Tag Archives: Neanderthals

Species

We have been treating Neanderthals here as a species, Homo neanderthalensis, distinct from our own species, Homo sapiens. Some researchers elect to call Neanderthals a subspecies, Homo sapiens neanderthalensis, and classify modern humans as another subspecies, Homo sapiens sapiens.

The line between subspecies and species is not clear cut, nor – given the way evolution works – should we expect it to be. Recent work on ancient DNA recovered from fossils has shown just how complicated the subject is. The spectacular finding of the last few years is that modern humans are hybrids, getting most of their ancestry from an African founding population (we can call them Homo sapiens), but incorporating limited ancestry from close relatives. Thus human beings outside Africa have 1-4% Neanderthal DNA. So it looks as if early in the course of expansion(s) out of Africa, there was a limited amount of interbreeding with Neanderthals.* And not just with Neanderthals. Populations in Melanesia get an additional 4-6% of their DNA from a widespread East/Southeast Asian population known as Denisovans. Actually these “Denisovans” may turn out to be several high divergent populations, and some of the interbreeding with Denisovans in or around New Guinea may have happened 30-15,000 years ago. And Neanderthals and Denisovans also interbred: just last year we learned about a girl whose mother was a Neandethal and father was a Denisovan. Meanwhile some African groups may have ancestry from non-sapiens populations in Africa. (The fossil record for Denisovans is a lot sparser than for Neanderthals, and it’s even sparser for African non-sapiens.)

This isn’t reason enough to put Neanderthals and sapiens in a single species: plenty of species occasionally hybridize with related species. And in fact the DNA evidence implies that sapiens and Neanderthals were moving toward being reproductively isolated. Specifically, we find that a lot of Neanderthal genes related to testis development and male fertility are underrepresented (i.e. at a lot less than 1-4% frequency) in modern humans. The likely explanation is that those genes didn’t work well against a H. sapiens genetic background. In other words, if you were mixed sapiens/Neanderthal man, you probably had fertility problems, albeit not to the point of complete sterility. On the other hand, other Neanderthal genes  – especially genes related to immune function – were useful to modern humans moving into Neanderthal territory and are found at high frequency in Europeans today.

There is an extensive older literature in physical anthropology on “race crossing.” Researchers were concerned with whether people with mixed racial ancestry might have reduced fitness as a result of combining incompatible genes. This literature is reviewed at book length here. The overwhelming evidence is that “race crossing” has no harmful biological consequences (in contrast to close inbreeding, which is a bad idea: check out this post on the Habsburgs.)

Some new data put this in perspective. My colleagues Alan Rogers, Chad Huff and Ryan Bohlender have shown that the population ancestral to Neanderthals and  Denisovans separated from the ancestors of Homo sapiens somewhat more than 750,000 years ago, passing through a narrow population bottleneck, probably in an early Out Of Africa episode (before the later modern human Out Of Africa episode). This population then split somewhat less than 750,000 years ago into Neanderthal and Denisovan branches. So Homo sapiens and Homo neanderthalensisevolved separately for the better part of a million years, and were some way on the path to reproductive isolation. By contrast, different populations (“races”) within Homo sapiens have been evolving separately for 100,000 years or less outside Africa, and perhaps 250,000 years within Africa. This has been enough time to evolve major differences in traits like skin color and hair form, but apparently not to create appreciable biological barriers to interbreeding.

And here’s a link covering some recent research suggesting that across a wide range of organisms it takes a surprisingly clock-like average of two million years separation to split one species into two.

* Hence, my Neanderthal name, Carg, my website, cargshome, and my Utah car license plate, NEANDR.

The Inheritors

“The Inheritors” is a novel by William Golding about the encounter between Neanderthals and modern humans. Like another Golding novel, “Lord of the Flies,” it is written with a mid-twentieth century awareness that advanced societies don’t leave behind the potential for cruelty. The novel isn’t all that scientifically accurate, though: Golding’s early humans have bows and arrows, for example.

Neanderthal 1, the first Neanderthal fossil recognized as probably belonging to another species, was discovered in the Neander Thal (=Neander Valley) in 1856. He is close in time to the last Neanderthals: the most recent review of the evidence finds that Neanderthals disappear as a distinct group around 40 thousand years ago. They were almost certainly outcompeted by Homo sapiens who had arrived in Europe earlier. There was probably some kind of coexistence between Neanderthals and H. sapiens over many thousands of years. Regional cultures from this period, like the Châtelperronian, may represent Neanderthals copying the Aurignacian culture of incoming H. sapiens. The final blow may have come between 39 and 38 thousand years ago, when a “Heinrich event” sent cascades of icebergs into the North Atlantic, drastically chilling Europe. Homo sapiens recovered from the cold spell; Neanderthals did not.

