Out of Africa revisited? pt 2

nature-siberian-neanderthals-17.02.16-v2The out-of-Africa theory basically says that humans evolved in Africa, then spread in several pulses across the rest of the planet. The first hominin to leave Africa–as far as we know–was Erectus, followed by the Neanderthals/Denisovans, and finally Sapiens. Where exactly smaller, less well-known hominins like Homo Floresiensis fit into the picture we don’t know, yet.)

One of the incredible things about human evolution is just how many other human species we used to co-exist with. We shared this earth with at least 8 other species of human, met and mated with at least 4 of them. Before us came a proliferation of australopithecines.

Today, there is only us. This stunning diversity of upright apes has been winnowed to a single line. Species that had survived for thousands if not millions of years disappeared, either because they died out or were wiped out. We, sapiens, are the last ones standing.

Humans met Neanderthals. We interbred, briefly. Then the Neanderthals died out. Humans met Denisovans. We interbred, briefly. Then the Denisovans disappeared. Humans met so-called “Ghost populations” in west and southern Africa and interbred. The ghosts then disappeared. It’s all very mysterious how every other species of hominin and australopithecine seems to have died out immediately after we sapiens arrived in the area.

This implies, then, that sapiens didn’t live in these areas during the thousands or so years before we wiped out the locals (though some small exceptions may exist.)

So where did we live?

The West African Ghost Population contributed a big chunk of DNA to modern humans a mere 50,000 years ago–around the same time as sapiens were mating with Neanderthals. This seems to have been a much more significant encounter than the one with Neanderthals–perhaps many of these “ghosts” joined the sapiens who moved into their area.

So west Africa was likely not inhabited by modern humans before 50,000 years ago.

Homo naledi is too small to have co-existed with us, effectively ruling out their part of South Africa during that period, and the Pygmies probably interbred with their mystery hominin around 35,000 years ago, so that rules out the Congolese forest area.

The Neanderthal ancestry is in pretty much everyone not in Africa, (and a little in Africa due to recent back-migration) which is pretty strong support for the out-of-Africa theory. The most parsimonious explanation is that a single population split, and half of that population, as it entered Eurasia, encountered Neanderthals, while the other half traveled deeper into Africa and encountered African hominins.

East Africa/the horn of Africa region remains, therefore, the most logical spot to locate Homo sapiens immediately before this splitting phase, but I wouldn’t rule out the Middle East.

On the other hand, Homo sapiens’s ancestor, Homo heidelbergensis, lived in Africa, Europe, and the Middle East for thousands, possibly a million years (depending on how we classify the similar bones of Homo antecessor, who lived near Norfolk, England, about 950,000 years ago. Homo heidelbergensis’s (probable) ancestor, Homo erectus, lived in Africa, Europe, and Asia for over a million years.

Here’s where it gets complicated, because while species like the little hobbits from Flores are clearly different from other varieties of Homo, there are no clear dividing lines between folks like erectus, heidelbergensis, and ergastor. We have a bunch of bones, a few nice skulls, scattered across continents and centuries, from which we try to derive a vague sense of whether this population and that population were similar enough to consider them a single species. Quoting Wikipedia:

Although “Homo ergaster” has gained some acceptance as a valid taxon since its proposal in 1975, ergaster and erectus since the 1980s have increasingly come to be seen as separate (that is, African or Asian) populations of the larger species H. erectus. … The question was described as “famously unresolved” as of 2003.[10] Sura et al (2007) concluded that Homo erectus “was a likely source of multiple events of gene flow to the Eurasian continent”.[11]

The discoveries of the Dmanisi skulls in the South Caucasus since 2005 have re-opened this question. Their great morphological diversity suggests that the variability of Eurasian H. erectus already includes the African fossils dubbed H. ergaster. The discovery of Dmanisi skull 5 in 2013, dated to 1.8 million years ago, now dates evidence of H. erectus in Eurasia as of virtually the same age as evidence for H. ergaster in Africa, so that it is unclear if the speciation of H. erectus/ergaster from H. habilis took place in Africa or Asia.[12] This has reinforced the trend of considering H. ergaster as synonymous with H. erectus, a species which would have evolved just after 2 million years ago, either in Africa or West Asia, and later dispersed throughout Africa and Eurasia.[13][14]

Homo habilis, by contrast, is (so far) only found in east Africa.

What does it mean to evolve in a place? Habilis, as far as we know, actually did evolve in Africa. It didn’t leave Africa; neither did the australopithecines (unless one of those little hobbity folks out in the Philippines turn out to be australopiths, but that would be very remarkable). But after that, “humans” spread from Africa to Europe and Asia with remarkable speed. They lived in England almost a million years ago. And within this range, we seem to have become repeatedly isolated, speciated, and then met back up again when the weather improved.

