our contacts with archaic hominins?

Precisely when, where, why, and how (within Africa) did modern humans evolve from archaic hominins?

Which archaic hominin species interacted directly with modern humans?

To what species should the Julurens archaic hominin remains in China be assigned?

Do the Homo erectus-homo sapien mosaic feature skulls in China represent hybrid species individuals, or separate species of the genus Homo?

Prehistory and Ancient History

Why is the archaeological evidence for modern humans in the range from Arabia to India so much earlier than the genetic indications of the main Out of Africa expansion?

What connection was there between the expansion of modern humans from India to Southern Asia, the extinction of Homo erectus, and the Toba eruption?

What were the main waves of modern human expansion into Asia? How much did later waves replace earlier waves?

How much substructure was there in the founding population of the Americas settlement of the Americas?

There is evidence of a modern human presence in the Americas many thousands of years before the main founding population wave(s). Why didn't this early modern human presence thrive and leave more of a mark? Was this a single continuous event, or were there multiple false start migrations that successively failed? Where there any modern humans left in the Americas when the first wave of the founding population of the Americas arrived?

What narrative explains the apparent Paleo-Asian ancestry in select indigenous tribes in South America?

What post-founding era, pre-Columbian contracts were there between the Americas and modern humans from the "Old World"?

What was the biggest level of societal structure in the hunter-gatherer era of humanity? What was life like in those tribes?

Was Göbekli Tepe really pre-Neolithic? Was it connected with a Neolithic era false start? What made it possible? Do its inscriptions document a Younger Dryas causing extra-terrestrial impact?

What did the process of assembling a full Neolithic package of domesticates in the Fertile Crescent from multiple places of domestication in that region look like? What were relations like between Caucasian hunter-gatherers and their first farmer descendants, and Levantine hunter-gatherers and their first farmer descendants, as the two populations were very genetically distinct but cooperated to assemble the full Fertile Crescent Neolithic package?

What did the pre-Indo-European linguistic landscape look like? Did the languages of the European hunter-gatherers leave any trace (e.g. in linguistic substrates or loan words)? Were the languages of the pre-Indo-European farmers of Europe, presumably including Basque, all derived from a single language family of the first farmers of Western Anatolia?

Was there a macro-family of ergative languages in Mesopotamia, Anatolia, the Caucuses, and West Asia? Do the languages of the Caucuses have a common origin, and if so, are they related to this possibly macro-family of ergative languages? Was the Harappan language part of one or both of these language families? Did this language family extend to North Africa?

Was there a cultural and linguistic and religious replacement by conquest in Anatolian sometime between the late Neolithic era and the early Bronze Age giving rise to the Hattic people with a demic component?

When did the various pre-Indo-European languages of Europe and West Asia (except Basque) go extinct?  

Where and how did the Indo-European languages originate?

What is the timeline and geography of Indo-European languages? What is the correct phylogeny of the Indo-European languages? What is the correct origin story for each Indo-European language, particularly, ambiguous and possibly complex cases like Armenian?

Did the Corded Ware people, the Yamnaya people, and the Bell Beaker people speak the same Indo-European language? Why did the Corded Ware people and the Yamnaya people have such distinct Y-DNA ancestry despite having similar autosomal ancestry, familial patterns, and a shared presumed language family?

What Indo-European languages were spoken by the Bell Beaker people and their descendants before Celtic and Germanic languages in the narrow sense emerged? How similar were they culturally and linguistically to the historically attested early Celtic and Germanic peoples? What was the nature of the interactions and feelings of the Bell Beaker people and Corded Ware people towards each other?

What is the story behind the dramatic surge in lactose tolerance genes shortly after Indo-Europeans arrived in Western Europe?

When did the Indo-European Anatolian languages arise and why were they so distinct from other Indo-European languages?

Was the Minoan culture an offshoot of the pre-Hittite Anatolian Hattic culture or a larger linguistic and cultural family?

What was the Harappan culture like and what languages, if any, was its language related to?

What was the exact chronology of Indo-European migration to what is now Iran and to South Asia? What were the main outlines of its waves of expansion within India?

How did Hinduism emerge from Harappan and Indo-Iranian religious practices and beliefs? What caused the divergence between it and the ancient Iranian religion? When did particular practices and beliefs, like vegetarianism and the sacred cow emerge?

What was the social structure in India like between the Indo-Aryan arrival and the establishment of strict jati endogamy much later?

