Note: I’m not an expert on human evolution, so this post is largely derived from some catch-up reading I had to do, and there may be some errors. Feel free to comment or correct me in the comments. I use the subspecies designation H. sapiens sapiens as a synonym for “modern H. sapiens” and to distinguish them from Neanderthals, which on reproductive grounds (see below) I consider a subspecies: H. sapiens neanderthalensis.
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Hominins migrated out of Africa several times, including Homo erectus, whose members left Africa about 1.8 million years ago and spread throughout Eurasia, making it as far as to what are now China, Vietnam, and India. But for reasons unknown that species went completely extinct about 140,000 years ago, and contributed nothing to the modern human genome.
The extant species, our own Homo sapiens sapiens, evolved in Africa but also left the continent—several times. The most recent exodus was about 60,000-90,000 years ago, and descendants of those migrants include all living non-African populations of our species (we know this from genetic data). However, most modern humans also carry a bit of genome from earlier migrations: most notably that of the Neanderthals, whose ancestors probably left Africa about 300,000 years ago and went extinct between 40,000 and 25,000 years ago. Before they died out, though, they certainly interbred to some extent with the lineage that produced modern humans, so that many of us carry a handful of Neanderthal genes. (As I said at the top, I consider Neanderthals a subspecies of Homo sapiens—H. sapiens neanderthalensis—because they produced viable and fertile hybrids with “modern” H. sapiens, which I call H. sapiens sapiens to simplify matters. Some anthropologists, however, consider Neanderthals a full species: H. neanderthalensis.)
The characteristics of H. sapiens sapiens, compared to other hominins, include, as a summary in Science describes (“When did modern humans leave Africa?“; reference and link below), “a globular braincase, brow ridges that are divided into central and side portions, a flat and retracted midface, a chin on the lower jaw, and a narrow pelvis.” Hominins with these modern features, probably having split off from the H. erectus lineage, first appear roughly 300,000 years ago in Africa. There followed several bouts of migration out of Africa, producing groups like the Denisovans and Neanderthals, but until now H. sapiens sapiens fossils found outside Africa date from 120,000-90,000 years ago—in Israel. These emigrants probably went extinct, too, so though they are considered members of H. sapiens sapiens, they were a group that didn’t survive.
Now a new paper in Science by Israel Hershkovitz et al. (and there are a lot of “al.”s; see reference below with free access and full pdf here) pushes back the date of H. sapiens emigrants a long way—to roughly 180,000 years ago. These emigrants, too, apparently went extinct (we don’t know why—perhaps their population was too small?), and left no genetic contribution to the modern human genome. But the paper suggests that there were excursions of H. sapiens sapiens to lands outside Africa even longer ago than we thought.
The new data come from a single jawbone collected in Misliya cave on Mount Carmel in Israel. Here’s the collecting site from the Science paper (all captions from that paper):
What the authors found was the left side of the left upper jaw, including all eight teeth, some of the cheekbone and the roof of the mouth, and a bit of the nasal cavity (left in photo below). The specimen was dated in several ways, including uranium/thorium dating of the dentine and sediments adhering to the jawbone, uranium and combined uranium/electron-spin data on the enamel, and thermoluminescence on burnt stone tools associated with the fossils. The dating ranges are shown to the right:
The dates are pretty concordant except for the U-series on the dentine, which gives an age of about 70,000 years, not different from the most recent migration out of Africa that led to all modern extra-African H. sapiens sapiens populations. That outlier bothers me, but the authors, combining the data, come up with an age of the specimen between 177,000 and 194,000 years (dark band in the figure to the right above). This being above my pay grade, I’ll take their word that the youngest date of 70,000 years is wrong.
How do we know this is “modern” H. sapiens? The authors did morphological analysis of the teeth and show that they fall well within the boundaries of the teeth of that group. Here’s a principal component analysis of the crown shape of one molar from the specimen. (This analysis combines several features of morphology into two main axes that capture most of the variation among specimens.) In the figure below, the new molar is “Misliya1” on the left, grouping nicely with the gray diamonds of modern H. sapiens and shaped differently from the teeth of Neanderthals (black diamonds), early modern humans (presumably from Africa; greenish-yellow x’s), early and middle Pleistocene humans from Europe, which aren’t H. sapiens but in the genus Homo (purple squares), and specimens from Africa of that same age (burgundy + sign), and Middle Pleistocene Asian Homo (probably H. erectus; blue triangles). If you want the exact locations, check the paper’s supplementary data.
