Glimpses of Pre-Historic South Asia

[sayak83]

I thought I would share some insights about pre-historic South Asia that go beyond the Aryan migration debate that I personally find fascinating and others may enjoy too.

The first humans of South Asia

The first humans of South Asia were not modern humans but a more ancient species, Homo Erectus (LINK), who, having evolved in Africa at around 2 million years, migrated outside of Africa by 1.6 million years. By 1.5 million years they have migrated into India and begin their long inhabitance in the subcontinent which lasted up until 70,000 years before present.

The two most fruitful places from which evidence comes is from sub-Himalayan region in Pakistan (Soan culture named after Soan river) and from regions of Tamil Nadu in South India. Madhya Pradesh in Central India has also recently turned up lots of evidence of their stay in India.

North-West subcontinent and South India develop their own distinct technological traditions over time.

"Prehistorians have divided Indian Paleolithic culture into two major traditions with distinct geographical features. (A) The Soan culture or the chopper chopping tool tradition in the Punjab and (B) The Madras culture or Hand-axe tool tradition in peninsular region. Pre-historians have found a constant interaction between Soan and the Madras industries although there is a marked difference between these two industries.

The core-tool elements (bifacial hand axes) dominate in the south and southeast, while the flake or chopper type is very strong in the North. Moreover, in Central India, a fusion of technology (between two main traditions) has been observed. Certain stone industries from Kumool in the Deccan and near Mumbai represent a new type of tool tradition, based not on the massive flake but on the slender blade detached from a core."
Paleolithic Period in India: The Soan and Madras Culture

Because of the high erosion rates by rivers and weathering in the sub-Himalyan regions, the Soan period artifacts are quite scattered and difficult to place chronologically. This is not the case for the "Madras-culture" discoveries in South India. The most interesting place is the Attirampakkam region of Tamil Nadu where multiple dating techniques have confirmed that humans lived and made stone tools (including hand-axes like above) from 1.5 to 1 million years before present.

LINK

Attirampakkam

A deeper history for the humble handaxe - USATODAY.com

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But the new dates from the Indian site upset this hand-axe history, based on magnetic dating of the clay surrounding the stone tools at the dig site, about 30 feet deep. Some 780,000 years ago, the Earth's magnetic poles flipped (don't worry, no one was hurt). Iron molecules laid down earlier than that time in clays after that flip would have magnetic orientations pointing north. Instead the clay at this level has magnetic poles that correspond to 1.77 million to 1.07 million years old.

And because the 3,528 hand axes, cleavers and other tools discovered were made out of a quartz stone, they were also amenable to a kind of dating that relies on cosmic ray exposure. Until they were buried, the tools (like everything else on the surface of the planet) were exposed to cosmic rays, leaving a signature of radioactive beryllium and aluminum, which have very long half-lives on their surfaces. Even being conservative, the radioactive half-lives of these elements pin the age of the tools to about 1.5 million years ago. Much like the latest tools today, mit turns out good ones are quickly exported.

"The new evidence from Attirampakkam invalidates much of (the old) scenario," Dennell concludes. The hand axe likely spread out of Africa in the hands of Homo erectus or a related early human species, long-faced fellows that were also thought the first species to master fire, far earlier than had been thought likely. Dennell writes, "this new evidence from Attirampakkam makes it all the more important that we find out what type of (human species) first brought Acheulian artifacts to South Asia."
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But many other sites about throughout South and Central India that span periods from 1.5 million years to 70,000 years. The sites show progressive development of original hand-axe technology with greater more refined hand-axes and inclusion of other types of tools. For example Isampur in India show a more well developed hand-axe technology from 0.7 million years ago.

Handaxe making techniques continue to be used till 140,000-120,000 years before present ( excavations in Patpura in India) before being replaced by later methods characteristic of the Middle Stone Age. By this time, the descendents of Homo Erectus have evolved into archaic forms of Homo similar to Heidelbergensis.

