November 09, 2011

To survive: be fat or be smart

The bottom line is that it makes sense for an animal to combine the "fat" and "smart" strategies to survive. It makes sense: a very fat but very dumb animal has all the energy reserves it will ever need, but at the expense of locomotion efficiency, avoidance of predators, etc. A very smart but very lean animal has all the brain power needed to survive, but has very little "in the tank" if it finds itself in a bad spot and has to go without food for a long time.

The versatile strategy is best, and humans are the one species that seems to have gone the "brain power" way, without sacrificing completely other traits needed for survival.

Nature (2011) doi:10.1038/nature10629

Energetics and the evolution of human brain size

Ana Navarrete et al.

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.

Link

4 comments:

john said...

"...we find that the size of brains and adipose depots are negatively correlated in mammals."

But is this true among only primates? Humans are comparatively overly fat and undermuscled, as noted in a similar paper on encephalization (sorry don't have the link on hand).

Pascvaks said...

"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."

Ahhhhh... While water and food are, after O2 and temperature (aka Clinate), keys to "life", one does not 'take the cake' over the others (so to speak) in the matter of intelligence. One could argue just as well that climate determines water and food availability and, therefore, is the driving force of the energy trade offs with brain size. The need to compensate for change forces change?

Pascvaks said...

A question on a somewhat related item, Oetzi the Iceman. Dienekes, are you aware of any information regarding analysis of the stomach and intestenial contents, as well as, the teeth and lower jaw (late molars, wear, jaw density/strength)? This would be most interesting in regard to anatomical changes since Oetzi due to diet changes (hard food then vs soft food now), as well as flora and fauna changes in the digestive track that may have occured due to the many diet changes in Europeans since Oetzi's day.

Pascvaks said...

FYI Diet and Teeth -
"On The Evolution of Human Jaws and Teeth: A Review"; from srce.hr, Y Emes, B Aybar… - Bull Int Assoc Paleodont. Volume, 2011 - hrcak.srce.hr

http://hrcak.srce.hr/file/103618

PS: It naturally follows that the softer the food the smaller the jaw. Change the diet, change the man.