Climate Drives History: A Big Picture Recap

The chart above shows the climate history of the world in a nutshell for the last 10,500 years with a chronology from Greenland that matches a larger global climate history. It is a comprehensive big picture summary of climate history for the entire Holocene era.

History, Prehistory and Climate

There have been eleven distinct global climate events (many of which are Bond events; a more comprehensive list is available here), staring with the Younger Dryas event, when there was a substantial and rapid drop in global temperatures in the amount indicated during the era when modern humans ceased to be exclusively hunters and gatherers. There was also at least one major volcanic erruption not clearly associated with a global climate event in the same era, that is discussed below. These twelve events were historical turning points that can be associated with the rise and fall of historic civilizations and empires, and with mass migrations.

Some of the notable historical events associated with each of these events, predominantly in West Eurasia where I know the history and prehistory best, are set forth below.

1. The chart begins on the right with the end of the warming global temperatures after the Younger Dryas cold spell (5 degrees C to 15 degrees C) that produced the coldest in absolute terms since the Last Glacial Maximum (ca 18000 BCE), brought about the steepest drop in global temperatures in the period discussed by this post. This caused by an impact from outer space in North America and produced a cool period that lasted from roughly 10,800 BCE to 9,500 BCE.

The Younger Dryas brought about the end of the Clovis culture in North America and may have contributed to the megafauna extinction in the Americas.

It coincided with the Neolithic revolution in the Fertile Crescent (first appearing in the Levant and Southeastern Turkey). It was followed by an arid period in North Africa that produced a dry Sahara and concentrated the people who have lived in a wet Sahara around water, particularly, the Nile basin.

2. The 8.2 kiloyear event begins around 6200 BCE (3 degrees C). This is the deepest cooling event from the Younger Dryas through the present, and it led to the coldest temperatures in absolute terms since the Younger Dryas.

According to Wikipedia during the 9.2 kiloyear event: "Drier conditions were notable in North Africa, while East Africa suffered five centuries of general drought. In West Asia and especially Mesopotamia, the 8.2ky event was a three-hundred year aridification and cooling episode, which provided the natural force for Mesopotamian irrigation agriculture and surplus production that were essential for the earliest class-formation and urban life."

This coincides with the divide between the Pre-Pottery Neolithic and the Pottery Neolithic in the Fertile Crescent. The prepottery Neolithic in the Indus River Valley was already in place at this point, as was the early Neolithic civilization in Egypt (domesticated cattle were present no later than about 7000 BCE).

It is around the time that the Neolithic practices of herding and farming starts to spread to Europe from West Asia and the Levant. Farming, herding and pottery arrive simultaneously to Europe. In Southeastern Europe this is when the First Temperate Neolithic archaeological horizon emerges including the Starčevo–Kőrös–Criş culture the included the Balkans and most of Greece (or its immediate Neolithic predecesors depending on the classification system used).

The Neolithic arrives in coastal Southern Europe starting around this point via the Cardium Pottery culture (aka Impressed Ware) starting near the Northern border of modern Greece and then from their up the Adriatic coast and into Southern Italy from a source in the vicinity of Syria and neighboring Southern Turkey; the Cardium Pottery expansion leap frogged over existing Neolithic cultures in Crete and Eastern Greece.

3. A cooling period from about 5500 BCE to 5100 BCE (2.5 degrees C).

The first wave Neolithic Cardium Pottery culture expands from Southern Italy to Northern Italy, Sardinia, Corsica, Southern France and eastern Spain at around this point in time over a 100-200 year period. The oldest known Atlantic megalithic structures appear in Portugal around 5000 BCE, just after this cooling period ends and several centuries after Cardium Pottery arrives there. (There are much older Mealithic structures in the North Levant and Southern Turkey where the Cardium Pottery culture has its origins, but there do not appear to be meaglithic structures in the Balkan, Southern Italian and Western Greek areas that were an intermediate stage of the arrival of Cardium Pottery in Iberia that are old enough to date to predate the arrival of the Cardium Pottery culture in Iberia. Megalithic structure in Southern Italy, Malta and elsewhere appear to have been built long after the earliest megalithic structures of Portugal.)

The Turdaș-Vinča culture of the Balkans (in which the oldest copper metallurgy is attested and an undeciphered symbol system comes into use, although not strictly part of the "Copper Age") starts to emerge in this time period and further North the Danubian Linear Pottery (LBK) culture begins to expand in this time period.

In the Indus River Valley, the cermaic Neolthic era begins at this point in time from the pre-existing Neolithic Indus River Valley civilization.

4. A cooling period starting around 4700 BCE (2.2 degrees C).

This takes place in the prehistoric early Neolithic era. This coincides with the divide between the early and late period of the Vinča archaeological culture in the Balkans, and with the emergence of the Cucuteni-Trypillian culture in Romania, Moldova and the Ukraine. Pre-literate Sumerian civilization starts to emerge after this cooling period ends.   The Chalcolithic era (aka Eneolithic era aka Copper Age) commences at this point.

Atlantic megalithic civilization structures start to appear around the time of this event, although a number of megalithic structures in Portugal appear to be several centuries older. This is also when farming and herding (i.e. the Neolithic revolution) arrived in prehistoric Britain, quite possibly as part of the Atlantic megalithic civilization from the start.

The "formative phase" of the Harappan civilization commences at around this point in time.

5. A cooling period starting around 3600 BCE (1.5 degrees C) (aka the 5.9 kiloyear event).

This is roughly the time that the Kurgan hypothesis of Indo-European origins views the Yamna culture (aka Pit Grave culture) of the Pontic steppe as the proto-Indo-Europeans whose language was ancestral to all of the modern Indo-European language families.

Minoan prepalatial civilization begins to emerge around this time in Crete. This is approximately when the Aegean Bronze Age begins. The first of the Megalithic temples of Malta were built at this time.

6. A cooling period starting around 2900 BCE (2 degrees C). This gave rise to temperatures almost as cold in absolute terms as those at the 8.2 kiloyear event.

Sumerian historical records start at around this point in time as its city-state civilization matures. The original city of Troy is founded at around this time. The Harappan phase of the Indus River Valley civilization and Harappan written symbols begin to emerge around this point in time.

The Bell Beaker culture appears in Portugal at around this time.

7. A cooling period starting around 2100 BCE (1.1 degrees C). (The >4.2 kiloyear event (I eyeballed my dates from the chart).

This coincides with the historically documented drought that caused the collapse of the Akkadian Empire (followed by a brief Sumerian renaissance that soon collapses itself) and also with the historically documented First Intermediate period in ancient Egypt.  This drought is probably when the Semitic taboo against eating pork arose.

The Indo-European Hittite culture begins to expand in Anatolia conquering the non-Indo-European Hattic empire The earliest archaeological evidence of the Indo-Aryan entry into South Asia is found at this point. Tocharian Indo-Europeans establish an easternmost outpost in the Tarim Basin at this point. The Saravesti River that had been at the core of Harappan/pre-Vedic South Asian society dries up in South Asia around that time that this cooling period ends. 

This is approximately when the El Argar civilization of Southeastern Spain is founds its first city at La Bastida, which was the largest city in Bronze Age Europe. Architecture at the city of Las Bastida has precedents "in the second city of Troy (Turkey) and in the urban world of the Middle East (Palestine, Israel and Jordan), influenced by the civilisations of Mesopotamia and Egypt" indicating that this civilization had some cultural ties to an Anatolia and/or the Levant. The Bell Beaker culture appears in Britain at this time.

8. While the global climate impact of the major eruption of the Thera volcano (in modern Santorini, Greece) in the Eastern Mediterranean sometime between 1627 BCE and 1600 BCE was modest in global climate impact compared to the climate events discussed in this post, it is a natural event that may have had important historical consequences.

It had a pivotal impact the Minoan civilization which included the city that was destroyed (excavation of the ash covered Minoan city there has revealed that it was evacuated before the erruption, apparently sparing the lives of everyone there); Mycenean conquest of most of the Minoan civilization followed soon after this event.

