Thursday, October 27, 2011

More on the True Story of the evolution of the human hand

The other day, we posted our clearly rigorous explanation of the new human ancestral fossil find, originally named Australopithecus sediba but properly renamed by us Australopithecus erotimanis.  We'll not go over old ground here (and some may have been  too squeamish with our explanation anyway to have it repeated here).  Suffice it to say that one Commenter seemed unconvinced.

The issue surrounds the delicate opposable thumb-endowed hand of A. erotimanis.  How did this evolve? Now we must admit that this Commenter (who hides behind the moniker 'occamseraser') can do circles around us in terms of actual knowledge of human paleontology.  He (or she) clearly knows the fossil record bone by bone, which we unhappily must confess that we don't.

To flesh out our view, we thought making it even more convincing, we wrote a Comment of our own, a short bit of fictionalized history, that might be called "The misadventures of P'Qeeb" (since Jean Auel makes millions doing that, a point made by Holly, we felt we ought to be allowed to relay our views in that way, too).  Our tale tried to bring to life some of the on-the-ground realities of our past evolution.  We offered a rather, we think, totally convincing scenario for the evolution of the dextrous hand.  But 'occam' suggested that perhaps  A. erotimanii may have evolved their thumbs for other functions than we suggested.

We're not stupid (despite occasional appearances), and had thought of other explanations on our own, thank you very much.  A thumb could be of great advantage for hitch-hiking, but no hub-caps were found at the site, so that seemed like a rather weak hypothesis.  Perhaps the most obvious alternative to an origin by natural selection for a kind of sexual behavioral trait, is that the opposable thumb was evolved for picking one's nose.  But, convenient as that may doubtlessly be, how could that confer a fitness advantage--enabling the picker to out-reproduce those with less manicured (so to speak) nares?  Indeed, it could be argued that such behavior would actually have a negative fitness effect: who wants to do what needs to be done with someone too habituated to digital nostrillary grooming?  Would they not be put off instead?

No, we don't want to be picky in what we'll accept as an adequate evolutionary explanation. But then our correspondent 'occam' suggested that the A. erotimanii may have evolved to be able to thumb their noses at their crude Alley-Ooopish paranthropine contemporaries (see our story, in the Comments, to get at taste of what they were like, the brutes).

We wrote, calmly, to defend our own ideas, by noting that they may not have had noses to thumb!  Clearly 'occam' was wrong.  But then in a riposte he snidely just said "who nose?", a cheap pun if there ever was one, and not one we can take lying down!

So herewith is exhibit A:  the noseless Australopithecine, easily found on the web it is so obvious.  Now, if you look very hard you can see that, yes, they do have a nose---of sorts.  It might be pickable, but it certainly isn't thumb-able!  No, occam, we're sorry (not!), but your idea simply won't fly.

In case you need a reminder, here is exhibit B, a real nose (also courtesy of the web)!  This one's worth thumbing, if you see any disgusting brutes around.

Now, again, we can flesh out our argument against occam's idea in another way.  How on earth would there be an advantage for the erotimanii to have a thumb or dextrous hand so they could pick (so to speak) fights with paranthropines?  How could that have had any but negative effects on fitness.  A picking explanation might gross out the paranthropines, but thumbing noses (even if they had noses to thumb) would have provoked the paranthropines to dangerous assaults.

Think again (and, yes, seriously if that's possible) about what we're debating when it comes to Darwinian explanations:  we need to offer scenarios that are directly relevant to reproductive success. If picking one's nose, or hitchhiking, or even thumbing at wild hominids are true aspects of behavior, even if very satisfying, they are not obviously connected to reproductive success.

In thinking about this we had momentarily wondered if the dextrous hand were designed for holding broad leaves to use when blowing one's nose.  But it's not clear, given the nature of Australopithecine noses, that that would not be just an uncontrollable mess.  So we dropped such nose-related explanations.  And we suggest that occam do the same.

Compare that to our explanation, and unless one really wants some actual evidence that has sound epistemology about it, our original explanation, immediately tied to reproductive success, is the clear winner.  If one admits that there really isn't serious data on which to construct a story, well, we should acknowledge it openly.  And, indeed, keep in mind that no matter how squeamish (or puritanical) you may be, the real world of animals involves many squeamish things and there's no reason they cannot be important in Nature's cold and very un-squeamish, judgments.

The bottom line is that it is not at all easy to understand how things evolved way back when in the days before blog-posts.  Incredibly, that is true even when you have the bodies of the actual individuals who did the evolving!   Getting correct explanations, and knowing that you have them, are great challenges that even the best of science needs to take seriously.


Tian Liang said...

Professor Weiss,

The Australopithecus sediba fossils are being interpreted many different ways and I was interested to see which interpretations were the most controversial. The one you mentioned has definitely raised an eyebrow for me. Let me call your attention to another alternative interpretation of the sediba fossils.

