Few more comments on evolution of behavior—evolutionary psychology approach before moving on to our next topic of neuroanatomy.

One difference that seems to be present between primates that pass vs. those that fail the mark test is size…large primates pass, small primates fail, regardless of social behaviors. Clambering hypothesis states that large primates developed a sense of body awareness as a consequence of navigating through the jungle canopy…tall trees. Understanding oneself as a causal agent…I’m making those branches bend and tip, so I better figure out how to get myself from one branch to another. Over the course of millions of years, those that didn’t figure this out were splattered over the jungle floor. What about small animals? Falls from trees were not as dangerous nor was maneuvering through treetops—unlikely to break branches while traversing the trees.

If animals have self-awareness, they understand themselves as causal agents…I made that happen, I can make that animal in the mirror do all sorts of things, I am that animal in the mirror.

However, there are other behaviors that aren't obviously related to survival and reproductive success, although we may be able to see correlates of such behaviors in non-human animals. For example, we can see animal origins of art (e, suggesting that even our most abstract, seemingly non-survival related behaviors can be thought of in evolutionary terms, when done comparatively…material from Diamond Chapter 9 on bower building behavior in bowerbirds.

What distinguishes human art from art-like behavior (e.g, singing in birds)?

Human art:

-non-utilitarian (serves no purpose)

-done only for aesthetic pleasure

-learned

When examining bower building (as distinguished from bird singing) it appears to satisfy the learning criterion (pleasure criterion is unknown). However, they serve a clear reproductive related purpose. But it is unrealistic to assume that acquiring or producing art is also non-utilitarian in humans, since it serves much of the same purpose in humans as in animals. It is a signal of “fitness”…in the sense that producing art is difficult to do, and expensive to acquire…it serves as a symbol of status or wealth which is very strongly associated with reproductive success.

Finding such links between seemingly unique human behavior and distantly related species like birds suggests that these behaviors have strong reproductive value.

Also suggests that if we are going to use the comparative approach to understand the evolution of particular behaviors, we may be able to look for parallels of human behavior in other species, particularly other primate species. If we can understand what function behavior serves in those species, we may be able to apply functional explanations to human behavior.

Evolution of the brain:

Studies of brain size tell us very little about the intellectual capacity of a species-- a more reasonable approach to the study of the brain has been to compare the evolution of different brain regions.

-Brain stem: regulates reflex activities that are critical for survival (heart rate, respiration, blood glucose levels)--there is much "homology" between brain structures in this region across species. It is this region that is most usefully studied by using the comparative approach.
-Cerebral hemispheres: involved in more complex adaptive processes such as learning, language, perception and motivation. These processes are often more difficult to study using the comparative approach, but not impossible.

Three important points about human brain evolution:

-increase in brain size (relative to body weight)
-most of the increase in brain size is located in the cerebrum--the size of the brain stem (relative to body size) is fairly consistent across species.
-there is an increase in the number of convolutions (folds) on the cerebral cortex--the surface of the cerebrum. This structural change has allowed for a far increased volume of cerebral cortex.

Neuroanatomy: several ways to learn (“Telegraph line” video)

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