Evolution of Modern Humans: Homo heidelbergensis


Distribution and tool making techniques of Middle Stone Age India


Overall what the evidence shows is that the earliest human species H. erectus entered India around 1.5 million years and spread all over the sub-continent developing and refining their stone tool technology and leading a foraging life-style in small bands. While the pace of cultural change is slow, over the eons, different regions show distinct tool making styles that continue to be improved and refined in accordance with environmental needs. They continue to exist though the lower and the Middle Stone age upto 60,000 years when a rapid introduction of new stone tool technology show the arrival of the first wave of modern humans into the subcontinent.

Discussion on ancient pre-history of India is welcome

 

[George-ananda]

Now the leading theory today is the so-called 'Out of Africa' theory that says all living humans can be traced back to a Mitochondrial Eve and a Y-chromosomal Adam that both lived around 200,000 years ago in Africa. I think that would say all these more ancient types of humans in the article above went completely extinct and have left no living descendants.

Correct me, if someone thinks I am misunderstanding something.

 

[sayak83]

Now the leading theory today is the so-called 'Out of Africa' theory that says all living humans can be traced back to a Mitochondrial Eve and a Y-chromosomal Adam that both lived around 200,000 years ago in Africa. I think that would say all these more ancient types of humans in the article above went completely extinct and have left no living descendants.

Correct me, if someone thinks I am misunderstanding something.

There was some admixture with the native populations but not much. Thus all humans that live out of Africa have 2-4% Neanderthal genome and many polynesians and Australian natives have 5 % Denisovian (an descendent of Erectus in East and South East Asia) genomes. Other such small admixtures may come up over time. But that is it.

 

[Vinayaka]

Who knows?

 

[George-ananda]

There was some admixture with the native populations but not much. Thus all humans that live out of Africa have 2-4% Neanderthal genome and many polynesians and Australian natives have 5 % Denisovian (an descendent of Erectus in East and South East Asia) genomes. Other such small admixtures may come up over time. But that is it.

Right, so these ancient people in India are not related to current Indians (except maybe very, very slightly).

 

[sayak83]

Right, so these ancient people in India are not related to current Indians (except maybe very, very slightly).

As far as current science goes, that is correct.
I will be going into modern humans in later posts

 

[George-ananda]

As far as current science goes, that is correct.
I will be going into modern humans in later posts

Yeah, I have my suspicions it is all way more than complicated than current science knows. Looking forward to your more to come.

 

[Aupmanyav]

Yeah, it is complicated. It is not necessary that the Y-Chromosomal Adam must have lived in Africa. "The discovery of archaic Y-haplogroup has pushed back the estimated age of the Y-MRCA beyond the most likely age of the mt-MRCA. As of 2015, estimates of the age of the Y-MRCA range around 200,000 to 300,000 years ago, roughly consistent with the emergence of anatomically modern humans."

"Mitochondrial Eve lived later than Homo heidelbergensis and the emergence of Homo neanderthalensis, but earlier than the out of Africa migration, but her age is not known with certainty; a 2009 estimate cites an age between c. 152 and 234 thousand years ago (95% CI); a 2013 study cites a range of 99–148 thousand years ago."
(Quotes from Wikipedia)

 

[sayak83]

Modern Humans the Global View

The origin and migration of modern humans generates a lot of nationalistic (and religious) heat. So first I will briefly outline what the evidence so far suggests to be the most plausible scenario.

1)Single Out of Africa Migration to Rest of the World

The genetic evidence overwhelmingly suggests that all humans are primarily descendants from a single migration event out of East-African populations with pick of some (2-5 %) genetic heritage from localized populations of earlier Eurasian humans that were descendants of Homo erectus (makers of the hand axe tools and its evolution..basically all of early stone age)

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Massive Genetic Study Supports "Out of Africa" Theory

A massive new study of human genetic diversity reveals surprising insights into our species' evolution and migrations—including support for the theory that the first modern humans originated in Africa—scientists said today....In particular, the pattern of variation shows that the route of migration out of Africa was into the Middle East and then to the rest of Eurasia, the Americas, and Oceania, he pointed out. Populations in the Middle East have a unique signature of African, European, and Asian characteristics, Meyers, the geneticist, added.