The Thera erruption coincides in time with the fall of the Xia dynasty in China which describes events consistent with the atmospheric impacts of a major volcanic erruption historically, and with the Second Intermediate period in Egypt during which a Semitic Hyskos elite from the Levant conquered Egypt.

Some researchers hypothesize that this erruption may have been the historical root of the story of the demise of the lost city of Atlantis described by Plato (another theory proposes the ancient Iberian city of Tartessos as an Atlantis candidate). 

9. A cooling period starting around 1200 BCE (2 degrees C), something that may be associated with the aftermath of the Hekla 3 erruption in Iceland (1159 BCE).

This coincides with Bronze Age collapse noted for the demise of the Bell Beaker culture, major disruptions of cultural patterns in Britain and other parts of the Atlantic Megalithic cultural region, Homer's Trojan War, the fall of the last Minoan palace at Knossos, the Hittite empire's collapse, invasions of "Sea people" including the ethnically Mycenean Philistines who invade Egypt (the Philistines ultimately migrate to the Levant) and the beginning a period during which the Egyptian empire declines and experiences famine.

Bronze Age collapse is followed by the "Iron Age" and coincides with the arrival of Celtic civilization in Western Europe and Italic language speakers in Italy. This is also the approximate dividing line between the early and late periods of the Nordic Bronze Age (a divide that may mark the arrival or emergence of the Indo-European Germanic languages in that region). Thus, the Indo-European languages were probably spoken in Western Europe only after the Bronze Age collapse.

10. A cooling period starting around 100 BCE (1.5 degrees C).

The two century old ethnically Greek-Macedonian Seleuicid Empire created by Alexander the Great that at its greatest extent had included included central Anatolia, the Levant, Mesopotamia, Persia, today's Turkmenistan, Pamir and parts of Pakistan collapses. The Jewish Maccabees in what is now mostly Israel revolt and declare independence from their Seleucid King only to see their new kingdom fall into civil war over succession issues, and solicit a Roman conquest of their kingdom to end this war without enduring rule by the priests. In Egypt, the Hellanistic Ptolemaic Kingdom, a successor kingdom to the one created by Alexander the Great, fell to the Romans during the reign of Cleopatra VII, in this time period.

Germanic tribes (the Cimbri and Teutones) cross the river Rhone and migrate to Roman era Italy engaging Roman soldiers there who prevent them from taking Italy.  The Roman Republic and the other formerly allied city-states of Italy fight a nine year conflict called the Social War and there are three successive serious slave uprisings (the Servile Wars). The Etruscan civilization and language which arrived in Tuscan Italy sometime after 800 BCE (which called themselves the Rasna) finally went extinct in this time period. The last era of the city of Troy ends in this time period and it is no longer inhabited and is not rediscovered for another two millenia.

11. A cooling period starting around 500 CE (1.7 degrees C).  The bottom of this decline was the coldest moment of time in absolute terms, other than the 8.2 kiloyear event, since the Younger Dryas.

This coincides with the fall of the Western Roman Empire (476 CE) and the beginning of the Middle Ages. The Islamic empire's expansion then fills the vacuum created by the fall of the Roman empire in North Africa and Spain. 

12. A cooling period starting around 1100 CE (1.5 degrees C). This cooling period was followed by the Little Ice Age a sustained cooler period, conventionally dated from 1350 CE to 1850 CE, which in turn was followed by a warming period which is probably due to human contributions to climate change associated mostly with the use of fossil fuels like coal and oil, and with deforestation.

The English kings fall to Norman Conquest (1066 CE), and Scandinavian kings also conquer kingdoms in Northern France and Kiev Russia. A North American Viking colony fails soon after it is founded. The Crusades begin.

Colonial era New England was significantly colder as a consequence of the Little Ice Age than it is now.

Human Mutation Rate Is Gender Biased And Low

A new study published this month at Nature Genetics confirms with a direct measurement, multiple lines of evidence suggesting that mutation rates in modern humans are about half what had been assumed based on a presumed human-chimpanzee divergence date by most of the last decade's genetics papers. This factor of two difference is sufficient to make almost every interesting conclusion about pre-history that could be drawn from genetic data using the old dates wrong.

More intriguingly, it also suggests that about 85% of new mutations come from fathers, rather than mothers. While it has long been known that advanced paternal age is associated with new disease causing mutations, and the likely culprits behind this discrepancy have been identified, the general bias towards mutations having a paternal rather than a maternal source has been less widely appreciated.

The key line of the paper states: "we obtained an SNV mutation rate of 1.20 × 10−8 (95% confidence interval 0.89–1.43 × 10−8) mutations per base pair per generation. . . . there was strong evidence (P = 2.67 × 10−4) for a paternal bias in the origin of new mutations (85% paternal)."

For most of the genome, this gender bias isn't very important when trying to determine the age of a mutation. Everyone has a mother and a father. Everyone gets about half of their autosomal genome from each parent. So, gender differences in mutation rates all average out.

But, this may indicate that the proper mutation rate to use when determining the actual historic date when a mutation arose based on mutations observed in non-recombining Y-DNA may be higher than it is when attempting to estimate a historic date based upon mutations in autosomal DNA. Likewise, the mutation rates for autosomal X chromosomes may be somewhat lower than for autosomal DNA generally, because a disproportionate share of its lineage, although not 100% as in mtDNA, is from mother to child transmissions that are less mutation prone.

The difference in mutation rates in father to child genetic transmission as opposed to mother to daughter transmission could also adds to our understanding of the apparent discrepancies between the age of the root of the Y-DNA tree and estimates of the historic era of the most recent common ancestor of modern humans based on other population genetic methods (although this seems to make the problem worse rather than better).

Physics Journal Pay Walls Tumbling Down

The widespread adoption of the open access arXiv.org preprint server has forced the hands of twelve journals in particle physics that account for about 90% of published particle physics papers.  They are on the verge of dropping their pay walls.  The deal would be fully in place by the end of 2014.  The journals will receive $650 to $2,000 per paper in exchange for releasing their content to the general public, rather than merely journal subscribers.  Journal subscription fees will also fall.

The reality is that almost nobody ever actually pays for access to a physics paper behind a pay wall (which costs as much as an entire used college physics textbook in good condition).  The pay wall simply serves as a means of compelling professionals who regularly use the articles to have their institutions pay the hefty journal subscription fees. 

The lives of the institutionally affiliated journal subscribers will change little under the deal, which also had little net financial impact on their institutions.  But, the deal will tremendously increase access to these articles in their final published form for the educated lay public and physicists in industry, working in high schools, or working at small institutions who can't afford journal subscriptions, for example. 

Wider distribution benefits the scientists publishing the articles, whose ideas are more widely distributed as a result.  For example, nobody wants a Congressional staffer or lobbyist considering science funding to overlook their latest paper because the staffer or lobbyist doesn't have a journal subscription and doesn't have time to get a copy from someone who does.  This is part of the reason that arXiv.org received such a warm reception and wide adoption by the people whose ideas were supposedly being managed in a revenue maximizing way by the journals. 

The lag between pre-print publication and journal publication has also reduced the bargaining power of journals for established authors whose ultimate publication is almost certain, because the official version is almost always scooped and an active science blog and science journalism and professional physicist community monitors new pre-print releases very actively.

The journals themselves are mostly organized as non-profit organizations, really de facto producer cooperatives, that essentially just need a way to finance the process of organizing the administrative and printing work that goes into sorting the wheat from the chaff of new publications and organizing the work of quality scientists into presentable form.  The printing part of that process has almost vanished.  These days, the publications are written in electronic formats, edited electronically, and mostly read in electronic formats as well by journal subscribers.  Every year more academic journals drop their print versions entirely, or print just a handful of copies as collectors editions that are more for show than for practical use.  The thinning of the amount of work done by the journals themselves in house with the decline of printing as also reduced their clout.  For the most part, their in house staffs could easily be replaced if the institutions who subscribe to their journals mutually agreed that they were being gouged and started a new publication over which they had more control instead.

