There was a special meeting here at Penn State this weekend. It was a gathering to honor the distinguished, perhaps nearly legendary, Masatoshi Nei on his recent 80th birthday. Nei's work has been on molecular evolutionary genetics as it applies in particular to the evolution of DNA sequence. A rather incredible array of distinguished people, including Prof. Nei's many distinguished former students, and other distinguished population geneticists were in attendance.
Many interesting papers were given, but in particular we wanted to mention some work presented by Michael Lynch. He has been stressing the role of chance (drift) in the assembly of genomes by evolutionary processes. In particular, he has shown that much of our genome has not been the result of strong, highly focused natural selection as is the widespread mythology about evolution. Instead, or in addition to natural selection, many variants that are not the most 'fit' in their time, can still advance even to fixation, replacing other variants at their respective locus. This can happen, for example, if their fitness 'deficit' is quite small relative to the most fit variant in the population.
Mike Lynch's talk here concerned the way in which the mutation rate was molded in the ancestry of species living today. The main idea is that if mutations, or mutation rates, are only slightly deleterious, then selection is rather powerless to mold them. Much that happens again depends on drift. There are regular relationships between mutational rates, the amount of genetic variation, and genome and population sizes (the latter affects the power of drift--chance--in determining what survives or raises in frequency and what doesn't). If you're interested in this, his book ("The Origins of Genome Architecture") and a recent paper in Trends in Genetics (2010) are very much worth reading.
The point of mentioning this here on Mermaid's Tale is that the idea that fine-tuning by natural selection is the, or even the major, factor in evolution is exaggerated, as we've often said. Every species here today is the result of a 4-billion-year successful ancestry, so we're all 'adapted' to what we do (if not, we're headed for extinction). Selection removes what really doesn't work. But evolution is very slow generally and the evidence strongly suggests that there are many ways to be successful enough, and that is good enough to proliferate. While there are many instances of what appear to be finely selected, exotically specialized adaptations (and Darwin wrote about many of them!), that is not the whole story (and perhaps not the main story?) of evolution.