Evolving Brain Stuff, Y’all (part 2)

****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.

Size Matters

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.

Structure Matters

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.

Connections Matter

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.

13 thoughts on “Evolving Brain Stuff, Y’all (part 2)”

  1. Great posts folks,
    One thing I find very interesting is the role of sociality in the formation of our complex brains. You state “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(s). 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.” I am interested in hearing your thoughts as to the role of ritual behaviors in contributing to the human brain’s (and non-human primates) ability to situate the self in a maze of complex social relationships. Do you think ritual behaviors were present in our distant ancestors?

  2. I’m also interested in the social aspect of the brain’s evolution. In modern times, we live in a socially complex world, more complex than at any other point in our history. We can instantly connect with people across the world, and people are constantly obsessed with social media such as Facebook and Twitter. I wonder if this new level of societal complexity has or will be translated into physiological changes in human brains.

  3. I found the “invasion” of the neocortex into the area of the brain that controls the muscles of the larynx really interesting, I had never heard that before. You always hear about the physical change regarding the position of the larynx when speech is discussed, but never the neurological aspect of it. I think it’s a good example that really highlights why the development of the brain is important when talking about evolution.

  4. Downey and Lende’s chapter 4is an excellent overview of the different avenues and aspects of the evolution of the human brain. The subsection on structure really grabbed my attention. We tend to think of the brain as ultra special but it is just another part of the body. Just as the bones and muscles of the torso and lower legs adjusted to a bipedal gait, as laid out by Lovejoy (1988), so too did the brain evolve by rearranging the building blocks already at its disposal. I like that Downey and Lende introduce the idea of trade-offs when speaking about hemispheric specializations, olfactory bulbs, and the primary visual cortex in humans. Changes in the brain such as these, in my opinion, uphold Striedter’s compromise (that brain growth is mosaic, but most dramatically concerted) and that a combination of models including social intelligence, brain-development niche, and sensory/motivational/bodily changes are probably at play in human brain evolution. The brain is full of connections, and so too is the environment in which we find ourselves. The interplay between our biology, culture, and the physical landscape is complex.

    In the article “Evolution of the Cerebellar Cortex: The Selective Expansion of Prefrontal-Projecting Cerebellar Lobules,” Balsters et al. (2009) dove into the mosaic-concerted brain evolution debate. By comparing high-resolution MRI scans of capuchins, humans, and chimpanzees, they determined that the highest degree of interspecies differentiation occurred in the Crus I and II, indicating that evolution of lobules parallels the evolution of related neocortical areas. The authors also link enlarged brain areas to specialized functions, seemingly indicating support for the converted evolution hypothesis.

    “Evo-devo,” perhaps the most fruitful scientific fusion since the modern synthesis, involves one of my favorite theories: life history. In the most basic of terms, life histories are packages of phenotypes that are selected for or against based on inherent trade-offs of strategy choice. Energy is finite and allocated for different and diametrically opposed purposes: to survive or to reproduce. Should the organism have offspring sooner rather than later? Would it be better to have a high quantity of offspring or high quality? It is easy to see how a choice in one area necessarily implies a choice in another area of inquiry. Life history is a very popular way to describe human evolution and why certain developmental characteristics like extended adolescence or reproductive senescence might have been selected for (Crews and Stewart 2010). Aktipis et al.’s article “Life history trade-offs in cancer evolution” shows cancer progression to be a great example of niche construction and life history theory on the micro scale. Life history theory is used to understand the ebb and flow of fast and slow reproduction strategies in cancer growth and the nature of the diversity of phenotypes found in neoplastic cells. The authors suggest that cancer cells proliferate until they start to tax their resources. Angiogenesis, or niche construction, is then selected for as competition for resources increases and a slow reproductive strategy is promoted. Once a cell is able to invade larger areas, the process repeats itself. Ultimately, invasions lead to metastasis (led by cancer cells that are excellent invaders and adapters). The great news about heterogeneous cancers and cancer growth is that we may be able to now manage the cancer by adjusting their environments to promote a slow reproductive strategy. These adaptive therapies aim to stabilize the tumor instead of decreasing its growth or removing it. The information presented in this article has impressive implications not only for the treatment of cancer but also for evolution. It is easy to see how the environment shapes the life history cancer cells but also how cancer cells have equal agency in shaping the environment.

  5. I agree, especially in Today’s society, that a collaboration of actions has definitely benefited countless individuals. Technology is constantly involving; it’s also a great example of multiple brains working at the same time. For instance, databases, they are constantly changing and increasing in size. I wonder just how many people it takes just to maintain the Google search engine. Human commutation has caused people to develop bigger brains, and has created more connections within the brain. I wonder how the increase of creating, sharing, and storage of knowledge, or information, will affect our brains in the future.

    1. In studying the evolution of the human brain, it becomes clear that sociality was selected for. But sociality has many forms. As the Balsters et al. (2009) article showed, differing brain proportions have emerged among primates and can be linked to brain ability and animal behavior. The article states that more research needs to be done on the allometric trends associated with the growth of one brain region over another. To me, it seems natural to work backwards. There are tons of studies out there that connect behavior to brain via theory. For example, Heywood took Panskepp’s theory of emotion and Porges’ Polyvagal theory and applied them to sport. Sport encompasses all levels of social play, interactions which can be overly competitive or based on fulfilling the need for human contact. Let’s take research like this and project it back in time using the soiobioloigcal evidence we have regarding humans and other primate species. Really, what we seem to be talking about is viewing human behavior through a biocultural lens within a life history framework. Along these lines, Downey and Lende are right that we need to understand the process through which the brain evolved. Maybe then, we will reach some sort of clarity concerning how we came to be special (through the not so special force of natural selection), what similar or dissimilar journeys other primate species embarked on, and why we aren’t living on the planet of the apes.