Unlike music, television, movie and authors who write books that are sold in bookstores, scientists do not receive substantial royalty income from the publication of articles, even though they do receive considerable financial benefit from publishing articles.  Indeed, the time that published scientists contribute to the peer review process as volunteers pretty much outweighs any services they receive from journals in connection with the articles that they publish themselves.  Some of this flows from the fact that basic scientific laws and principles can't be protected by patent law anyway, and that copyright protects particular ways of expressing an idea rather than the idea itself. 

Instead, scientists benefit from having published articles by using that signal in the hiring and promotion process within the world of professional scientists in and out of academia, in attracting top talent to join their labs as graduate students and post-docs, in selling higher level science textbooks that do bring in meaningful royalties, and by bringing their work to the attention of people who award grants and prizes for work in their field.

Dirt Tells The Story

Usually, archaeologists are mostly concerned about what they can dig up out of the dirt.  But, sometimes the dirt itself also tells a story. 

A recent example comes from ongoing research into prehistoric Copper Age and Bronze Age structures and Bell Beaker culture artifacts in Southern Portugal.  This archaeological evidence is found in a well defined geographic region within Southern Portugal.  Why is this the case?

It turns out that the area where this evidence has been found is notable for "its geological diversity and good soils and plains" while the adjacent areas where these structures and artifacts are mostly absent are marked by a "poor littoral sandy platform."  Thus, the places that have dirt that is good for farming were home to this well developed prehistoric Iberian civilization, while this civilization didn't settle adjacent areas with dirt that is ill suited for farming.

As one of the researchers involved in this investigation, A.C. Valera, explains, there is still more work to be done in order to better understand the details:

[D]uring Neolithic and Chalcolithic . . . the different geological and ecological conditions naturally contributed to different human strategies of occupations (and, please, I am not talking about any kind of geographic determinism). So, in a general common frame of Southwest Iberia, we can see diversities and local and sub-regional specificities in interaction. Establishing the terms of these interactions is an actual target for reasearch.
 

Context

Why care?

Because the sites that A.C. Valera and his team are investigating in Southwestern Iberia sheds light on what was going on at the proximate source, in time and place, of the biggest demographic transition in European history that your professors in college never told you about.  They didn't know until recently that it even took place.

The Old Conventional Wisdom Was "Pots Not People."

We have known for a long time when farming and herding commenced in Iberia (two or three thousand years after it did in the Fertile Crescent, give or take) and that the crops and domesticated animals used by early farmers and herders in Iberia were mostly domesticated in the Fertile Cresecent.  This event is called the arrival of the "Neolithic revolution" in the area. 

Few thousand years later, starting around the 8th century BCE, the archaeology of the region can be tied into historical accounts of the Celto-Iberians and some ancient relatives and predecessors of the Basques in Northeastern Iberia, and possibly some other populations.  Using archaeology to look at the immediate predecessors of the civilizations documented historically can stretch the relatively solid ground of historical knowledge back a few centuries more, but not all of the way back to the Bronze Age.

For a long time, the prevailing assumption was that the events in between were mostly gradual evolutions from one point to the other.  The archaeological cultures that existed in between have been classified into distinct groupings in particular places and time periods.  But, it has been unclear which dividing lines between archaeological cultures were most abrupt, when (if ever) there were major demographic transitions (for example, due to population replacement or mass migrations), and what the underlying logic drove transitions from one archaeological culture to the next.

In the 1970s, the prevailing orthodoxy regarding the transitions in archaeological cultures of Europe had been summed up in the motto "pots not people."  The understanding was that cultural technology transfers were more important than mass migrations in bringing about the transitions from one archaeological culture to the next.

Genetics Uprooted Conventional Wisdom About The Neolithic Transition.

Ancient DNA evidence has now made clear that there was a major demographic transition probably due to populations migrating into Europe as they brought farming and herding lifestyles to the region.  In much of Europe, this demographic transition was much more abrupt than had widely been believed

The modern evidence, particularly from population genetics and ancient DNA samples, makes clear that this was wrong.  Generally speaking, the story is of "pots and people" moving together.

The transition from hunting and gathering to producing food from domesticated plants and animals didn't necessarily give rise to a complete population replacement, but the demographic component of the transition was far larger than conventional wisdom had supposed before genetics were brought to bear on the question.

In twenty-twenty hindsight, it isn't terribly surprising that people who can product their own food from domesticated plants and domesticated animals might have a decisive edge over the hunter-gatherers who preceded them, and that in a pre-literate era, that these transitions might have needed whole populations of people migrating with their seeds and animals to take place.

Genetics Has Revealed A Post-Neolithic Demographic Transition.

Even more surprisingly, ancient DNA evidence is making it increasingly clear that there was at least one other major demographic transition (and quite possibly two) between the arrival of the first farmers and the beginning of written accounts of European history in the Iron Age. 

Ancient DNA from middle to late Iron Age burial sites in most of Europe show a population genetic mix in Europe that looks a lot like that of modern Europeans in the same regions, and very unlike that of the earliest available ancient DNA from prehistoric European hunters and gatherers in the Upper Paleolithic era.  But, ancient DNA from the earliest farmers in much of Europe (i.e. the earliest Neolithic) doesn't match either the prehistoric European hunters and gathers that preceded them, nor the Iron Age populations that followed them.  Sophisticated statistical analysis of the autosomal genetics of modern European populations confirm and elucidate the ancient DNA findings.

It was far less obvious, before this ancient DNA evidence became available, that one group of prehistoric people who had the ability to produce food with domesticated plants and animals could have such a dramatic demographic impact on another prehistoric population that could also produce its own food.

The Bell Beaker Culture Is A Likely Source Of The Post-Neolithic Demographic Transition.

A distinctive archaeological Bell Beaker culture starts to appear in Europe in the Chalcolithic era (i.e. Copper Age).  Radiocarbon dating confirms the inference arising from the presence of metals in Bell Beaker contexts and also allows archaeologists to accurate determine which Bell Beaker sites are the oldest.  The radiocarbon dated Bell Beaker archaeological finds put the origin of this archaeological culture sometime between 3000 BCE and 2500 BCE in Southern Iberia, although where the people who were involved in appearance of this culture came from is less clear. 

This Bell Beaker culture increasingly looks like a major source of the demographic transition that took place sometime between the arrival of the first farmers of Western Europe and the populations who lived there by the time that Roman historians started to arrive on the scene to document the situation. 

There are only so many archaeological cultures in right time frame that have been identified to date. In Europe, there has been enough archaeological research to assure us that this list of archaeological cultures is pretty much complete.  And, many of the archaeological cultures which are in the right time frame are a poor fit to the geographic scope of this demographic event, or are less attactive candidates because they show more continuity with prior archaeological cultures where they are found and were accompanied by a less distinctive break with previous archaeological cultures. 

The fact that Bell Beaker era human skeletal remains show differences in physical type of prior populations in many places is particularly telling.  While a difference in physical type could be due, for example, to changes in diet rather than mass migrations, any mass migration that did happen would be expected to produce some shift in the physical type seem in skeletal remains.

Put another way, the modern genetic mix found in Western Europe wasn't really in place until the Bell Beaker culture swept across the region (and perhaps as late as the early Iron Age in much of Europe, if there was more than one major prehistoric, post-Neolithic, demographic transition).  Many of the ancestors of modern Western Europeans probably arrived in Western Europe together with the Bell Beaker culture.

Portugal, where the Western and Northern European Bell Beaker culture apparently emerged around 2900 BCE and seems to have radiated from, is the natural place both to look forward and identify the elements of this archaeological culture that caused the descendants of these people to transform Western Europe, and is also the nature place to look backward and identify the source of this new cultural transformation and the population that delivered it. 

