This Week's Citation Classic

Ayala F J, Powell J R, Tracey M L, Mourao C A & Perez-Salas S. Enzyme variability in the Drosophila willistoni group. IV. Genic variation in natural populations of Drosophila willistoni. Genetics 70:113-39, 1972.

Francisco Ayala is an amazing scientist; his work includes more than 950 articles and 30 books. He has been President and Chairman of the Board of the American Association for the Advancement of Science, President of the Society for the Study of Evolution, a National Medal of Science winner and much more. He recieved his doctorate under the guidance of Theodosius Dobzhansky in 1964.

None of his work has received more citations (888 at last count) than the present article.

Ayala et al. took advantage of the newly discovered technology of gel electrophoresis. Lewontin and Hubby used gel electrophoresis to demonstrate the existence of high levels of genetic variation back in Drosopila pseudoobscura in 1966.

Ayala et al. took this a step further. Lewontin and Hubby used essentially lab strains (33 of 43 strains were reared in lab for 5+ years) . A criticism of Lewontin and Hubby was "Yeah, well you see lots of variation, but these strains have been in the lab for a long time. Maybe genetic changes are taking place in the lab and maybe there is less variation in the "wild" because of the effects of natural selection". To counter these arguments, Ayala et al. used strains much more recently caught from the wild.

Ayala writes, "It was, therefore, essential to collect wild flies and, indeed, most of the results concern wild flies. Collecting D. willistoni flies is, however, a pleasant task since the species lives in the forest of the American tropics. Several collecting trips to the Amazon basin and other regions of the American tropics were done."

Ayala et al. conclude that, "There is a great deal of variation —on the average, 58% of the loci are polymorphic and an individual fly is heterozygous at 18.4% of the loci."

Despite the variation, the pattern of allele frequencies was remarkably similar throughout the several million square mile area occupied by the species. This suggests the variation is maintained by balancing selection rather than being selectively neutral.

However, one of the interesting observations was that the D. willistoni did not form a single large panmixic population. There were found chromosomal polymorphisms that were very different from each other. This suggests that genetic mixing is rare among sub-populations and admits the possibility of speciation.

Not bad for an ex-priest! Yes, Francisco Ayala is a former priest of the Dominican order. An interview with Ayala can be found in the New York Times. Here he comments on religion and science, "Most mainstream theologians, and most people who have read the bible thoughtfully, realize that the Bible it is not an elementary book of biology, or an elementary book of cosmology or of physics. It amounts to blasphemy to try to understand the world of physics and biology by reading the Bible. That was not the purpose of the Bible....It is a travesty to interpret the Bible that way."

Another good article can be found here.