Brain Size and the Diversification of Body Size in Birds:
Large brains are associated with increased cognitive skills, enabling animals to use new environments and resources more successfully. Such behavioral flexibility is theoretically expected to have macroevolutionary consequences. First, populations of big-brained individuals should more easily become established in new locations, increasing opportunities for allopatric speciation and decreasing chances that the species as a whole becomes extinct. Second, the ability to use new resources should place new selection pressures on populations, promoting adaptive diversification, a process termed "behavioral drive." In this article, we show that the average brain size of a bird family explains a significant fraction...of the rate at which body size diversifies within the family. The association is independent of the number of species in the family, geographic range, and correlates of speciosity, providing the first general support for the importance of behavioral drive in evolution.
Here is what ScienceDaily has:
However, is it possible that biological diversification not only depends on the properties of the environment an ancestral species finds itself in, but also on the features of the species itself? Now a study supports this possibility, suggesting that possessing a large brain might have facilitated the evolutionary diversification of some avian lineages.
My first thought on reading this paragraph was "no shit." The idea that evolution is driven purely exogenous environmental parameters seems to be very common, and probably facilitated by the very term natural selection. But animals are part of nature too, our parasites are part of nature, etc. Selection happens, and there is intraspecific and interspecific competition as well as the fitness implications of environmental pressures. Last year when the story about accelerated human evolution broke I pointed out that the authors were focusing on one parameter, the population size, and how it impacted the number of positively selected new mutations. But for human beings population size is not the only parameter of note, the fact that our cultures rapidly change and reshape the environment likely matters a great deal. A few years ago Bruce Lahn was mocked by some for suggesting that humans were on the verge of speciating before modern transportation increased the rate of gene flow. But the data from birds above suggests that Lahn's logic was probably not faulty. We're a big-brained beast which is always changing the selection parameters because of the protean nature of our culture.
