Thursday, November 29, 2007

A Zombie’s Inquiry Into the Evolution of his Most Favorite Meal II

In my last post I listed some important factors in the evolution of the human brain, or better imagined what a zombie evolutionary biologist, named George, might dig up when investigating the evolutionary path of his Dinner Nr. 1. As Terrence Deacon (1997) puts it, there is no escaping the fact that human brains are unusually large. There are several factors why humans could develop large brains, but what is still at stake is the question why they actually did, and how they came into a position that allowed them to devote so much energy to a walnut-shaped pink lump of tissue with the consistency of a half-baked egg.
This question is critical, because organisms do not normally develop new traits just because they can. This of course also happens, in combination with random genetic drift and populations bottlenecks. But because evolution is a ‘miserable and greedy tinkerer’, or put more nicely, an economical process, it is highly unlikely that it produces needless and incredibly complex capacities that are extremely costly to maintain. As a consequence,
“some proportionately beneficial advantage must have driven brain evolution against the steep selection gradient created by the high costs of brain tissue.” (Dunbar & Shultz 2007)
Why, Dunbar and Shultz ask further, do primates have so much bigger brains than squirrel, with both facing about the same foraging decisions? (Dunbar & Shultz argue that ecological explanations fail to account for this differences, but their Chimpanzee-Squirrel dichotomy nevertheless is a bit hyperbolical, given that, among primates, those whose diet includes insects and fruits show higher encephalization rates than leaf-eaters, and strategic hunting and gathering of food and prey places additional demands on navigational, representational and other cognitive skills. However, their general argument is still valid. (Park et al. 2007))

To shed light on this issue, we can divide the big picture into several smaller ones. Useful questions include: What are we good at? Split into What are we (primates) good at? And What are we (humans) even better at than other primates? What could the ecological niche favoring big brains in humans have looked like? How exactly does our brain differ from that of other primates?
These questions essentially depend on comparative ethology (how do our minds work compared to how the minds of other animals work?), comparative (neuro)anatomy (On which evolutionary foundations are our modern cognitive abilities, and other phenotypic traits built upon?), and the kind of scenario we envision or infer from these observations togther with the fossil record and other lines of evidence. Of course it is also crucial what we think what the most salient and essentially aspects of our ancestors were. Do we see our ancestor as “Man the Tool Maker”, “Man the Hunter” or “Man the Social Animal”, or just as “Man with the extraordinarily big & expensive (and extremely delicious, George might add) brain”.

Well, of course Man should probably rather be seen as “Man the cooperative, competitive, tool-making, hunting, {…}, articulate social animal.” And all of these property probably contributed (co-evolutionary, we might say, without adding much in terms of explanatory adequacy) to our cognitive abilities and brain size, but in which order? And which driving forces were a little more pushy than others?
As Cheney & Seyfarth (2007) have show in baboons, interactions in primate groups are cognitively highly demanding and require sophisticated representational and predictive abilities, because of the intricate and complex networks and ‘friendships’ they inherit. Thus rising complexity in social life could be seen as a key selection pressure in the evolution of cognitive abilities in primates in general, and especially in humans. (Lewin 2005: 220f.)
Depending on which aspect one wants to stress, this correlations can be described in different terms. Scholars who wanted to stress the competitive aspect of social life dubbed it the “Machiavellian Intelligence Hypothesis.” (Byrne & Whiten 1988: who themselves, interestingly, didn’t want to stress the competitive aspect by giving the hypothesis the title). Now it is most widely called the “Social Brain Hypothesis” to emphasize the general complexity of primate groups including all arising affordances (Dunbar 1998, Dunbar & Shultz 2007).
Unfortunately, this is still rather vague. To get a clearer picture, it is important to make explicit the advantages and disadvantages of large social groups and the specific problems which need to be solved. However, group size indeed seem to contribute advantageously to genetic fitness by minimizing predation risk, but paired with greater ecological and reproductive competition and suppression, affording higher behavioral flexibility (Dunbar & Shultz 2007). Brain expansion theories stressing the importance of ’technological intelligence’ as a driving force. (without neglecting the importance of social factors, but seeing the latter as less crucial). According to these views, the ‘behavioral drive’ for cultural transmission and innovation is more frequent in species with large brains. As a consequence these species are led to exploit the environment in new way, opening up new possibilities regarding new selective pressures. ´(Reader and Laland 2002). Certainly, these tendencies were important, but where do they come from? Big-brains seem to be a prerequisite for ‘technological intelligence’, but how did these evolve in the first place? Rather it seems probable that
“Although innovation, tool use, and technological invention may have played a crucial role in the evolution of ape and human brains, these skills were probably built upon mental computations that had their origins and foundations in social interactions.” (Cheney & Seyfarth 2007: 283).
Supporting Reader and Laland’s emphasis on the importance of technological aspects on human cognitive evolution, Tomasello and his colleagues propose that human’s advanced Theory of Mind-skills were amplified not in the context of intention-reading present in great apes, but rather during learning and imitation of hierarchical planned and structured tool-making and tool-using. (Tomasello et al. 2005: 687). I’m not sure whether George would like this speculation. Probably, he would argue this to be a ‘just-so story’ and propose that all scientist coming up with these should be eaten. So thank God scientists are not really zombies, I wouldn’t miss the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany (and especially its co-director) for anything in the world (OK, except for the really important things such as love, life, family, donuts.

I haven’t addressed much of the questions stated in the beginning, especially What we as humans are especially better at than other primates. I will come to this issue in my next post (relying again on research done by scientists from the Max Planck Institute for Evolutionary Anthropology, so again, glad they haven’t been eaten.)


Cheney, Dorothy L. and Robert M. Seyfarth. 2007. Baboon Metaphysics: The Evolution of a Social Mind. Chicago: University of Chicago Press.

Deacon, Terrence William 1998. The Symbolic Species. The Co-evolution ofLanguage and the Brain. New York / London: W.W. Norton

Dunbar, Robin I.M.1998.“The Social Brain Hypothesis” Evolutionary Anthropology 6: 178-190.

Dunbar, R. I. M. and Susanne Shultz. 2007.“Evolution in the Social Brain” Science 317: 1344-1347

Park, Min S., Andrew D. Nguyen, Henry E. Aryan, Hoi Sang U, Michael L. Levy, Katerina Semendeferi. 2007. “Evolution of the Human Brain: Changing Brain Size and the Fossil Record.” Neurosurgery 60:555–562.

Reader, S.M. and K.N. Laland. 2002. “Social Intelligence, innovation, and enhanced brain size in primates” PNAS 99: 4436-4441

Tomasello, Michael, Malinda Carpenter, Josep Call, Tanya Behne, and Henrike Moll. 2004. “Understanding and Sharing Intentions: The Origins of Cultural Cognition.” Behavioral and Brain Sciences 28

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