Personally, I wouldn’t say that the out of Africa theory is wrong. It is still the most parsimonious explanation of human evolutionary history. However, I would say that it simplifies a huge chunk of our history, since for most of our time on this earth, our range has been quite a bit larger than Africa.

Cracks in the Out of Africa Theory?

The most exciting finding of the past two decades in biological anthropology has been, without a doubt, evidence for interbreeding between Homo sapiens, Neanderthals, Denisovans, etc. and the sheer multiplicity of new hominin species being uncovered.

Exactly where the lines between species lie is a bit of a matter of semantic debate–where exactly did our ancestors end and Homo sapiens begin? Should we classify Neanderthals and Sapiens as one species if we interbred? etc–but if we accept the current classifications as decent approximations, we have:

Capture
Source: Wikipedia

Sorry, I realized it would be much more efficient if I just grabbed the family tree off Wikipedia instead of copying it over bit by bit. The top part of the tree got cut off, so I’ll note that Homini (6.3 million years ago) includes us + chimps, while Hominina (5.7 million years ago) has no chimps, but includes australopithecines. Gorillas are way back in Homininae, with an e. Homo, our genus, includes all of the “human” species, but usually doesn’t include australopithecines.

There is further debate on exactly who descended from whom. We’re finding new fossils all the time, which is quite exciting, but our current record is not nearly as complete as we’d like it to be. So sometimes branches get moved around or re-categorized as more data comes to light.

The most recent notable additions to our genus are the Denisovans, Homo floresiensis, Homo luzonensis, Homo Naledi, Homo doesn’t have a name yet, and more Denisovans.

You have probably heard of the “hobbit,” Homo floresiensis. The remains we have uncovered of this diminutive hominin are remarkably good, including a skull in great condition (despite some damage caused after excavation.) They lived on the island of Flores from about 200,000 to 50,000 years ago (though their arrival may get pushed back considerably because there are stone tools on Flores that are much older–700,000 years old–we just don’t know yet who used them.)

The hobbits are remarkable in multiple ways. First, they lived in an area that was not connected to the mainland by any landbridges–that is, they had to swim, boat, or otherwise be carried to their island. I am skeptical of the idea of anyone surviving a tsunami as a means of populating an island, but they arrived in an era when, as far as we know, humans had yet to build boats. So perhaps their ancestors were among the first humans to build boats, and we just haven’t found the remains of their crafts (wood being a material that degenerates very quickly.)

Second, the Hobbits are most likely descended from Homo erectus, who lived nearby on mainland Indonesia (at the time, connected to the rest of Asia via a landbridge), but are morphologically very different. They are tiny–shorter than pygmies, Homo erectus, or even australopithecines.

There is much debate about whether they are descended directly from erectus, or part of a sister-clade to erectus that descended from a common ancestor. It was previously believed that erectus was the first hominin to leave Africa, but if Floresiensis is not descended from erectus, Flores could be the first.

Now a similarly diminutive hominin has turned up in the Philippines, also past a significant water barrier that would require some effort to cross. It has been dubbed Homo luzonensis. Not much is known, yet, about luzonensis, (we haven’t found as many of its bones), but what we do know is tantalizing:

It was soon apparent to Détroit that the remains featured a puzzling mosaic of traits both modern and ancient. “Each of the features [of Homo luzonensis] corresponds to some hominin or another,” he says. “But the combination makes for something really unique. There’s no known species with this same suite of features.”

They’re small, possibly even smaller than the Hobbits. Their feet resemble australopithecines, but australopithecines supposedly died out a couple million years before Luzonensis arrived on the scene. And their teeth were “remarkably uniform,” which probably sounds boring to anyone who isn’t a dentist, but provides strong evidence of them being a different species.

Two island dwelling species in the same area supports the idea that their ancestors either developed boats or were remarkably skilled at surviving tsunamis, and that southeast Asia was a remarkable hotspot of hominin diversity.

And then there are the Denisovans!

Denisovans are mysterious because we have so few of their bones–a chunk of skull was recently uncovered, but we have no jaws, no faces, no ribs, etc–so we don’t have a good idea of what they looked like. What we do have are Denisovan DNA (extracted from those fragments of skeletons) and traces of Denisovan DNA in modern humans.

Oddly, those Denisovan bones turned up in Siberia (a good place for preserving old bones, but not such a great place for humans adapted to warm climates) while the humans with Denisovan DNA live in modern Papua New Guinea and nearby areas.