Granted, it’s only one molar, but the age is pretty compelling, and it does fall out with modern H. sapiens. Other data I haven’t shown, on the maxilla (jawbone) shape as well as features of other teeth, show that these, too, group with recent modern humans and not with earlier non-sapiens Homo.
Further, the tools found in the same stratum and dated with thermal methods show what is called “Levallois technology,” which is explained and animated by Wikipedia:
A striking platform is formed at one end and then the core’s edges are trimmed by flaking off pieces around the outline of the intended lithic flake. This creates a domed shape on the side of the core, known as a tortoise core, as the various scars and rounded form are reminiscent of a tortoise’s shell. When the striking platform is finally hit, a lithic flake separates from the lithic core with a distinctive plano-convex profile and with all of its edges sharpened by the earlier trimming work.
This way of making cutting tools is also seen in African specimens of H. sapiens sapiens dated about the same time, further supporting the notion that the Israel specimen came from modern H. sapiens and does go back about 200,000 years.
THE UPSHOT: This finding does not “revolutionize the story of human evolution”: after all, if these specimens are about 180,000 years old, they’re from a population of our species that went extinct without leaving descendants. But what it does show is that modern H. sapiens sapiens—members of our own subspecies—left Africa considerably earlier than we thought. And it shows that there were several migrations of H. sapiens sapiens out of Africa at different times. All modern “out of Africa” populations, however, do descend from the most recent exodus, roughly 60,000-90,000 years ago. The story is complex, and also involves mating of “modern” H. sapiens with the H. sapiens neanderthalensis lineage—both in and out of Africa.
More surprises surely await, as hominin fossils are rare, and each one can potentially tell us something amazing. As Steve Gould once said, every time he taught human evolution he threw away all of his previous notes and completely rewrote the course.
Here’s a figure from the Stringer and Galway-Witham “news and views” piece showing the different migrations of modern humans, with an even older one within Africa:
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Hershkovitz, I., G. W. Weber, R. Quam, M. Duval, R. Grün, L. Kinsley, A. Ayalon, M. Bar-Matthews, H. Valladas, N. Mercier, J. L. Arsuaga, M. Martinón-Torres, J. M. Bermúdez de Castro, C. Fornai, L. Martín-Francés, R. Sarig, H. May, V. A. Krenn, V. Slon, L. Rodríguez, R. García, C. Lorenzo, J. M. Carretero, A. Frumkin, R. Shahack-Gross, D. E. Bar-Yosef Mayer, Y. Cui, X. Wu, N. Peled, I. Groman-Yaroslavski, L. Weissbrod, R. Yeshurun, A. Tsatskin, Y. Zaidner, and M. Weinstein-Evron. 2018. The earliest modern humans outside Africa. Science 359:456-459.
Stringer, C. and J. Galway-Witham. When did modern humans leave Africa? Science 359:389-390.
I have some questions that reflect the fact that I am a non-scientist and that my understanding of the details of human evolution is appalling. Specifically, what does it mean to say that modern humans carry a small amount of Neanderthal DNA, presumably due to interbreeding? How is this DNA manifested in human anatomy and biology? How would modern humans be different if they had not interbred with Neanderthals? I do not know if these questions can be answered, but I am curious.
We know this from having sequenced the genome of Neanderthals (sequencing like this is one of the amazing accomplishments of modern genetics), and in modern human DNA we find odd bits–a few percent–of that ancient DNA. We know because those bits are old and resemble the Neanderthal genome far more than “modern” human genome (not all humans have these bits). We had to have gotten it from our lineage interbreeding with Neandertals long ago. As far as I know, the bits we got don’t have any perceptible effect on our phenotype, as humans with Neandertal DNA don’t seem to look any different than those lacking it (I’m not sure those studies have been done, though.)
Thanks a lot for your response. You’ve clarified something that I have been thinking about for a long time and couldn’t find an answer to.
I thought there were some Neanderthal-derived phenotypic traits that had been identified… red hair (I think?) and higher propensity for diabetes?
Per 23andMe, my own Neanderthal genes include one for “less back hair”, a change from a G to a T in a DNA sequence near the EN1 gene. (Not that I know what exactly the EN1 gene is!)
EN1 is the human homolog of the Engrailed HOX gene. It encodes a transcription factor involved in spatial tissue patterning (particularly anterior/posterior polarity) during early embryonic development. It obviously worked just fine with you despite the transversion 🙂
Thanks for the education! Not sure how that translates into less back hair, but I’ll take it!
