Brains and guts were not in competition

Humans have large brains and small digestive tracts, relatively speaking.  One theory holds that these two energetically expensive organs are inversely related.  That is, in order for brain size to increase, gut size must decrease.  However, Ana Navarrete, Carel van Schaik and Karin Isler from the University of Zurich have found that this is not the case. 

The researchers compared the organ sizes of 100 different mammalian species, including 23 primates.  The amount of adipose tissue (body fat) was calculated separately.  When fat-free body mass alone was considered, there was no correlation, inverse or otherwise, between brain size and digestive tract size.  In fact, there was no correlation between brain size and any other organ sizes either.  Interestingly, there was a correlation between fat storage and brain size.  Animals with larger amounts of adipose tissue had smaller brains.

The authors postulate that storing fat and accumulating brain power are two methods of combating starvation.  Bears evolved to take advantage of one strategy, and humans the other.  


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