Researchers compared 650,000 genetic markers in nearly a thousand individuals from 51 populations around the globe—an unprecedented level of detail for a human genetic study.
"You get less and less variation the further you go from Africa," said Marcus Feldman, an evolutionary biologist at Stanford University in California and a study co-author.Such a pattern fits the theory that the first modern humans settled the world in stepping-stone fashion after leaving Africa less than 100,000 years ago.As each small group of people broke away to found a new region, it took only a sample of the parent population's genetic diversity.
"If you keep sampling like that, then mathematically you must lose variation," Feldman explained.

But perhaps even more striking, Myers said, is how similar humans are to each other. Some 90 percent of the genetic variation occurs within populations, not among them. In fact, there's no single genetic marker that identifies a person as French or Japanese or Papuan. Rather, patterns of thousands of these little markers within the group distinguish one population from the next. "Those genes which we classically use like skin color and eye color and hair structure to differentiate what we commonly call races is a tiny fraction of all the variation there is," Feldman, the evolutionary biologist, noted.
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A good paper detailing all the genetic evidence and open for view is linked below

The great human expansion

A more recent research brought together even more genetic data from all types of populations throughout the world to come to the same basic conclusion. There was a single out-of-Africa migration event from which all people of the world today descend.
https://www.sciencedaily.com/releases/2016/09/160921131354.htm

The sampling spread is impressive

Reich, Mallick and their international team of colleagues began by selecting two genomes each from 51 populations represented in a collection called the Human Genome Diversity Project. Next, they assembled samples from members of 91 other groups, including diverse Native American, South Asian, and African populations not previously included in genome-wide studies, and sent the DNA for sequencing. In all, the project analyzed the genomes of 300 people.


A key conclusion -- that the vast majority of modern human ancestry in non-Africans derives from a single population that migrated out of Africa -- is also supported by two other whole-genome sequencing studies appearing simultaneously in Nature.
Together, the three studies put to rest a lingering question about whether indigenous peoples of Australia, New Guinea and the Andaman Islands descend in large part from a second group that left Africa earlier and skirted the coast of the Indian Ocean. They do not, the HMS researchers say.
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Conclusion

So what do we get? We get a single migration event of modern humans out of Africa. This group enters Middle East and subsequently spread east and west and north to migrate into India, China, South East Asia, Europe, Siberia and the America-s picking up some genomic heritage from previous ancient humans who were descendants of H. erectus along the way. But they remain dominantly and overwhelmingly African.


2) When did modern Humans Migrate out of Africa?

Now I will look at the more harder question of when did all this happen. When did humans migrate out of Africa into the Levant? When and how did they travel to the other parts of the world. Here is a basic graphic that illustrates a series of most plausible routes. Modern humans are in red.

Now, its important to realize what genetic studies like the one above is good at. It can fix relationships of descent and relative chronology far better than absolute chronology especially when the divergences drop below 1 million years. (see links to previous paper). Thus the genetic evidence shows that Australian, Chinese, Siberian and European populations descend from Mid-East, which in turn descend from East Africa. It also shows that American populations descend from Siberian offshoots at a later time. But the absolute dates have far greater lee-way and are estimates that can be doubled or trebled (or halved) provided all the branching dates are multiplied by the same factor. It cannot be ten times less or ten times more , but halving or doubling are very much possible

So here one must look at evidence of fossils and archaeology/tools to determine the absolute dates of these genetic divergences to fix when and how the migration occurred.

That will be in the next post.

 

[Aupmanyav]

So, we mated with Ergaster, Erectus and the Neanderthals ! ?

I suppose that is what gave rise to stories like Bhim and Hidimba.

 

[sayak83]

So, we mated with Ergaster, Erectus and the Neanderthals ! ?

I suppose that is what gave rise to stories like Bhim and Hidimba.

Its possible that stories of non-human people do stem from early contacts with such groups. But its difficult to say for sure. For example rock art in either India or Europe or Australia do not show depiction of non-human people at all even though they were drawn much closer in time to actual contacts. So there is room for doubt.

 

[Aupmanyav]

Cave paintings are non-committal.
How can one know that the figure is an ergaster, erectus or Neanderthal?
Moreover they are not as old as when we mated with them. By that time, none of them survived.
The oldest are hand prints.

