Evolution of the human brain

2/2/2016

by Myra Barrett

Downey and Lende discuss the evolution of the human brain, as well as research gathered on its various mechanisms for such an extraordinary development. Not surprisingly, the evolutionary path the brain has followed makes it as complex as it is resilient. However, the authors unpack the basic principles leading this intricate and fascinating journey to modern humanity.

They start the chapter with a short explanation about the many theories within the scientific field in relation to the evolution of the brain. The many theories surrounding brain evolution come with their own challenges and limitations. As they put it, “evolutionary theory also needs to be checked against biological and anthropological plausibility” (2012). The remainder of this chapter attempts to check the plausibility of several theories, as well as explains the many mechanisms that make our brains so unique.

The authors then analyze the brain's size in proportion to the human body. One of the more puzzling facets about the human brain is how much energy it uses. It actually seems that it would be maladaptive to supply that much energy for just one organ. However, the amount of energy it uses provides us humans with the capacities to form complex societies and sophisticated cognition. However, Downey and Lende (2012) write, “human cognitive distinctiveness presents a problem as well, however, since smaller animals have proportionally larger brains.” The solution to this problem is to measure brain size using “encephalization quotients” because this method of measuring brain size incorporates allometric scaling.

Comparatively, the phylogeny of the brain is correlated with its growth. For example, Downey and Lende (2012) say that starting around 2 million years ago, our ancestors' brains tripled in size within a short amount of time. However, chimps' brains are quite similar to ours, meaning that we can see them as homologous to our own in the evolutionary context.

Considering this, the human brain is not a new structure, but a homologous organ that corresponds to many other primates'. However, Downey and Lende (2012) point out that “as brains grow larger among related species, every part of the brain does not increase at the same rate, so species with large brains demonstrate predictable changes in the size of regions relative to each other.” Despite all the similarities in ape and human brains, ours are still the largest, comparatively.

Along with the structural qualities of our brains, it also grows and develops in some interesting ways. There are two main growth patterns described in this chapter: mosaic and concerted. Both are believed to have had a significant role in the evolution of the brain. Also, the brain grows, or develops, connections between neurons. These connections are an important piece of how our brains have developed. For example, brains can go through “connectional invasion,” in which they develop connections between regions that were not common in ancestors. These connections can also be maintained through “neuronal group selection,” which allows for connections that are not in use to essentially fade away.

Just as connections can be naturally selected for, so too can social mechanisms. However, social traits also have an affect on the environment that individuals are in. With the environment having influence over brain connections, and the social traits of a group having an affect on the environment, humans have been able to manipulate our own situations.

Similarly, individuals could be in competition within a group. This requires the development of certain social traits in order to survive in an environment. Downey and Lende suggest that in this kind of situation, those certain traits will become advantageous to develop, which in turn will adapt the brain of those exhibiting some trait. However, they also present a different perspective of the affect of sociality on the brain. There are some theories that suggest that learning and participating in a culture is advantageous for groups. If there are many people to pass on beneficial traits, not just by reproductive means, but by simply teaching and imitating, that would allow for the success of that group. Also, the ability to assess the emotions of other people would be beneficial in social context. The brain supplies humans with a good amount of empathy, making it possible to share in experiences and understanding.

Downey and Lende conclude this chapter with the thought that information on the evolution of the brain is vital in understanding ourselves in a neuroanthropological perspective. Evolutionary theory of the brain requires many different fields of study, including biology, anthropology, and physiology. There is new information being discovered every day on the human brains history and present. Our brains are constantly revealing new things about social structure as well as cognition.

References:
Lende, Daniel H.; Downey, Greg (2012-08-24). The Encultured Brain: An Introduction to Neuroanthropology (Kindle Locations 2312-2809). The MIT Press. Kindle Edition.

25 Comments

Danielle Long

2/2/2016 09:10:35 pm

How much energy is needed to "fuel" the brain and that each section of the brain does not grow at the same time as other parts; I found that it is crazy to think that our brain takes up so much energy to process things (like for example: it seems to only take a few seconds to answer a question, but we don't realize how much energy we actually burn in completing the task).

Going off of what you said about learning and understanding different things (like emotions) from other people- during brain formation we need a lot of non-genetic information from society that shapes the interactions within the brain, within the body, and within the environment because everything is connected by the actions of a society.