Is the Dravidian language related to any other existing or extinct language? When did it arise? When did its branches arise? How did the Brahui come to speak a version of it? Why does the language family seem less diverse and younger than plausible theories about its time of origin? Did it contract in the face of Indo-Aryan expansion and then reclaim much of South Asia? Does the Dravidian language family and the culture of the Dravidian people have any connections to Niger-Congo languages and the cultures of the people in the Sahel of Africa who domesticated many key crops of the South Indian Neolithic Revolution? Does Y-DNA T, which has a peculiar geographic distribution in India have any connection to the origin story of the Dravidian languages?

What is the origin story of the Chadic people? What about the Fulani people and their languages?

How are the Afro-Asiatic languages related to each other and what are there respective origin stories in time and space?

When did the Berber languages emerge? What preceded them?

What is the origin story of the emergence and spread of the Nilo-Saharan languages?

When did the languages spoken by the Pygmies in Africa die? Are there any traces, such as in linguistic substates or loan words of Bantu languages, of those lost languages?

Was there a historical Atlantis, and if so, when and where was it?

Why do the genealogies of Genesis and the Mesopotamian king lists have such seemingly long lived people?

How much of the books of Genesis and Exodus in the Bible derive from Mesopotamian lore? When and by whom were the various parts of these books of the Bible written? How much did Egyptian beliefs influence the early Hebrews?

Exactly what happened to the Jews in the diaspora after 70 CE and how did they come to be the Jewish peoples we know today?

What was the origin story of the gypsies?

Do the polytheistic deities of Greece, Scandinavia, Egypt, the ancient Mediterranean, the Americas, and India have any connections to real historic people? Is so, when and in what context?

What does the prehistoric and legendary history era chronology of human inhabitation of Southeast Asia and East Asia look like?

How far back can oral histories reliably describe the past? What are the most notable examples of this?

What is the origin story of the Japanese people? Where did the Jomon come from? How representative is the Ainu language of the language(s) of the Jomon people?

Are Korean and Japanese related linguistically? How? Is the larger Altaic linguistic family a legitimate linguistically related group of languages?

What undecipherable scripts of lost languages can we decipher?

What explains the relative strength and weaknesses of polygamy in different cultures at different times?

What was the lost agricultural civilization of the Amazon like?

What was the Mississippian culture like?

What were the dynamics of changing political/cultural region/linguistic control in the Americans in the pre-Columbian era that changed over time?

In Africa, was there an expansion within Africa parallel to the Out of Africa expansion? Why were modern humans suddenly so dynamic and behaviorally modern starting in the Upper Paleolithic era? What were the histories of the pre-Bantu language family expansions of languages in Africa? What is the story of the genetically distinct culture of click language speakers in Mozambique that left no pure blooded members of the "race" and no relict speakers of that language?

Is there any merit to the existence of a mostly lost Indo-Pacific language family made up of relict language isolates across Southern Asia?

Deep Genetic Modern Human Ancestry And Structure In Africa

A new paper at bioRxiv finds that:

The deep history of humans in Africa and the complex divergences and migrations among ancient human genetic lineages remain poorly understood and are the subject of ongoing debate. We produced 73 high-quality whole genome sequences from 14 Central and Southern African populations with diverse, well-documented, languages, subsistence strategies, and socio-cultural practices, and jointly analyze this novel data with 104 African and non-African previously-released whole genomes. We find vast genome-wide diversity and individual pairwise differentiation within and among African populations at continental, regional, and even local geographical scales, often uncorrelated with linguistic affiliations and cultural practices. 

We combine populations in 54 different ways and, for each population combination separately, we conduct extensive machine-learning Approximate Bayesian Computation inferences relying on genome-wide simulations of 48 competing evolutionary scenarios. We thus reconstruct jointly the tree-topologies and migration processes among ancient and recent lineages best explaining the diversity of extant genomic patterns. Our results show the necessity to explicitly consider the genomic diversity of African populations at a local scale, without merging population samples indiscriminately into larger a priori categories based on geography, subsistence-strategy, and/or linguistics criteria, in order to reconstruct the diverse evolutionary histories of our species. 

We find that, for all different combinations of Central and Southern African populations, a tree-like evolution with long periods of drift between short periods of unidirectional gene-flow among pairs of ancient or recent lineages best explain observed genomic patterns compared to recurring gene-flow processes among lineages. 

Moreover, we find that, for 25 combinations of populations, the lineage ancestral to extant Southern African Khoe-San populations diverged around 300,000 years ago from a lineage ancestral to Rainforest Hunter-Gatherers and neighboring agriculturalist populations. 

We also find that short periods of ancient or recent asymmetrical gene-flow among lineages often coincided with epochs of major cultural and ecological changes previously identified by paleo-climatologists and archaeologists in Sub-Saharan Africa.