 

Physics Blogger Down

Lubos Motl, one of the most prominent physics bloggers in the world and a professional physicist, who is an earnest man if something of a curmudgeon, has taken a very serious turn for the worse in his health due to a life threatening out of control yeast infection.  Here in Turtle Island, we hope for his full recovery.

Updated Mutation Rate Dates Make More Sense

Slowly but more or less surely, the human archeogenetics community is coming to the realization that the mutation rate used to estimate the age of various human and primate lineages was miscalibrated at a rate roughly twice as fast as it is, as we are coming to realize from a variety of new measurements of it. The dates calculated using the new calibration methods make much more sense in light of the likely archaeological corrolates of the human lineages to which dates have been assigned using mutation rate dating.

The four key points may be summarized as follows.

First, the divergence between modern humans and both Neanderthals and Denisovans, which was originally estimated to be 272,000–435,000 years ago, is revised to 400,000–600,000 years ago. This is in better agreement with the range of estimated split times from mtDNA and also with the idea that the ancestral population of these groups may have been H. heidelbergensis.

Second, for the split between the Khoe–San and other modern humans, revised estimates from nuclear genomic data suggest a divergence 250,000–300,000 years ago, older than single locus estimates for the root of the human tree.

Third, revised estimates of the separation time between Africans and non-Africans suggest that this predates the appearance of modern humans in Europe and Asia by up to 60,000 years. We have suggested a scenario of exodus from Africa via an intermediate population in East Africa and the Middle East, which may fit better with growing evidence for modern human occupation of the latter region before the wider colonization of Eurasia and may provide a longer interval for Neanderthal admixture with non-African populations.

Finally, revised split times of 40,000–80,000 years ago for Europeans and Asians agree better with the palaeoanthropological record and with estimates from mtDNA.

From here quoting Aylwyn Scally & Richard Durbin, "Revising the human mutation rate: implications for understanding human evolution," Nature Reviews Genetics, advance online publication, 11 September 2012. doi:10.1038/nrg3295.

General Analysis

The difference between the old faster mutation rate estimate and the new slower mutation rate estimate in sufficiently great to make essentially every historically interesting hypothesis conclusion reached with the old dates invalid. The implausibility of the old dates is one of the reasons that people who have looked at the old estimates from an interdisciplinary perspective, myself included, have long been skeptical of them, even before direct evidence that the slower mutation rate estimate was more accurate emerged.

The new dates for Neanderthal divergence from modern humans, for the appearance of anatomically modern humans, for Out of Africa, and for a staged migration scenario that causes the West Eurasian-East Eurasian divide within non-Africans to occur much later than the African-non-African divide all make much more sense with the slower automsomal mutation rate than the old dates. With the new calibrations, other dates estimated via mutation rates for which we don't have archaeological data to calibrate against may also become more credible.

The fact that is possible to come up with a calibration of mutation rate dates that coroborates the archaeological data and has internal coherence is also a relief. It had looked possible in the last year or two that meaningful absolute dating based on mutation rates might simply be impossible, because the assumption that there was a stable genetic mutation rate in humans that could be applied across the nuclear genome might have been fundamentallly flawed. If this was the case, the population genetic contribution to discerning the course of prehistory in a scientifically reliable way could have been virtually destroyed. This fear increasingly looks unfounded, at least outside areas of the genome where neutral genetic drift rather than strong natural selection. Some parts of the non-recombining Y-DNA genome may remain particularly problematic due to strong selective effects, and cofounding instances of introgression of multiple populations that make populations look older than they actually are may also continue to be an issue, however.

Analysis of Discrepency In The New Dates

The archaeological date typically cited for the appearance of anatomically modern humans in Africa is around 230,000 to 250,000 years ago, both the genetic and the archaeological dates have a margin of error, and the archaeological dates are always subject to significant adjustment if a new, older archaeological find is found and reliably dated. The archaeological date is the latest possible date at which anatomically modern humans could have arisen. The archaeological record of hominin remains generally that are that old is quite thin in the period from, for example, 200,000 years ago until 350,000 years ago, and the total number of anatomically modern humans alive at first would have been very small, so it wouldn't be very surprising at all for an accurate date for the origin of modern humans to have a genetic date to be a bit older than the oldest discovered anatomoically modern human remains. So, the Khoe-San divergence date cited isn't far off from the likely point of origin of modern humans in the archaeological record.

The possibility that the most recent common ancestor of modern humans as determined by non-recombining Y-DNA genetics and mitochondrial genetics could be younger than the date determined by autosomal genetics isn't necessarily very troubling either.

As the presence of Neanderthal and Denisovian autosomal genetic contributions in the human genome despite the absence of any Y-DNA or mtDNA traces of this admixture (or archaic African admixture that indirect methods suggest is found in Paleo-African populations at a fraction lower than that of Neanderthal admixture in non-Africas), all uniparental genetic traces of an introgressing population can be lost yet still leave autosomal genetic traces.

There are some very specific considerations that apply to the purging of uniparental mutations in the case of archaic hominin admixture that I have discussed in previous posts and that may not apply to early anatomically modern humans pre-Out of Africa. In general, low frequency uniparental gene in a population are unlikely to drop out of the gene pool during periods when a population is expanding, but do drop out of the gene pool with some frequency when the size of the population is small and stable, fluctuates up and down multiple times, or when it is getting smaller due to a population bottleneck. Some of these conditions were probably present for some of the period betweeen the evolution of the earliest modern humans and the Out of Africa date, so it wouldn't be surprising if age of the most recent common Y-DNA or mtDNA ancestor of modern humans is at least somewhat less than that of the same date determined looking at the richer set of automomal genetic data.

Could Population Structure And Admixture Explain Automsomal Genetic Ages Much Older Than Uniparental Genetic Ages?

If I recall correctly, uniparental mutation rate dating has pointed to a Paleo-African divergence from other modern humans more or less around the time of the Out of Africa event when consistent dating methods are used to fix both dates (ca. 60,000-70,000 years ago in the old calibration and closer to 100,000-140,000 years ago with the newly calibrated dates, if my memory served me). Uniparental phylogenies of non-recombining Y-DNA and mtDNA have also implied that the Khoe-San and Pygmies may share a common ancestor distinct from other modern humans at this point.

This is a big discrepency with the 250,000-300,000 year old date above, which may be hard to fit to a model of uniparental haplogroup purging solely due to random genetic drift. This is no genetic evidence so far for a modern human population bottleneck in Africa itself in early human prehistory, slow population size growth in Africa over these many tens of thousands of years is a plausible demographic scenario used in most population genetic models with success, and estimates of African effective population sizes are generally greater than estimates of non-African founding population effective population sizes.

But, admixture of diverse populations can make the automsomal genetic of the population look older. The same effect, by the way, is also seen when one estimates the time of emergence of two languages from each other based on lexical data, that is quite visible in recent efforts to date Indo-European linguistic origins on this basis.

It also seems unlikely, however that the modest amount of archaic admixture inferred to be present in modern Paleo-African populations is enough to give rise to this discrepency. There simply isn't enough of inferred archaic admixture in these populations (we have no ancient DNA from Africa which we can use to test the hypothesis directly as we do with Neanderthals and Denisovans). While Dienekes' has suspected that admixture with archaic hominins may be producing an artificially old autosomal estimate for Paleo-African population divergence, my own intuition is that admixture of diverse modern human African populations, some of which no longer have unadmixed survivors, seems like a more likely variant of this hypothesis.

A Plausible Admixture Scenario That Could Explain The Discrepency

Consider the following scenario that could explain why Paleo-African populations look older from an autosomal genetic perpsective, dating to around the time that modern human arise, than the apparent date of their divergence from other modern humans based on mutations in their uniparental genetics.

Suppose that anatomically modern humans began to fracture into diverse and geographically structured populations within Africa, with limited admixture with populations other than ones immediately bordering them, almost immediately upon evolving from one of the Homo heidelbergensis hominin species branches around 250,000-300,000 years ago.