Leang Timpuseng Cave, Sulawesi, Indonesia, 35000 yrs. BP, Chauvet Cave, France, 30000 yrs. BP.

Cave paintings, Human figures - Google Search

 

[sayak83]

In the last post, I outlined the genetic evidence of out of Africa migration of modern humans to all corners of the world. Here I will briefly focus on the fossil and archaeological evidence that aids in fixing posisble dates of emergence of modern humans in Africa and their trek into Asia and Europe. I will focus mostly on Asia as my eventual goal is to connect with the arrival of modern humans in India.

The children of Erectus

Since the ancient times when 1000 cc brained Homo erectus ventured out of Africa much have happened in the world. The Erectus population split into multiple subgroups that were partially isolated from each other and developed their own skeletal and cultural features. Yet there was some iner-group love making and also quite a lot of competition between the groups. Thus when a new method of tool making was invented (like the Lavalois method in Armenia) it spread relatively quickly among the descendants of Erectus in Europe, Asia and Africa..so that the technique with its own distinctive regional variations were adopted all over the old world. This kind of competition as well as some gene flow meant that while the descendants of Erectus were developing differences in features, they were all becoming brainier (bigger brain) and using more or less the same technology through diffusion over the successive period. They were not quite the same species anymore, but neither were they very different. Thus melange of big brained archaic sapiens are all binned into one "species" called the Heidelberg man whose European, Mediterranean, East African, South Asian, Chinese and South East Asian variants all show features and brain sizes intermediate between Erectus and later modern humans.

Homo heidelbergensis - Australian Museum

Heidelberg man of Ethiopia

Also Heidelberg man of China
Dali Chinese archaic Homo sapiens cranium

From these transitional forms
1) Homo sapiens (modern humans) evolve in East Africa
2) Neanderthals evolve in Europe and Central Asia
3) Denisovians evolve in China, Siberia and South East Asia
4) As yet unknown species arise in South Asia


Origin and Development of modern Humans in Africa

OMO humans

The earliest recorded fossil of modern humans is dated to 195,000 years ago from the Turkana region in Kenya (East Africa). They are called OMO I and OMO II. The fossils contain significant parts of the skull and also some of the leg bones. There is considerable amount of stone tools also present. The features of the skull put the two individuals as the oldest anatomical exemplars of our species. Their stone tool making methods were not much different from the descendants of Homo Erectus (i.e. Heidelberg man) who were living a bit to the north, in North Africa and Southern Europe. They were using the Levallois method of stone tool making like all the rest of that time.
File:Levallois Preferencial-Animation.gif - Wikimedia Commons

The skulls were discovered quite a while back and progressively the methods of dating were improved till, in 2012, the date was fixed by direct dating of the bones themselves. Overall it provides an excellent example of how good archaeology has gotten in dating its finds in the last two decades.

The earliest dates on the Omo I skeleton were quite controversial--they were uranium-series age estimates on Etheria freshwater mollusk shells that provided a date of 130,000 years ago, which in the 1960's was deemed too early for Homo sapiens. Serious questions arose in the latter half of the 20th century about the reliability of any dates on mollusks; but in the early 21st century Argon dates on the strata in which Omo lay returned ages between 172,000 and 195,000, with the most likely date nearer 195,000 years ago. A possibility then arose that Omo I had been an intrusive burial into an older layer.

Omo I was finally direct-dated by laser ablation elemental Uranium, Thorium, and Uranium-series isotope analysis (Aubert et al. 2012), and that date confirms its age as 195,000+/- 5000. In addition, a correlation of the makeup of the KHS volcanic tuff to the Kulkuletti Tuff in the Ethiopian Rift Valley indicates the skeleton is likely aged 183,000 or older: even that is 20,000 years older than the next oldest AMH representative in the Herto formation also in Ethiopia (154,000-160,000).

When we have three different techniques all converging on the same time zone, one can be quite confident.