Gwenna Breton, et al., "Ancient tree-topologies and gene-flow processes among human lineages in Africa" bioRxiv (July 16, 2024).

Thus, human evolution and genetic structure in Africa is not well-described by more or less random genetic exchanges between neighboring populations. Instead, massive, short, unidirectional introgression (i.e. one people conquering another) is the norm.

African and Arabian Paleoclimate

This paper leans heavily on Beyer, R.M. et al., "Climatic windows for human migration out of Africa in the past 300,000 years", 12(1) Nature Communications 4889 (2021) (open access), for its inferences based upon paleoclimate. Beyer (2021) concludes that:

there were a number of windows during the past 300k years when either northern or southern expansions out of Africa would have been climatically feasible. Prior to the last interglacial period, the Nile-Sinai-Land Bridge would have been crossable at several time intervals between 246k and 200k years ago. Following a reopening at 130k years ago, exits would have been intermittently possible until 96k years ago, and again later around 78k and 67k years ago. 

After that, this route likely remained closed until the wet Holocene. Provided that maritime travel was in principle possible, climatic conditions would have made southern exits feasible for a substantial proportion of the last 300k years. 

Before the last interglacial, there were three extended intervals of sufficient rainfall paired with relatively low sea level, from 275k to 242k years ago, from 230k to 221k years ago, and from 182k to 145k years ago. During most of the following window from 135k to 115k years ago, sea levels were particularly high, except at its beginning 135k years ago. This date is close to the proposed timing of an early northern exit; thus, if migration did occur, southern migrants might have encountered their northern counterparts on the Arabian Peninsula. Following a long period when the southern route was blocked, there was a sizeable window of sufficiently wet climate between 65k and 30k years ago. 

Further connections existed just after the Last Glacial Maximum, and during the mid-Holocene, consistent with evidence of Eurasian backflow into Africa. 

A threshold analogous to our estimate for precipitation exists for a Köppen aridity level around 1.7 based on the contemporary hunter-gatherer data, and the inferred periods of climatic connectivity between Africa and Eurasia are almost identical to those estimated for precipitation.

Our reconstructions suggest that there were several windows of suitable climate along either of the two possible dispersal routes that could have allowed the expansion of Homo sapiens out of Africa. 

Some of these windows predate the earliest remains outside of Africa, but are entirely compatible with genetic dating of introgression from Homo sapiens into Neanderthal, sometime between 250k and 130k years ago, and recent dating of material from Israel to possibly 194k years ago and from Greece to 210k years ago. 

Migrations into Eurasia were also likely feasible along both routes during the last interglacial period, when archaeological evidence points to a more sizeable exit. Two distinct scenarios for an exit around 65k years ago, the time that has been long suggested as the main moment of expansion out of the African continent based on archaeological and genetic evidence, are compatible with our estimates. This timing marks both the point shortly after which the northern route last was open before a period of 40k years of unsuitable climate, and the point at which the southern route first reopened for an extended period since the last interglacial period. 

The latter scenario has been a subject of debate based on the empirical palaeoenvironmental record, with conclusions ranging from the Arabian Peninsula being continually too arid for human migration, to intermittent wet intervals, and extended pluvial periods during marine isotope stage 3 (57–29k years ago). 

In any case, these inferences are not directly comparable with our results, both because several empirical proxies are not suitable for detecting rainfall of the small magnitude considered here (e.g. speleothems), and because, for each route, the specific path out of Africa that requires the least tolerance to low precipitation out of all possible paths varies over time, as does the geographic location of its driest segment; thus, our estimates would not be expected to necessarily display the same patterns over time as a localised empirical climate reconstruction. . . .

While archaeological and genetic data strongly suggest that Homo sapiens expanded its range towards Eurasia at least once prior to the large-scale colonisation wave beginning around 65k years ago, the reason for its initial failure to permanently settle outside Africa is less clear. 

Migration beyond the Arabian Peninsula would have been predicated on the ability to cross the Taurus-Zagros Mountain range while competing with Neanderthals in the north, which has previously been argued to have limited human expansions during the last interglacial period, and possibly other hominins, such as Denisovans (whose geographic range is unknown but likely covered a large portion of East Asia), in the east. 

In addition, our reconstructions suggest that climatically favourable intervals along both routes were frequently interrupted by periods of rainfall insufficient to support humans, which would have effectively isolated any of the earlier colonists that might have made it out of Africa. With a lack of demographic influx from further migration out of Africa, remnant populations on the Arabian Peninsula would have been susceptible to stochastic local extinctions driven by climatic fluctuations. 

