Tuesday, December 09, 2008

Natural Selection does not explain Evolution

I have been reading Dr Dawkins' book "The God Delusion". In chapter 4 he reiterates a statement I have heard time and again that is simply not true. The statement is that natural selection removes the improbability of apparent design from biological structures (that means us :-). This is not true. Before you warm up your flamethrowers, please hear me out.

First let me say that I am not saying that the theory of evolution is wrong. Nor am I likely to go on about how evolution is "only" a theory. Most of science is a theory because it is very difficult to prove something true.

Still, I feel that there is a fundamental misunderstanding of the process of natural selection. You see natural selection does not result in speciation. What's speciation? Speciation is the process or processes that result in a new species. Though it is widely accepted that natural selection play a role in speciation, its role is to remove the cruft from the work table. I know of noone who suggests that natural selection causes new trait to come into being. Rather natural selection is the tendency over time to select traights that are beneficial (assuming they are genetic in origin). So, given a black moth and a white moth of the same species, natural selection causes the black moths to become a large percentage of the overall population because toxins introduced into the moth's environment kill lichens that had previously hidden the white moths. Still natural selection did not cause the black mutation. You see natural selection can only work on traits that exist.

Another interesting thing about natural selection is that it works very quickly. I am speaking in terms of evolutionary time scales here. Say four or five generations is enough for a species to become predominantly of one trait. This time will vary depending on the animal, but even if it where 500 years, that is a minor amount of time on an evolutionary scale (millions and billions of years). If fact the combination of natural selection and genetic drift, obviously play a predominant role in the shaping of species on the planet. I make this statement because they act so quickly and are always exerting their influence. So what does that say for evolution?

Lets say that evolution introduces change at a rate of 1 change per year (I suspect this is high, but lets go with it). Lets say that on average 50-100 changes are necessary to create a new species. A new species is defined as enough genetic difference to make sharing genetic material impractical. Lets assume a one year gestation period on average (I suspect this is a little high, but we are talking in generalities here). What does that mean? It means that we are creating new species at a rate of approximately one every 50 years. The number of species in the world is declining at the same time at a rate of about 1 every 5 years. This means that we should expect to see the number of species in the world in decline. Most biologist accept that the number of species in the world is currently declining. But evolution predicts that the number of species in the world should be increasing.

Wait, if you think I just proved that evolution does not work, you need to wait. There is another shoe. The numbers I was throwing around there where general averages. They were probably not right even at that. Most biologist today believe that something happens every so often that results in many new species. Then the number of species declines over time, until again something happens. There is little consensus about that something. My point in spelling all this out was to show that though natural selection explains a portion of evolutionary theory, it is also an issue for other portions of the theory. Rarely in science is anything a slam dunk. One must be careful of ones statements. I agree with Dr Dawkins regarding the beauty of natural selection, but it is selection, not creation. Until we have a better idea of how speciation works, there is little reason to get excited. On the other hand, this stumbling point is no reason to toss evolution out with its own bath water.

It needs work, but that is what science is all about.