Thursday, 14 November 2013

Tree trunks are not wasteful selfishness

I re-read the Dawkins essay "Gods Utility Function" recently. Dawkins offers an argument against high-level selection in it. However, the article gives a string of dodgy examples. He argues that tree trunks are wasteful:

Why are forest trees so tall? Simply to overtop rival trees. A “sensible” utility function would see to it that they were all short. They would get exactly the same amount of sunlight, with far less expenditure on thick trucks and massive supporting buttresses. But if they were all short, natural selection couldn’t help favoring a variant individual that grew a little taller. The ante having been upped, others would have to follow suit. Nothing can stop the whole game escalating until all trees are ludicrously and wastefully tall. It is ludicrous and wasteful only from the point of view of a rational economic planner thinking in terms of maximizing efficiency. But it all makes sense once you understand the true utility function-genes are maximizing their own survival.
This is wrong. Very tall tree trunks are found in the most efficient dissipating regions of the earth: rain forests. These extract far more energy from incident sunlight that the grasslands that resemble the type of ecosystem which Dawkins is describing as more efficient. Those tree trunks pay off in efficiency terms. If you have a flat surface, it heats up - and the incident energy radiates back into space. You need a lot of surface area to allow water evaporation to keep you cool. The depth produced by tall trees helps to provides such a surface.

In the essay, Dawkins also describes elephant seal sex ratios as "inefficient":

The sex ratio-the proportion of males to females-in wild populations is usually 50:50. This seems to make no economic sense in those many species in which a minority of males has an unfair monopoly of the females: the harem system. In one well-studied population of elephant seals, 4 percent of the males accounted for 88 percent of all the copulations. Never mind that God’s Utility Function in this case seems so unfair for the bachelor majority. What is worse, a cost-cutting, efficiency-minded deity would be bound to spot that the deprived 96 percent are consuming half the population’s food resources (actually more than half, because adult male elephant seals are much bigger than females). The surplus bachelors do nothing except wait for an opportunity to displace one of the lucky 4 percent of harem masters. How can the existence of these unconscionable bachelor herds possibly be justified? Any utility function that paid even a little attention to the economic efficiency of the community would dispense with the bachelors. Instead, there would be just enough males born to fertilize the females.
Unfortunately for this argument, the surplus of males helps the population weed out parasite-ridden and mutation-loaded individuals. A population with fewer males would mean males of lower quality breeding - with the quality of individuals cumulatively declining over the generations. Dawkins' economic argument about how the makes are redundant is simply mistaken. The deaths of the failed males helps the population to adapt by marking out the adjacent gene-space that represent reduced quality - helping the population flee from its parasites and decrease its mutational load.

Perhaps it is possible for trees to be too tall - and for there to be too many elephant seal males. However tall trees and numerous male elephant seals proves very little.

Of course, the basic theme of this essay - that "the true utility function of life, that which is being maximized in the natural world, is DNA survival" is hopelessly mistaken.

Dawkins' argument against multi-level selection in this essay is also incoherent.

No comments:

Post a Comment