****Pictures coming soon***
I was especially excited to review “Evolution and the Brain ” from The Encultured Brain because evolution is something that interests me. I really like to see how evolutionary theory applies to different disciplines (can anybody say EvoS?). Theodosius Dobzhansky said “Nothing in biology makes sense except in the light of evolution.” I have found that this can apply to many different fields other than biology.
I have studied development in the context of evolution before, but never in a neurological context. This chapter really built onto my existing understanding of human evolution. As someone studying anthropology (I guess this is a neuroanthropology blog), I was especially excited to read about how the human brain and culture interact and how we can understand this interaction in an evolutionary context. Below is a quick summary of the chapter.
About the Authors
Greg Downey is Head of Department and Associate Professor of anthropology at Macquarie University. His interests include, but are not limited to, neuroanthropology, ethnomusicology, economic anthropology, and evolutionary theory. His main research focus is on skill acquisition from a neuroanthropological perspective.
Daniel H. Lende is an Associate Professor at the University of South Florida. His interests include neuroanthropology and biocultural medical anthropology. His research interests focus on substance and abuse, stress, cancer, PTSD, among others.
Together, Downey and Lende run the PLOS (Public Library of Science) blog site. The PLOS blog site is intended to facilitate discussion about science and medicine.
When we talk about how special human brains are, we typically first talk about size. Although size itself is not the only feature important when studying the brain, it is especially important to consider in an evolutionary context. It takes a lot of energy from high quality food sources to develop and maintain large brains. However, absolute size isn’t the determining factor of intelligence, and neither is relative brain size. Rather, the encephalization quotient of an animal best predicts brain and body size relationships. Humans are outliers, with a ~6X higher encephaliztion quotient for mammals our size.
Before our ancestors enjoyed an increase in brain size, they were distinguished by bipedalism. After this initial divergence, our ancestors’ brains tripled in size by two million years ago. Body size also increased, but not at the same rate. Another jump in brain size occurred about 500,000 years ago. Genetic research has revealed a great deal of similarity between humans and chimpanzees (our closest relatives) especially compared to our other primate relatives. Even the small differences in our genes account for huge phenotypic variation.
“Evo-devo” is a recently developed paradigm combining evolutionary theory and developmental biology. The idea that we can look at developmental processes to get an idea of how evolution has shaped us is not a new idea, but only recently has it been a widely accepted way of evaluating how evolution has shaped us.
Comparative neuroscience is a great way to see how evolution has acted on the brain structure itself. By looking at human brains along with other primates we can see that evolution acts on existing structures, changing the function of a structure instead of creating a completely new structure. One way this is exhibited is by increasing the size of certain regions in proportion to others. There are often trade-offs when this happens; when one region increase another must decrease in order to remain metabolically stable. Humans are especially unique in our hemispheric specializations. This creates a streamlined process for quicker and more varied neural processing but also leaves us highly susceptible to injury (trade-off). Brain regions growing disproportionately is a demonstration of natural selection acting on this growth.
The larger our brains get, the more neurons we possess, opening up more connections in neural pathways. Evolution acts, not only on the number of neurons in a region, but also on connections within and between regions. In humans, control of our larynx has been affected by a neocortical “invasion,” which is important for language. Other animals do not have these connections, and are therefore missing brain function vital to speech.
Not a Brain Alone
I think it is hard for people to grasp that intelligence is not shaped entirely within. Culture plays a big role in our learning and brain development. During the first three months after birth, there are many neurons in an infant’s brain that adults will not possess. During these three months, vital connections are made, and there is a pruning of neurons that go unused. It is during this time that a lot of cultural cues become ingrained in people. The social intelligence hypothesis places paramount importance on intelligence as a tool for cooperation. The focus is on the individual and how collaborative actions benefit the individual. In the cultural niche hypothesis, emphasis is on the interaction between multiple brain. Many human intelligence innovations could not be possible without the collaboration of multiple peoples’ brains. Regardless, sociality is a large contributing factor to human intelligence.