In a very stable environment, the theory predicts that genetic variability will decrease,
No. In fact, a stable environment is only half of the problem. Stasis only comes about when there is a well-adapted population in a stable environment. So, for example, we had a very stable environment in Hawaii before it was colonized by insects and birds. But because of all the open niches, there was an explosive radiation of species unique to Hawaii before they were fully adapted, and then stasis returned. As a result, fruit flies (for example) have much more variation than is found in most other places.
with the genome coming to the content best suited to the constant environment. We’ve looked at stable environments, in cave and benthos settings. We did not find the same degree of genetic variability in the populations there as in more variable environments.
It’s called “stabilizing selection.”
However, we did not find less variability, as evolutionary theory suggests. We found more, and to a statistically significant degree.
Which would suggest that the populations are not yet fully adapted. The age of the population in that environment would be an important clue. Did you check that?
Ecological genetics of the cave beetle Neaphaenops tellkampfii (Coleoptera: Carabidae)
Volume 44, Number 1 / December, 1979
Edwin J. Turanchik, Thomas C. Kane
Department of Biological Sciences, University of Cincinnati, 45221 Cincinnati, Ohio, USA
Department of Zoology, Michigan State University, 48823 East Lansing, Michigan, USA
Genetic variability and similarity were examined in eight populations of the Kentucky cave beetle Neaphaenops tellkampfii (Coleoptera: Carabidae) using the technique of polyacrylamide gel electrophoresis. Results indicate that N. tellkampfii has high genetic variation within and high genetic similarity among local populations. These results are in sharp contrast to the patterns of low variability and similarity reported for other cave dwelling species in the same region. It is concluded that the differences in genetical population structure among cave species in the Central Kentucky Karst are related to ecological differences among the species.**
What we have here is a scientifically useful, but quite unproven, theory.
In science, nothing is actually “proven.” Science is inductive, making inferences from evidence, and the truth is always provisional on finding new information.