I took a look at “The Mermaid’s Tale” on and found the concept that “life generally works on the basis of cooperation” intriguing (must read for my Thanksgiving holiday). The question is how and why cooperation between non-kin individuals of the same species evolves (and fails to evolve) in the first place. According to Hamilton’s Law, close kin individuals will cooperate with each other. However, cooperation very rarely and only narrowly happens between non-kin; rather competition becomes the dominant strategy between non-kin individuals – except in humans. Why is that?

Recently, I finished reading “Death from a Distance and the Birth of a Humane Universe” by Stony Brook University Professors Bingham and Souza. Their book states that in order for cooperation between non-kin to take place, individual conflicts of interest must be managed cost-effectively. In addition, they argue that humans’ elite throwing abilities allowed management of conflicts of interests or inexpensive law enforcement among many non-kin individuals for the first time resulting in what they call the ancestral human village. On this view, elite throwing probably originally evolved as part of a new hunting or power-scavenging strategy; but, it would quickly have had another highly adaptive effect, allowing the evolution of the greatly expanded social cooperation characteristic of humans. Cheaters or potential cheaters on a cooperative enterprise (such as hunting) could now be ostracized cost effectively for each individual cooperator allowing such cooperation to now become an adaptive strategy. Without such cost effective law enforcement, such cooperation could not evolve.

Tying back to Australopithecus sediba, I copied their interpretation of the A. sediba fossils from their book’s Facebook page:

“The new A. sediba fossils are important. Sediba hands & pelves suggest possible elite throwing-the crucial human novelty, on our theory. We await additional tests of this possibility. Sediba brains show suggestive hints of early language-like behavior. If this possibility is corroborated, our theory predicts that sediba MUST have been an elite thrower–language can only evolve in an animal who can control conflicts of interest with non-kin of their own species through cost-effective social coercion (Chapter 9).”

I would like to hear your thoughts on this theoretical view and their interpretation of A. sediba. Thank you!

Ken Weiss said...

If I share half my genetic variants with my brother, then if I cooperate in a way that costs me, say one child of my own, but I help him have at least 2 more children than he would have had without my help, then genetic variants that are responsible for my being a 'helper' can advance--it's called 'kin selection' and is what Hamilton's rule was about. You could hardly gain in this way by helping distant relatives who have only a small probability of sharing alleles with you.

That's the theory, but of course the world is more complex, local groups are made of various levels of kin, and so on. But it at least provides a theoretical basis for the idea of the evolution of self-sacrifice.

I don't know the book by Bingham and Souza but my reaction to your description would be (without reading the book!) that it goes far beyond any serious level of evidence and in that sense is pure speculation, based on some plausible ideas observed in various ways in various places.

Our 'theory' for sediba is really a hopefully entertaining way to address these kinds of speculations.

See our post from the previous day, plus the comments, and another one tomorrow. And a little while ago I think Holly had posted about these finds as well.

Basically, what constrains hypotheses? Just because they're strange or even humerous doesn't make them wrong, and just because they seem to make sense relative to what we know and see in our own time doesn't make them a correct explanation of things 3 million years ago.

Tian Liang said...

Professor Weiss,

Thank you for your response.

You are certainly right. A surprising or even counterintuitive theory can still be a good one – witness quantum mechanics, for example.
The issues for any theory are clear, logical development and evidence sufficient for strong possible falsification. By both criteria Bingham and Souza’s theory is well-developed (see,%202008.pdf for the detailed game theory and their book for extensive empirical evidence).

Your description of kin-selection is excellent; the question is why human cooperation goes so much further. In my opinion, Bingham and Souza have developed an apparently useful answer.

I look forward to reading your post tomorrow.

occamseraser said...

Death from a a special pleading theory of everything, although it's only slightly more silly than Lovejoy's rehashed, ueber alles carry-out food for sex scenario. Posthoc, ad hoc, and slipperier than a Spandrel. But it is a fun read if you don't take it too seriously. It obviously hasn't yet penetrated the field of paleoanthropology, but then again it wasn't featured in Science Mag and primetime TV either.

I relent and withdraw my hypothesis on thumbs and noses. BUT what about sexual selection for longer thumbs? The pollical equivalent of the proboscis monkey, if you will. This can be tested -- if males turn out to have REALLy long thimbs, thumbs even longer than the rest of the digits, then...well, er... I rest my case.

Ken Weiss said...

Maybe we have gone as far down this road as we can...or ought. Since Anne and I are both igoramii when it comes to the fossils, and you are obviously an expert, we'll cede the last round to you.

However, I think one can predict that tales like the Misadventures of P'Qeeb may return some time to these hallowed pages....