Brain Size: Another Evolutionary Assumption Shot in the Head

Brain size can’t be used as an independent measure of fitness, five evolutionary anthropologists contend.

How long have evolutionists told us that our relative brain size gave us the fitness edge as we evolved from apes?  That assumption has been called into question by Jeroen B. Smaers and four European colleagues in a new paper in PNAS (Smaers et al., “Comparative analyses of evolutionary rates reveal different pathways to encephalization in bats, carnivorans, and primates,” PNAS October 15, 2012, doi: 10.1073/pnas.1212181109).

First, Smaers & friends pointed out the long history of the assumption.  A summary of the paper on Science Daily says,

Dr Jeroen Smaers (UCL Anthropology and UCL Genetics, Evolution & Environment), lead author of the study said: “When using brain size relative to body size as a measure of intelligence, the assumption has always been that this measure is primarily driven by changes in brain size. It now appears that the relationship between changes in brain and body size in animals is more complex than has long been assumed.

“Changes in body size often occur independently of changes in brain size and vice versa. Moreover, the nature of these independent changes in brain and body size, are different in different groups of animals.”

Brain size and body size interact in evolution, they claim, and interact differently in bats, carnivores, and primates.  It’s incorrect to assume, therefore, that natural selection is simply trying to increase neuronal capacity when brain size increases relative to body size.  It’s possible, as with some species of bats, that evolution favored some species with smaller bodies to improve maneuverability, while leaving brain size intact.  More often than not, they inferred, nature seemed to be selecting for body size, not brain size.That’s why Science Daily used the headline from the UCL press release, “Evolution mostly driven by brawn, not brains.”  No, it’s not a return to “might makes right.”  It’s an acknowledgement that evolutionists have been misinterpreting the evidence.

The problem is deeper, though, and many touch on many other evolutionary assumptions.  “Considering that one-way tradeoff mechanisms are unlikely to provide satisfactory evolutionary explanations,” they wrote, “we introduce an analytical framework that describes and quantifies all possible evolutionary scenarios between two traits.”

Because of the disconnect they inferred in animal body/brain dynamics, they concluded that “Our approach allows a more detailed interpretation of correlated trait evolution and variation in the underlying evolutionary pathways.”  Focusing on one trait to the exclusion of others “confounds the effects” and thereby risks “hiding important aspects that may contribute to explaining animal diversity.”

Being evolutionists, they would never conclude that animal bodies and brains are intelligently tailored for their lifestyle needs, no matter how clear the adaptive evidence.  Instead, their take-home lesson is “that relative brain size can not be used unequivocally as evidence of selection for intelligence.”

Someone should tally up the debunked evolutionary assumptions we have uncovered in these pages.  A quick search on “evolutionary assumption” got 63 hits; there are undoubtedly more.

Project: Write up a description of evolutionary theory, one phrase per line.  Then link a scientific finding (like this one) that debunks the assumptions behind each statement.  Will there be anything left?