Who you are

This is second in my current series about human origins, which began with Who you aren’t. Now I’m talking mainly about our own genus, Homo, regarding a kind of diversity which outweighs the ordinary use of the word by a solid quantum.

I realized I’ll have to save some historical taxonomic hysteria about humans/apes for some later posting; please picture me twitching with suppressed fury.

Let’s start this one with the big difference between alpha taxonomy vs. systematic revision. The first is what you call creatures or their remains when you first collect them from somewhere, which is also what drawer you first stick them into in a museum collection. It’s explicitly provisional. The second is what you call them given a lot of work on organizing the phylogeny they’re part of, and after reviewing any and all names they could be called and have been called, and it leads to reorganizing and re-labeling a lot of museum drawers. A revision is serious science and usually entails intense debate. It’s certainly harder regarding paleontological remains, which is understandable, and particularly fraught regarding humans, because the naming is shot through and through with constructing heartfelt narratives. The latter situation led to a lot of resistance and tradition in preserving the alpha taxonomy for fossil humans and their relatives, and things are still a bit rattly. (To esteemed colleagues: so you’re just gonna have to put up with some choices I made about whom to call what.)

Technical term #1: mosaic evolution, which is to say that across a bunch of closely related species, you can see different parts undergoing independent evolutionary change. In a complex group like this one, a later species can end up with lots of changes that did not evolve at the same time or in tandem in any other way. Crudely, we stood up first, our heads got big later; also crudely, Paranthropus went “jaw” and Homo (eventually) went “brain.” See also my replies in the comments for My favorite human.

Bottom three (l to r): Australopithecus (note cranial similarity to chimp [c], Paranthropus, Homo (the sizes are not equal contrary to the graphic)

But rather than dive into that, try this basic point: don’t use Homo sapiens as the “search image” for who was or wasn’t “truly” human, or “fully” bipedal, or “truly/fully” any other thing. This group of creatures messed with lots of variables and we happen to have one particular profile of changed and unchanged versions.

Now I’m refining the focus to the early known forms we put into Homo, however dubiously, and with however much uncertainty about how many species are represented. The most familiar name is Homo habilis, with not a whole lot of visible difference from Australopithecus except for – as I see it too – an interesting bulbous aspect to the cranium, although not much size change. But the coolest one, available in tons of finds all over Africa, is H. ergaster, to the right, or if you insist, African H. erectus, whose postcranial skeleton is strikingly similar to ours – nice long gams and all the details of bipedalism to use’em with. Some researchers doubt that Australopithecus was a “true” biped (I think they split some unnecessary hairs there), but H. ergaster nails it that our genus stood up long, long before we got our freakishly huge cranium.

For a long time, during the celebrity personality-dominated era of physical anthropology, there were considered to be three non-sapiens species of Homo: H. habilis, H. erectus, and H. neanderthalensis, making a too-neat and usually not well-depicted “climb up from bestiality” which has characterized narratives of human evolution throughout its history. Partly through cladistic thinking, it’s been completely dismantled. Some of you may recall the first phase in which much hair was torn regarding “single-origin” vs. “multiregional” stories (well, people said “hypotheses,” but …), itself riddled with complications regarding new technologies like DNA sequencing and new systematic techniques. That’s been dismantled too. It turns out we didn’t have too little fossil evidence for nifty species of Homo to work with; we had too much, and when younger biologists got into the collections, they realized that no real revision had ever taken place.

At present there are at least six well-supported named species of fossil species of Homo, and their history is at least now divided into solid-evidence units vs. open questions.

I am endlessly fascinated by the nuances of reconstruction: cover hair distribution, vibrissae hair prominence (e.g. eyebrows), breasts, penis size, small iris (of the eye) … no one knows to what extent these appeared among the relevant species or in which order or combinations. Another post someday for sure!

Here’s technical term #2, and this is a big one: cladogenesis.

Every non-biologist I know thinks speciation works like anagenesis, on the left: a species is replaced by its own descendants, going extinct in the process. However, if this ever happens in the real world, it’s extremely rare. Cladogenesis is the observed default: a species splits with its older form persisting and some subset, usually a small group in an isolated situation, is the new species. The appearance of the new form doesn’t include the disappearance of the prior one. Therefore we talk about ancestral vs. derived traits, but since the 1980s, we are, or should be, no longer so hung up about who was whose ancestral species.

Just as the three genera I discussed first do not present a “Y replaces X, then Z replaces Y” history, neither do the various species within Z, relative to one another.

Crucially and related, we regard extinction as a completely different phenomenon which has nothing to do with some new “superior” form coming along. When you apply cladistic thinking to human species history, it instantly junks all talk of who replaced or outdid whom, or of each new species being “better” at being human. Forget all that crap about the “march to humanity.”

Now for the more recent species in Homo.

There’s the technical term #3 for the post: relict. By definition, all relictual species are funny-looking compared to their living relatives. In many mammal groups today, you can see the effects of both background and mass extinction, the latter sustained by all large land mammals during the Pleistocene, not just us. Furthermore, our persistence is most likely due to our broad, populous distribution rather than any particular toughness of form or character or intellect. The result: we’re a very typical relict, a single species which is rather funny-looking compared to its living relatives, due to its closest relatives being absent and therefore invisible.

Whereas the observing eye and mind, of course, interprets this as saltation, a rapid “jump” in evolutionary change. Saltation does occur and is a cool thing to discuss, but here it’s an illusion. Unfortunately, it’s an illusion which feeds our need to see something special and even heroic. Nearly all accounts of human evolution include this heroic element, even using terms like “achievement” and “unique” … despite relictual mammals being all over the place and in many cases much funnier-looking, relative to their living relatives, than we are. You don’t see people blithering similarly about elephants, (i) whose difference from their living relatives is profound and (ii) whose social and cognitive lives are clearly sophisticated. No one lauds their distinctiveness as an unusual evolutionary event; it’s immediately explainable upon examining the wide array of diverse related fossil species, some of which show different “variables profiles” and many of which are more ordinary-mammal looking. Sound familiar?

