Evolution: Puzzled by the Puzzlement

[jducoeur]

So the big science news I've been stumbling across repeatedly for the past week is the new evidence that indicates that homo habilus and homo erectus co-existed for half a million years. Gasp, shock, says the news: does this mean that erectus didn't evolve from habilus?

What?

Okay, am I missing something, or are these science writers *seriously* missing the point here? Unless you take the most ridiculously extreme view of evolution, an X-Men-ish view that a new species will not only inevitably but quickly supplant the old one, it's entirely reasonable that a successor species will co-exist with its progenitors for quite some time. Indeed, it would seem to me to be a perfectly normal state of affairs unless at least one of the following pertains:

• there is an environmental shift that greatly benefits one species over the other;


• the two species are inherently in deep competition with one another;


• the resources available to both species aren't sufficient to support both.

Sure, these factors do tend to come into play eventually, but why is everyone so sure that it's immediate? It doesn't seem any more obvious to me that there must be only one species of genus homo at a time than that there would be only one species of bird at a time.

If the species aren't in direct competition for scarce resources, the effects of evolution are going to be strictly statistical, and I don't see any reason why that would be quick. The better-adapted species will *eventually* outproduce the less-adapted one, sure. But if there's enough space and resources for both, it just doesn't strike me as surprising that that could take a very long time. Am I missing something here?

Comments

[rufinia.livejournal.com]

Yup. You're using that whole logic thing.

[osewalrus.livejournal.com]

Most folks have this rather ridiculous view of the time frames for evolution. This is summed up by the question (usually asked mockingly) If humans evolved from monkeys, why are there any monkeys left?

I think what actual scientists are impressed with is the length of time (500,000 years). Species differentiation and the disappearance of the "parent" species is not a well understood phenomenom. The length of time here runs counter to previous estimates.

[dlevey.livejournal.com]

It is indeed the 500,000 year overlap. That's a long time when you consider that Homo Sapien Sapiens is thought to have existed for 10,000 years or less. It's this same sort of thing which finally led physical anthropologists to the idea that Neanderthal and Cro Magnon may not have been ancestor/descendant but cousins of some form.

[quantumkitty.livejournal.com]

People don't realize evolution is tree-like, not linear.

[fairdice.livejournal.com]

If two species are in direct competition — that is, if they're competing for the same resources, or colloquially, if they're trying to inhabit the same ecological niche — then the conventional wisdom is that it really doesn't take long for one to out-compete the other. I mean, how well you reproduce is the base of your exponential growth equation. If my species out-performs yours by 1%, then in only 100 generations I'll have e ≈ 2.7 times as many descendants; in 1000 generations there are 20,000 of me for every one of you.

So if you see two species geographically intermingled, and then see it again half a million years later, the natural conclusion is that they are not indirect competition, that they are somehow differentiated from one another (to the extent that the thing limiting each of their population sizes is not the other's).

So if you had held the view "H. habilis held a certain ecological niche, and H. erectus was the result of habilis evolving over time to become better suited to that niche" — not at all an implausible view of how one species changes over time — this news is good reason to reconsider.

I think that's what's going on, however hard it is to make that out from the media coverage.

[dervishspin.livejournal.com]

I think the astonishment comes from a limitation of our culture, not a limitation of our understanding of science.
Logically, yes, of course you are correct.
But our (meaning in this case the media's) cultural understanding of "man's place in the universe" tells us that we are the top of the pyramid, the end of the food chain, the supreme acheivement of either God or Evolution. In the part of our heads where our understanding of our cultural ego lies there is no room for sharing the top spot. Co-existance of a similar and competitive species does not compute. Even though we can look around and see for ourselves there is co-existance of competitive species for whales and cows and antelopes and sharks and chickens and...and...and...