Herto Humans

The next oldest set of skulls come from Ethiopia (also East Africa). Discovered in 2003, they are around 160,000 years old. The skull is very well preserved, has a volume of 1450 cc (bigger than many of us) and is undoubtedly modern human with some older features (the brow is still a bit formidable)

The Latest Dirt - Ethiopia

Migration into Asia and the long stalemate

An excellent series of fossils in Israel and tool assemblages in Arabia show that modern humans entered this region by 130,000 years, thus securely dating their first (and only) large scale migration out of Africa at 130,000 years before present. They were successful and spread quite quickly into China by 100,000 years and hence (by inference) probably in the rest of the Middle East and parts of Central Asia.

Yet evidence also shows (see below) that they did not replace the other descendants of Homo erectus from their perch. Neaderthals flourished in Europe and even extended their range, replacing modern humans in Israel and Syria for long periods of time (90,000-60,000 years in the past). The Denisovian people of China and Siberia also continue to live there and continue to be found in many places till 45,000 years. Modern humans have no presence in India or Indo-China till 60,000 years where descendants of Homo erectus and their tool technology continue as before.

Thus from 130,000 years on, modern humans live in many parts of Eurasia. But they cannot penetrate many parts of the continent (Europe, Deccan India) where other types of humans flourish and live in relatively close proximity to them in other places (Levant, China). This goes on until 60,000 years before present, i.e. a period of 70,000 years, during which modern humans show no superiority over other sister human species of the continent. This is also the time of limited gene flow between modern humans and Neanderthals and Denisovians (and maybe a few others).

When Neanderthals replaced us

About 100,000 years ago, tall, long-limbed humans lived in the caves of Qafzeh, east of Nazareth, and Skhul, on Israel’s Mount Carmel. Their remains suggest a surprisingly sophisticated people defying the conventional timeline of Homo sapiens’ migration out of Africa. But ultimately, the Skhul and Qafzeh residents did not survive.

The Skhul-Qafzeh people gathered shells from a shoreline more than 20 miles away, decorated them and strung them as jewelry. They buried their dead, most likely with grave goods, and cared for their living: A child born with hydrocephalus, sometimes called water on the brain, lived with profound disability until the age of 3 or so, a feat only possible with patient, loving care.

Beginning in the late 1980s, however, more precise dating techniques upended that notion. The Qafzeh humans were around 92,000 years old, and the Skhul people were even older, averaging about 115,000 years. The age of the Skhul-Qafzeh people challenged the widely held idea that Homo sapiens had not left Africa until about 60,000 years ago. Even more startling: Almost all the Neanderthal remains were significantly younger. The Skhul-Qafzeh people were not an elusive missing link between Neanderthals and humans. They were humans, and Neanderthals had replaced them.

Skhul-Qafzeh may be one example of Neanderthals outcompeting humans, albeit indirectly; Shea and other researchers note there is no strong evidence of direct physical conflict, or even that both species occupied the area at the same time...The dominant theory for Neanderthal success at Skhul-Qafzeh is that 21st-century bête noire: climate change. Around 75,000 years ago, close to the time the Homo sapiens of Skhul and Qafzeh disappear from the fossil record, the climate in the Levant shifted in Neanderthals’ favor. Rapid glaciation left the region both cooler and drier. Steppe-deserts advanced, and forests retreated.

In Saudi Arabia’s Empty Quarter, University of Oxford professor Michael Petraglia is in the middle of a multidisciplinary project called Paleodeserts. These desert landscapes were once fertile lake lands, and Petraglia’s team aims to unlock the role they played in human expansion. So far they have found many tools, but not one human fossil. “We know that some form of human definitely penetrated Arabia, and that some of the dates of those sites coincide with the appearance of Homo sapiens in the Levant around 100,000 years ago,” says Petraglia. According to this hypothesis, the Skhul-Qafzeh people represent the western edge of a larger wave of migration that likely continued into Eurasia.

 

[sayak83]

Modern Humans in China

They show that, between roughly 900,000 and 125,000 years ago, east Asia was teeming with hominins endowed with features that would place them somewhere between H. erectus and H. sapiens.
Such transitional forms persisted for hundreds of thousands of years in China, until species appeared with such modern traits that some researchers have classified them as H. sapiens. One of the most recent of these is represented by two teeth and a lower jawbone, dating to about 100,000 years ago, unearthed in 2007 by IVPP palaeoanthropologist Liu Wu and his colleagues4. Discovered in Zhirendong, a cave in Guangxi province, the jaw has a classic modern-human appearance, but retains some archaic features of Peking Man, such as a more robust build and a less-protruding chin.