The obvious answer to this puzzle is that both the Denisovans had a much broader range than one cave in Siberia and the ancestors of modern folks from PNG used to live in different areas than they do now.

A more detailed analysis of PNG DNA was recently released, which reveals three separate, significant groups of Denisovans who interbred with sapiens:

… modern Papuans carry hundreds of gene variants from two deeply divergent Denisovan lineages that separated [from each other] over 350 thousand years ago. Spatial and temporal structure among these lineages suggest that introgression from one of these Denisovan groups predominantly took place east of the Wallace line and continued until near the end of the Pleistocene. A third Denisovan lineage occurs in modern East Asians. This regional mosaic suggests considerable complexity in archaic contact, with modern humans interbreeding with multiple Denisovan groups that were geographically isolated from each other over deep evolutionary time.

The Wallace line is a place that’s too deep for a landbridge, and thus the area to the east was an island even during the Ice Age. In other words, it looks like Denisovans could use boats. (Or survive tsunamis, pfft.)

Next, we sought to retrieve dates of divergence between D1, D2, and the Altai Denisovan genome … to encompass two deeply divergent Denisovan-related components, our best fitting model indicates that D1 and D2 split from the Altai Denisovan approximately 283 kya … respectively (Figure 4B). While clearly branching off the Denisovan line, D2 diverged so closely to the Neanderthal-Denisovan split that it is perhaps better considered as a third sister group… For context, even the youngest of these divergence times is similar to the evolutionary age of anatomically modern humans … Our model implies substantial reproductive separation of multiple Denisovan-like populations over a period of hundreds of thousands of years. … 

The genetic diversity within the Denisovan clade is consistent with their deep divergence and separation into at least three geographically disparate branches, with one contributing an introgression signal in Oceania and to a lesser extent across Asia (D2), another apparently restricted to New Guinea and nearby islands (D1), and a third in East Asia and Siberia (D0). This suggests that Denisovans were capable of crossing major geographical barriers, including the persistent sea lanes that separated Asia from Wallacea and New Guinea. They therefore spanned an incredible diversity of environments, from temperate continental steppes to tropical equatorial islands.

(We will probably reclassify some of the older fossils from Asia as Denisovans once we figure out what they looked like.)

Then we have Homo naledi, from South Africa. Naledi lived around 250,000 years ago, about the same time as Homo sapiens were differentiating from their ancestors. We have a wonderful array of Homo naledi fossils, preserved in the bottom of a cave pit. If they were placed here intentionally, this was pretty advanced behavior, though I wonder if perhaps they just got lost in the cave from time to time and then died in the pit.

At about 5 ft tall, (male height) naledi was short, but not nearly as short as Floresiensis, and taller than some groups of sapiens. Its skull was significantly smaller than a modern skull, however, and I find it odd that, out of the thousands of bones and fragments discovered, we have not yet recovered much of the front of their faces. Perhaps their faces were shattered when they fell into the cave?

Naledi, like Floresiensis and Luzonensis, shares some more modern traits with other members of the homo genus, and some traits with the older australopithecines. Unlike them, we have yet to uncover evidence that Naledi used tools.

The we have a couple of unnamed hominins

These so-called “ghost populations” are known entirely from their presence in the DNA of modern humans. We don’t have any fossils from them, either because they lived in areas where the weather didn’t favor preservation, or the modern political climate makes searching for fossils difficult.

The pygmies and Bushmen derive about 2% of their DNA from an archaic population or two that we estimate split off from the rest of us about 700,000 years ago. They met and mated with these other hominins around 35,000 years ago.

More interesting is another ghost population that shows up in the genomes of west African groups like the Mende. Now, the average non-African has about 1-4% Neanderthal DNA, and Melanesians have about 4-6% Denisovan, but some tribes in west Africa, such as the Yoruba, Mende, Gambians, and Esan, may derive about 10% of their DNA from an otherwise unknown ghost population that split off before the Neanderthals! (Razib’s very nice article summarizing the paper.)

 

Oh, jeeze, it’s three am, let me finish this in the next post…

 

 

Neanderthal DNA–hey!–what is it good for?

Quite a bit.

First, a bit of history:

neanderthalmap
map of Neanderthal DNA in humans

It appears that there were (at least) 3 main cross-breeding events with Neanderthals. The first event most likely happened when one small band of humans had left Africa and ventured into the Middle East, where Neanderthals were living. The DNA acquired from that partnership can be found in all modern non-Africans, since they are all descended from this same group. (Since there has also been back-migration from the Middle East into Africa sometime in the past 70,000 years, many African groups also have a small amount of this DNA.)