Suppose also that anatomically modern humans did not admix with peoples other than anatomically modern humans after the emergence of this new species, except for a few clearly defined episodes of admixture with archaic hominins. Specifically, Neanderthal and Denisovian admixture outside Africa, and one or two smaller episodes of admixture with archaic hominins with Paleo-Africans within Africa where larger effective population sizes of anatomically modern humans may have reduced the impact of archaic hominin introgression.

Suppose that some of the "first wave" Paleo-African populations that began to diverge immediately from a core single modern human population near where anatomically modern humans evolved in the first place, probably somewhere in East Africa, which was more or less homogeneous genetically. There would have been many smaller first wave Paleo-African populations at diverse locations elsewhere in Africa, most of which were less successful because they had not evolved as specifically to be adapted to the conditions elsewhere in Africa.

Suppose that the core of extant Paleo-African populations in Africa are traceable not to this first wave of Paleo-Africans, but to a second wave of hunter-gatherers that split off from the core East African hunter-gatherer population much later. This second wave of Paleo-Africans would have evolved genetically and culturally in a way that made them more fit than first wave Paleo-Africans in environments less like the one that modern humans had originally evolved in, in other words, generalist advantages. These adaptations, present in non-Africans and second wave Paleo-Africans, but not in archaic hominins and first wave Paleo-Africans, gave the second wave Paleo-Africans a selective advantage over the existing "fringe" hominin populations of Africa and over archaic hominin populations outside Africa.

The remnants of first wave Paleo-African may have eventually been absorbed as minor components of other African populations. In extant Paleo-African populations, genetic drift could have eliminated uniparental markers of the existence other Paleo-African populations at the fringe of the pre-Out of Africa modern human world, while still leaving enough of an autosomal genetic impact on populations of extant mostly "second wave" Paleo-African populations to make the autosomal genomes of extant Paleo-Africans look older than the point in time at which the bulk of their ancestors diverged from a modern human core population in Africa. But, any automsomal contribution from introgression of "first wave" Paleo-African populations into the core modern human population in Africa, if there was one, may have been too slight to be detectable in the genomes of populations derived from this core modern human African population because it was larger relative to the introgressing first wave Paleo-Africans.

A Brief History of Prehistoric Europe

Preface

A rush of new abstracts of genetics papers were released last week at a major academic conference, and before posting about them, it is really time to take a step back and recap the broad outlines of what we believe we know about prehistoric Europe to put those discoveries in a context in which the papers, which often make predictions based on modern and/or ancient populations genetics about the timing of the geographic and demographic expansions of historical linguistic proto-populations.

In my view, these new genetic data points must ultimately be fit to the more concrete, more direct and more accurately dated and characterized archaeological evidence of radiographically and deposit stratum dates relics and remains.

This post  outlines the history of prehistoric West Eurasia with a particular eye towards the phenomena of Indo-European language expansion prior to the Medieveal period. Ultimately, this post concludes when the main subfamilies of the Indo-European languages in Europe and South Asia are in place sometime in the Iron Age, with some footnotes on some of the later linguistic developments in Europe.

Very little of Europe was part of the Indo-European language family at the dawn of the Bronze Age, but by the end of the Iron Age that followed, the Indo-European language family had experienced most of its ultimate expansion in geographic range.  It has also exterminated almost all of Europe's other languages as well as many relatively basal branches of the Indo-European language family itself in Europe.  Most of the later expansions and migrations of Indo-European language speaking peoples, prior to the era of European colonial empires, would be into areas where other Indo-European languages were already spoken.

Twenty-five centuries later after the Indo-European languages began to experience this massive expansion, the only non-Indo-European languages left in Europe by the end of the first century of the current era (i.e. AD aka CE) at the height of the Roman Empire were Basque (in Northern Spain and Southwestern France), the Finno-Uralic languages of Finland and other parts of far Northeastern Europe and North Central Asia, and the various language families of the Caucasus Mountains that form one of the boundaries between Europe and Asia (together with the Ural Mountains, and various bodies of water).  All other non-Indo-European languages now spoken in Europe arrived in the Medieval period.

Almost all of the non-Indo-European and non-Semitic languages of Western Asia were also extinct by then.  The Sumerian language of Mesopotamia, the language of the Harappans, and all of the ever attested non-Indo-European languages of Anatolia and the Zargos Mountains such as Hattic, Hurrian, Kassite, Elamite, and at least one other lost non-Indo-European language family spoken between the Kassite and Elamite linguistic regions in the Zargos Mountains were extinct or moribund by then.

The non-Latin Celtic and Italic languages of Continental Europe were extinct or moribund, although some of the Celtic languages lived on in the British Isles.  The Anatolian languages were also all extinct or moribund by then, as were many of the Indo-European Aegean languages.

This post fits known archaeological cultures whose ages and geographic extend are largely established to particular hypothesized language family affiliations. This post states what is my most likely hypothesis without spelling out in detail the degree of uncertainty with each component of the hypothesis.  But, some of the points are definitely less certain than others.  The short sketch of the Indo-European speaking people's expansion in time and space from a proto-language that I have provided starts with the language spoken by the Yamna people on the Pontic steppe, arguably the last point in time at during which there was a single proto-Indo-European languages spoken in a geographically compact area.  This analysis largely tracks the leading Kurgan hypothesis regarding this process.

An Big Picture Outline of The Main Eras Of Early European Prehistory

The Paleolithic Era

The first hominins to leave Africa, Homo Erectus, evolved in Africa around 2 million years ago and had spread as far as the island of Java in Indonesia by about 1,800,000 years ago.

Neanderthals, the prior hominin residents of Europe and West Asia became distinct from earlier hominins in Europe or Africa around 500,000 to 750,000 years ago.  Neanderthals probably share a branch of the tree of life of the genus homo called Homo Heidelbergus with modern humans that originated in Europe or Africa that broke away from Homo Erectus after Homo Erectus left Africa.  Neanderthals had a range that included all but the coldest parts of Europe, Pakistan, some of India and Central Asia.  It isn't entirely clear to what extent Neanderthals were present in high alpine environments.

Archaeological evidence from the interior of Arabia and Israel place the earliest modern humans to leave Africa, who are the primary source of genetic ancestry for all people who lack African descent in the last five hundred years or so, starting around 100,000 to 125,000 years ago from a population whose civilization in called the Nuba complex in the Nile River Basin until about 80,000 to 75,000 years ago, after which there was a roughly twenty-five thousand year long period of discontinuity in the places where remains of anatomically modern humans first left Africa.  Most modern human Neanderthal admixture today in non-Africans appears to have its origins in this era of non-African prehistory rather than the thousands of years of co-existence in rough geographical proximity to each other that followed.

The reappearance of signs that modern humans lived there again around 50,000 years ago.  In the interim, they spread out of Arabia to destinations including the highlands of West Asia (somewhere), possibly interior oasises in Arabia or the Persian Gulf, and India. 

Neanderthals decline in population in Europe close in time to the arrival of modern humans and some major volcanic eruptions in Europe, and may have declined in population of gone extinct in West Asia and South Asia sooner than then.  Anatomically modern humans called Cro-Magnons arrive in Europe in an era called the Upper Paleolithic which commences in Europe about 43,000 years ago, give or take.  But, Neanderthals do not go extinct entirely in the last caves where their remains have been discovered until around 28,000 years ago.

Before they go extinct, Neanderthals provide via admixture about 10% to the autosomal genome of Cro-Magnon hunter-gatherers in Europe (compared to something like 3% in modern Europeans), but subsequent migrations from areas that had far less Neanderthal admixture ultimately dilute this elevated contribution to barely distinguishable levels.  Some remains show signs that later Neanderthals had visible modern human admixture as well and this may have been what gave rise to many thousands of years that marked the first period during which there had been major advances in Neanderthal material culture since they established their signature Mousterian set of stone tools hundreds of thousands of years earlier.