This constraint would have been less important along the southern route during the unprecedentedly long period of largely favourable climate between 65k and 30k years ago, provided that maritime travel across a then 4 km wide strait of the Bab e-Mandeb made migration along this route possible. This long window would have provided ideal preconditions for a successful large-scale dispersal, allowing for a regular demographic influx from Africa that would have stabilised populations on the Arabian Peninsula, thus facilitating further expansion of Homo sapiens into Eurasia. 

These dynamics would have complemented technological, economic, social, and cognitive changes in human societies, which, possibly combined with the decline of Neanderthal, very probably accounted for the success of the late exit in the subsequent colonisation of Eurasia by Homo sapiens.

Khoisan Origins 

The Khoisan hunter gatherers of Africa have had distinct northern and southern subpopulations since roughly the time of genetic Out of Africa (ca. 50,000-80,000 years ago). This is a branch depth as deep as the divisions between Australian Aboriginal people and Swedish people in populations that live on opposite sides of the Kalahari desert in Southern Africa. The authors hypothesize that:

the global climatic shifts inducing massive ecological changes that have occurred in Africa at that time (e.g. (Beyer et al., 2021)), sometimes proposed to have triggered ancient Homo sapiens movements Out-of-Africa, may also have triggered, independently, the genetic isolation among ancestral Khoe-San populations. Nevertheless, where the ancestors of extant Khoe-San populations lived at that time remains unknown and is nevertheless crucial to further elaborate possible scenarios for the causes of the genetic divergence here inferred.

The common Khoisan ancestor population became distinct from other modern humans around 300,000 years ago, around the time that the modern human species emerged.

The Origins Of The Pygmies And Their Neighbors

Among Rainforest Hunter Gathers (RHG) in the Congo jungle, a.k.a. the Pygmies, there are genetically distinct populations in the West and in the East that date roughly to the Last Glacial Maximum (17,000 to 27,000 years ago). The authors explain that:

Rainforest Hunter-Gatherer populations across the Congo Basin diverged roughly between 17,000 and 27,000 years ago, relatively consistently across pairs of sampled populations used for inferences; estimates highly consistent with previous studies, despite major differences in gene-flow specifications across RHG groups between studies. Interestingly, this divergence time is relatively synchronic with absolute estimates for the Last-Glacial Maximum in Sub-Saharan Africa. The fragmentation of the rainforest massif during this period in the Congo Basin may have induced isolation between Eastern and Western RHG extant populations, as plausibly previously proposed. However, similarly as above for the Northern and Southern Khoe-San populations divergence, where the ancestors of extant Eastern and Western Rainforest Hunter-Gatherers lived remains unknown, which prevents us from formally testing this hypothesis.

This is around the time of the division between the founding population of the Americas and the populations of East Asia and Northeast Asia from which they originated. It is also a time frame during which Europe was depopulated except for relict populations in Iberia, the Italian Peninsula, and the Caucuses. 

The population ancestral to Rain Forest Hunter gathers and their agricultural neighbors branched between the neighboring population and the Rain Forest Hunter gatherer population, about 165,000 years ago. 

Key Short Duration Admixture Events In Africa

But, there were admixture events after that date. The authors explain that:

we found strong indications for almost synchronic events of introgressions having occurred during the Last Interglacial Maximum in Africa (Mazet et al., 2016), between ~90,000 and ~135,000 years ago (when considering 20 or 30 years per generation). They involved gene-flow between lineages ancestral to Khoe-San populations and ancestors of Rainforest Hunter-Gatherer neighbors on the one hand and, on the other hand, between lineages ancestral to Khoe-San populations and the lineage ancestral to all Rainforest Hunter-Gatherers. 

An increase in material-based culture diversification and innovation, possibly linked to climatic and environmental changes locally, has previously been observed during this period of the Middle Stone Age in diverse regions of continental Africa; prompting a long-standing debate as to its causes if human populations were subdivided and isolated biologically and culturally at the time[.] . . .

the instantaneous gene-flow event between the ancestral Rainforest Hunter-Gatherers lineage and that of their extant neighbors seemingly occurred synchronically to the genetic Out-of-Africa ((Beyer et al., 2021); see above). This would imply that possible climatic and ecological shifts at that time may not have only induced population divergences and displacement, but may also have triggered population gene-flow.

