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Thursday, April 20, 2006

Darwinian Speciation

The Hardy-Weinberg definition of evolution, part of the modern synthesis of evolutionary biology and genetics, is a change in gene frequency over time. There are 4 forces which produce this evolution: natural selection, drift, mutation, and migration. Forces of nature, such as a particular genotype, weed out different genes through natural selection.

A population has a trait expressed by two alleles, R and T. Let's say a disease strikes the population and more strongly affects individuals with the T allele. Because of this, 100% of RR individuals survive to reproduce, 65% of RT individuals survive to reproduce, and 25% of TT individuals survive to reproduce. Over multiple generations, there is a high probability that the T allele will be lost from the population, meaning all the population would be RR. So the entire population evolves by shifting to a particular trait, but is still the same species. This is convergent evolution.

On the contrary, rare occurances such as genetic drift, mutation, or migration, could cause divergent evolution. So lets say 1 in 50,000 alleles mutates. Now let's say 1 in 10 (a liberal estimate) is actually a positive mutation. This new allele is W. So in an individual or two we see RW. Now, for divergent evolution to occur, this W must be able to defend against natural forces and have a higher survival rate than the RR gene. Over a LONG time, this W allele takes over, just like the R allele did. This same process happens in the majority of the genes of a species population and now, the idea is, it is a whole new species.

Final questions:
Is it really a new species, or just an extreme case of the same species? At what point would we claim it as a completely new species? There appears to be no defendable place. This cuts at the heart of Darwin's ideas, for he said that everyone knows what a species is but we can't really define it, almost as if we recognize the species in as much as it participates in the form of the species. But I digress.

My point is that evolution, however unlikely, is pretty awesome, if it works. There are too many "ifs" and random chances for it to mesh with the world around us. Basically, evolution is chaos in an ordered world. The idea of an ordered universe descended from chaos through chaos doesn't make much sense. So it appears that either there is something ordering evolution or the theory is not true. I maintain that through the seeming chaos, God directs the "undirected" causes of evolution (drift, mutation, migration). [Insert Aquinas' fifth way to prove the existence of God] Through the same unnoticable direction by which God hold the universe in existence, He also unnoticibly directs the forces of evolution.

Basically, I hold to the most evolutionist side of the intelligent design camp.


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