On page 107 it talks about brain size is crucial to the cognitive complexity due to the fact that larger brains may require structural and functional changes like: greater specialization of brain regions, shifts in proportional size in the different parts, and systems of long-distance connections among increase regions. So in the larger brains all of these things are happening but the neurons do not match in larger shape but the larger brains have more neuron count.

Danielle Long

3/1/2016 09:01:28 pm

When reviewing this chapter for the test I was thinking about the movies that we watched the other day in class and wondered how much energy is used to fuel the brain in either Tourettes or Autism? For example with Anne when she is trying to keep her nervous twitch under control so that the other kids in her class don't make fun of her- how much energy is required for the brain to stop the movements? And much energy is needed for Autistic people to focus on conversations with others? Both of these questions are very interesting to me and I would love to see the data on this.

Kelly Likos

2/3/2016 06:36:25 am

I found the basic mechanics of the evolving brain structure very interesting. That is definitely a subject I would like to expand my knowledge about. I found it very interesting that minor neurological plasticity has the ability to change major brain structures over time.
I particularly enjoyed this quote in the “Phylogenetic Trajectory” section of the chapter: “Growing the extravagantly large and peculiar human brain over evolutionary time has meant tinkering with the developmental processes at the structural, connectional, cellular, and genetic levels”. The use of the word “tinkering” lends to a more fluid perception of the brain.
This theory changes the perception of the brain as “concrete” or a more fluid structure. I believe this perception has tremendous effects on the way neurosciences are viewed, as well as biocultural advancements. At the opening of the chapter in the overview section, it is touched on that gene expression, epigenetics, and neuronal selection can kick start brain development and growth. I find the field of epigenetics interesting in that, once again, our brain is not set in stone. As we grow on the outside, we continue to grow on the inside- neurologically. Epigenetics, from a biocultural point of view, open the door into understanding profound ways in which our culture has the ability to change brain structures.

Kelly Likos

3/1/2016 07:54:26 pm

While re-reading this chapter, I was still interested in the different factors that can alter brain development during growth. This chapter talks quite a bit about how the brain works with a "mosaic" collaboration of brain structures, and how these structures can be altered during development. After all we have talked about the last few weeks, I appreciate this so much more. We really must stop thinking of the brain as "hardwired". It can be developed through time.

Mirjam Holleman

2/3/2016 07:46:30 am

What stuck with me most from this chapter was the reiteration of idea that the brain is not simply a hard-wired genetic blueprint, but rather an adaptive organism, that is constructed and developed over a lifetime and generations, in response to, or rather, in interaction with “the brain itself, the body, and the environment” (p. 115).

However, in this regard the human brain is not all that unique. Yes, we do have a longer period of brain maturation, after birth, compared to other mammals thus making us “more responsive to the environment and susceptible to enculturation” (p. 117), but other species have “wet-wired” brains too, as demonstrated by experiments on, for example, ferrets (p. 116), that show that the brain can reconfigure itself in response to varying conditions (be it “injuries disability, and even structures with no evolutionary precedent” p. 117).

What then makes human brains unique (apart from our longer period of enculturation)? Donald (2001) suggests that “the key to understanding the human intellect is not so much the design of the individual brain, but the synergy of many brains […] from our earliest birth as a species humanity has relied upon ‘distributed’ systems of though and memory, in which intellectual work is shared across many nervous systems” (Downey & Lende 2012: 122).

However, (and I feel like the ‘answer’ or a theory with regard to this has already come up previously in this or another course I’ve taken, but I can’t reach it in my mind), I wonder how human cognitive sharing is so different or unique from the interdependence of other species (e.g. ants, bees) upon one another, and in fact, the interconnectivity of an entire ecosystem. Is it really so unique that we are not merely an “individual brain” but exist in a synergy with other brains, other species, and the environment?

Well, this chapter brought up many more questions (and also interesting insights!) for me, but I’ll end this here, lest this turn into a full chapter review, rather than a brief comment.

Mirjam Holleman

2/5/2016 02:07:27 pm

2nd reflection: In class I learned that what propelled the human brain on a different evolutionary path compared to monkey brains, was not so much brain growth or development of new 'modules;' rather, our enhanced cognitive capacities are primarily a result of enhanced interconnectivity within the brain. Human brains have more specialised brain regions (grey matter) and, importantly, contain more mass dedicated to bridging the brain regions (white matter).

