Your points are well taken. Any modeling of early hominid behavior based on extant species is loaded with pitfalls. As you say, their social and ecological context is different, and, of course, they’ve been doing their own evolving for (at least) 4 million years.

However, chimps and bonobos are our best behavioral models for early hominids and are often used as such. Also, although this spear-using behavior is obviously highly ecologically influenced, if we accept it as a genuinely cultural behavior, then there is no reason that we should view it as entirely ecologically determined, just as we don’t take human cultural behaviors to be simple products of environment.

In any case, I wasn’t suggesting that this behavior was literally contiguous through time with ancestral populations, more that it speaks to the ingenuity and capacity for innovation in hominoid intelligence and the contexts in which we might have been experimenting for some time.

However, I do think there are two really interesting aspects of this:

First – it appears to be a rather detailed sequence of actions to build the tool. This is more impressive than the tool behavior that we’ve seen before, but nowhere near as cool as New Caledonian Crows [1].

Second – the fact that it’s only been seen in a very small subset of the population suggests that it’s a recently invented cultural behavior. We’ve seen this happen before in food washing behavior in Japanese Macaques [2] and a few others.

–Simon

[1] http://language.psy.auckland.ac.nz/crows/
[2] http://news.nationalgeographic.com/news/2004/02/0206_040206_tvmacaques.html

For example, which chimps are using them doesn’t pan out entirely to all of hominid evolution. Sub-populations of chimps have completely different mannerisms and behaviors from others, so there’s no consistency to say this happened in subsequent hominids… but I won’t rule out the case that hominids that hunted together and cooperated could have been selected for.

That said, I agree this is an interesting study for the matters you laid out but I think it’s plagued with looking for a adaptation in a related species, which is wrong.