Question: You discover that there are actually 2 different species of Drosophila living at Picaroons brewer…

You discover that there are actually 2 different species
of Drosophila living at Picaroons brewery, but one is much more
common (possibly it is much more successful at competing for
resources). You sequence to genes in both species and use the
McDonald Kreitman test to assess the role of natural selection in
driving the patterns of DNA divergence. The first locus is glucose
phosphate isomerase (Gpi), at which you detect 16 fixed differences
(3 replacement and 8 silent changes) and 30 polymorphisms (9
replacement and 21 silent). The second locus is alchohol
dehydrogenase (Adh) at which you detect 12 fixed differences (9
replacement and 3 silent) and 24 polymorphisms (8 replacement and
16 silent). Is genetic drift or natural selection driving the
evolution of each gene?