What I've Learned About Human Origins

We have learned a few things about the human lineage since 1946, but much remains obscure.

Last Thursday, September 18, marked Babel’s Dawn’s second anniversary. I’m taking note of the date by posting a couple of pieces about what I have learned from the experience of maintaining this blog. Last week I described what I have learned about language (here). This week I’m reporting what I have learned about human origins.

One thing is for sure. There are lots of rival opinions about what makes humans different from the rest of the animal world. Bipedalism gets more votes than you might expect an anatomical peculiarity to muster. Tool-use racks up hefty support as well, despite the fact that plenty of other animals use tools at least a little bit. Language gets some votes, but more typical seems to be explanations for what makes language different from other forms of communication. Recursive thinking, symbolic thinking, and metaphorical thinking lead that secondary list. Some attention has also been paid to the species-wide presence of moral codes and a moral sensibility.

There is an understandable tendency to focus on differences we admire rather than those that seem trivial or disreputable. Our limited body hair once drew some attention (see: Desmond Morris, The Naked Ape) but the argument does not appear to have attracted many disciples. The absence of sexual seasons has drawn some notice too, but surprisingly little in a supposedly anti-puritan world. Religious, or mythological thinking, seems very prominent in human society, absent in all other life forms, and yet it too seems to be downplayed these days and called a mistake. Another human peculiarity is our physical weakness. Chimpanzees and gorillas are much stronger than people, dangerously so, but most discussions prefer to focus on our big brains.

This blog pays special attention to the rise of joint attention and the shift to multilevels of selection (I and us). So there is plenty of room for quarreling, but it might be more productive to take all these points seriously and notice that in the past five million years a really different animal has been taking shape. We have passed through a series of one-way gates that led to a species that is unprecedented in its adaptive capacities. By one-way, I mean there is no turning back. Evolution usually leaves open the door for a retreat. Thus, the beaks of the finches on the Galapagos Islands can change quickly in response to environmental shifts. A fat beak can evolve into a thin beak, and devolve to fat again. No such devolution is possible once a gateway has been fully passed.

Gate 1: Bipedalism. Bipedalism gets a lot of credit for setting us on the road to tool use by freeing our hands, but the path seems pretty loose since the new tool use came tens of thousands of generations after the rise of bipedalism. The lasting thing the switch to upright walking did was get us out of the trees. Even groups that live in the Congo and Amazonian forests live there as ground animals. When our heads moved directly above our bodies, the bipedal gate closed behind us. We were on the ground to stay. There is abundant speculation about why we became upright walkers, most of it quite unimaginative. Personally, I like the idea that upright primates in brush country (the woodlands that replaced forests) could use their bodies as levers, pulling up bushes to get at the roots. But it does not really matter for this blog since any connection between bipedalism and language is quite indirect. What does matter is that the lineage had passed through a gate that closed off the arboreal evolutionary paths that are typically available to primates.

Gate 2: Hairlessness. The date for our loss of body hair is controversial, but I like the 3.3 million year date based on body lice DNA. (See: Lousy Timelines) Apparently we cannot go back to being hairy because of the sweat glands that we have developed on our back and front. Thus, for example, modern Inuit peoples of the Arctic have not become unusually hairy, despite the cold, and Ice Age humans and Neanderthals do not appear to have become especially hairy either. Robin Dunbar's book Grooming, Gossip, and the Evolution of Language makes the case that the loss of hair led to the loss of grooming and language took its place. Many have countered by pointing out that you don't need something as complex as language for a social bonding substiture. Babbling and the bonding it brings, which eventually leads to speech, however, could indeed date to this loss of hair.

Gate 3: Multilevel Selection.  So many human peculiarities depend on a trusting co-operation that group-level selection must have become important early. I lean toward 3 million years and the start of Homo, when the brain began to grow and stone-tool use appeared. Multilevel selection is probably a recurring, short-term phenomenon in many lineages; group-level adaptations are required for it to become irreversible. With our group-oriented emotions—shame, guilt, hatred, and love—our use of language, and our moral sense, we cannot go back to single level selection (gene-based competition). Instead we have been moving the other way, becoming more and more dependent on a variety of groups for our survival.

Gate 4: Brain/Tool Dependence. One of the truly peculiar features of human fossil history is the rapid expansion of the Homo brain. Primate brains are relatively big to begin with, and ape brains are big for primates, so we started off with a generous heaping of brain matter. About 3 million years ago our lineage’s brain began growing and has now quadrupled in size. The growth of the brain marks a serious evolutionary commitment because it takes so much energy to sustain the brain’s operation. Was there a quadrupling of caloric intake during that period, or have there been trade-offs? I suspect the latter. If we gave up some muscle strength to support the brain, and transferred muscle work to tool work we could, perhaps, get the brain growth without requiring a commensurate increase in calories. Of course, this solution makes us permanently dependent on technology. Thanks to our oversized brains we cannot cease to be a tool-dependent species.

Those four gates had surely been passed by the time of Homo erectus, two million years ago. The last of the non-Homo, bipedal primates were disappearing into extinction. Erectus spread over many different niches, demonstrating a remarkable ability to adapt to different climates, diets, and terrains. I would be astonished to learn they could do all that without a protolanguage. After that the lineage adapted to a world of speech. The first three gateways above are unusual, but all are adaptations to the physical environment. The fourth gateway, brain/tool dependence, appears to combine adaptation to the natural environment and the artificial one of tools. The gateways that followed then adapted us to life in a cultural environment by moving the lineage beyond a protolanguage.