  6. Great post. I can agree also that a combination of what was once considered individual “ideas” to formulate and connect other disciplines make looking at the bigger picture much easier. I also appreciate the evo-devo theory being more widely accepted because it makes the history of the human body (and of course other organisms also) flow better. Which leaves me to wonder on the cultural aspects of brain development, besides the initial 3 months where the vital connections are made..how much is our culture helping or hurting us? I know there’s research on this, but I wish there was almost a comparative research from say 50 years ago to today within the same cultures.

  7. The development of language with regard to te neocortical invasion really fascinates me. This gives humans the “hardware” for language–the ability to control the larynx– but where does the “software” or the ability to process language come into play? Other apes, such as gorillas, are able to recognize and respond (with sign language) to human language. Is their lack of the hardware necessary the only reason that gorillas and other great apes can’t speak with us?

  8. I love that in Ch.4 they essentially say that the “brain is like computer hardware analogy” is basically wrong because I know this is exactly what I learned at some point in secondary school and what many people probably learn and still believe. This chapter did a great job of putting into perspective the way in which the brain is encultured and some of the ways in which biology effects it as well. Something I had never thought of that was brought up under the cultural niche construction model was that we’re essentially an invasive species (and here we are complaining about the kudzu!). This should have been obvious to me. However, they go on to explain that its not just a big, well connected brain and social groups that lead to the success in this model its the ability to build a “scaffolding” and transfer knowledge onto a successive generation within the cultural group.

  9. I am currently in the psychology department’s Physiological Psychology course and we are studying the evolution and brain development mentioned here. It’s really interesting to be taking these two courses side by side because oftentimes the evolution of the brain is not explored from a cultural context. I really enjoy having another lens through which to view the evolution of the brain. It’s a really curious interaction, and what I get hung up on most is the chicken-or-the-egg of lot of these developments. For example, was developing a more complex larynx necessary because of a growing need for communication between early humans, or did a more complex larynx contribute to a greater level of communication between early humans? This concept was explored a bit in the primate chapter as well, and is probably a mix of the two that fed into each other, but it’s still really interesting. I’m also blown away by the brain’s plasticity. In both my psych course and this course I’ve read about the study with ferrets’ optic nerves being rewired and the brain’s ability to adapt to that. It’s crazy. But another thing to consider is how much of intelligence is gained and how much the brain changes AFTER birth — intelligence and changes that aren’t necessarily in the gene code to passed on to offspring. That plasticity makes the evolution of brains even more fascinating.

  10. Although I am late in posting a comment, I would like to make a comment regarding yesterday’s class. I believe that domain specificity is incredibly important to use as a lens in looking at social normalities. In addition, I wanted to upload the split brain experiment onto this blog. It has a nice little game that you can play, and it’s pretty amusing (you have to get a research proposal approved before you can move on). It helps really visualize the various processes that occur on each side of the brain. http://www.nobelprize.org/educational/medicine/split-brain/index.html

    I also wanted to leave y’all with this really interesting video that displays neural plasticity, and what the brain can actually do. http://www.youtube.com/watch?v=2MKNsI5CWoU

  11. After the discussion in class, I read an article that was posted on my Facebook page by the Neuroanthropology Interest Group, which was, “Inside the Brain’s Amazing Ability to Re-Map Your Body.” The article was originally posted to smithsonianmag.com and written by Sam Kean. According to Kean, there are two maps inside the brain and each are found within a vertical strip of gray matter that originates behind the ears and stretches to the top of the head. The first strip is the sensory cortex, which receives and responds to messages, and the second strip, the motor cortex, which sends messages to move. Each contains an inverted map to the body. Richard Norris, Kean claims, had a shot gun accident in 1997 that took off the lower part of his face, leaving him with no lower lips or lower jaw. Eduardo Rodriguez, who is a plastic surgeon, from New York, put Mr. Norris into a brain scanner to see if the corresponding brain regions devoid of activity on the scan, and what he found was that those regions were asleep, according to Sam Kean. After undergoing a face transplant, Norris, thanks to the ability of the brain to re-map itself, was able to have his lower lips and jaw replaced. Kean explains that doctors were able to establish hard wired nerve connections between the face and brain, and that the communication is clumsy and slow at first, that the nerves and neurons need practice working together, but eventually come together. Therapy, which involves making sounds, or opening and closing lips, and that this facial reanimation helps the maps learn to send messages so that the new face can respond, according to Kean. A facial transplant is a great example, I thought, of how neuroplasticity works. Although, I do wonder about the psychological changes someone would go through when looking in the mirror every day.

  12. One part of modern medical research that excites me is the new discoveries of prosthetics. Prototypical prosthetics can be connected to neurons to enable the patient to move the prosthetic and manipulate objects, and some prosthetics actually include sensory feelings. This chapter talks about plasticity and how the brain is “wet-wired,” but this takes the adaptive capabilities of the brain to a whole new level. Neurons can actually be connected to synthetic wires to allow motion and feeling. Science fiction is actually becoming science.


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