Nick Roy

2/3/2016 08:18:34 am

What caught my eye the most in the chapter was the importance Lende & Downey placed on viewing the evolution of our brains as more than just and account of adaptation. Coming from a background in psychology, I am aware of evolutionary psychology's strengths and weaknesses. Lende & Downey rightly criticized viewing evolution in this model by referencing Gould's comments of many adaption models being "just-so stories." Instead, Lende & Downey argue that adaption should be balanced with other factors like evolutionary constraints, development, and niche construction. I find that this synthesis of multiple perspectives critical in furthering discussions on evolutionary models for the development of our brains.

Nick Roy

2/29/2016 12:00:04 pm

Looking back on the idea of niche construction, I still have lingering concerns about how and where it is applied in neuroanthropology. Intuitively, it makes sense: we create our own selective pressures through culture. As the case studies have shown, cultural practices can affect the brain as they become embodied, yet they do not project the studies' findings into evolutionary theory. I wonder if we could find examples of niche construction in modern or at least historical times.

Amanda Oldani

2/3/2016 08:20:45 am

I agree with Kelly’s statements about the fluidity of the perception of our brain, and I also find the epigenetics highly interesting. I think it touches back on the niche construction model and how there is a loop of influence between organisms, their environments, and their genetics.

I found the section of the chapter (118-120) that discusses how cultural niches can be both adaptive resources and selective pressures to be interesting and a little surprising. In early anthropology classes, we learned the idea that culture can help us adapt to environments. Because evolution and adaptation are slow processes, cultural adaptation can help us in the meantime. However, Downey and Lende provide a more detailed view that culture can also create selective pressures that act on the population. At the end of the chapter, the authors say, “we need to get away from seeing “culture” as merely information that is transmitted over evolutionary time and recognize that enculturation is, equally, the ways that our interaction with each other shapes our biological endowment, and has been doing so for a very long time. We do not just adapt through culture, but must also adapt to culture” (126). This statement was important for me, and I think it is important to remember when considering niche construction and its influence on individuals. It provides a broader way to understand how organisms operate in an environment. I found it important that Falk also emphasized lifestyle and niche in her article.

Amanda Oldani (2nd)

3/1/2016 08:17:05 pm

After reflecting on this initial post, I have been thinking about how it relates to some of the studies we came up with in class. My group’s study would examine how parental styles, which are strategies that create a developmental niche, influence stress and anxiety in children. The methods that parents choose create a niche that ultimately affects the children, and the children often have to adapt to this created culture. I have also considered the case study involving capoeira. I think this is a perfect example of how life experience and training can be so deeply encultured to have an impact on unconscious brain functions, like balance. The brain and nervous system cannot be seen as hardwired anymore.

Paige Ridley

2/3/2016 08:20:48 am

I have always been fascinated with the brain and how it works. This chapter in particular for me not only expanded on my knowledge of the brain but leaves me curious and wanting to learn more about this complex organ.

"Not surprisingly, the evolutionary path the brain has followed makes it as complex as it is resilient " as stated by Myra is a very strong statement. We first must allow our minds to wrap around the concept of evolution and the changes that occurred over time to be able to fully submerse ourselves into understanding just how much we can learn from the brain and power that it takes to energize it.

This particular citation really stuck out to me "social and cultural life is just not cognitively demanding because we scheme and cooperate... but we are also drawn to social interaction for its intrinsic emotional awards" ( Pg123) It really puts things into perceptive as I take for granted how much brain energy is used on a daily basis . We are in fact drawn to social interaction and as humans we "don't want to miss a thing" therefore we will use most of our brain power because we forget that our brains need to recharge as well.

Paige Ridley

3/1/2016 08:32:11 pm

The idea of understanding brain fuel was a very pivotal moment in time as it creates this idea of the brain being “energy- greedy” (Pg. 106). The brain is so much more than just housing for cognition but it also allows signals to pass through the grey matter of our brains allowing the rest of our body to function properly. Since it is “energy-greedy” the brain tissue is very expensive in both the knowledge that it obtains and functions in which it performs both in a perpetual and periodic sense (Pg. 106).

