Monday, May 19, 2014

Evolution

Recently, Rex F. May posted an article entitled. Wading and Dancing with Darwin in which he references Nicholas Wade's book A Troublesome Inheritance: Genes, Race and Human History. I thought he was making too much out of Wade's book and I said so in a comment.

I think you may be taking Wade's thesis too far. The last thirty-odd years of evolutionary biology have shown that the majority of evolutionary change is not adaptational. Most of what happens at the genome level is, in fact, not adaptive but is, at best, neutral. Wade does demonstrate that current science indicates there are measurable genetic difference in populations that can be called "race". What he does not do is demonstrate how this matters at the individual level where natural selection actually happens. Ultimately I think the genetic evidence renders evolution fundamentally anti-collectivist. Groups -- whether called race or religion or whatever, are just a survival tool for the individuals that make them up, not a useful classification tool.

BTW, I found, "You have to have all of Darwin or none of him." in juxtaposition with a quote from Vox Day to be amusing. I assume you do know he rejects all but the wimpiest version of biological evolution. He invokes Darwin when it is convenient but leaves the dance with Ken Ham.

Mr. May replied with Darwin: All or None and seems to be asking for some clarification. I'll try.

This confuses me a bit, and I'd be glad if parabarbarian would elaborate. I may be punching above my weight here, but my concept is that when mutations occur, the adaptive ones tend to spread through the population, while the maladaptive ones tend to die out. And neutral ones may or may not spread, randomly. And I do think the math would indicate that only a tiny percentage are adaptive, but I don't have an instinct for the relative percentages of maladaptive and neutral. I'd think the vast majority would be maladaptive, but someone needs to enlighten me about that.

Naural selection was, arguably, Darwin's greatest contribution to the then nascent theory of evolution. He described a mechanism by which variations in the phenotype between individual organisms can be filtered. In modern terms it means that if an allele increases an organism's probability of producing offspring, the frequency of that allele in the population will increase. Similarly, if an allele decreases the probability of offspring the frequency will decrease. However, I think it is important to recognize that it only works if there is sufficient genetic diversity in the population -- It can only select for what exists. Also keep in mind that natural selection is "blind" to the source of a trait and operates on the individual holistically. Heritable and non-heritable traits alike are filtered for "fitness". A difference can confer a reproductive advantage regardless of whether it is cultural, genetic or a result of an outside force like charity or welfare.

I am not aware of any good studies of how often mutations in humans are beneficial. The perception that most mutations are harmful may simply be an artifact -- we notice a harmful one more precisely because it is harmful. However, studies done with the fruit fly suggest that, if a mutation changes the protein produced by a gene (not all mutations do), about 70 percent of those mutations will have damaging effects with the remainder being either neutral or beneficial. Since natural selection minimizes the spread of detrimental mutations in the population, their impact is minor. Evolution by natural selection is driven by the beneficial changes.

Also, while it's valid to say that evolution takes place at the individual level, but not at group level, nevertheless I think it's fair to say that there is an emergent evolution at the group level, made up of the sum total of individual evolutions. Taking the popular idea that harsh winters in Europe caused individuals to become more cooperative and capable of gratification-deferral in order to survive, this resulted in groups of that sort, with such an ethic, and the culture that developed tended to intensify selection on the individual level for those characteristics.

Over the years I've encountered many different definitions of evolution and I am not sure what definition Mr. May is using here. I said that natural selection happens to the individual but I don't equate the process (natural selection) with the result (evolution).

There is a simple and relatively uncontroversial definition that evolution is the change in a population's allele frequencies over time. This is distinct from the theory of evolution which is a continuously developing attempt to explain how evolution works.

In that sense, evolution can be measured at the level of the group. If two groups that share a common ancestor vary by P number of alleles and I have a good guess about the rate of mutation then I can conclude they diverged Q generations ago. That may be an interesting number for classification but it does not tell me much of anything useful about the individuals within those groups. For example, just knowing a person's group is French Canadian, Ashkenazi Jew or Cajun doesn't tell me if he or she carries the mutation for Tay-Sachs disease. The probability of an individual being a carrier in those three populations is higher than normal but it is only a probability.

Discosure: I am not a geneticist nor am I a biologist. I'm just a dumb 'ol engineer who reads too much. Make of that what you will. I have not finished Wade's new book and it may well be he answers all my questions by the final chapter.

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