Wednesday, July 18, 2007

Dawkins #2: Unfair to Elephants?

[ This post is number 2 of a series. They will be of interest mainly to those who've read Richard Dawkins' book, The Selfish Gene. I recommend they be read in order. ]

From Richard Dawkins' Extended Phenotype, pp. 254-255 [references removed]:
The many-celled body is a machine for the production of single-celled propagules. Large bodies, like elephants, are best seen as heavy plant and machinery, a temporary resource drain, invested in so as to improve later propagule production. In a sense the germ-line would 'like' to reduce capital investment in heavy machinery, reduce the number of cell divisions in the growth part of the cycle, so as to reduce the interval between recurrence of the reproduction part of the cycle. But this recurrence interval has an optimal length which is different for different ways of life. Genes that caused elephants to reproduce when too young and small would propagate themselves less efficiently than alleles tending to produce an optimal recurrence interval. The optimal recurrence interval for genes that happen to find themselves in elephant gene-pools is much longer than the optimal recurrence interval for genes in mouse gene-pools. In the elephant case, more capital investment is required to be laid down before returns on investment are sought. A protozoan largely dispenses with the growth phase of the cycle altogether, and its cell divisions are all 'reproductive' cell divisions.

The delights of reading Dawkins include frequent passages where he submits his own views to unsparing examination. Certainly it seems here that the proboscis touches on a problem of pachydermic proportions, one that if allowed to get out of control could trample his theory into the dirt.

In my previous post I noted that while Richard Dawkins usually states that genes seek to "survive", sometimes he describes their goal as being to "increase" their numbers. I also noted that in applying his theory he reverses this preference -- in his examples he usually has genes striving to increase the number of germline genes. I pointed out that "survival" and "increase" are not the same thing. They produce different mathematical models and, in real life, they will often predict different results. Where the models predict different results, it cannot be the case that genes are optimizing both for "increase" in numbers and "survival". Of the two models, at least one must be wrong.

Now why, if the goal is to increase germline gene count, does the elephant propagule produce an animal weighing several tons and almost entirely made up of gene-copies which are reproductive dead ends? Why does it keep that animal alive for decades? Why do the few DNA copies that reproduce, do so at such a leisurely pace? The gestation period of an elephant is over a year.

If we regard the "goal" of the gene as increasing its numbers, the elephant is a evolutionary failure of comic proportion, and it takes no very intelligent designer to see that a "fix" for the elephant just isn't in the cards. Yet elephants are clearly the product of a long process of natural selection. If it is the goal of germline genes to increase their population, nobody told the elephant or his ancestors.

But what if Dawkins' elephant genes are in fact even more selfish than he claims? What if an elephant germline gene just doesn't give a hoot whether there are any other copies of itself, so long as it survives? From this point of view, elephants make sense. An elephant is the way for elephant germline DNA to maximize its chances of being around a hundred, a thousand or a million years from now. It doesn't care if it's present in one copy or a billion, so long as it survives.

From a "survival" point of view, the elephant biomass expended in dead-end cells is no loss for the elephant's germline DNA. It costs an individual gene-copy in the elephant germline nothing to take over as much dead-end biomass as it finds useful for increasing its chances of survival. Neither does the germline gene-copy care how long reproduction takes. It seeks only to maximize the chances that it will still be around when they rake in all the chips.

If we make Dawkins' genes more selfish, so that every individual gene-copy is out for itself and nobody else, not even it's exact "brother" copies, elephants are no longer a paradox. Elephants no longer look like losers in comparison with Antartic krill. The krill germline gene uses fast, easy, high-risk reproduction to increase its survival chances, and the germline cells don't pause to take on a lot of extra biomass. Elephant genes are risk-averse. They seek out a slower, surer path, and they find a lot of non-germline biomass can be useful in the process. If we take the goal as "survival" and not "increase", and the "unit of selfishness" as the individual germline gene-copy, elephants are no problem to explain.

I've been following Dawkins in speaking of the "goals" of genes, what they "care" about, and what their "plans" are. This is a metaphor. Neither Dawkins or I imagine it as anything except a useful fiction to allow our intuitions to assist our brains in understanding natural selection. But metaphors and intuitions can mislead. We need to take this metaphor apart and look at the reality in more detailed and material terms. I'll do this in my next post.

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