There was also a gene flow event between populations in Rain Forest Hunter Gather neighbors population, and the northern and southern Khoisan populations:

around 30,000 years ago, we found two loosely synchronic gene-flow events between ancestors to extant Central African Rainforest Hunter-Gatherer neighbors’ lineages and, separately, Northern and Southern Khoe-San lineages. This corresponds to the end of the Interglacial Maximum and a period of major cultural changes and innovations during the complex transition from Middle Stone Age to Late Stone Age in Central and Southern Africa. Nevertheless, connecting the two lines of genetic and archaeological evidence to conclude for increased population movements at the time and their possible causes should be considered with caution. Indeed, in addition to genetic-dating credibility-intervals being inherently much larger than archaeological dating, this period remains highly debated in paleoanthropology mainly due to the scarcity and complexity of the material-based culture records, and that of climatic and ecological changes locally, across vast regions going from the Congo Basin to the Cape of Good Hope.

And, there were also multiple gene flow events in the early Holocene era (roughly corresponding to the Neolithic era in Europe and into the European Copper/early Bronze Age):

we found strong signals for multiple instantaneous gene-flow events having occurred between almost all five recent Central and Southern African lineages between 6000 and 12,000 years ago, during the onset of the Holocene in that region, shortly before or during the beginning of the last Post Glacial Maximum climatic crisis in Western Central Africa, the emergence and spread of agricultural techniques, and the demic expansion of now-Bantu speaking populations from West Central Africa into the rest of Central and Southern Africa. These results are consistent with previous investigations that demonstrated the determining influence of Rainforest Hunter-Gatherer neighboring populations’ migrations through the Congo Basin in shaping complex socio-culturally determined admixture patterns, including admixture-related natural selection processes.

As our estimates for introgression events are in the upper bound of previous estimates for the onset of the so called “Bantu expansion” throughout Central and Southern Africa, we may hypothesize here that major climatic and ecological changes that have occurred at that time may have triggered increased population mobility and gene-flow events between previously isolated populations, rather than consider that the Bantu-expansions themselves were the cause for all the gene-flow events here identified.

Finally, we did not find signals of more recent introgression events from Bantu-speaking agriculturalists populations into Northern or Southern Khoe-San populations, in particular among the !Xun, albeit such events have been identified in several previous studies (see (Schlebusch and Jakobsson, 2018)). This is likely due to the fact that we considered only a limited number of individual samples from each population, and therefore may lack power to detect these very recent events with our data and approach.

Was There Archaic Admixture In Africa?

The new paper finds that it is possible to fit their data to a narrative without admixture with a ghost population of archaic hominins in Africa, as some studies have suggested, although that possibility is not ruled out either, and the authors of this study acknowledge that they are using fewer kinds of data to build their historical narratives than studies that found evidence of admixture with ghost archaic hominin populations in Africa.

Ragsdale and colleagues included in their models possible very ancient genetic structures, long before Homo sapiens emergence, a feature that is unspecified in our scenarios which considered simply a single ancestral population in which all extant lineages ultimately coalesce. Nevertheless, note that substructure and reticulation within the ancestral population is not per se incompatible with our scenarios. In fact, it may be compatible with our posterior estimates of a large effective population ancestral to all extant populations here investigated, the largest among all inferred ancient and recent Central and Southern African effective population sizes. . . . . 

We did not explore possible contributions from unsampled lineages, whether from non-Homo sapiens or from ancient “ghost” human populations, and therefore cannot formally evaluate the likeliness of the occurrence of such events to explain observed data. In all cases, our results demonstrate that explicitly considering ancient admixture from unsampled populations is not a necessity to explain satisfactorily large parts of the observed genomic diversity of extant Central and Southern African populations, consistently with a previous study (Ragsdale et al., 2023), and conversely to others (Lipson et al., 2022; Fan et al., 2023; Pfennig et al., 2023); at least when considering jointly the 337 relatively classical population genetics summary-statistics used here for demographic inferences. As discussed above, our results formally comparing competing-scenarios rather than comparing posterior likelihoods of highly complex yet vastly differing models, provide a clear and reasonable starting point for future complexification of scenarios comprising possible contributions from ancient or ghost unsampled populations, which will unquestionably benefit from the explicit use of additional novel summary statistics ((Ragsdale and Gravel, 2019; Fan et al., 2023; Ragsdale et al., 2023); see also above). 

In any case, the complexification of scenario-specifications to account for possible past “archaic” or “ancient” introgressions will not fundamentally solve the issue of the current lack of reliable ancient genomic data older than a few hundreds or thousands of years from Sub-Saharan Africa. Indeed, analogously to archaic admixture signals that were unambiguously identified outside Africa only when ancient DNA data were made available for Neanderthals and Denisovans (e.g. (Meyer et al., 2012; Prüfer et al., 2014)), we imperatively need to overcome this lack of empirical ancient DNA data in Africa to formally test whether, or not, ancient human or non-human now extinct lineages have contributed to shaping extant African diversity.