So much for our stereotypes of Neanderthals…
About the only distinctive trait to emerge from my 23andMe work-up was a higher than average proportion of Neanderthal DNA. My late husband would have had a field day with this…
Heh.
I’m lucky (in my mind) to have a pretty high percentage. 23andMe tells me I’m in the top 13% of their data set. My daughter turns out to be higher than me. So my wife must be really neanderthal!
Many of the Neanderthal contributions in our genomes are in regions involved in adaptive immune responses, especially in areas that are subject to somatic recombination.
The hand waving explanation for this is that some of the Neanderthal genes that persisted were those that conferred some resistance to pathogens found outside Africa. The idea being as modern humans migrated out, they encountered and mated with neanderthals who’d been living in the region for millennia. The Neanderthals had obtained some residence to extant pathogens and passed those traits on to us.
That’s the idea, anyway. I think the evidence isn’t all that solid though the case can be made.
resistance, not residence.
Stoopid autocowreck.
Interesting hypothesis, though–thanks!
I suppose they’re now looking at various human survival stats to see if/how they correlate with proportions of Neanderthal DNA?
I think it’s correct to say that ALL living humans with any non-African ancestry have a significant amount (around 1 to 3 percent) of Neanderthal DNA. East Asian and Melanesian populations also have DNA derived from the poorly known Denisovan lineage. Some of this appears to have been exposed to selection — it’s thought that Tibetans carry a gene derived from the Denisovan populations that provides better oxygen transport at high elevations.. Other sections of both Neanderthal and Denisovan genome were “wiped”, eg, large chunks on various chromosomes seem to be absent in modern populations.
Oh, one other thing — there are signals in the Denisovan genome of hybridization with Neanderthal, but also a yet-unknown hominin outside the sapiens-Neanderthal-denisovan lineage — just possibly H.erectus..
Most of the above taken from online lectures by Svante Paabo, especially those given at UC-Berkeley [see UCTV channel] and at University of Wisconsin.
“As far as I know, the bits we got don’t have any perceptible effect on our phenotype,”
Strictly speaking we can’t really say that, because it could be masked by bigger racial differences. Non-African populations (plus North-Africans, who are closer to non-Africans than to Sub-Saharan Africans) all have a comparable level of Neanderthal genetic heritage, and Sub-Saharan Africans have much lower. Neanderthal genes already reached equilibrium or close to it, because the interbreeding happened a very long time ago, so Neanderthal genetic impact does not vary too much between two random Europeans or between two random East Asians.
Nevertheless, this question was asked and studied by researchers, and if I remember correctly (just from the top of mind, I read on the topic a long time ago) and indeed they found that most of the intact heritage is genes connected to food metabolism and immune system, so “inside” things that helped modern humans to adapt new habitats and not optical things. (But then, metabolism and immune system are phenotype, so these genes most certainly do influence phenotype.) Also our Neanderthal genetic heritage was under heavy selection, therefore its percentage does not represent the number of interbreeding events.
My guess is that many of the Neanderthal genes were adaptations to colder climates since modern humans were from warmer Africa and Neanderthal were from colder Europe.
As mentioned by Matthew Cobb in his video about what makes great biology (Jerry recently posted it on WEIT), Tibetans carry a Denisovan gene that confers an advantage at high altitude. The gene regulates hemoglobin production and enables more efficient use of oxygen.
Yes. And what I also meant to say was that Europeans may have been selected for more cold weather Neanderthal genes and appear to have more Neanderthal ancestry than people from warmer climes.
I suspect skin pigmentation, eye color would have been high latitude genetic traits that would have been transferred.
As far as current genetic studies go, we inherited from the Neanderthals neither skin pigmentation nor eye color related genes or at least not with great impact.
For eye color: do not forget that East Asians and South/South-East Asians have as much or sightly more Neanderthal heritage than Europeans and the yet the those lighter eye colors do not show up there. Of course their Neanderthal alleles are not completely identical to the European or Central Asian ones, but still.
As for skin pigmentation: it is effected by a bewilderingly high number of genes, making it difficult to know the pigmentation of ancient populations, but it seems to be a consensus that the very light skin color of modern Europeans is a very recent evolutionary phenomenon, as recent as the Neolithic.
Also, light eye color does not seem to have any know advantage at higher latitudes (it have most likely spread by sexual selection), while very light skin color is an advantage only, if the D-vitamin intake from food is insufficient. Hunters/fishers had better D-vitamin intake than farmers.
