Food Preparation and Its Impact

It's widely recognized that the practice of cooking food significantly contributed to both the social evolution of the Homo genus and the enhancement of cognitive functions. The development of larger brains was an evolutionary trend that progressed independently of other transformations, facilitating the consumption of meat alongside a reduction in jaw size.

A 2012 study sheds light on this phenomenon, indicating that modern humans possess more neurons than many larger mammals, like orangutans and gorillas. The disparity in brain weight relative to body size suggests that our brain's development didn't follow a proportional growth pattern, which is a defining characteristic of our species and correlates with notable cognitive advancement. But does a larger brain equate to superior cognitive abilities?

Not necessarily. It is suggested that the balance between body and brain size is crucial among primates. Environmental factors favored individuals with either larger brains or larger bodies, as it's metabolically challenging to sustain both. We see this dichotomy in large herbivores, known as Megafauna, versus more slender species with larger cranial capacities.

Furthermore, possessing a larger brain entails increased energy demands. The brain is the third highest consumer of energy in the body, following the liver and muscles, despite comprising only about 2% of overall body mass. It accounts for approximately 20% of total energy expenditure, even at rest, while in primates, this figure averages around 9%.

This creates constraints for humans, necessitating a consistent and substantial energy supply, which is influenced by the availability of food and resources, as well as the efficiency of intake and digestion. Simply put, individuals who spent considerable time searching for low-calorie food had brain sizes comparable to larger apes. In contrast, those like H. erectus, who utilized cooking techniques, displayed larger brain volumes.

Cooking enhances the caloric value of food compared to its raw counterparts, thereby decreasing the time required for food gathering. In summary:

• Shorter search times allowed Homo individuals to socialize and enhance cognitive skills.
• Reduced search efforts favored the selection of individuals with larger, energetically demanding brains as part of this “evolutionary trade-off” (large brain + metabolic cost).

Ecological and Adaptive Factors

As previously mentioned, various environmental factors have driven the selection of individuals with larger brains, adapting to different habitats, such as savannahs, and social circumstances, including intergroup competition and cooperation. A 2018 study investigates why human brains are so large. Essentially, a mix of ecological and social elements has favored individuals with enhanced brain sizes.

It’s vital to keep in mind the significant energy requirements of the brain. The larger the brain, the greater its energy consumption, consistently proportional to its size. But what are the benefits and drawbacks of such a trait? The primary hypotheses focus on improved cognitive capacities, which would enable individuals to navigate complex ecological challenges and, to a lesser extent, socio-cultural issues.

Research has examined the correlation between various hominin species and cranial sizes, but establishing the causes and consequences of larger brains remains complex. One can objectively assess the metabolic costs associated with brain size concerning age, the increase in brain tissue, and other developmental factors. This analysis reveals four potential ecological-social scenarios:

• Individuals adapting to environmental challenges.
• Individuals collaborating with others to address environmental demands.
• Individual and group competitiveness in socio-cultural contexts.

In summary, larger brains facilitate tackling various challenges and emerged as a result of ecological and environmental shifts (60%), with 10% attributed to intergroup competition and 30% to cooperation.

Genetic Factors Influencing Brain Size

The enlargement of the brain is believed to be linked to three genes that emerged in our genome many millennia ago, resulting from repeated duplications of a gene responsible for neuronal progenitor stem cell development. Two studies published in PNAS indicate that these three genes are responsible for the remarkable growth of the human brain. One of these genes appeared approximately 3–4 million years ago, while the other two emerged later. Over time, these genes have played a significant role in brain development, tripling its size.

These three genes, identified as NOTCH2NL A, NOTCH2NL B, and NOTCH2NL C, belong to a conserved gene group known as “Notch,” which has been vital in embryonic development for hundreds of millions of years. They are located on chromosome 1, an area associated with genetic disorders linked to variations in brain size, such as macrocephaly and autism, and microcephaly and schizophrenia when there are genetic duplications or deletions.

These genes resulted from “copying errors” of the NOTCH2 gene, which is involved in stem cell differentiation, leading to three episodes of partial duplication and unsuccessful attempts at cellular repair. Generally, stem cells can regenerate into two neurons; however, in the cerebral cortex, the NOTCH2NL genes seem to favor the generation of additional stem cells, resulting in the production of more neurons.