Side Observations Re Non-African Admixture

The study also made some side observations. For example, in its ancestry analysis at K=2 it effectively shows that amount of non-sub-Saharan African admixture present in various African populations. 

Unsurprisingly, this admixture is lowest in hunter-gather populations, modestly higher among non-hunter-gatherer Central and Southern Africans, higher still among the most northern East Africans, high among "Coloured" South Africans who have substantial non-African admixture, and predominantly non-African among North Africans.

Within non-Africans, Papuans pop out as a distinct population at K=5, and indigenous peoples of the Americas pop out as distinct at K=6.

Genetic Variation and Diversity

The paper also confirms conventional wisdom that African populations have more genetic diversity than non-Africans, even within sub-populations (and not merely because it is a large continent with many subpopulation that differ from each other). The amount of genetic variation in any subpopulation is strongly correlated with the amount of non-African admixture in a subpopulation (which less genetic variation associated with more non-African ancestry).

Weaknesses In The Paper

The most notable gap in the sample is a lack of DNA from Mozambique, whose people in Southeast Africa are known to be genetically quite distinct from other Africans, which local Bantu languages have click phonemes, presumably from a pre-Bantu substrate language.

The paper would also benefit from straying beyond its focus on the most basal populations of Africa to explore, at an at least superficial level, how this Central and Southern African population history fits into the larger global population of Homo sapiens.

The Black Plague Swept Northern Europe Ca. 3400 BCE

We've been aware of the population collapse that hit Northern Europe around 5400 years ago (around 3400 BCE) for a long time, for example, in the article below from 2013. 

But new evidence points to the black plague as a major contributing cause. Climate and exhaustion of soils with primitive Neolithic agricultural methods have also been suggested as causes. Of course, causes can interact and aren't mutually exclusive. For example, people can be much more vulnerable to pandemics during period of famine caused by poor agricultural practices and climate events.

Following its initial arrival in SE Europe 8,500 years ago agriculture spread throughout the continent, changing food production and consumption patterns and increasing population densities. 

Here we show that, in contrast to the steady population growth usually assumed, the introduction of agriculture into Europe was followed by a boom-and-bust pattern in the density of regional populations. We demonstrate that summed calibrated radiocarbon date distributions and simulation can be used to test the significance of these demographic booms and busts in the context of uncertainty in the radiocarbon date calibration curve and archaeological sampling. 

We report these results for Central and Northwest Europe between 8,000 and 4,000 cal. BP and investigate the relationship between these patterns and climate. However, we find no evidence to support a relationship. Our results thus suggest that the demographic patterns may have arisen from endogenous causes, although this remains speculative.

Stephen Shennan, "Regional population collapse followed initial agriculture booms in mid-Holocene Europe" 4 Nature Communications 2486 (October 1, 2013).

The new paper is:

In the period between 5,300 and 4,900 calibrated years before present (cal. BP), populations across large parts of Europe underwent a period of demographic decline. However, the cause of this so-called Neolithic decline is still debated. Some argue for an agricultural crisis resulting in the decline, others for the spread of an early form of plague. 

Here we use population-scale ancient genomics to infer ancestry, social structure and pathogen infection in 108 Scandinavian Neolithic individuals from eight megalithic graves and a stone cist. 

We find that the Neolithic plague was widespread, detected in at least 17% of the sampled population and across large geographical distances. We demonstrate that the disease spread within the Neolithic community in three distinct infection events within a period of around 120 years. 

Variant graph-based pan-genomics shows that the Neolithic plague genomes retained ancestral genomic variation present in Yersinia pseudotuberculosis, including virulence factors associated with disease outcomes. 

In addition, we reconstruct four multigeneration pedigrees, the largest of which consists of 38 individuals spanning six generations, showing a patrilineal social organization. 

Lastly, we document direct genomic evidence for Neolithic female exogamy in a woman buried in a different megalithic tomb than her brothers. 

Taken together, our findings provide a detailed reconstruction of plague spread within a large patrilineal kinship group and identify multiple plague infections in a population dated to the beginning of the Neolithic decline.

Frederik Valeur Seersholm, "Repeated plague infections across six generations of Neolithic Farmers" Nature (July 10, 2024).

olume

There Is No Muon g-2 Anomaly

The updated BMW calculation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment a(μ) in the Standard Model is squarely consistent, at 0.9 sigma with the experimental measurement of muon g-2 (even without one or two additional tweaks to parts of the calculation other than the HVP component that improve the fit further) despite the fact that its uncertainty in this new and improved HVP calculation is 40% smaller (producing a 31% reduction in the uncertainty of the overall theoretical calculation) and the fact that the 2023 experimental measurement has 55% less uncertainty, making agreement of the two values a harder to hit target.

