Energetics and the evolution of human brain size.
The human brain stands out among mammals by being unusually large. The expensive-tissue hypothesis 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.
Insulin resistance as a mechanism of adaptation during human evolution.
"...The current paradigm describes an interaction between the metabolic and the immune systems resulting from their coevolution, promoted by evolutionary pressures triggered by fasting, infection and intake of different foods. The activation and regulation of these ancient mechanisms in integrated and interdependent areas defines insulin resistance as a survival strategy that is critical during fasting and in the fight against infection."
W. Ricart and J.M. Fernández-Real
Profound changes in the environment (lifestyle conditions, diet) began with the introduction of animal husbandry and agricolture. The evolutionary time scale of human genome do not permit adjustment.
The hypotesis is that the "disease of civilization" emerges from the discordance between our ancient biology and nutritional and social pattern.
Some ancestral hominin diets characteristics have been changed during Neolithic and industrial period:
* glycemic load,
* fatty acid composition,
* macronutrient composition,
* micronutrient density,
* acid-base balance,
* sodium-potassium ratio,
* fiber content.
The evolutionary collision of our ancient genome with the nutritional qualities of recently introduced foods may underlie many of the chronic diseases of Western civilization. (Am. J. Clin Nutr, 2005;81(2):341-354)
The Contribution of Psychosocial Stress to the Obesity Epidemic
An Evolutionary Approach
Obesity: lessons from evolution and the environment.
Obes Rev. 2012 May 29
Point of View:
Evolutionary endocrinology: a pending matter
The Malthusian-Darwinian dynamic and the trajectory of civilization