Speculations on the subject of alcohol dehydrogenase and its properties in Drosophila and other flies.

The alcohol dehydrogenases (ADH) and their genes (Adh) of Drosophila have been much studied by population and evolutionary biologists. I attempt to put some of these studies into a broad adaptionist perspective, suggesting the co-evolution of this enzyme with the fleshy fruits of angiosperms and fermenting yeasts. I suggest that these events occurred at about the K/T boundary (65 million years ago) and that the typical Drosophila (as exemplified by D. melanogaster) evolved from flies unable to use fermenting substrates as breeding sites. I also hint that the ADH enzymes of other flies (e.g., the tephritid fruit flies) may have evolved independently of those of Drosophila, but from a common ancestral gene.