The Paradox:the Human Brain

[Armat]

This thread is inspired from our discussion in food section about Vegi etc.I think this is a wonderful subject to dive in deeper.

 

 

The paradox: Where does the energy for the large human brain come from?

 

In any event, as we have seen, what begs explanation is that humans "spend" far more energy on the brain than other primates: 20-25% of RMR vs. roughly 8% in the great apes. Yet the total human RMR remains in line with predictions based purely on body size. This presents a paradox: where do humans get the extra energy to "spend" on our large brains? As we will see later in the research of Aiello and Wheeler, the most feasible hypothesis is that the answer lies in considerations of dietary efficiency and quality. Leonard and Robertson [1994, p. 83] conclude:

 

These results imply that changes in diet quality during hominid evolution were linked with the evolution of brain size. The shift to a more calorically dense diet was probably needed in order to substantially increase the amount of metabolic energy being used by the hominid brain. Thus, while nutritional factors alone are not sufficient to explain the evolution of our large brains, it seems clear that certain dietary changes were necessary for substantial brain evolution to take place.

 

In other words, while the evolutionary causes of the enlarging human brain themselves are thought to have been due to factors that go beyond diet alone (increasing social organization being prime among the proposed factors usually cited), a diet of sufficient quality would nevertheless have been an important prerequisite. That is, diet would have been an important hurdle--or limiting factor--to surmount in providing the necessary physiological basis for brain enlargement to occur within the context of whatever those other primary selective pressures might have been.

 

To summarize:

 

The significance of Leonard and Robertson's research [1992, 1994] lies in their analysis of energy metabolism, which reveals the paradox: How do humans meet the dramatically higher energy needs of our brains, without a corresponding increase in RMR (which is related to our body size)? They argue that the factor that allows us to overcome the paradox is our higher-quality diet compared to other primates. Of course, prior to the advent of agriculture and the availability of grains, the primary source of such increased dietary quality was the consumption of fauna--animal foods, including insects.