Molly Jaworski

2/3/2016 08:44:25 am

This chapter expanded my knowledge on brain structure as well as provided many new ideas and theories to explore when thinking about cognition and evolutionary development of humans as well. It is important to note that though size is a factor in complexity of the human brain it is connections and proportions that increase this complexity more so than just general size. (The folding of the brain allows for more connections and shorter distances for signals to travel as opposed to just a large brain with few folds by which signals have to travel large distances)

In reading this chapter I found Downey and Lende's connection to MacKinnon Fuentes "niche construction" hypothesis quite interesting. In utilizing niche construction Downey and Lende proposed 3 new hypotheses to explain brain body interactions in human brain evolution while applying social context to them. The social intelligence hypotheses highlights the life longevity and social need of the species as bringing about competition amongst one another whereas the brain-development niche model embraces cultural traditions, technology, transfer of information, foraging and social skills. The final hypothesis is that the brain is not only changed directly but the body's sensory and other physiological systems are changed as well in the brain's evolutionary developmental function (E-book location 2371).

Molly Jaworski

3/2/2016 07:49:26 am

This idea of niche construction has become prominent in the readings of Neuroanthropology. After rereading I found that Downey and Lende had a similar question when it comes to the application of various cultural social interactions in discussing the niche construction. In their 3 hypotheses they apply the interdisciplinary fields of Neuroanthropology and focus on the cultural aspects that can influence the niche.

Issac

2/3/2016 08:52:05 am

Since the title of this chapter is " Evolution and the Brain " it may be trivial to point out the fact that an acceptance of the " theory" of evolution is absolutely essential , but it is true. If we wish to understand any of these concepts from the idea of " tinkering " to phylogenetic trajectory, I would submit that any perspective that did not take evolution into account would be incomplete. The chapter provides a simple and straight forward quote by Theodosius Dobzhansky that I think supports this idea, " Nothing makes sense in biology except in the light of evolution "(104).

Jessica Muzzo

2/3/2016 09:05:05 am

I've often wondered how we come to assume that humans are capable of the most advanced cognitive functions in the animal kingdom. We far surpass other animals when it comes to production, but animals tend to be more intuitive. We typically call it "instinct" but there is a great deal of learning involved with it--learning that is not done with the help of language. I feel that I myself would be incapable of learning anything without language to guide me, to organize my thoughts. My dog, however, knows where the other friendly neighborhood animals live. In an unfamiliar situation, she assesses the details she knows and thinks about how to behave. She cannot draw a picture or write a poem, but she appreciates music. And sometimes, she goes outside at night just to look up at the stars. The book states that animals are capable of understanding others intentions but do not form a "we" intentionality. I would really like to see how that conclusion came about.

Jake Aronoff

2/3/2016 09:25:26 am

This reading highlighted how brain size alone is not a sufficient explanation for understanding primate brain evolution. Rather, the structural modifications that came along with this brain size expansion have also played a significant role. For example, on page 112, Downey & Lende note the asymmetry in hemispheres as a result of specialization of certain regions of the brain. This makes sense, as a larger brain creates problems for neuron communication because distances for communication become longer.

One part of this reading I found particularly interesting was Edelman’s “neuronal group selection” idea. Downey & Lende (115-117) explain this idea, in which genetic information underdetermines brain structure. They note that during embryonic development, a massive number of neurons are produced, and that by adulthood only a fraction of these neurons are still alive. This is due to neuronal group selection, through which environmental input triggers usage preferentially of these neuronal groups or series of connections, and the connections that are not used gradually weaken, disappear, or become dormant. This is very important, because it allows for an enormous amount of developmental plasticity in the human brain based on a wide range of possible environmental inputs.

Jake Aronoff (2nd Post)

3/1/2016 11:28:11 am

I still find this idea of neuronal group selection very interesting, and upon further reflection I have two additional thoughts on it. First, I wonder if neuronal group selection has more of an affect (or more plasticity) in certain regions of the brain versus other. I think this is important to consider because, as Downey & Lende mention in chapter two of "The Encultured Brain" (28), some regions of the brain are more plastic in response to environmental stimuli than others (they were discussing this in relation to the impact of enculturation). My second thought is that this neuronal group selection (connections made stronger or weaker between neurons based on experience) extends past very early development. For example, as Robert Sapolsky highlights in his book "Why Zebras Don't Get Ulcers" long term stress can erode connections in the hippocampus, thus resulting in declining memory capabilities, and this is not solely determined early in life.

