Larger brain size not governed by shrinking gut

Doctoral student Ana Navarrete from the University of Zurich, Switzerland, who led the research, studied hundreds of carcasses from zoos and museums, the journal Nature reports.

"The data set contains a hundred species, from the stag to the shrew," explains Navarrete, according to a university statement.

The scientists then compared the brain size with the fat-free body mass.
Study co-author Karin Isler stresses: "It is extremely important to take an animal's adipose (fat) deposits into consideration as, in some species, these constitute up to half of the body mass in autumn."

But even compared with fat-free body mass, the size of the brain does not correlate negatively with the mass of other organs.

Nevertheless, the storage of fat plays a key role in brain size evolution. The researchers discovered another rather surprising correlation: the more fat an animal species can store, the smaller its brain.

Although adipose tissue itself does not use much energy, fat animals need a lot of energy to carry extra weight, especially when climbing or running. This energy is then lacking for potential brain expansion.

The rapid increase in brain size and the associated increase in energy intake began about two million years ago in the genus Homo.