Gate 5: True Language. After Derik Bickerton’s presentation in Barcelona (see: Words Are More Human than Syntax), a linguist in private conversation raised the question of the protolanguage/true language distinction. Bickerton had originally introduced the protolanguage concept to refer to an early form of language without recursion, but if he was now rejecting the idea that languages are recursive, where did that leave protolanguage? I don’t know Bickerton’s answer, but on this blog “true language” refers to language that is capable of putting a predicate into a context. Protolanguage might say, “I sail.” True language gives that statement some context, “Some years ago—never mind how long precisely—having little or no money in my purse, and nothing particular to interest me on shore, I thought I would sail about a little and see the watery part of the world.” True language probably came after H. erectus, making it less than a million years old.

Gate 6: Metaphor. Metaphors have many uses, but the one that is unparalleled is its ability to put subjective experiences into an imaginary context. I can say, “I’m thinking,” which is protolanguage, but “I’m wrestling with an idea,” gives a sense of what that thinking is like. I remember an African girl writing, “When I hear the word ‘freedom’ my mind spreads wide like a river.’” There is no non-metaphorical way to express that experience. Speakers with metaphors know one another as people with internal lives; speakers without metaphors may not recognize that commonality. I have put this gateway after true language, but that order is not certain. Metaphors are possible in protolanguage and may have come first. Or perhaps they came as part of the next gateway.

Gateway 7: Mystery Symbols. Symbolic and logical thought are older than the Homo lineage and symbol manipulation can be taught to chimpanzees, bonobos, etc, but mystery symbols are something else, because they represent things you cannot point to, count, or feel. A sentence like, “He was married in the Catholic Church,” is syntactically uninteresting, but the verb refers to a mystery action beyond the discovery of the best trained ape and (I’m guessing) probably beyond the discovery of the smartest erectus. The sentence's indirect object “the Catholic Church,” is another mystery symbol, a collection of people who understand themselves to be members of a group distributed in both space and time. Again, apes cannot understand themselves to be members of such a mystery collective. People, however, will struggle to become married or unmarried and will quarrel over membership and the nature of the Catholic Church.  Although there has been an enormous amount of inquiry into the philosophy of symbols, mystery symbols seem to me to be grossly understudied. It’s a topic worthy of its own blog, but I’m going to skip all that and just say that you cannot have Homo sapiens society—even one of 125 thousand years ago—without them. As for Neanderthals, I’m not so sure. At best, they may have gotten only partially through this gateway. Perhaps they could identify nouns (i.e., themselves) with a mystery symbol but did not have verbs for creating such identities. In other words, they could adorn themselves with things that showed them to be members of this or that group (we have archaeological evidence of that ability), but had no speech acts for creating identities.

Once our lineage had passed this gateway, we were humans of the type we know today and there was no going back. The achievements of the past hundred thousand years seem quite solid. We know the earth and its uses; we can farm and herd; we can write and build information tools, and yet all that could be lost through time’s marauding. Even so, the survivors would have passed the seven gateways listed above. Extinction is possible; going back through those gates is not.

Comments

[Gordon Worley]

I find your argument about gateways that can't be passed back through highly suspicious. It's tempting to think that an adaptation is so useful that it can't be evolved away, but really I think a better metaphor here is that of momentum. For example, symmetry in organisms evolved early on, so in order to remove symmetry requires either developing symmetrically and then activating additional genes to skew the symmetry (cf. the flounder) or following a path of successive adaptations that peals away the functions of various genes to eventually remove symmetric body development. Symmetry is an adaptation that has so much momentum, though, that to the best of my knowledge the latter has not happened, and if it has was likely near the point that symmetry was introduced.

As for your gateways, I'm not sure I would consider any of these particularly high momentum. Full bipedalism is a complex adaptation made up of many smaller adaptations, hence it would be harder to evolve out of but still possible (cf. dinosaurs, where this transition happened a couple times). Similarly, hairiness could be evolved again, given the right conditions and enough time, where sweating was less useful than a fur coat. As for the others, evolving out of them might require an event which would cause extinction first, but it would still be theoretically possible. So other than the first two I agree with you in spirit, if not in the details.

[María]

After 1 y 2, there is a third anatomical change. Human beings and only human beings (at least amongst the species alive nowadays) possess the ‘white of the eye’. (Cf. Kobayashi & Koshima, 2001)
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BLOGGER: Yes, that's a notable feature of humans, but that is the kind of change that could easily be reversed if need be.

[JoseAngel]

Well, the whole notion of "reverting" through these evolutionary doors is a kind of counterfactual imagining, which may have some heuristic interest, but it is more in the line of evolutionary studies to explain actual historical facts, rather than hypothetical or improbable ones. Therefore, I prefer to take the post's multiangled explanation on what makes us human (there must be more things besides) and say that I won't leave any of them out, though I might list them from top to bottom. Humanity has somewhat fuzzy limits, but the ability to use language, along with having a human shape, seem to head the list. Keep them all, though, because leaving one of them out would change all the others to a greater or lesser extent.