Northern Europe and Siberia are completely depopulated during the Last Glacial Maxmium ca. 20,000 years ago, and is repopulated from the South, in part from a Franco-Cantabrian refugium, from the Italian Peninsula and a Southeastern European refugium starting around 16,000 years ago. The period of the repopulation of Europe, or at least the last few thousand years of it, starting around 12,000 years ago (two thousand years before the Fertile Crescent Neolithic revolution) is called the Epipaleolithic era and is a time of considerable West Asian/Southwest Asian migration into Southern Europe and Northern Africa.

The Neolithic Revolution 

The Neolithic Revolution that commences the Neolithic era is marked by replacement of hunting and gathering modes of food production with farming and herding. In the Fertile Crescent (including the Levant, Anatolia and Mesopotamia), and probably some adjacent areas, there are multiple stages of the Pre-Pottery Neolithic era, but pottery is part of the Neolithic culture by the time it spreads very far into Europe, moving beyond the far Southeastern corner of Europe, mostly in connection with two first wave Neolithic cultures, the Linear Pottery Neolithic (more or less making its way up the Danube River) in the East and the Cardial Pottery Neolithic which makes its way across Southern Europe in the East.  These two waves of migrants, who bring about the Neolithic transition more by migration of entire peoples than by cultural transmission to pre-existing hunter-gather populations.

The early Neolithic era originates in the Fertile Crescent around 8000 BCE (10,000 years ago, aka the start of the Holocene era).  Around a thousand years later, around 7000 BCE, and also about a thousand years before the Neolithic culture spreads into Europe via the Fertile Crescent Neolithic had already spread to the Indus River Valley and the Nile River basin in Europe around 7000 BCE. 

The commencement of the Neolithic era varies from place to place in Europe (from roughly 6000 BCE in the Balkans to 3500 BCE in Scandinavia).

The Atlantic megalithic culture emerged from the Cardial Pottery first wave Neolithic people of Southern Europe.  They may spoken languages that were part of the same linguistic family as Etruscan and the contemporaneous and related Alpine Rhaetic language (not to be confused with the modern Rhaetic language of Switzerland which is Indo-European). The Rhaetic and Etruscan people, in my opinion, most likely had their origins in Southern French Cardial Pottery wave peoples until incoming Urnfield people or Celts drove them out in the Iron Age. The Cardial Pottery people, in turn, had origins in the general vicinity of the Aegean and Anatolia at the dawn on the European Neolithic.

The Cardial Pottery Neolithic migration from which emerged the Atlantic Megalithic people and the next wave Vasconic Bell Beaker peoples, combined, mostly replaced local Mesolithic people, at least in the Southern part of the Bell Beaker area, from a population genetic perspective.

The Copper Age

In Western Eurasia, recognizable civilization begins in the Copper Age, which follows the early Neolithic era, starting around the last half of the 3000s BCE, and ends when the Bronze Age begins, about a thousand years later.  There are places in the Northern fringes of Europe where the arrival of the earliest farming and herding peoples sometimes called the arrival of the Neolithic people in the region, actually involved Copper Age people rather than true early Neolithic populations. 

The Copper Age is when the first cities appear and the Sumerians and Egyptians independently invent writing, as well as the earliest widespread manufacturing of metal. It may also coincide with important, but somewhat obscure, advances in herding and farming technologies including the increased importance of milking cows as a part of people's diet in Europe.

The Minoan Palace civilization in Crete, the Sumerian city-state federation's cultural zenith in Mesopotamia, the pinnacle of the Harappan civilization in the Indus River Valley, and the first historically attested dynasties of ancient, pyramid building, hieroglyphic using, Coptic language speaking Egypt date to the Copper Age.  Some of the Biblical book of Genesis (e.g. at least some of the story of the Creation, the Garden of Eden, the Tower of Babel, and Noah's flood) and the birth story of Moses in the Biblical book of Exodus, clearly draw on Sumerian legends from the Copper Age.

Horses were domesticated in the European Steppe and wheeled vehicles were invented around 3500 BCE, close in time to the start of the Copper Age.

The Bell Beaker culture starts its expansion into Western Europe in the Copper Age.  The Copper Age to Bronze Age Bell Beaker culture was in my best estimate, a non-Indo-European, probably proto-Vasconic (i.e. Basque linguistic family) superstrate imposed on a linguistically non-Indo-European Neolithic Atlantic Megalithic culture substrate that spoke languages in a single language family that were not part of either the Indo-European or Vasconic language families, probably the language derived from the original Cardial Ware pottery Neolithic migrants.

The Pit Comb Ware aka Comb Ceramic culture starts about 3200 BCE and continues until the mid-Bronze Age.  It was linguistically Uralic, is derived from further East in Northern Asia, and is probably the main genetic source for the East Eurasian affinities seen in Northern European autosomal genetics and in uniparental haplogroups like N1a which are seen in Northern Europeans.

The megalithic Funnelbeaker (TRB) people were a declining phase of the LBK Neolithic wave migrants under pressure from both the hunter-gatherer Pit Ware peoples and the emerging Indo-European people who were their neighbors. The pressure from the Indo-Europeans reaches a tipping point around 2900BCE-2400BCE when Indo-Europeans gains a decisive edge over TRB people for some reason. The TRB culture is probably where most of the admixture of Mesolithic hunter-gatherer people and first wave Neolithic people revealed by modern Northern European population genetics took place.  The Funnelbeaker culture is noted archaeologically for showing signs of admixture between hunter-gatherer peoples and the successors to the LBK farmers, probably as a result of declining climate conditions for farming causing hunting and gathering and farming to reach a point of rough economic prestige equity.

Indo-European languages are present only in a proto-Indo-European (PIE) Yamna culture limited to the Pontic steppe (basically, the Ukraine) until the dawn of the Bronze Age, with perhaps a small proto-Tocharian group leaving around 3500 BCE to make a long journal across the Russian steppe via intermediate settlements who arrive in Tarim Basin ca. 2000 BCE, and a proto-Corded Ware culture group that arrives in Poland around 3000 BCE. The current theory is that the Proto-Indo-Europeans of the Yamna culture were mostly nomadic herders who had a minor involvement in farming, but this remains a controversial point.

The Bronze Age

The Bronze Age starts sometime in the mid-2000s BCE and ends with "Bronze Age collapse" around 1200 BCE.  It is associated among other things with the widespread use of Bronze metals (an alloy of copper and zinc from which is more suitable than pure copper in many applications).  The Bronze Age is a period of legendary history in Europe full of heroes, demigods, epic battles, empire builders, warriors, revenge, and explorers, in which it is hard to separate fact from fiction. It is the setting for most Classical Greco-Roman mythology, for most Norse mythology, for most Hindu mythology, for most Greek mythology and for numerous Egyptian legends.

This is the era when chariot warfare became widespread from Egypt to Central Europe to Iran to India, mostly from driven by warriors in expanding linguistically Indo-European populations, and by the peoples reacting to encounters with them.

As set forth below, it was also a period of massive expansions and conquests for two societies in Western Eurasia historically made up of nomadic herders, the Semites and the Indo-Europeans. 

While I don't emphasize the point here given the expressly West Eurasian focus of this post, it is likely although not certain, that the Bronze Age technological package was exported, mostly culturally rather than demically, via the Silk Road from the Pontic Steppe to Northern Asia, triggering the emergence of Bronze Age societies in China and its vicinity with a distinctly Asian character.  Ultimately, these developments may have made possible later expansions across Northern Asia and into West Eurasia of first the Turks and later the Mongols in the first fifteen decades of the current era.

*** A Footnote On Armenian

I discuss the expansions of all of the major branches of the Indo-European languages during the Bronze Age here except Armenian which has a small current geographic scope, a modern population history from the Armenian genocide not reflected in its current geographic distribution, a complex set of areal influences from other Indo-European languages that is reflected in its varied isoglosses, a historically ill established origin until the Middle Ages, and a possible origin in the Aegean or Eastern Turkey followed by a long distance migration.  This is too much to fit into a "brief" one post history of prehistoric Europe.