The experimental value is based upon the first three phases of a six phase experiment. Phase four, whose results are tentatively expected late in 2024 (but could easily be delayed until 2025 or even 2026), will significantly reduce the uncertainty in the experimental result. The improvements from phases five and six are expected to be much smaller. The uncertainty in the experimental result is already about 42% smaller than the uncertainty in the calculation of the Standard Model predicted value. The experimentally measured value will probably continue to have less uncertainty than the Standard Model predicted value calculation for several years to come, at least.

The bottom line value for the new 2024 BMW calculation is:

a(µ) = 116,592,019(38) × 10^−11.

Partial calculations confirm the BMW result vis-a-vis the partially experimentally based analysis in the so called "window" part of the calculation (as does the recent CMD-3 experimental measurement of the same experimental inputs that went into the "Theory Initiative" calculation):

The apparent discrepancy between the Theory Initiative calculation of the Standard Model prediction and the experimental results has been the source of countless papers proposing proposals for new physics.

This discrepancy was a result of an inaccurate calculation of the Standard Model prediction for muon g-2 by the Theory Initiative. This was mostly a result of the incorporation of slightly inaccurate experimental data (regarding electron-positron annihilations that produce pion pairs) into their hadronic vacuum polarization calculation. Their source for the experimental data that it used, despite the source's good faith efforts to estimate the uncertainty accurately, understated the uncertainty of that experimental data by roughly a factor of four (as revealed by the spread of the results of subsequent experimental measurements of the same phenomena).

The paper presenting the new lattice QCD calculation of muon g-2 and its abstract are as follows:

We present a new lattice QCD calculation of the leading order hadronic vacuum polarization contribution to the muon anomalous magnetic moment a(μ). We reduce uncertainties compared to our earlier computation by 40%, arXiv:2002.12347. We perform simulations on finer lattices allowing for an even more accurate continuum extrapolation. We also include a small, long-distance contribution obtained using input from experiments in a low-energy regime where they all agree. Combined with other standard model contributions our result leads to a prediction that differs from the measurement of a(μ) by only 0.9 standard deviations. This provides a remarkable validation of the standard model to 0.37ppm.

A. Boccaletti, et al., "High precision calculation of the hadronic vacuum polarisation contribution to the muon anomaly" arXiv:2407.10913 (July 15, 2024).

The new paper also notes that:

In the near future we expect that other lattice collaborations will also provide precise calculations of a(LO-HVP)(µ) that can confirm or refute our results. Also, more data for the e+e− → π+π− cross section is expected soon.

For those of you who aren't visual learners (with values times 10^11 shown below):

New BMW calculation (2024): 116,592,019(38)

BMW calculation (2020): 116,591,954(55)

Theory Initiative calculation (2020): 116,591,810(43)

World Experimental Average (2023) : 116,592,059(22)

Fermilab Run 1+2+3 data (2023): 116,592,055(24)

Combined measurement (2021): 116,592,061(41)

Brookhaven's E821 data (2006): 116,592,089(63)

Why Does This Calculation Matter?

The consistency between the experimentally measured value of muon g-2 and the calculation of the value of muon g-2 predicted by the Standard Model, is important because it a strong global test, at high precision, of the accuracy of all parts of the Standard Model at once.

In this test, the experimentally measured result matches the theoretical calculation of muon g-2's value (at a precision of about 4 parts per ten million).

This rules out many kinds of new physics that a next generation particle collider could detect.

While there are still legitimate reasons to build a next generation particle collider (e.g., to refine the precision of the Standard Model's constants, some of which are known to a less than parts per thousand level), the likelihood that a next generation particle collider will reveal new physics beyond the Standard Model is greatly diminished by the current state of the art muon g-2 experimental results and the current state of the art calculation of the Standard Model predicted value for muon g-2. So, the physics justification for a next generation particle collider (which will cost something on the order of $17 billion U.S. dollars if built) as a means of discovering new physics is greatly undermined by this result.

Muon g-2 is less sensitive to new physics at energy scales higher than those of any of the proposed next generation particle colliders, however, so it doesn't rule out new physics at those energies as strongly.

QCD v. Non-QCD Calculations In Muon g-2

The QED + Electroweak (EW) predicted value (omitting the Hadronic Vacuum Polarization (HVP) and Hadronic Light by Light (HLbL) components, and before the latest QED component tweak) is: 116,584,872.53 (101). Thus, it accounts for only about 3% of the total uncertainty in the value of muon g-2. Given the experimental results, the implied combined hadronic (i.e. QCD) contribution to the total is about 7186.47 times 10^-11. This is 0.00616% of the total value, despite the fact that it is the source of 97% of the uncertainty in the calculation, because QCD calculations are vastly less precise than QED calculations.

