The problem with defining our ancestors

ResearchBlogging.orgAlmost every paper on human evolution commences with an obligatory paragraph about how these particular scientists are defining the species in question.

“Today we’re calling Homo erectus outside of Africa Homo ergaster,” they’ll say and you accept that and it’s all well and good.  But then the next paper will turn around and say “Homo erectus in Africa is called H.rodesiensis, in China it’s called H. erectus.”

You begin to scratch your head, somewhat confused. And you’re not the only one. It’s gotten so bad some papers are actively refusing to state what species the specimens their examining because of the confusion associated with doing so. “Our find is called AL 288–1 and it doesn’t look like KNM-WT”

Hands up if you recognise AL 288–1

But of course, having to memorise a bunch of fossil identification numbers isn’t much better. So you cry out in frustration “how can you people not make up your minds?!?”

EvoAnth turns back to you and says “evolution.” They may also add “dumbass” depending upon what side of the bed they woke up on that morning.

Richard Dawkins, renowned evolutionary biologist, often talks about how if one had all the skulls of a rabbit and its ancestors and lined them up it would be hard to pick out when it “stops being a rabbit.” Yet if one takes a skull from each endpoint they are clearly different species.

This is the problem with human evolution. Take, for example, Homo heidelbergensis transitioning into Homo neanderthalensis. At each end are two clearly different species, with H. heidelbergensis  being taller, having a smaller brain, differently shaped teeth and jaws and taller skull with a less protruding (or prognathic, if you want to use the fancy sciency word) than H. neanderthalensis.

H. heidelbergensis (left) and H. neanderthalensis (right). Which one stole your purse?

But if you take specimens from the middle of this transition it becomes a lot harder to differentiate between them. For example, the skeletons from Atapuerca in Spain come from just before shit got neanderthal (which I propose replaces the phrase “shit got real”).

Whilst some neanderthal traits are emerging, they have always been classified as H. heidelbergensis because, well, they’re still H. heidelbergensis. But new research has found yet another neanderthal trait – their teeth.

Indeed, it would seem that most of the specimens have teeth more commonly found in H. neanderthalensis despite the fact that the rest of them still pretty much looks like H. heidelbergensis.

Which is quite a twist for a species defined by its teeth (specifically these ones).

In fact, some of them appear to have teeth more neanderthal than later neanderthals, as if the whole issue isn’t confusing enough already.

It would seem 500,000 years ago Europe was full of multiple lineages, all emerging, evolving and co-existing from/with one another. It’s evolution in action and boy does it make it hard for one to come to a consensus on what to call them.

I mean, do we call these toothy critters H. heidelbergensis or neanderthals…or something new? And if we go for something new, where do we decide they and and heidel/neanderthal begins? That’s a few dozen possiblities right there, all from a discovery that a few teeth look like somebody else’s teeth.

They don't know the horror they've unleased upon the world

For another example, take Homo habilis. It’s a loosely defined species so it’s obvious there are a few extra ones within it, but what are they?

If you take two opposite points you can get H. rudolfensis and H. gautengensis. That might not seem like much but these species seem rather close to H. helmei and H. rhodesiensis, which are in turn very similar to H. erectus.

It’s one vast chain of species that are all so similar that it’s difficult to disentangle them all and identifying where one stops and another starts is night impossible. Once again, it’s evolution and it makes life very difficult.

So next time an evolutionary anthropologist uses a strange definition of a species please have a little patience.

And the next time a creationist says there are no transitional forms, punch them. There are they make life hell.

Martinón-Torres, M., Bermúdez de Castro, J., Gómez-Robles, A., Prado-Simón, L., & Arsuaga, J. (2012). Morphological description and comparison of the dental remains from Atapuerca-Sima de los Huesos site (Spain) Journal of Human Evolution, 62 (1), 7-58 DOI: 10.1016/j.jhevol.2011.08.007
Wood, B., & Leakey, M. (2011). The Omo-Turkana Basin Fossil Hominins and Their Contribution to Our Understanding of Human Evolution in Africa Evolutionary Anthropology: Issues, News, and Reviews, 20 (6), 264-292 DOI: 10.1002/evan.20335

7 thoughts on “The problem with defining our ancestors

  1. Great post, it’s been so long since I studied paleo-anthro, it’s probably all completely changed by now. I’d argue too that the problem is not just “evolution,” but how we conceive of species, and how we conceive of their fluidity over time. Jody Hey has written at length about how our language contributes to problems with understanding what species are. Here’s a post I wrote about his book on the species problem:

    • Defining species is a sticky concept. I do like the idea that it’s a population of organism which can interbreed, but in that case neanderthals would be H. sapiens neanderthalensis (or we’d be H. neanderthalensis sapiens if you want to be controversial).

      But then, as I said, neanderthals grade into heidelbergensis so could likely reproduce too. What does that make them now? H. heidelbergensis neanthalensis sapiens? It starts to get very confusing very fast and I don’t see much of a way out of it, a point your post expands on quite well.

      I suppose one could preface something with “archaic” to cover the transition (i.e. neanderthal-like H. heidelbergensis could also be considered archaic H. neanderthalensis) but I’ve never liked the idea of including non italiced words in species names. Silly, I know, but it just doesn’t sit right.

      At any rate I’m glad you liked the post.

  2. I guess in the end everyone wants to have named something? and EvoAnth seems to be the place to name something!

    I’m kind of shocked that people argue about ‘the missing link’.. Seems like there are a whole load of links…

    • Whilst there’s likely an element of egocentricity involved – everyone wants to name a species, and if it’s our ancestor so much better – the definitions used do have to pass through a few hoops before they’re accepted. So the scientists involved do have a point, regardless of whether the ultimate cause of their naming attempt is self-promotion.

  3. I am pleased that the group of fishes I most study have, so far as I know, no fossil representatives. Is there some saying about lack of evidence simplifying life?

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