*** Bronze Age Semites

A historically documented drought in Mesopotamia at this time finished off the linguistically Sumerian civilization of Mesopotamia (which was replaced by the Semitic Akkadian language except for religious purposes) and this is probably the time period when the Semitic taboo against eating pork shared by Jews and Muslims today arose.

The Bronze Age definitely preceded Islamic ethnogenesis (which required the prophet Muhammad to deliver his revelations in the 7th century CE), and probably also preceded Jewish ethnogenesis, as distinct from a merely generalized Semitic ethnic identity. The Semitic Mediterranean maritime trading civilization called the Phoenicians emerged in the late Bronze Age and continued to remain vital through the subsequent Iron Age.

This event lead to the first "intermediate period" in the written history of dynastic Egypt, during which Semitic Hyskos people ruled Egypt. The early Bronze Age was also probably roughly the time that the speakers of the Ethio-Semitic proto-language arrived in Ethiopia, had a meaningful male biased genetic impact, and probably replaced the existing Afro-Asiatic languages from the Cushitic language family.

*** Bronze Age Indo-European Indo-Aryan Expansions

The severe climate events at the start of the Bronze Age reroute the course of the Saravasti River (between the modern Indus and Ganges Rivers of South Asia) which is a key geographic feature in the proto-Hindu Rig Vedas, thereby destroying much of the Harappan civilization of the Indus River Valley that had been built up on its banks.  Indo-Aryans arrive in South Asia about 2000 BCE with room to be a up to few hundred years older (before which Harappan cultural traces preclude earlier dates) if new archaeological discoveries find something a bit older.  The main expansion into the Indian Peninsula continues over a few hundred years to include all of the areas where Indo-Aryan languages derived from their original language, Sanskrit, in which the Rig Vedas, which probably started to be composed around 2000 BCE, are spoken today in South Asia (of which Hindi is the most widely spoken) linguistically.  Religiously all of India's Dravidian language speaking areas as well. 

In the late Bronze Age around around 1500 BCE, the Mittani Empire in the Zargos Mountains of Iran and Northern Mesoptomia was ruled by a Sanskrit speaking elite (rather than the proto-Persian language speaking ruling class one might expect) who ruled over a mostly non-Indo-European Kassite language speaking population and are remembers most for their equestrian manuals which survive to this day in Hittite translation that preserved many of the original Sanskrit derived technical terms.

Genetic traces of the Indo-Aryan superstate dated with genetic evidence to roughly the right historical time period for the arrival of the Indo-Aryans documented by other means are generally much stronger in high caste Indians in general, than in lower caste Indians.  They Indo-Aryans may have invented the caste system, but could also have simply placed themselves in their own caste or a previously much smaller caste at the top of a pre-existing caste system.  Indo-Aryan genetic influences is somewhat difficult to parse because it is superimposed on a pre-existing genetic divided between Ancestral North Indians and Ancestral South Indians that probably predates the Indo-Aryan invasion by at least five thousand years when the Indus River Valley civilization was established by Fertile Crescent Neolithic culture migrants and perhaps even further back into the Paleolithic era.

*** Expansion Of Other Bronze Age Indo-Iranian Populations

The larger Indo-Iranian language macrofamily within the Indo-European language family includes not only Sanskrit derived Indo-Aryan languages, but also most of the languages of modern Iran (including Persian) and most of the languages of modern Afghanistan.  The origins of the Indo-Iranian languages are probably a century or three earlier than the origins of the Sanskrit branch that gave rise to the languages of India a bit closer to Central India than the Cemetery H in Northeast India which is the oldest reliably dated, culturally Indo-Aryan site. 

One possible place of origin for Indo-Iranian society could have been in the conquest of the BMAC archaeological complex of Central Asia, which was the furthest flung colony in the Harappan sphere of influence, allowing them to absorb cultural influences that nomadic herders of Central Asia couldn't have acquired otherwise such as irrigated agriculture concepts.  There are aspects of Zoroastrian religion that seems to parallel BMAC religious ideas.

From the Bronze Age until the arrival of Turkic warriors on horses in the first millenium of the current era (for example, the original Huns and in time the Turks who became as superstate population in Anatolia and gave it the Turkish language spoken there today), the languages of Central Asia's herders were Indo-Iranian ones, like Scythian.

An early form of the Persian language was the language of the proto-Zoroastrian Persian religious text called the Avesta, which was composed in the late Bronze Age, around 1500 BCE and is the main intellectual source for the stark religious good-evil duality with God and the Angels in Heaven fighting for good against Satan and his demons in Hell fighting for evil that emerges within Judaism during the intertestamentary period and makes its way into early Christian theology and metaphysics. This probably derived as a result contacts with Zoroastrian ideas during an intertestamentary period of exile to Mesopotamia and was also found in other Jewish sects during the formative period of early Christianity. This kind of dualism was not a part of Hebrew Bible era Judaism in the same way. The recent fantasy movie "Prince of Persia" is set in Bronze Age Iran.

Evidence of non-Indo-European languages including Elamite and a previously unknown language of people from the Zargos mountains, suggest that the Indo-Iranian linguistic monopoly in Iran may have come much later to Southern Iran than had been previously assumed.

One of the confounding issues in historical Indo-European linguistics has been the inability of linguists to meaningfully characterize substrate influences for the Indo-Aryan or other Indo-Iranian languages, nor is there the legendary tradition of migration into the region found in most other Indo-European societies.  This confounding question is accompanied by other ones.  What historical language could have been a source for or influence on Proto-Indo-European as spoken by the Yamna people?  How did the nomadic herders of the Pontic-Caspian steppe develop such an advanced agricultural and metallurgical vocabulary?  What is the cause that drove the sudden expansion of Indo-European languages somewhat before the beginning of the Bronze Age wrecked havoc in Mesopotamia and the Levant?  If horses and the wheel were really important to Indo-European expansion, why was most of the expansion delayed for another thousand years after these technologies were developed by the Indo-Europeans?

Given that the Proto-Indo-European culture was near the fringe of the expansive Harappan empire's advanced civilization, as well as the advanced metallurgy of the Caucasian civilizations of the time, one possibility is that a Harappan cultural infusion to Proto-Indo-European society, fueled by desperate exiles from a rapidly collapsing civilization built around millenia of warless stability and intruding into their territory in search of new homelands, provided an infusion of cultural material that when melded with an otherwise not particularly exceptional Yamna culture created the right combination to gain a decisive advantage over their neighbors.

*** Bronze Age Indo-European Hittite Expansions

It was in the Bronze Age that the Indo-European Hittites, starting with just a two city kingdom, built the first historically attested empire to include all of Anatolia and some of Northern Mesopotamia and the Northern Levant.  The zone of Hittite control extended all of the way to the Levantine northern border of Egyptian control in the vicinity of modern Lebanon.  This was the furthest South that any linguistically Indo-European empire would extend until the Roman empire came to rule the North African coast.  The Hittites and Egyptians fought chariot battles with each other and exchanged royal brides to make alliances.

Hittite expansion which is fairly well documented in Akkadian and Hittite documents (impressed in clay and first written by Mesopotamian traders at frontier trading posts) and also fairly well documented archaeologically, starts in the Bronze Age in Anatolia at about 2000 BCE and leads to the end of Hattic languages.

There is not bona fide dispute over when the Anatolian Indo-European languages became the overwhelmingly dominant language family in Anatolia, even if there is dispute over the pre-Hittite language mix in Anatolia with some arguing for an Indo-European proto-language origin in pockets of Anatolia that were not Hattic or Hurrian, rather than a proto-language origin with the Yamna culture on the other side of the Black Sea from Anatolia that extended to Anatolia's fringes on both the East and West.

The highly divergent character of Anatolian languages in the Indo-European language family has more to do with the great differences between the non-Indo-European language family substrates in Europe and the non-Indo-European language substrates in Anatolia, than it does with its great antiquity or particularly basal position in the Indo-European linguistic tree.

