Brain size ∝ rate of evolution?

By Razib Khan | August 15, 2008 6:13 am

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.

  • Jeff

    Yeah, I’m very disappointed with evolution related news. It seems that lots of evolutionary scientists and organizations either A) don’t understand the fundamentals of evolutionary theory and the historical ideas within the field or B) just make stupid announcements to try and grab headlines and maybe justify some funding by acting like they’ve discovered something new. I mean its very clear that A) changes to environment drive evolution of populations, and that B) humans have radically changed our environment over the past 10,000 years, thus C) the expectation evolutionarily should be (and should have always been, and has always been in my mind) that the rate of change in human populations should be accelerating over the past 10,000 years as we have changed our environments. This is really evolution 101 and should not be any kind of surprise to anyone. I’m also baffled when I see scientists today asking surprised to reach conclusions that Darwin had already reached 200 years, which seems to be common in fields dealing with behavior and emotion, areas that he focused on.

  • gcochran

    Or as I said about humans, “The ultimate cause of this accelerated evolution was the set of genetic changes that led to an increased ability to innovate. Sophisticated language abilities may well have been the key. We would say that the new alleles (the product of mutation and/or genetic introgression) that led to this increase in creativity were ‘gateway mutations’, because innovations they made possible led to further evolutionary change, just as the development of the first simple insect wings eventually led to bees, butterflies, and an inordinate number of beetles.
    Every major innovation led to new selective pressures, which led to more evolutionary change. ”


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

Gene Expression

This blog is about evolution, genetics, genomics and their interstices. Please beware that comments are aggressively moderated. Uncivil or churlish comments will likely get you banned immediately, so make any contribution count!

About Razib Khan

I have degrees in biology and biochemistry, a passion for genetics, history, and philosophy, and shrimp is my favorite food. In relation to nationality I'm a American Northwesterner, in politics I'm a reactionary, and as for religion I have none (I'm an atheist). If you want to know more, see the links at


See More


RSS Razib’s Pinboard

Edifying books

Collapse bottom bar