Soon after, the group that became the Melanesians, Papuans, and Aborigines split off from the rest and headed east, where they encountered–and interbred with–the mysterious Denisovans, a third human species that we know mostly from DNA. Various sources claim this happened before the second neanderthal inter-breeding event, but just looking at the amount of admixed neanderthal in Oceanans suggests this is wrong.

Meanwhile, the rest of the non-African humans, probably still living in the Middle East or Eurasian Steppe, encountered a second band of Neanderthals, resulting in a second admixture event, shared by all Asians and Europeans, but not Melanesians &c. Then the Asians and Europeans went their separate ways, and the Asians encountered yet a third group of Neanderthals, giving them the highest rates of Neanderthal ancestry.

nature-siberian-neanderthals-17.02.16-v2

During their wanderings, some of these Asians encountered Melanesians, resulting in a little Denisovan DNA in today’s south Asians (especially Tibetans, who appear to have acquired some useful adaptations to Tibet’s high altitude from ancient Denisovans.)

There were other interbreeding events, including a much older one that left homo sapiens DNA in Neanderthals, and one that produced Denny, a Neanderthal/Denisovan hybrid. There were also interbreeding events in Africa, involving as-yet unidentified hominins. (In the human family tree to the right/above, Melanesians are included within the greater Asian clade.)

Who married whom? So far, we’ve found no evidence of Neanderthal mitochondrial DNA–passed from mothers to their children–in modern humans, so the pairings most likely involved Neanderthal men and human women. But we have also found extremely little Neanderthal DNA on the Y chromosome–so it is likely that they only had female children, or any male children they had were infertile.

Anthropogenesis-DenisovaAlleleMapInterestingly, we find higher amounts of Neanderthal DNA in older skeletons, like the 40,000 year old Tianyuan Man, or this fellow from Romania with 10% Neanderthal DNA, than in modern humans. Two potential explanations for the decrease: later mixing with groups that didn’t have Neanderthal DNA resulted in dilution, or people with more Neanderthal DNA just got out-competed by people with less.

Given the dearth of DNA on the Y chromosome and the number of diseases linked to Neanderthal DNA, including Lupus, Crohn’s, cirrhosis, and Type-2 diabetes, the fact that morphological differences between Sapiens and Neanderthals are large enough that we classify them as different species, and the fact that Neanderthals had larger craniums than Sapiens but Sapiens women attempting to give birth to hybrid children still had regular old Sapiens pelvises, gradual selection against Neanderthal DNA in humans seems likely.

However, the Neanderthals probably contributed some useful DNA that has been sorted out of the general mix and come down the ages to us. For example, the trait that allows Tibetans to live at high altitudes likely came from a Denisovan ancestor:

Researchers discovered in 2010 that Tibetans have several genes that help them use smaller amounts of oxygen efficiently, allowing them to deliver enough of it to their limbs while exercising at high altitude. Most notable is a version of a gene called EPAS1, which regulates the body’s production of hemoglobin. They were surprised, however, by how rapidly the variant of EPAS1spread—initially, they thought it spread in 3000 years through 40% of high-altitude Tibetans, which is the fastest genetic sweep ever observed in humans—and they wondered where it came from.

Modern humans have Neanderthal DNA variants for keratin (a protein found in skin, nails, hair, etc.,) and UV-light adaptations that likely helped us deal with the lower light levels found outside Africa. There’s circumstantial evidence that microcephalin D could have Neanderthal origins (it appeared about 37,000 years ago and is located primarily outside of Africa,) but no one has found microcephalin D in a Neanderthal, so this has not been proven. (And, indeed, another study has found that Neanderthal DNA tends not to be expressed in the brain.)

Yet on the other hand, Neanderthal admixture affected sapiens’ skull shapes:

Here, using MRI in a large cohort of healthy individuals of European-descent, we show that the amount of Neanderthal-originating polymorphism carried in living humans is related to cranial and brain morphology. First, as a validation of our approach, we demonstrate that a greater load of Neanderthal-derived genetic variants (higher “NeanderScore”) is associated with skull shapes resembling those of known Neanderthal cranial remains, particularly in occipital and parietal bones. Next, we demonstrate convergent NeanderScore-related findings in the brain (measured by gray- and white-matter volume, sulcal depth, and gyrification index) that localize to the visual cortex and intraparietal sulcus. This work provides insights into ancestral human neurobiology and suggests that Neanderthal-derived genetic variation is neurologically functional in the contemporary population.

(Not too surprising, given Neanderthals’ enormous craniums.)

