http://www.nature.com/nature/journal/v480/n7375/full/nature10629.html

Energetics and the evolution of human brain size

Ana Navarrete
Carel P. van Schaik
Karin Isler

Journal name: Nature
Volume: 480
Pages: 91–93
Date published: 01 December 2011
DOI: 10.1038/nature10629

Abstract:

The human brain stands out among mammals by being unusually large. The
expensive-tissue hypothesis1 explains its evolution by proposing a trade-off
between the size of the brain and that of the digestive tract, which is
smaller than expected for a primate of our body size. Although this
hypothesis is widely accepted, empirical support so far has been equivocal.
Here we test it in a sample of 100 mammalian species, including 23 primates,
by analysing brain size and organ mass data. We found that, controlling for
fat-free body mass, brain size is not negatively correlated with the mass of
the digestive tract or any other expensive organ, thus refuting the
expensive-tissue hypothesis. Nonetheless, consistent with the existence of
energy trade-offs with brain size, we find that the size of brains and
adipose depots are negatively correlated in mammals, indicating that
encephalization and fat storage are compensatory strategies to buffer
against starvation. However, these two strategies can be combined if fat
storage does not unduly hamper locomotor efficiency. We propose that human
encephalization was made possible by a combination of stabilization of
energy inputs and a redirection of energy from locomotion, growth and
reproduction.

-Mikko