*** Bronze Age Indo-European Expansions Into Greece.

In what is now Greece, in the early Bronze Age, probably also around 2000 BCE, Indo-European Proto-Mycenaean Greek replaces first the non-Indo-European mainland pre-Greek language from the North or Northeast, and then from there goes on to replace the non-Indo-European Minoan language (both mainland pre-Greek and Minoan were probably part of the same non-Indo-European language family). Mycenaean Greek like the Anatolian languages, shows considerable influence from its substrate. Both of these substrate languages may well have been part of the same linguistic family as Hattic.

*** Bronze Age Indo-European Germanic Expansions.

It was in the Bronze Age that a proto-Germanic language was probably first spoken across a region including most of modern Germany and Poland, replacing some now lost non-Indo-European languages, some of which probably part of the same linguistic family as the modern Finnish and Uralic languages.  Other languages lost in the expansion of the proto-Germans would have been the languages in the linguistic family of the first European farmers in the region, the Linear Pottery Culture farmers, who arrived via Southeastern Europe, probably from Anatolia or the Caucusas across Balkans to the Danube and tracing this river and its tributaries into Europe.

The Corded Ware culture was a linguistically Indo-European population that dates from ca. 3000 BCE (at the earliest Polish sites) to 2400 BCE at its greatest extent in Western Germany, generally moving from East to West over that time period during the Copper Age to Bronze age transition with the geographic gains weighted towards the tail end of that period. The Corded Ware culture's language was probably either proto-Germanic and the main substrate language in proto-Germanic.

*** Bronze Age Indo-European Tocharian Expansions.

It was in the Bronze Age that the linguistically Indo-European and racially Caucasian people of the Tarim Basin, called the Tocharians established themselves there after migrating from their settlement to the North (around 2000 BCE) and then continued their civilization until well into the Iron Age.  Their civilization would last uninterrupted at this last West Eurasian stop on the Silk Road because East Eurasian lands began for about two and a half thousand years, before being lost to history until the 20th century of the current era.

Since the Tocharians appear to have broken off from the Yamna culture proto-Indo-Europeans earlier than any of the other Indo-European branches and unlike other Indo-European migrants moved into essentially unsettled territory where there were no substrate influences of any kind, their branch of the Indo-European linguistic family tree was probably the most conservative of the original proto-Indo-European language.

*** Bronze Age Collapse.

Bronze Age collapse is associated with the demise of the Hittite Empire in Anatolia, the Trojan War, an "intermediate period" in Egypt, the arrival by boat of the Mycenaean Greek Philistine people referred to in the Bible in the Southern Levant, and the collapse of the pre-Indo-European Atlantic megalithic culture as transformed by the subsequent Bell Beaker culture.  Both its beginning and its end are punctuated by severe extended droughts in the Fertile Crescent region and areas adjacent to it. 

The Iron Age

Bronze Age collapse is followed by the Iron Age which extends at least until, and arguably includes the Classical Greek and Roman civilizations.  Iron implements, which were rare and valuable prior to the Iron Age whose workings were closely held secrets, became ubiquitous after Bronze Age collapse when the secrets of working it and mining finally it got out.  Iron is actually in many ways inferior to Bronze in the applications to which it was put, but was much more amenable to being cheaply mass produced to outfit large armies with metal weapons and armor.

The tail end of the Biblical book of Genesis, the Biblical book of Exodus and the rest of the Hebrew Bible appear from their references to peoples, places and regimes, to be set in a period during or after Bronze Age collapse.

The Celtic and Italic wave probably have its origins in the Urnfield culture which moves from Central Europe into Italy and Western Europe starting around 1300 BCE in the late Bronze Age, and these languages expand into the various Indo-European languages of Italy and Western Europe.  The Italic languages survive today largely via the Romance languages (French, Spanish, Italian, Portuguese, Romanian, etc.) which themselves are remnants of the disintegration of the common Latin language of the Roman empire falling the Western Roman Empire's collapse.  Rome was established some time in the early Iron Age.

Slavic expansion comes much later, not earlier than 200 CE and probably more like the 6th century CE.  This expansion erases most linguistic clues about earlier language in the Slavic region.

The Medieval Period and Beyond

The period after the fall of the Western Roman Empire, around 430 CE, is normally called the Medieval period.

This characterization as an in between period in history makes less sense, however, when describing the late Byzantine Empire (previously the Eastern Roman Empire, which was much more densely populated and affluent, where Greek rather than Latin was the primary language) which didn't experience the defining moment that commenced the Dark Ages, the rise of Islam and expansion of the Islamic empire starting in the 7th century CE which gave rise to a Golden Age of Islam at the intellectual center of the world, and the successor states to the early Islamic empire in the European Medieval period, and moved onto a really new era only much later than the Italian Renaissance.

The non-Indo-European languages of Europe other than Basque and the Finno-Urgric languages of Northeastern Europe which are not attributable to European colonial era immigration to Europe or subsequent immigration to Europe, were established in Europe in the Medieval period. They are Hungarian (Uralic family), Turkish (Turkic family), Hebrew (Semitic family), Maltese (Semitic), and Yiddish (a Hebrew-German creole). In addition, the Indo-European Slavic languages reach their present extent in Europe, and Latin differentiates into the modern Romance languages, only after Rome falls. 

A recent genetic study suggests that all Ashkenazi Jews derive from an effective population of about 400 people around the time of the Crusades which was also the time of the first post-Roman pogroms and exiles, many of which were very extreme.  For example, Jews were expelled from Britain and any Jews who remained were forced to do so in secrets that were well kept from history as well, for approximately four hundred years after being common place almost all of the major cities across Britain before then. 

European historians call the era starting around 1500 CE in with the Renaissance, and continuing up to the present, the "modern" era.

Sun Exposure Drives Apparent Gamma Decay Rate

Radioactive isotypes of atoms naturally experience alpha, beta and gamma decay at particular characteristic rates tied to fundamental laws of physics and the structure of very large atomic nuclei.

Detectors that try to measure gamma decay rates show seasonal and daily variation matching differences in the angle with which the suns rays hit the laboratory site.

Lubos Motl, correctly in my view, reasons that the variations in gamma decay rates observed by the detectors don't actually involve seasonal and daily shifts in gamma decay rates. Instead, he reasons, seasonal and daily variation probably actually involve collisions between something emitted by the sun and the radioactive materials that varies with the directness of angular exposure to the sun, that merely looks like gamma decay to the detector, when it is in fact something entirely different.

The thing that is triggering the collisions could be (1) photons (of wavelengths that can penetrate the materials containing the radioactive isotypes, or that trigger collisions outside the containing materials that in turn generate secondary effects that reach the detectors), (2) neutrinos (which he disfavors on the theory that neutrinos would disproportionately influence beta rather than gamma decay, which is a neutrino generating process), or (3) something else emitted by the sun.  Neutrinos also ought to have peaks twice a day, rather than once, because the Earth provides little shielding from them since they are so unreactive, and so should peak when the sun is mostly directly above and below the experiment, rather than merely once a day as shown.

The finding matters not just because a previously unknown source of collisions related to sun exposure was discovered, but also because the study suggests that prior measurements of gamma decay rates that don't account for the influence of sun exposure and simply rely on average gamma decay rates, systemically overestimate true gamma decay rates due to false positives from sun exposure correlated collisions.  Without this correction, we might misinterpret future deep space experiments measuring gamma decay rates that lack this sun exposure induced collision effect.  The systemic error of experiments that don't account for this factor could even lead to incorrect parameter estimation of Standard Model constants that give rise to gamma decay, although most of these parameters are estimated are far "cleaner" experiments than the decay of large radioactive isotypes.

The results may very well be the source of "new physics", but probably not new "fundamental physics."  Instead, it may help us better understand what the sun emits and at what energies and how those emitted products interact with the kind of materials found in radioactive decay measurement laboratories.  This may tell us more about the complex structure of a fairly typical star, but doesn't tell us much about the fundamental physics of radioactive decay, other than to use trough rather than average values for many purposes.