Homo sapiens also received Neanderthal genes affecting the immune system, which were probably quite useful when encountering new pathogens outside of Africa, and genes for the “lipid catabolic process,”[19] which probably means they were eating new, fattier diets that Neanderthals were better adapted to digest.

Even Neanderthal-derived traits that today we cast as problems, like Type II Diabetes and depression, might have been beneficial to our ancestors:

“Depression risk in modern human populations is influenced by sunlight exposure, which differs between high and low latitudes, and we found enrichment of circadian clock genes near the Neanderthal alleles that contribute most to this association.”

Why would we find an association between Neanderthal DNA and circadian clock genes? Neanderthals had thousands of years more exposure to Europe’s long nights and cold winters than homo Sapiens’; it is unlikely that they developed these adaptations in order to become less well-adapted to their environment. It is more likely that Neanderthals downregulated their activity levels during the winter–to put it colloquially, they hibernated.

No problem for furry hunter-gatherers who lived in caves–much more problematic for information age workers who are expected to show up at the office at 9 am every day.

Type II diabetes affects digestion by decreasing the production of insulin, necessary for transporting converting carbs (glucose) into cells so it can be transformed into energy. However, your body can make up for a total lack of carbs via ketosis–essentially converting fats into energy.

Our hunter-gatherer ancestors–whether Neanderthal or Sapiens–didn’t eat a lot of plants during the European and Siberian winters because no a lot of plants grow during the winter. If they were lucky enough to eat at all, they ate meat and fat, like the modern Inuit and Eskimo.

And if your diet is meat and fat, then you don’t need insulin–you need ketosis and maybe some superior lipid digestion. (Incidentally, the data on ketogenic diets and type II diabetes looks pretty good.)

In sum, Neanderthal and Denisovan DNA, while not always useful, seems to have helped Homo sapiens adapt to colder winters, high altitudes, new pathogens, new foods, and maybe changed how we think and perceive the world.

 

 

2 Interesting studies: Early Humans in SE Asia and Genetics, Relationships, and Mental Illness

Ancient Teeth Push Back Early Arrival of Humans in Southeast Asia :

New tests on two ancient teeth found in a cave in Indonesia more than 120 years ago have established that early modern humans arrived in Southeast Asia at least 20,000 years earlier than scientists previously thought, according to a new study. …

The findings push back the date of the earliest known modern human presence in tropical Southeast Asia to between 63,000 and 73,000 years ago. The new study also suggests that early modern humans could have made the crossing to Australia much earlier than the commonly accepted time frame of 60,000 to 65,000 years ago.

I would like to emphasize that nothing based on a couple of teeth is conclusive, “settled,” or “proven” science. Samples can get contaminated, machines make errors, people play tricks–in the end, we’re looking for the weight of the evidence.

I am personally of the opinion that there were (at least) two ancient human migrations into south east Asia, but only time will tell if I am correct.

Genome-wide association study of social relationship satisfaction: significant loci and correlations with psychiatric conditions, by Varun Warrier, Thomas Bourgeron, Simon Baron-Cohen:

We investigated the genetic architecture of family relationship satisfaction and friendship satisfaction in the UK Biobank. …

In the DSM-55, difficulties in social functioning is one of the criteria for diagnosing conditions such as autism, anorexia nervosa, schizophrenia, and bipolar disorder. However, little is known about the genetic architecture of social relationship satisfaction, and if social relationship dissatisfaction genetically contributes to risk for psychiatric conditions. …

We present the results of a large-scale genome-wide association study of social
relationship satisfaction in the UK Biobank measured using family relationship satisfaction and friendship satisfaction. Despite the modest phenotypic correlations, there was a significant and high genetic correlation between the two phenotypes, suggesting a similar genetic architecture between the two phenotypes.

Note: the two “phenotypes” here are “family relationship satisfaction” and “friendship satisfaction.”

We first investigated if the two phenotypes were genetically correlated with
psychiatric conditions. As predicted, most if not all psychiatric conditions had a significant negative correlation for the two phenotypes. … We observed significant negative genetic correlation between the two phenotypes and a large cross-condition psychiatric GWAS38. This underscores the importance of social relationship dissatisfaction in psychiatric conditions. …

In other words, people with mental illnesses generally don’t have a lot of friends nor get along with their families.

One notable exception is the negative genetic correlation between measures of cognition and the two phenotypes. Whilst subjective wellbeing is positively genetically correlated with measures of cognition, we identify a small but statistically significant negative correlation between measures of correlation and the two phenotypes.

Are they saying that smart people have fewer friends? Or that dumber people are happier with their friends and families? I think they are clouding this finding in intentionally obtuse language.

