Comparitive Frontal Lobe Size

In 1997, Katerina Semendeferi and her colleagues published their study on comparative frontal lobe sizes in the Journal of Human Evolution. The subjects whose frontal lobe sizes were determined were ten humans, six chimpanzees, three bonobos, two gorillas, four orangutans, four gibbons, and five monkeys. The number of primates exceeded the sample numbers of all previous studies of primate neuroanatomy (Gazzaniga 19).
There was not much surprise felt by the smug Homo sapiens when the results showed that their frontal lobe volumes were the largest in the group. However, it was previously supposed that the proportional size in humans would also exceed expectations, which it did not. In fact, the frontal lobe, compared to the rest of the brain, was quite similar amongst all of the test subjects (Gazzaniga 19).
The factual conclusion of what Semendeferi’s study found was that the human frontal lobe is the size that would be predicted for a brain that size among primates. Since the frontal lobe is significant to language and thought, the researchers offered a few explanations for these higher functions. The first is that the region could have been reorganized with selective cortical area enlargement. Another option is the development of increased intra and interconnectedness of neural circuits in brain sectors. There is the also the possibility for the modification of local circuitry within subsectors of the frontal lobe. Finally, subsectors could have been added or dropped as deemed most beneficial. Upon hearing these results, Todd Preuss noted that it is important to differentiate between the frontal and the prefrontal cortex (the prefrontal is further towards the front and has an extra later of neurons). He suggests that there might be a percentage difference between these two sectors, allowing the more sophisticated prefrontal cortex to comprise more of the area. Semendeferi confirms the potential in this hypothesis by mentioning that area 10, which is in the prefrontal cortex, is close to two times larger in humans than in apes (Gazzaniga 20).
At first, the results of Semendeferi’s study turn the world of common opinion on its head. When many are discovering things, such as higher intelligence and mental capabilities, which point towards the uniqueness of humanity, it is unsettling to hear that there is nothing great about the area of the human brain so involved in higher functioning. Preuss’ explanation and the final suggestion of the researchers make a lot of sense from an evolutionary standpoint – an organism minimizing or even eliminating less beneficial parts in order to maximize space available for new advantageous areas. It also maintains a closer link with apes. It is for that same reason that the lack of difference becomes a bit disconcerting. The uniqueness of Homo sapiens is in danger, if the ability for higher functioning could be realized in other apes as their prefrontal and frontal cortexes became more efficient. If the natural course of evolution produces apes with advanced language, memory, and moral abilities, it will be more difficult to classify humanity as distinct. It is more comforting to presume that the conditions which led to the development of those abilities are unique to Homo sapiens, and the possibility for them to present themselves to another species is past. Essentially, what is most adaptive for humanity is advanced intelligence, but even the “perfect” orangutan would never develop a sophisticated theory of mind. This then begs the question of what would determine that humans should be the lucky ones; which enforces the uniqueness. Yet who is to say that the intelligence developed in Homo sapiens is superior to the songs of whales? However, uniqueness has never required superiority.

Gazzaniga, Michael S. Human: The Science Behind What Makes Us Unique. New York: Harper Collins, 2008. pp. 19-20.

Preuss, T.M. (2001). The dsicovery of cerebral diversity: An unwelcome scientific revolution. In Falk, D., and Gibson, K. (eds.), Evolutionary Anatomy of the Primate Cerebral Cortex (pp. 138-64). Cambridge: Cambridge University Press.

Semendeferi, K., et al. (1997). The evolution of the frontal lobes: A volumetric analysis based on three-dimensional reconstructions of magnetic resonance scans of human and ape brains. Journal of Human Evolution 32: 375-88.

Semendeferi, K., et al. (2001). Prefrontal cortex in humans and apes: A comparitive study of area 10. American Journal of Physical Anthropology 114: 224-41.