More specifically, in theoretical calculation, the QED calculation is the source of 0.2% of the total uncertainty, the weak force calculation is the source of 2.9% of the total uncertainty, and the QCD calculation is the source of 96.9% of the total uncertainty (with about 10% of the total muon g-2 calculation uncertainty coming from the Hadronic light by light calculation and about 87% of the total muon g-2 calculation uncertainty coming from the Hadronic vacuum polarization calculation).

The QED calculation is the source of 99.994% of the total value of muon g-2, the weak force calculation is the source of 0.00013% (153.6 x 10^-11 ± 1 x 10^-11), and the QCD calculation is the source of about 0.006% (about 99% of which is from the hadronic vacuum polarization calculation and about 1% of which is from the hadronic light by light calculation).

The relative error in the QED calculation is 0.000 000 0686%, the relative error in the weak force calculation is about 0.65%, and the relative error in the overall QCD calculation is about 0.5%. But since the weak force contribution to the calculation is only about 2% of the magnitude of the QCD contribution to the calculation, greater precision in weak force calculation isn't a priority in improving the precision of the total calculation.

Within the two QCD calculations, the Hadronic Vacuum Polarization calculation has a relative uncertainty of a little less than 0.5% and accounts for the bulk of the QCD contribution to muon g-2 (about 99% of the QCD contribution), while the Hadronic Light by Light calculation has a relative uncertainty of about 20%, but involves a much smaller total contribution to the total value of muon g-2 (about 1.0-1.3% of the QCD contribution and 0.000 08% of the total muon g-2 calculation). The Hadronic Light by Light calculation is the source of a little more than 10% of the uncertainty in the QCD contribution, and of about 10% of the uncertainty in the overall muon g-2 calculation.

These subcomponent breakdowns are spelled out in detail, for example, in T. Aoyama, et al., "The anomalous magnetic moment of the muon in the Standard Model" arXiv (June 8, 2020) (which obviously doesn't include the post-2020 develops in the calculation or in discussion of the experimentally measured value).

Other Tweaks To The Muon g-2 Calculation

Two other tweaks in parts of the muon g-2 calculation have also been made and aren't included in the new paper. They reduce the difference between the theoretical calculation and the experimentally measured calculation to about 0.6 sigma, which is a precision of about 2.2 parts per million.

Hadronic Light By Light Calculation (2021)

One is an increase of 14.8 x 10^-11, in the Hadronic light-by-light calculation from 2021. The relative uncertainty in this component of the calculation is reduced from 20% to 14%. Including this tweak also reduces the uncertainty in the latest BMW calculation of the total muon g-2 value (including its new HVP calculation) from ± 38 x 10^-11 to ± 37 x 10^-11.

The hadronic QCD component is the sum of two parts, the hadronic vacuum polarization (HVP) and the hadronic light by light (HLbL) components. In the Theory Initiative analysis the QCD amount is 6937(44) which is broken out as HVP = 6845(40), which is a 0.6% relative error and HLbL = 98(18), which is a 20% relative error.

The presentation doesn't note it, but there was also an adjustment bringing the result closer to the experimental result in the hadronic light-by-light calculation (which is the smaller of two QCD contributions to the total value of muon g-2 and wasn't included in the BMW calculation) which was announced on the same day as the previous data announcement. The new calculation of the hadronic light by light contribution to the muon g-2 calculation increases the contribution from that component from 92(18) x 10^-11 to 106.8(14.7) x 10^-11.

As the precision of the measurements and the calculations of the Standard Model Prediction improves, a 14.8 x 10^-11 discrepancy in the hadronic light by light portion of the calculation becomes more material.

QED Calculation (2024)

The other is a reduction of about 0.06 x 10^-11 in the QED part of the calculation from April of 2024, which is a five sigma downward shift in that calculation. But it is immaterial to the overall muon g-2 calculation because the original calculation was already so precise.

My prior posts on the subject were summarized on August 10, 2023. 

Bottom Line:

With values time 10^11 shown: 

New BMW calculation + new HLbL + new QED calculation (2024+2021+2024): 116,692,033.74 ±37.00 

 World Experimental Average (2023) : 116,592,059 ± 22

Considering the HLbL and QED tweaks as well, this is a bit less than a 0.6 sigma difference from the experimental value. This means that the prediction and measured value (as improved in 2023) are basically perfectly consistent with each other despite a 33% reduction in the uncertainty of the overall theoretical prediction and a 55% reduction in the uncertainty of the experimental measurement. The relative difference is 0.22 parts per million.