In particular, nothing suggests that speech, cognition, and culture had anything to do with our persistence, and although the debate rages, just how much of those things were the norm for humans until surprisingly recently, is still under debate. Is there more to say about this? You bet! The next post in this series concerns the history, dispersal, and diversity of our own species.

Next: A world of debate in a strand of hair

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7 thoughts on “Who you are

  1. “nothing suggests that speech, cognition, and culture had anything to do with our persistence”

    So I have this really neat Language System with a larynx, a brain, ears, and things.

    How did it get there?

    Big Skull > Big Brain w. lots of folds > Language System [emergent from BB w. folds] , huge social groups including non-Kin

    selective pressures for a big brain to deal with environmental demands and big kin groups > big skull for bigger brain > Language System (or pieces of it coming into play and then “snapping” into a functional relationship

    Big kin groups > selective pressure for a brain to deal with that > bigger and bigger skull

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    • Crikey, that was all over the place. Let me narrativize that:

      About 70k years ago, a hominid that was reduced to a small population made its way out of Southern Africa. Some think that a language & communication capacity (like the one I am using right now to compose this message) was the necessary condition for this to happen. Atran and Heinrich (2010), at Atran (2013) hold that some change happened in a relatively short time just before that outbreak. A physical chassis had to be in place for that to happen, presumably. Is there any sense of the evolutionary history in which big skulls, big brains, a larynx and other vocal organs, came together to make that change (mutation? adaptation?) even possible?

      Scott Atran & Joseph Henrich (2010). The Evolution of Religion: How Cognitive By-Products, Adaptive Learning Heuristics, Ritual Displays, and Group Competition Generate Deep Commitments to Prosocial Religions. Biological Theory 5 (1):18-30.

      Scott Atran (2013). 2013 : What Should We Be Worried About?https://edge.org/response-detail/23673

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      • Not to be obstructive, but this topic doesn’t have much to do with my post. I’m not questioning anything about human cognition and culture – we obviously have them – my only point was that we see no evidence that these features were a “species survival” variable, as we score high in ordinary/general variables that favor a species during mass extinctions.

        I don’t have any beefs with a by-product type hypothesis regarding human religiosity. However, note that all selection-based change is technically about by-products; there is no such thing as “selection for.”

        More importantly, much of the analysis that you’re referencing is far too committed to a hero-story. At least two or three other species of Homo dispersed far and wide, some with comparatively unimpressive cultural features; there’s no reason to associate one of our particular cognitive/social tricks with that phenomenon.

        I also think the perceived conundrums about human thinking and its evolution are shot through and through with exceptionalism. To try to overcome that, the immediate and necessary distinctions to make are:
        – density of neocortical neurons vs. thickness of that brain region’s layers (the latter is crudely “size”)
        – sophistication of social communication vs. syntactical speech
        – communication vs. representation
        – modeling vs. abstraction

        Finally, I find it absurd – even laughable – to associate strongly the cognitive/verbal details, what I like to call “I can say square root of two!” – with sophisticated socializing, religious inclinations, verbal communication including speech, and morality.

        But all of this needs to be reserved for the upcoming post which focuses on our own species.

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        • Sorry to have derailed things. I should have just dialled the question to a simple body structure evolution question. I am still curious as to when parts of the language system I am using — my big brain, my vocal apparatus — were acquired by my ancestors and whether any of the vanished hominid near relations had anything like them.

          Is that a little closer to the “who I am” and “who I am not” theme?

          There are physical capabilities that enable me to do the things that I consider essentially human. But I am a relict. There might have been other, similar beings, who had some of the same physique and may or may not have been doing some of those things. Meaning that those activities are not uniquely human.

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  2. Rebooting Erik’s conversation here … I hadn’t responded because your final reply in the above thread answered your own question, or so it seemed to me. But then I realized I hadn’t acknowledged it or phrased it fully technically.

    Point 1, mosaic: yes, the substantial numbers of species in Homo could have featured any number of the things we call “human” independently of one another, in any combination. One might have had boobs but didn’t speak; one might have spoken but featured full-body cover hair. (Side point: people forget that all ape body hair is sparse compared to most mammals, and that they all lack underfur.) Nor are our versions of these things the “ultimate” kind, necessarily – the living nonhuman apes and living human apes don’t automatically represent endpoints of variation for anything.

    Remember, we don’t know the order of these variables’ appearance across our genus, nor in what combinations. Working out the fossil phylogeny of birds was a BIG deal (see this and this too), because it showed how many things we mistakenly thought of as “for flight” were no such things. Some biologists call this sort of thing “pre-adaptation” but I think that’s the most anti-intellectual nonsense I ever heard.

    Point 2, relict: yes, looking at us on our lonesome creates a false perceived gestalt, which in turn implies evolutionary saltation, and an “it all came together” narrative. Not to mention the silly idea that the other species were rough drafts. I mean, good ol’ Paranthropus was on this planet for a damn long time – compared to that, the complex of H. heidelbergensis, H. neanderthalensis, and H. sapiens is by no means “successful” as yet.

    Is it any surprise that from the mid-90s onward, as the current understanding exploded the mystique of the bipedal posture, negated the clinal three-species model, and called into question the coevolution of tools-hand-brain-speech, that the term “human” is more and more being shunted into ineffables like “self-awareness” and “true morality?” That poor old representative cogntion – a fine and real thing – is being pressed yet again into service as representing “consciousness,” which is nothing more than the soul with its serial numbers scraped off?

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