Friday, September 25, 2015

What Darwin Got Wrong

Not So Natural Selection
Richard C. Lewontin

The modern skeletal formulation of evolution by natural selection consists of three principles that provide a purely mechanical basis for evolutionary change, stripped of its metaphorical elements:

(1) The principle of variation: among individuals in a population there is variation in form, physiology, and behavior.

(2) The principle of heredity: offspring resemble their parents more than they resemble unrelated individuals.

(3) The principle of differential reproduction: in a given environment, some forms are more likely to survive and produce more offspring than other forms.

Evolutionary change is then the mechanical consequence of variation in heritable differences between individuals whenever those differences are accompanied by differences in survival and reproduction. The evolution that can occur is limited by the available genetic variation, so in order to explain long-term continued evolution of quite new forms we must also add a fourth principle:

(4) The principle of mutation: new heritable variation is constantly occurring.

The trouble with this outline is that it does not explain the actual forms of life that have evolved. There is an immense amount of biology that is missing. It says nothing about why organisms with the evolved characteristic were more likely to survive or reproduce than those with the original one. Why, when vertebrates evolved wings, did they have to give up their front legs to do it? After all, insects can have two pairs of wings and six legs, so there cannot be any deep general biological constraint on development. Why don’t birds that live in trees make a living by eating the leaves as countless forms of insects do instead of spending so much of their energy looking for seeds or worms? 

It is by no means an anomaly that one of the authors of What Darwin Got Wrong comes to the subject from cognitive studies and linguistics. We have evolutionary schemes for history, psychology, culture, economics, political structures, and languages. The result has been that the telling of a plausible evolutionary story without any possibility of critical and empirical verification has become an accepted mode of intellectual work even in natural science.

The other source of anxiety and anger is that the argument made by Fodor and Piattelli-Palmarini strikes at the way in which evolutionary biologists provide adaptive natural historical explanations for a vast array of phenomena, as well as the use by a wider scholarly community of the metaphor of natural selection to provide theories of history, social structure, human psychological phenomena, and culture. If you make a living by inventing scenarios of how natural selection produced, say, xenophobia and racism or the love of music, you will not take kindly to the book.

Even biologists who have made fundamental contributions to our understanding of what the actual genetic changes are in the evolution of species cannot resist the temptation to defend evolution against its know-nothing enemies by appealing to the fact that biologists are always able to provide plausible scenarios for evolution by natural selection. But plausibility is not science. True and sufficient explanations of particular examples of evolution are extremely hard to arrive at because we do not have world enough and time.

1 comment:

  1. Refreshing candor about a king with no clothes.