Just recently we have learned that one of the earliest modern human fossils from Europe, Oase 1, from Romania (40 kya), has substantially more Neanderthal DNA, 6-9%, than living Europeans. Furthermore, this DNA comes in the form of long stretches of chromosomes, rather than little bits broken up by millennia of recombination, showing that his Neanderthal ancestors go back just a few generations, maybe to some great-great-great-grandparents. We’ve also learned from isotopic evidence that Oase 1 got the proteins in his diet from a broad array of sources, including freshwater fish.

And here is some of the art produced by Homo sapiens 40 thousand years ago. lionman The lion man from Hohlenstein-Fels

And the earliest known cave paintings, from Sulawesi, Indonesia. indonesiancaveart

African Exodoi

123-117 thousand years ago

Our genus, Homo, left Africa by 1.8 million years ago. On the latest genetic evidence, there was another Out Of Africa migration about 700,000 years ago, which led to the ancestors of Neanderthals and Denisovans splitting off from the ancestors of Homo sapiens (who stayed in Africa this time), and replacing Homo erectus in Eurasia. And there seems to have been another Out Of Africa migration around 200,000 years ago that introduced early Homo sapiens mitochondrial DNA into the Neanderthal gene pool. This early migration didn’t lead to major evolutionary change, however. Other Neanderthal genes (i.e. nuclear rather than mitochondrial DNA) show no evidence of it.

More consequential was another Out Of Africa migration by Homo sapiens around 120,000 years ago. This skull dates back to then.
skhul5
Skhul 5 was found back in 1935, in Israel, on the slopes of Mount Carmel, buried together with a boar mandible. It looked for a long time like the skull came late in the day, and might represent a transition from Neanderthals to Homo sapiens. But now that date has been moved back, thanks to the development of new dating techniques (thermoluminescence, electron spin resonance) that finally broke the 40,000 year limit for Carbon 14. Skhul 5 now looks like a representative of an early movement of Homo sapiens out of Africa. But the skull also has some Neandethal-like features (check out the “Neanderthal bun” at the back of the skull) and could have hybrid ancestry.

Until recently it looked like this and other very early Homo sapiens outside Africa were a side branch that left no descendants – think Leif Erickson, not Columbus – with the real move coming later. But recently there has been a recalibration of DNA mutation rates that suggests that the split between African and non-African branches of H. sapiens happened closer to 100,000 years ago than 50,000 years ago. And there have been discoveries of stone tools with African affinities in the Arabian Peninsula, in the United Arab Emirates (Jebel Faya, 125 kya) and Oman (106 kya). It may be that when Homo sapiens left Africa 125,000 years ago (perhaps across the Red Sea to Arabia, rather than across the Sinai), they spent a long time isolated in a corner of Southwest Asia before much later expanding more widely.

It’s even possible that more dramatic revisions of the Out Of Africa story will be called for in the future. It could be that the finishing touches in the evolution of modern Homo sapiens happened in North Africa or Southwest Asia, with the genes involved spreading to Sub-Saharan Africa by back migration.

The Goodness Paradox

194 – 184 thousand years ago.

We’re now taking (pre)history ten thousand years at a time.

Earth Abides is an early (1949) entry in the genre of post-apocalyptic science fiction, with some haunting reflections on what it takes to keep a civilization going, or just a human community. In this case the apocalypse takes the form of a lethal infectious disease that wipes out well over 99% of Earth’s human population, leaving scattered survivors to try and put things back together.

The drama is low-key. If you want to read about the remnants of civilized humanity defending themselves against zombies, or venomous man-eating walking plants, or a horde of cannibal anti-nuke zealots, you’ll have to look elsewhere. The threat to civilization in Earth Abides is more subtle. The generation born after the die-off has no understanding of what they have lost, of what the collapsing factories and powerlines and machines around them really were, or how they worked, or how to get them back up and running. The older generation, without the institutions of a complex society backing them up, can’t supply enough discipline and punishment to pass on the arts of civilization. The young will grow up as illiterate scavenger-foragers, skilled with bow and arrow, well-adapted in their own way to a rewilding Earth. Ish, the protagonist, will end his days as the Last American (a fictional counterpoint to the real-life Ishi, the last Yahi Indian).

The community is nonetheless capable of reacting decisively when their survival is threatened.

One day a newcomer enters the scene. Charlie is talkative, forceful, charismatic. The kids adore him. It looks like he might even take over as leader of the little group. But it becomes clear that there is something off about him, even sociopathic. He can turn on the charm, but when thwarted he is menacing. He always carries a gun, but keeps it hidden. He is sexually abandoned. And, in a world without antibiotics, he is infected with a slew of venereal diseases.