A recent study highlighted that people with very high IQ scores tend to report lower satisfaction with life with more frequent socialization.

Oh, I think I read that one. It’s not the socialization per se that’s the problem, but spending time away from the smart person’s intellectual activities. For example, I enjoy discussing the latest genetics findings with friends, but I don’t enjoy going on family vacations because they are a lot of work that does not involve genetics. (This is actually something my relatives complain about.)

…alleles that increase the risk for schizophrenia are in the same haplotype as
alleles that decrease friendship satisfaction. The functional consequences of this locus must be formally tested. …

Loss of function mutations in these genes lead to severe biochemical consequences, and are implicated in several neuropsychiatric conditions. For
example, de novo loss of function mutations in pLI intolerant genes confers significant risk for autism. Our results suggest that pLI > 0.9 genes contribute to psychiatric risk through both common and rare genetic variation.

No, Graecopithecus does not prove humans evolved in Europe

Hello! We’re in the midst of a series of posts on recent exciting news in the field of human evolution:

  • Ancient hominins in the US?
  • Homo naledi
  • Homo flores
  • Humans evolved in Europe?
  • In two days, first H Sap was pushed back to 260,000 years,
  • then to 300,000 years!
  • Bell beaker paper

Today we’re discussing the much-publicized claim that scientists have discovered that humans evolved in Europe. (If you haven’t read last week’s post on Homo naledi and flores, I encourage you to do so first.) The way reporters have framed their headlines about the recent Graecopithecus freybergi findings is itself a tale:

The Telegraph proclaimed, “Europe was the birthplace of mankind, not Africa, scientists find,” Newsweek similarly trumpeted, “First Human Ancestor Came from Europe Not Africa,” and CBS News stated, “Controversial study suggests earliest humans lived in Europe – not Africa.”

The Conversation more prudently inquired, “Did humans evolve in Europe rather than Africa? ” and NewScientist and the Washington Post, in a burst of knowing what a “human” is, stated, “Our common ancestor with chimps may be from Europe, not Africa” and “Ape that lived in Europe 7 million years ago could be human ancestor,” respectively.

This all occasioned some very annoying conversations along the lines of “White skin tone couldn’t possibly have evolved within the past 20,000 years because humans evolved in Europe! Don’t you know anything about science?”

Ohkay. Let’s step back a moment and take a look at what Graecopithecus is and what it isn’t.

This is Graecopithecus:

I think there is a second jawbone, but that’s basically it–and that’s not six teeth, that’s three teeth, shown from two different perspectives. There’s no skull, no shoulder blades, no pelvis, no legs.

Lucy
Naledi

By contrast, here are Lucy, the famous Australopithecus from Ethiopia, and a sample of the over 1,500 bones and pieces of Homo naledi recently recovered from a cave in South Africa.

Now, given what little scientists had to work with, the fact that they managed to figure out anything about Graecopithecus is quite impressive. The study, reasonably titled “Potential hominin affinities of Graecopithecus from the Late Miocene of Europe,” by
Jochen Fuss, Nikolai Spassov, David R. Begun, and Madelaine Böhm, used μCT and 3D reconstructions of the jawbones and teeth to compare Graecopithecus’s teeth to those of other apes. They decided the teeth were different enough to distinguish Graecopithecus from the nearby but older Ouranopithecus, while looking more like hominin teeth:

G. freybergi uniquely shares p4 partial root fusion and a possible canine root reduction with this tribe and therefore, provides intriguing evidence of what could be the oldest known hominin.

My hat’s off to the authors, but not to all of the reporters who dressed up “teeth look kind of like hominin teeth” as “Humans evolved in Europe!”

First of all, you cannot make that kind of jump based off of two jawbones and a handfull of teeth. Many of the hominin species we have recovered–such as Homo naledi and Homo floresiensis, as you know if you already read the previous post–possessed a mosaic of “ape like” and “human like” traits, ie:

The physical characteristics of H. naledi are described as having traits similar to the genus Australopithecus, mixed with traits more characteristic of the genus Homo, and traits not known in other hominin species. The skeletal anatomy displays plesiomorphic (“ancestral”) features found in the australopithecines and more apomorphic (“derived,” or traits arising separately from the ancestral state) features known from later hominins.[2]

Nebraska Man teeth compared to chimps, Homo erectus, and modern humans

If we only had six Homo naledi bones instead of 1,500 of them, we might be looking only at the part that looks like an Australopithecus instead of the parts that look like H. erectus or totally novel. You simply cannot make that kind of claim off a couple of jawbones. You’re far too likely to be wrong, and then not only will you end up with egg on your face, but you’ll only be giving more fuel to folks who like to proclaim that “Nebraska Man turned out to be a pig!”:

In February 1922, Harold Cook wrote to Dr. Henry Osborn to inform him of the tooth that he had had in his possession for some time. The tooth had been found years prior in the Upper Snake Creek beds of Nebraska along with other fossils typical of North America. … Osborn, along with Dr. William D. Matthew soon came to the conclusion that the tooth had belonged to an anthropoid ape. They then passed the tooth along to William K. Gregory and Dr. Milo Hellman who agreed that the tooth belonged to an anthropoid ape more closely related to humans than to other apes. Only a few months later, an article was published in Science announcing the discovery of a manlike ape in North America.[1] An illustration of H. haroldcookii was done by artist Amédée Forestier, who modeled the drawing on the proportions of “Pithecanthropus” (now Homo erectus), the “Java ape-man,” for the Illustrated London News. …

Examinations of the specimen continued, and the original describers continued to draw comparisons between Hesperopithecus and apes. Further field work on the site in the summers of 1925 and 1926 uncovered other parts of the skeleton. These discoveries revealed that the tooth was incorrectly identified. According to these discovered pieces, the tooth belonged neither to a man nor an ape, but to a fossil of an extinct species of peccary called Prosthennops serus.

That basically sums up everything I learned about human evolution in highschool.

Second, “HUMANS” DID NOT EVOLVE 7 MILLION YEARS AGO.

Scientists define “humans” as members of the genus Homo, which emerged around 3 million years ago. These are the guys with funny names like Homo habilis, Homo neanderthalensis, and the embarrassingly named Homo erectus. The genus also includes ourselves, Homo sapiens, who emerged around 200-300,000 years ago.

Homo habilis descended from an Australopithecus, perhaps Lucy herself. Australopithecines are not in the Homo genus; they are not “human,” though they are more like us than modern chimps and bonobos are. They evolved around 4 million years ago.

The Australopithecines evolved, in turn, from even older apes, such as–maybe–Ardipithecus (4-6 million years ago) or Sahelanthropus tchadensis.

Regardless, humans didn’t evolve 7 million years ago. Sahelanthropus and even Lucy do not look like anyone you would call “human.” Humans have only been around for about 3 million years, and our own specific species is only about 300,000 years old. Even if Graecopithecus turns out to be the missing link–the true ancestor of both modern chimps and modern humans–that still does not change where humans evolved, because Graecopithecus narrowly missed being a human by 4 million years.

If you want to challenge the Out of Africa narrative, I think you’d do far better arguing for a multi-regional model of human evolution that includes back-migration of H. erectus into Africa and interbreeding with hominins there as spurring the emergence of H. sapiens than arguing about a 7 million year old jawbone. (I just made that up, by the way. It has no basis in anything I have read. But it at least has the right characters, in the right time frame, in a reasonable situation.)

Sorry this was a bit of a rant; I am just rather passionate about the subject. Next time we’ll examine very exciting news about Bushmen and Pygmy DNA!

 

YES Two Out of Africa Events! (Also, Aborigines)

I’ve long suspected (given the archaeological evidence, like 80,000 year old human remains in China,) that there were two Out of Africa (OOA) events–an early one that headed east, toward Australia, and a later one that headed everywhere (including Australia)–and now it looks like this has been genetically confirmed:

Graphic created by the Estonian genetics team cited in the NY Times article. Their full article: Genomic analyses inform on migration events during the peopling of Eurasia
Graphic created by the Estonian genetics team cited in the NY Times article. Their full article: Genomic analyses inform on migration events during the peopling of Eurasia

Isn’t this a great graphic? My hat’s off to the Estonians. Beautiful work.

Graphic created by the Estonian genetics team cited in the NY Times article. Their full article: Genomic analyses inform on migration events during the peopling of Eurasia

Here’s another one they made (sadly small) with less color and more detail on the Eurasian lines. (IIRC, Chinese have more Neanderthal ancestry than Europeans, so technically the schematic ought to be a wee bit more complicated than this, but it’s already complicated enough and this is a solid general overview.)

It might just be the sleep dep + lots of coffee talking, but I am so excited about this.

Some quotes from the NY Times article:

In Israel, for example, researchers found a few distinctively modern human skeletons that are between 120,000 and 90,000 years old. In Saudi Arabia and India, sophisticated tools date back as far as 100,000 years.