Thanks. Good info.
Today’s edition of The Conversation also has a brief article about the find. I have not read it yet so I do not know how good it is.
OMG! EVERYTHING WE THOUGHT WE KNEW ABOUT HUMAN EVOLUTION IS WRONG!
I saw it earlier on a ‘popular’ science site with the usual reaction.
Nope,it is not (as yet).
Even the idea that there were multiple waves and modern humans reached SW Asia much earlier than 60 kya is not new at all. 10 years ago, when I started to read on the topic, it was already stated as a fact by some. This is just a new evidence.
“if these specimens are about 180,000 years old, they’re from a population of our species that went extinct without leaving descendants.”
How do we know that? Could they not have interbred with later waves? Or is it just that there’s a gap between this population and those that left later, which would not have been expected if they had prospered?
BTW, I hit a paywall when trying to access the original papers
If you have Chrome, you can install the Unpaywall App (http://unpaywall.org/), which is free and legal. That should enable you to access the papers through the links, though I don’t know for sure. I can access them, and I don’t think it’s through my university library as I didn’t use it to access the papers.
Unpaywall is a very handy tool and one reason Chrome rocks! There are some other really great, free Chrome add-ins that readers may appreciate:
Narrower: Makes text columns narrower so they are easier to read. This is especially handy if you have a large screen. Also especially good on Wikipedia.
High Contrast: Gives options to change the text color and/or contrast, making some sites easier to read.
Unpaywall is available for Firefox too.
Sadly, the icon stays grey for this article.
I’ve followed this story (I have a layman’s interest in paleontology) and it seems they have found something significant. Discoveries like this that have swell preserved teeth and jaw fossils and associated artifacts usually are strong finds. We’ll see how further finds and analysis supports this, but it is fascinating.
BTW, I am proud that approximately 2.1% of my genome comes from the Neanderthals (genetics today is a powerful tool). We know so much more about them now than when the name was used as an insult, so go ahead and call me one. Its a compliment.
Thank you for the interesting science post.
+1
I think there is enough evidence to confidentwly say that ‘modern’ humans left Africa more than once. The 120.000 year ago migration into the Near East being the best known. It is also generally accepted that it was not ‘successful’.
This one about 60 000 years earlier was not either, it seems, according to the authors.
I still think the one 90 to 80 000 years ago, during a glacial high, through the ‘Gates of Tears’, was the Big One.
One of the problems is that it is assumed, for some good reasons, that this migration followed the coast. But during much of that time the coast was where water is now (lower sea levels). I think that underwater archaeology is a challenging, but highly promising, field.
fascinating article, thanks!
Whoops! Meant to be a comment on PCC’s post, not a reply to nicky, although that is also interesting.
I like the subspecies treatment, but I would not toss around “extinction” quite so casually. Coalescent theory says that specific genetic lineages are constantly lost even in a stable (or growing) population. Look back far enough and we all share a common ancestor for any given segment of DNA, but that was just some random member of a population. Other members of that population contributed other segments,n ad some members of that population contributed no segments. They did not go extinct, they just lost out in the genetic lottery that constructed modern genomes.
But ALL their genes are gone, so it seems to be more than just gene lineages disappearing, no?
Neanderthals live on in me and others through our genes. If 23andMe is to be believed. Actually, there has been some press recently that sheds some doubt on their accuracy.
It is a bit hard for me to understand how a Sapiens from an earlier period would have no genetic connection to later Sapiens. Am I understanding this correctly?
It’s not that we’re unrelated, it’s that no one today (that we’ve found) share certain distinguishing genetic features of those earlier people. Usually researcher us SNPs or Single Nucleotide Polymorphisms to build trees of related genes (there are other methods). This kind of analysis can unmask SNPs that cluster in groups. When modern human genomes are compared to those ancient ones, there are differences in the clustering of SNPs. So far as we know, no one today have certain SNP clusters shared with those ancient peoples.
Think of a group of “settlers” taking off for new lands. For any number of reasons the group dies off. No one from that group passed on genes to anyone outside that group. Their genes were removed from the gene pool, so no later generations inherit any genes from them.
A lot of these “first out of Africa” finds are not surprisingly in Israel. But have there been missions to (say) the south of Spain, where just maybe the crossing of the Mediterranean might have happened?
Yes, actually. Many people are interested in that area. Though they aren’t modern humans, an exciting find of Neanderthals at Sima de los Huesos and Homo intercessor at Atapuerca both dating back to over 400k years. Early last year researchers claimed to have found a fossil of Homo sapiens in Morocco, just across the way from Gibraltar, dating back to 400k years as well.
