Re: Evolving altitude aptitude

Hey Brandon,

Yep, I’d say that both articles present very good examples of adaptation, not of Darwinian evolution, since in both cases, there was no change in the basic organism—the frogs were still frogs, and the people were still people.  Both the frogs and the humans adapted to their environment by using genetic information already present in a portion of the population.  In both studies, the assumption is that there was a mutation at some point, yet we already know that most mutations are harmful or, at best, almost neutral (or barely harmful).  In neither article is there proof that a mutation actually occurred—it is assumed to have occurred because the scientists were working from an evolutionary perspective.  What is known is that information in DNA allowed the frog and human populations to adapt to their environments—that information kicked in when needed in order for the population to adapt.  

The Berkeley article talked about gene variation frequency of a section of DNA called EPAS1.  Scientists compared the frequency of EPAS1 in the Tibetans and in other Chinese populations, and found that the Tibetans had the highest frequency.  Note that some non-Tibetans also had this gene, although at a much lower frequency—why would this be the case if the gene were a mutation among the Tibetans?  I suppose one might say that the mutation occurred in one or two individuals before humans migrated to Tibet, but then, why would such a mutation spread to the general population when there would be no need to select for it?  If none of the earliest Tibetans had the proper variant of the EPAS1 gene which allowed them to adapt to their environment, they would have had to deal with the altitude sickness that most others experience—why would they have continued to live in such a hostile environment for the ‘hundred or so generations” it took for them to adapt?  The more likely scenario is that the proper variant was already in place (though not necessarily active, because not needed) in a good number of Chinese, and those early Tibetan settlers that had it adapted and fared better.  Over time, as the Tibetans reproduced among themselves, the frequency of the trait increased, while it stayed low elsewhere.

He explained that the faster moving toads even reproduced more quickly. But this could point to a chink in their biological armour.
"They have to be trading something off to do that," he said. "And one of the things we suspect is that they're trading off their immune systems."

It was interesting to note that the researchers expected the ‘good’ mutation leading to faster movement would be accompanied by something negative (suspected lower immunity).  This goes along with what I’ve said before—that most mutations are negative, and when ‘good’ mutations are selected/activated, they will be accompanied by ‘bad’ ones, as selection is by phenotype and not genotype—one cannot select for ‘good’ traits only.  In truth, neither individual organisms nor nature actively selects anything.  Individuals live or die based on individual ability to adapt and on other environmental factors (war, sickness, natural disasters,  getting eaten by another animal, etc.), but they can’t choose which traits to pass on to the next generation.  Individuals with good traits could get eaten or die of sickness before producing offspring, while individuals with maladaptive traits might produce offspring before dying—either way, having a certain trait doesn’t guarantee that it will be passed on.

Susan