Last October, Chinese scientists reported finding teeth belonging to Homo sapiens that are at least 80,000 years old and perhaps as old as 120,000 years. …

Examining their data separately, all three groups came to the same conclusion: People everywhere descend from a single migration of early humans from Africa. The estimates from the studies point to an exodus somewhere between 80,000 and 50,000 years. …

n Papua New Guinea, Dr. Metspalu and his colleagues found, 98 percent of each person’s DNA can be traced to that single migration from Africa. But the other 2 percent seemed to be much older.

Dr. Metspalu concluded that all people in Papua New Guinea carry a trace of DNA from an earlier wave of Africans who left the continent as long as 140,000 years ago, and then vanished.

Obviously, in science, replication and caution are key. Don’t get too excited. These results might turn out to be wrong–sometimes samples get contaminated or data coded incorrectly and we get results that turn out to be completely wrong. And, okay, this isn’t really “huge” in the grand scheme of things–we’re only talking about 2% of Papuans’ ancestors, not, like, 40% of them. But it does explain all of those anomalously old findings.

Now someone needs to explain the Red Deer Cave People:

The Red Deer Cave People were the most recently known prehistoric Hominin population that did not look like modern humans. Fossils dated to between 14,500 and 11,500 years old were found in Red Deer Cave and Longlin Cave in China. Having a mix of archaic and modern features, they are (tentatively) thought to be a separate species of humans that persisted until recent times and became extinct without contributing to the gene pool of modern humans.[1]

On a related note, we have some awesome news about Aborigine DNA/language trees: A genomic history of Australia and Why Australia is home to one of the Largest Language Families in the World. (Well duh it’s because Aborigines spent thousands of years as tiny bands of hunter gatherers, in which each isolated band started developing its own language.) These articles have an oddly inverted structure, (burying the lead, I guess,) so let’s rearrange the abstract for coherency:

We estimate that Aboriginal Australians and Papuans diverged from Eurasians 51–72 kya, following a single out-of-Africa dispersal, and subsequently admixed with archaic populations. … Papuan and Aboriginal Australian ancestors diversified 25–40 thousand years ago (kya), suggesting pre-Holocene population structure in the ancient continent of Sahul (Australia, New Guinea and Tasmania). However, all of the studied Aboriginal Australians descend from a single founding population that differentiated ~10–32 kya. We infer a population expansion in northeast Australia during the Holocene epoch (past 10,000 years) associated with limited gene flow from this region to the rest of Australia, consistent with the spread of the Pama–Nyungan languages.

(kya = thousand years ago). So about 10-32 thousand years ago, one group of Australians conquered all of the other groups of Australians.

The science article notes:

To the researchers’ amazement, the genetic pattern mirrored the linguistic one. “It’s incredible that those two trees match. None of us expected that,” says paleoanthropologist Michael Westaway of Griffith University, Nathan, in Australia, a co-author on the Willerslev paper. “But it’s confusing: The [genetic splits] date to 30,000 years ago or more but the linguistic divisions are only maybe 6000 years old.”

Willerslev says he first thought the languages must be much older than thought. “But the linguists told me, ‘no way.'”

Both types of data also show that the population expanded from the northeast to the southwest. This migration occurred within the last 10,000 years and likely came in successive waves, Bowern says, in which existing languages were overlaid by new ones. This expansion also seems to correspond with a stone tool innovation called a backed edge blade. But the accompanying gene flow was just a trickle, suggesting that only a few people had an outsize cultural impact, Willerslev says. “It’s like you had two men entering a village, convincing everyone to speak a new language and adopt new tools, having a little sexual interaction, then disappearing,” he says. Then the new languages continued to develop, following the older patterns of population separation. “It’s really strange but it’s the best way we can interpret the data at this stage.”

Three things going on here. 1. The group from the north conquered the group from the south, raped their women, and imposed their language. They were able to do this because they had better weapons (“backed edge blades.”) But the group from the north was not very big, and so did not leave a very big genetic signature.

2. They conquered an existing population structure, at which point their language got absorbed into that structure, probably picking up some linguistic substrate from the groups’ previous languages along the way. Since most people learn language from their parents, it’s not too surprising to find cases where language and genetics line up. (Note that people do not always learn languages from their parents.)

3. Intellectuals are kind of naive.

The other really interesting thing here is that the linguistics team came to their conclusions by feeding a big database of Aboriginal words into a computer and having it run similar algorithms to the ones geneticists use for examining human ancestry (see the lovely graphics above.) I’ve been wondering for a long time why they don’t just do this, and am excited that they finally are.

Now please someone put all of the languages + reconstructed proto-langauges into the computer and find the most likely trees.

(Sorry, Nick. The regularly scheduled Anthropology Friday is going to have to wait a week. There just aren’t enough days.)