Something has to be done about Charlie, and the elders of the group meet to decide what. Their options are limited. Keeping him locked up is not a practical possibility. They could banish him. But who is to say he won’t find a gun, and come back, looking for revenge? They could execute him. But what actual harm has he done, so far? They decide to settle the matter with a vote.

Em located four pencils. Ish tore a sheet of paper into four small ballots.

This we do, not hastily; this we do, not in passion; this we do, without hatred. …

This is the one who killed his fellow unprovoked; this is the one who stole the child away; this is the one who spat upon the image of our God; this is the one who leagued himself with the Devil to be a witch; this is the one who corrupted our youth; this is the one who told the enemy of our secret places.

We are afraid but we do not talk of fear. … We say, “Justice”; we say, “The Law”; we say “We, the people”; we say, “The State.”

Ish sat with his pencil poised … He could not be sure. Yet, at the same time, he knew that The Tribe faced something real and dangerous and even dreadful, in the long run threatening its very existence. … In that final realization, he knew that he could write only the one word there, out of love and responsibility for his children and grandchildren. …

“Give me your slips,” he said.

They passed them in, and he laid them face up before him on the desk. Four times he looked, and he read: “Death … death … death … death.”

Keith Otterbein is an anthropologist who did a study of capital punishment across cultures. He expected to find that capital punishment is limited to complex societies, used to enforce social hierarchy. Instead he found that capital punishment is a universal, present in societies from the simplest to the most complex. It is an option that even the smallest, most easy-going communities – like The Tribe of Earth Abides – may find themselves resorting to. We can infer that for tens or even hundreds of thousands of years, our ancestors have been carrying out group-sanctioned executions of individuals deemed anti-social and a threat to group harmony and survival. This is long enough to have had evolutionary consequences. Long before human beings domesticated the wolf, the wild sheep and goat, the aurochs, we may have been domesticating ourselves, weeding out the wildest and most dangerous from our midst, replacing the old tyranny of the alpha male with the tyranny of Custom and The Law.

The idea that human beings are in some ways like domesticated animals is an old one. It has recently returned to the spotlight. The extraordinary long-term experiment in artificial selection for tameness in foxes carried out by Nikolai Belyaev, Lyudmila Trut, and their coworkers in Russia has demonstrated that selection for tameness ends up selecting for a whole suite of anatomical characteristics as byproducts. Strikingly, many of the features that differentiate Homo sapiens hundreds of thousands of years ago from Homo sapiens today are also features that distinguish tame from wild foxes, and dogs from wolves.

Richard Wrangham’s recent book, The Goodness Paradox: The Strange Relationship Between Virtue and Violence in Human Evolution connects the dots, setting out one long argument that an evolutionary history of capital punishment has reduced our disposition for reactive aggression (the hot-blooded, spur-of-the-moment, volatile, antisocial kind), while leaving intact our capacity for calculated, cold-blooded, proactive killing (“not hastily, … not in passion, … without hatred”).

Perhaps this explains a very recent finding in human evolution. Apparently 200,000 years ago, we were about evenly matched with Neanderthals, sometimes replacing them, sometimes being replaced by them. By 40,000 years ago however, Neanderthals lose out decisively to modern humans. It may be that what changed in the interim to give us the edge is that we improved our ability to get along peaceably with insiders (including distant insiders we don’t know personally) without losing our ability to apply lethal aggression to outsiders.

Heidelberg and Bodo

By 600 thousand years ago we’re finding people who don’t fit comfortably into Homo erectus. A jawbone from around this time was unearthed in Germany, near Heidelberg, in 1907. Another find from the same period, often assigned to the same species, comes from Bodo, Ethiopia (below).

bodo

This guy clearly isn’t modern Homo sapiens, but his brain is starting to get out of the Homo erectus range (1200 cubic centimeters cranial capacity), and his browridge is a double arch, rather than an erectus-style straight bar. He’s also got cut marks on skull and face, from someone “defleshing” him. A respectful mortuary ritual, or did somebody really not like him?

The exact relationship of these guys to later humans has been unclear. A popular theory assigned both to an intermediate species, Homo heidelbergensis. However yesterday we reviewed very recent genetic modeling by Rogers and coworkers that suggests that a three-way split between Homo sapiens, Neanderthals, and Denisovans has already happened by this point, although the lineages haven’t had long to differentiate. So probably Heidelbergers in Europe are ancestral to Neanderthals (or at least closely related to their ancestors), while Bodo man is ancestral to our variety of Homo sapiens, or represents some kind of African side branch.