So yeah, the mid-east is an obvious place to look for early dispersal, but so is the Northern tip of Africa and the Iberian peninsula.
Neat! Thanks for the info.
Sub
You stated:
“…including Homo erectus, whose members left Africa about 1.8 million years ago and spread throughout Eurasia, making it as far as to what are now China, Vietnam, and India. But for reasons unknown that species went completely extinct about 140,000 years ago, and contributed nothing to the modern human genome.”
Do you mean that members of H. Erectus that left Africa had no impact on modern human genome or the species itself? Later on you stated:
“Hominins with these modern features, probably having split off from the H. erectus lineage, first appear roughly 300,000 years ago in Africa”
I always thought (note, I have no expertise here) that modern humans and Neanderthals split from H. Erectus at different periods.
forgot to click checkbox.
I’ve wondered for years just how complete that split was – i kinda think it wasn’t very complete and that there was a lot more genetic swapping for a longer time than generally realized.
Because humans generally will have sex with anything.
The ones who left Africa.
Thanks
I wonder if they’ve tried to get DNA sequence from those teeth.
Isn’t it surprising that today’s non-african modern humans don’t have more Neanderthal sequences in their genomes? You’d think hundreds of thousands of years spent adapting to northern climates would have produced a lot of useful changes.
I assume that lighter skin isn’t one of the changes provided by Neanderthals, although I don’t know why not. They’re always depicted with light skin but I never hear that it was contributed by them.
Good post. Thanks. This will save me much time when I have to prepare a new lecture on human evolution for my Evolution class this semester, and when I have to throw out my lecture notes from last year’s course.
It seems likely that there was probably a constant flow of Homo sapiens out of Africa, though perhaps varying significantly in rate, but that given the great distance in time all we can resolve is significant peaks.
Yes, that’s likely; we can detect only the substantial migrations, or ones that left fossils.
Sub
Great summary. How does the new date fit into the “Great Leap Forward” theory which divides H. sapiens sapiens into anatomically and behaviorally modern groups? Behaviorally modern date is around 60K year ago.
For the WEIT statistician: I read this science post from top to bottom. Interesting stuff!
I just love this kind of discovery. It feeds into the continually evolving story of us. This makes it seem like humans expanded out of Africa like waves lapping along a beach. I guess in this analogy the last wave was a tsunami.
I remember reading many years ago about discoveries in East and Southern Africa. Since then many new layer of the onion have been pealed off. I regret I won’t live for a few hundred years more so I could keep following the discoveries.
This is a remarkable discovery that adds to the mix of what we know about the human past; there’s almost certainly a lot more to discover. What intrigues me is the way the discoveries of the past thirty or so years have overturned old ideas almost completely; when I was first studying it, back in the 1980s, my lecturers were doing back-flips to ‘prove’ that the multiregional hypothesis was true. I’m inclined to think that ‘out of Africa’ itself is a product of the way we see geography these days; at the time, humanity was simply following patterns of habitable territory, wherever those led, and as they changed over time.
While the new study shows seemingly that modern humans left Africa earlier than thought, it does not show that they got very far. If Egypt and the Sinai Peninsula are considered to be part of Africa, Mt. Carmel dig is less than 120 miles away from Africa up the coast. Nevertheless, it’s an interesting if not earth-shaking find.
I read an article (far less detailed than this one) about it this morning:
https://www.channelnewsasia.com/news/lifestyle/oldest-human-remains-outside-africa-found-in-israeli-cave-9897454
Great post, Jerry. Love the science posts. Learn a lot from them.
Do you consider polar bear and grizzlies as subspecies?
No, because although they can reportedly interbreed now that their ranges are changing, they were formerly separated by a genetically based isolating barrier: ecological isolation based on preference and physiology. Good species can fuse, and this is what is happening. I suppose you can say that ecological change is altering their.
What ideas are there about what could account for the U-series results on the dentine showing it to be so much younger than the enamel, calcite crusts, and burnt flints?
No idea; the authors don’t discuss it (they mention but dismiss infiltration from other places), and nobody else seems to, either.
A conscientiously applied program of oral hygiene and regular professional care?
(Certain Boomers will get that…)
Has anyone made any attempt to rationalize radiations out of Africa with Ice Ages? Or haven’t any of them provided any barriers?
I suppose that H. erectus was driven to extinction by later migrating hominins such as the Denisovans.