CogBlog

Evolutionary psychologists raise an interesting point. Across the globe, species are endowed with just enough ‘brainpower’ as is necessary for them to survive successfully, and little more. Brains take up an excessive amount of energy to keep fuels, and especially in humans, this overwhelming excess of intelligence, and intelligence that far surpasses that level that would have been necessary for our ancestors to survive all those years ago, seems improbable at best, and down right impossible at worst. It is very unlikely that something as efficient as natural selection would have caused the human brain to expand to such monstrous proportions when we could have very easily survived at mush less cost to us with a much smaller brain. If natural selection is thus eliminated from the realm of possibilities, it only makes sense that sexual selection is responsible for our massive brains. In many species, female mate selection has caused various traits that would appear to be good indicators of health and reproductive success to spread like wild fire in future generations, like the male peacock’s tail. It is cumbersome in flight and on foot, and is a distinct disadvantage for survival when it comes to predators. However, this disadvantage is balanced out by its potential for reproductive success. It really didn’t matter if you avoided death by predator if you couldn’t attract a mate to pass on your genes.
I agree with two of the previous posts. I feel like both the passed on genotype from father to daughter, as well as the arms race theory could potentially be the cause of the ‘unecessary’ size of the female brain instead of an acute sexual dimorphism. Men and women do not evolve in isolation; rather, each sex is constantly adapting to the other. For whatever reason, it was beneficial from the female brain to evolve right along with the male brain.

Over just the past two million years, the hominin brain has expanded three fold. Some experts accredit this unprecedented development to runaway sexual selection, a trait that accumulates in the gene pool simply because it is preferred in potential mates. However, our ancestors were actively pursuing mates throughout all evolutionary history and I therefore think that there are other important factors that merit consideration. Australopithecus prospered for several million years with a small brain comparable to that of an ape (approximately 450 cc). If a large brain is purely the product of competition for mates, why didn’t it develop earlier (say, for Australopithecus, who were obviously reproducing)? It wasn’t until the homo lineage that brain size really began to increase significantly. Foley implicates three factors in the expansion of the hominin brain: 1) life history parameters; 2) ecological parameters; and 3) social factors. I believe the most critical factor to be the shift in social dynamics experienced by the homo ancestry. A notable characteristic of H. erectus was the presence of larger, more cooperative tribal groups. One advantage of group living is that individuals are able to share burdens. But, for the group to be successful and maintain cohesion, the burdens must be equally distributed across all group members. Advantages will therefore accrue to group members who have the capacity to feel guilty when they allow others to take on the bulk of responsibility or fail to “pay back” another who performed a favor (maintain reciprocity). An advantage may also go to the individual who can avoid the work, focus his/her energies elsewhere, and effectively lie about it. Both of these emotional responses (guilt, deceit) are only possible with a larger brain. In McLean’s triune model of the brain, these emotions emerge from the third, newest layer- the neomammilian brain. The neomammilian brain is composed of the neocortex which allows animals to process and construct an ever-increasing number of finely distinguished emotional responses. When the hominin brain evolved, it not only got bigger, but also reorganized itself to suit adaptive needs. Eighty percent of today’s human brain consists of neocortex. During development, the prefrontal cortex made remarkable gains as well. The location of growth is important here, as it is indicative of what needs propelled the growth. The prefrontal cortex is responsible for higher order executive mental functions such as abstract and moralistic reasoning as well as planning and coordinating complex behaviors. The growth of the hominin brain, especially in these areas, was indubitably conducive to cooperative group living. Individuals with the capacity for these refined emotional responses were probably more successful group members, and consequently, more successful mates. Because both males and females lived in these groups, they were both subject to the pressures that necessitated brain growth and adapted accordingly.

There is no doubt that larger brains are sexually selected, but this does not necessarily mean that men use their intellectual intelligence to court females. Rather, having a larger brain provides an advantage for a male in that it enables him to think of many other ways in which to court a female. Have you ever noticed how the more sensitive men who are better able to relate to women are those who ultimately succeed in relationships? This may be because the mental capacity for such men to understand women enables them to court females by demonstrating their acute understanding of the female mind.

A larger female brain may well be a side effect of male competition to win females. Because genes are passed from generation from generation, it is entirely possible that the mere reason females evolved with bigger brains as well is because these brains were evolutionarily selected for males; in turn, fathers passed down the "big brain gene" to their female offspring.

I think that as males brains grew in size and as the consequences of that growth became appparent, such as language, it would be beneficial for the female to be able to communicate with the male. This is kind of like the arms race with the newt and the snake. So, as the male brain's largeness was sexually selected it would be beneficial if the woman's brain grew in size too. The consequence would be that the socail courtship changed from just show of brawn to a more sophisticated courtship.

I agree that big brains may well have been sexually selected. In a tribal setting, sheer brawn was initially all that a man needed to earn a female's affection, but this changed as larger brains evolved over thousands of years. With the larger brains, men were able to use reason, language, and abstract concepts to woo a mate, leaving those who relied solely on their strength at a reproductive disadvantage. As women chose to mate with those men with larger brains over those without, the trait was passed on.

A large brain is not, however, a sex-linked trait, so a female child could inherit the genotype and resulting phenotype from her father. As the larger brain was passed on this way, nature may have selected it and allowed it to continue to evolve. Just like it helped males pass on their genes, the more advanced thinking that it allowed females to perform would have supplied an important survival advantage, thus staying for future generations and evolving into the brain we have today.

Thousands of years ago it is very probable that big brains were sexually selected. This accounts for why our early ancestors had much smaller brains than those that we have today. Our larger brains allow us to carry out complex mental processes and they are the reason that we are the most intellectually advanced life forms on the planet today.
I think that human courtship in the past has not necessarily needed to be intellectually driven. It is an innate behavior that we engage in instinctually more than anything else. It is something that we see animals engaging in as well. Today, however, our culture and society have become more advanced and demanding, and our mate selection process more selective, making it necessary for us to become more savvy and strategic in the ways that we try to attract potential mates, therefore making modern human courtship an intellectual enterprise. Gone are the days when pure brute strength and status were enough to attract females. Modern day females look for much more in their potential mates.

If our female ancestors selected big brains in males thousands of years ago, there is no sexual dimorphism today in brain size because the male big brain genes were transferred to their offspring, both male and female, while the smaller-brained males were not being selected to reproduce with the females. Therefore at least half of the gene pool was more often than not contributing big-brained genes. The smaller-brained males died out, and as the larger-brained males passed their genes on to their daughters, the entire species' brains grew, bringing us to where we are today.