Post erectus

627-594 thousand years ago

We’re getting to a time on the blog when Homo erectus (and Homo ergaster, if we accept that erectus-like African specimens are another species) are starting to give way to the very earliest ancestors of later species – Homo sapiens, Neanderthals, and Denisovans. (Denisovans – known mainly from DNA rather than bones – are the contemporaries in East and Southeast Asia  of Neanderthals in West Eurasia, and early sapiens in Africa.) A recent article from Alan Rogers (a colleague of mine in Anthropology at the University of Utah) and Ryan Bohlender and Chad Huff (Utah Anthropology PhDs) sheds light on this period. The authors look at the distribution of shared derived mutations in two modern human genomes (African and Eurasian) and two ancient genomes (Neanderthal and Denisovan). They fit a model involving past divergence times and population sizes to the data. The model says that about 700,000 years ago. a small population split from the rest of humanity and then quickly split again to give rise to the ancestors of Neanderthals and Denisovans. In other words, it looks like there was an Out Of Africa event in the Middle Pleistocene, well before the better known Out Of Africa event that gave rise to modern human populations around the world. The ancestors of Neanderthals and Denisovans then replaced Homo erectus in Eurasia, although the authors find signs that some erectus genes may have made it into the Denisovan gene pool. This also implies that Homo antecessor in Europe was a dead-end branch of Homo erectus, not a Neanderthal ancestor.

As paleoanthropologist John Hawks notes, in a commentary on the article, “Humans stand out among our close primate relatives as effective biological invaders. Our recent history has included range expansions into remote and harsh geographic regions, and invasions by some populations into areas long occupied by others.” We’ll be seeing more instances of this in days to come on the blog.

And here’s me on what a later history of population replacement might mean for the evolution of ethnicity and ethnocentrism.

Talk Like a Neanderthal Day

Like “Talk Like a Pirate Day,” but more scientific!

Human language is probably more than One Weird Trick. It’s multiple weird tricks. We’ve already posted about phonemes, and how they can be strung together to make words. That’s (at least) one trick. And then words are strung together to make phrases and sentences: but there are a multiple weird tricks here as well. Consider this quotation from some language researchers:

Every human language sentence is composed of two layers of meaning: a lexical structure that contains the lexical meaning, and an expression structure that is composed of function elements that give shape to the expression. In the question, Did John eat pizza?, the lexical layer is composed of the words Johneatpizza … The sentence also contains did, which has two functions: it marks tense, and by occurring at the head of the sentence, it also signifies a question. (Miyagawa et. al.)

The lexical level of language includes content words: nouns, most verbs, adjectives. The expressive level contains functional words (auxiliary verbs, conjunctions, articles, and so on), as well as tenses and other inflections, and even functional operations like moving around the parts of a phrase. We can think of a sentence like a piece of carpentry, a bookshelf, say. A typical bookshelf will consist of the parts that hold things up (shelves, sides, etc., analogous to lexical structure), and parts that fasten these parts together (dowels, screws, bolts, nuts, nails, glue, etc., analogous to expressive structure).
bookshelf1
So language gets its open-ended expressive power by fastening together expressive and functional constructions in (more-or-less) alternating levels. Here’s an illustration, a Christmas tree of a phrase with expressive levels in green and functional levels in red:

language tree

But there are other ways to build furniture. For example, here’s a desk with no fasteners. Instead, the load bearing parts have slots and tabs that fit together. This is simpler but less flexible than having boards and fasteners that you can put together however you see fit.
bookshelf2

The analogy with language would be a protolanguage with nothing but content words – nouns, verbs, and adjectives, say – and lexical structure. The analogy works because verbs come with built in slots that nouns can fit into, even without any extra “fasteners” to hold them together. Linguists call this the “argument structure” of a verb. (Think about functions and their arguments if you’re into math or computer science.) For example fear and frighten are both transitive verbs, but they have different argument structures

  • Carg fear thunder.
  • Thunder frighten Carg.

In one case the experiencer goes in the subject slot, and the agent goes in the direct object slot. In the other case it’s the reverse. Some verbs, like burn, have more than one argument structure.

  • Carg burn meat.
  • Meat burn.

English verbs have some tens of different argument structures. (Note that I haven’t put any tense on the verbs. That would be part of expressive structure, which we’re leaving off here.)

So a protolanguage, one step along the way to a full blown language, could consist of a bunch of verbs and their argument structures, together with nouns slotted in the appropriate spaces as needed, and adjectives added to convey additional information. Is this what Neanderthal language was like? There is evidence that Neanderthal ancestors as far back as 430,000 years had hearing specialized for the frequencies of speech. (This is not the case with chimpanzees, or earlier hominins.*) But we don’t know yet how complex Neanderthal speech was. Eventually, as we figure out the genetics of language, we’ll find out. For now though, let’s make today – just about the last day on Logarithmic History that Neanderthals are around – “Talk Like a Neanderthal Day.”

Carg publish blogpost now. Tonight Carg dance. Goodbye!