The Zhirendong hominins, for instance, could represent an exodus of early modern humans from Africa between 120,000 and 80,000 years ago. Instead of remaining in the Levant in the Middle East, as was thought previously, these people could have expanded into east Asia, says Michael Petraglia, an archaeologist at the University of Oxford, UK.

Other evidence backs up this hypothesis: excavations at a cave in Daoxian in China's Hunan province have yielded 47 fossil teeth so modern-looking that they could have come from the mouths of people today. But the fossils are at least 80,000 years old, and perhaps 120,000 years old, Liu and his colleagues reported last year6. “Those early migrants may have interbred with archaic populations along the way or in Asia, which could explain Zhirendong people's primitive traits,” says Petraglia.



Summary:-
1) Modern humans evolved from Heidelberg humans in East Africa at 200,000 years.
2) Modern Humans migrated in Syria-Palestine by 130,000 years and moved into China by 100,000 years.
3) They lived along with other human descendants of Erectus in Asia and Europe, particularly in the regions of Syria and in China and had limited inter-breeding with the Neanderthals and Denisovians
4) Till 60,000 years ago they were unable to enter either Europe or the Deccan or Indo-China regions of South Asia due to flourishing and successful groups of Homo erectus descendants living there.

From about 55,000 years things begin to change rapidly. Modern humans quickly penetrate Europe, India and Indo-China establishing populations there by 50,000-45,000 years and driving other human species to extinction. By 50,000 years H. erectus descendants in India are gone, Australia has been colonized by boat building modern humans who have replaced most of other human species in that region (except some islands). Denisovians also become rarer and the last populations in Siberia are gone by 30,000 years. Similar is the case for Neanderthals in Europe . Thus after 70,000 years of cohabitation, modern humans decisively replace all other human species in a space of 20,000 years and have rapidly expanded their range.

Why did this happen? That is question that is still being researched. But it is clear that modern humans gain a decisive technological advantage at around this time that other humans fail to copy. This is the the technology of making microliths, small sharp pointed stones that can be used as needles, blades and spear, harpoon and arrow points. This technology comes associated with much greater flexibility and range of tool making that is not seen previously either in modern humans or in other humans. The techniques, spreading widely along modern human populations, give them a decisive advantage over other human kinds in both hunting and foraging and they are competed out of their living spaces and eventually to extinctions.

In the next post, I will, finally, look at the arrival of modern humans into India at 50,000 years and the tool-kits they brought with them.

 

[Aupmanyav]

This is the the technology of making microliths, small sharp pointed stones that can be used as needles, blades and spear, harpoon and arrow points. This technology comes associated with much greater flexibility and range of tool making that is not seen previously either in modern humans or in other humans.

The purpose of initial strikes with another stone is to heat the other piece, IMHO.

 

[Jainarayan]

Now the leading theory today is the so-called 'Out of Africa' theory that says all living humans can be traced back to a Mitochondrial Eve and a Y-chromosomal Adam that both lived around 200,000 years ago in Africa. I think that would say all these more ancient types of humans in the article above went completely extinct and have left no living descendants.

Correct me, if someone thinks I am misunderstanding something.

Actually what Mitochondrial Eve and Y Chromosome Adam means is not that there were two progenitors of modern humans, ala biblical Adam and Eve. M/E and Y/A means each one of us descend from a single male and female, though they probably did not live at the same time. Those are the two people whose mitochondrial and y chromosome mutations we carry. The science of it has been horribly dumbed-down.

 

[sayak83]

Actually what Mitochondrial Eve and Y Chromosome Adam means is not that there were two progenitors of modern humans, ala biblical Adam and Eve. M/E and Y/A means each one of us descend from a single male and female, though they probably did not live at the same time. Those are the two people whose mitochondrial and y chromosome mutations we carry. The science of it has been horribly dumbed-down.

