Brains, muscles, promoters, and selection

A number of interesting evolution papers have come out recently, but I don't have time to write any proper science blog posts. Instead, here's an easy-to-write summary of what I found most intriguing.

Larger brains are not needed for social organization in animals
Based on data from carnivores (cats, dogs, bears, weasels, etc.) and fossils, Finarelli and Flynn (PNAS, May 27, 2009) conclude that no association exists between sociality and encephalization (larger brain volume/body mass ratio) across Carnivora and that support for sociality as a causal agent of encephalization increase disappears for this clade.

Those sexy muscles are bad for the immune system
Lassek and Gaulin (Evolution and Human Behavior, May 22, 2009) reports that testosterone not only leads to bigger muscles in men, but that, it also decreases the number of white blood cells, which are important for immune function. The more muscular men have more sex than weaker men, they found, but they also have worse immune systems than the slimmer ones. Since there is selection for both having lots of sex (sexual selection) and having a good immune response (viability selection), I conclude that women are not good enough at assessing male immune systems. Disappointing.

Duplication of DNA drives rapid evolution of gene expression
The promoter regions of yeast is enriched with tandem repeats, and genes whose expression is controlled by these promoters have increased rates of transcriptional divergence. Preliminary evidence suggests that it affects human evolution in a similar way. Vinces et al. (Science, May 29, 2009).

Group selection not necessary to explain lower parasite virulence
Wild, Gardner, and West (Nature, May 27, 2009) theoretically show that group selection is not needed to explain the reduced virulence of parasites, but that inclusive fitness theory suffices (i.e. selection at the level of the (parasite) organism does explain decreasing growth rates of the parasites).