The scientists are responsible for this. Using the labels Adam and Eve or using the label God particle for Higgs Boson. Scientists should all be educated in how to properly and simply convey their discoveries to the public without causing severe misunderstandings. Its not that difficult. After all school level textbooks of modern science exist.

 

[George-ananda]

The scientists are responsible for this. Using the labels Adam and Eve or using the label God particle for Higgs Boson. Scientists should all be educated in how to properly and simply convey their discoveries to the public without causing severe misunderstandings. Its not that difficult. After all school level textbooks of modern science exist.

Do you know how this Adam and Eve thing could be better understood?

 

[sayak83]

Do you know how this Adam and Eve thing could be better understood?

1)That they have nothing to do with Adam or Eve

2) They are not the first humans, not even the population representing first humans

3) The individual woman and the individual man (separated by thousands of years and by hundreds of mile) happen to be "retrospectively" the humans from whom the X and Y chromosome genes of today's people were inherited. This means if you (or any human who lives today) trace back your mother-to-mother line, you get back to her and similarly for father-to-father line. Here today means today. This may not have been the case in 1600 CE, when a lot more aboriginal tribes with greater diversity remained in the world and may not be the case in 2400 CE if the population explosion from certain centers wipes out more diversity of genetic heritage in humans. So the common mother'sand the common father's identity and date changes with time.

4) Other human genes in other chromosomes have different people as the Last common ancestor, some much earlier and some much later. This is because the common mother (as calculated in a given era) does not mate with the common father (who is thousands of years before or later) and vice-versa, but mates with a different man (or woman) or may have children with multiple partners all of whose genes are also in you with all their heritage. Each of the thousands of genes in human population today have their own most recent common ancestor, and they are all different.

5) The mitochondrial eve and y-chromosome adam only tells us the common ancestor of today's people if you trace ancestry from mother to mother and father to father respectively. But there is many other ways of tracing ancestry:- like alternating between mother and father in various combos like

mother-father-mother-father...
or
father-father-mother-mother-father-father

etc. And each such way of chaining will give you a different common ancestor. So the entire thing is subjective if biological common ancestor is what you are chiefly interested in. Needless to say, scientists are not even remotely interested in such a thing.

6) The objective basis of genetic common ancestry is the gene-tree. Each gene in modern humans have their own distinct most recent common ancestor in the past. Scientists use various experiment based models and mathematics to trace each of these genes back to the time when this common ancestor lived. When done for all genes, it provides a statistical spread of the times when the various genes had a common ancestor and important information about evolution, migration and divergence can be mined from this statistical spread of common ancestry and tracing the divergence history of the various genes. All of this is the subject matter of population genetics, a highly mathematically heavy but crucial field of biology that traces, among other things, the gene trees and descendence lines of pathogens like AIDS, Zika, Swine Flu as well as human mutations that confer either immunity or cause rare genetic diseases.
Population genetics — University of Leicester

7) Now that whole genome based gene trees have become possible, the importance of Y chromosome or mitochondria based gene trees have decreased. They were only done the earliest as, due to their clean manner of inheritance, they could be modeled using the low powered computers of early times.

Finally I will link a very interesting write-ups on this. Read them at leisure
RETHINKING "OUT OF AFRICA" | Edge.org
GENETICS AND RECENT HUMAN EVOLUTION

 

[sayak83]

Just a funny picture as a recent homage to the Valentine' day:- Make love not war

Evidence mounts for interbreeding bonanza in ancient human species

100,000 year old Neanderthals have portions of DNA from modern humans showing crossbreeding impacted both groups.


“We’re looking at a Lord of the Rings-type world — that there were many hominid populations,” one evolutionary geneticist told Nature when the findings were presented at a conference in 2013.


Human evolution was shaped by interbreeding

In June 2015, researchers announced that a 40,000-year-old skeleton from Romania had the most Neanderthal DNA of any human analysed to date. The "Oase individual" inherited between 6% and 9% of his DNA from the Neanderthals. Furthermore, the team found that his Neanderthal ancestor lived only 200 years before his death. The genetic evidence confirmed something that anatomists had previously suggested: the Oase individual's jawbone had some clear Neanderthal traits.