Larry Monocello

2/3/2016 09:38:15 am

One of the things I thought was particularly important from this chapter was its emphasis that the computer analogy of the brain is an imperfect one. The authors point out that the brain is not "hard-wired," rather, it is "wet wired" or grown within its own ecological niche. The Constantine-Paton (1981) experiment of transplanting the third eye onto the frog with the subsequent change in brain morphology reflecting overlapping fields of vision was especially enlightening.
It made me think that the brain's development is not unlike bone development, in a sense. For instance, the brain gets the "striped pattern of ocular dominance" when fields of vision overlap; likewise, the femur only receives its distinctive curvature in humans as a result of the physical demands of bipedality. Both of these examples are developmental, not genetic. And this neurological "training" then lends credence to the possibility that enculturation (and possibly even acculturation) can be found in the brain with the right tools.

Larry Monocello (2nd)

2/23/2016 06:55:25 pm

Although I find the concept of an ecological niche to be an overall logically consistent framework for thinking about human brain evolution, I do wonder whether the framework of an ecological niche is actually tautological, and therefore ontologically unhelpful. Of all of the theories I've heard in the past for the big brain, though, this explanation seems to be the most robust.

Olivia Davis

2/3/2016 09:50:16 am

To think of the brain as anything less than an active participant in it's own formation and upkeep in the biological sense of the words is unwise. This chapter in Downey and Lende's book does an exceptional job of incorporating both the evolutionary perspective of the brain as well as the contemporary understanding of brain function and the structures that we consider "uniquely" human today.

One section that really stuck out to me, titled "Connections Matter," included an impressive amount of information regarding gyrification and synaptic pruning that I think is very pertinent to understanding the current organization and processes in the human nervous system. One of the reasons why society considers children "sponges" when it comes to information is because they accept up to 80% of their surroundings and those experiences are then either reenforced or 'weeded out' by the synaptic pruning process. I think this example is representative of the affect that one's environment has on their nervous system as a whole and supports the idea that nervous systems are adaptive to their idiosyncratic ecologies.

Olivia Davis

3/2/2016 08:30:22 am

After further discussion in class, I've come to realize that connection and the ability to connect is (arguably) the crux of culture. Both neurologically and socially, connections are what propel societies outward and provide the framework in which we study these things. Synaptic pruning is only one example of how our bodies make use of connections that our brains make and the fact that it exists only supports the idea that connection is key in being human.

Edward Quinn

2/3/2016 10:58:16 am

I was interested in the theory of brain evolution regarding emotional, motivational, and perceptual changes in the brain. Particularly interesting is the idea that the need for self control and lowered reactivity became an important capacity to have in the pursuit of selective fitness. Group living and tightly bonded relationships supply endless situations provoking an emotional and physiological response, either positive or negative. It’s easy to imagine a situation in which high reactivity would be exhausting in social group living. If every interaction were to induce a huge physiological or emotional response, we might see a gradual “aging” or “weathering” of physiological systems. That is, repeated stimulation with physiological response may lead to maladaptive health profiles over time, or the “wearing out” of physiological systems resulting in altered control over reactivity. These ideas are currently studied in my area of research interest (embodiment of social inequality), and this process is sometimes referred to as “weathering” or increasing “allostatic load.” It’s interesting to think about this from a neuroanthropological perspective, framing control over reactivity as an evolved trait important for selective fitness.

Edward Quinn (2nd post)

3/1/2016 10:11:01 am

The study of human brain evolution is enormously complex, and is of central importance to neuroanthropology. Understanding the evolutionary history of the brain allows us to understand why the human brain develops the way that it does. Why is the brain so open to environmental input? What does this mean for the development of the nervous system? These are important questions not just for neuroanthropologists to ask, but also policy makers. When we understand that the brains of children are especially sensitive to sociocultural conditions, and that these conditions are literally embodied in the brain, does that change how we look at our current social structure and levels of inequality? Neuroanthropology brings methods (discussed in Week 5) and theory (Week 1 and 2) to address the embodiment of social inequality, and other issues relevant to the well-being of the body politic.

Michelle Bird 2nd post

3/2/2016 09:13:45 am

Coming back to primate brain evolution, I keep finding myself drawn to the capacity of humans for abstract thought. We are capable of understanding and implementing so many complex behaviors, like creating abstractions and recognizing symbols, our capacities for self-recognition and future planning, our understanding of “theory of mind” and meta-cognition, tool use, cognitive performativity, etc. We have such a deep understanding (or the capacity to understand, anyway) of ourselves that we have created a series of professions dedicated to helping people understand their own minds (eg. counseling, therapy). These phenomena occur in other mammals in varying degrees, but the amount of complexity and discrepancy among humans is staggering. I think theory of mind is particularly fascinating because I see it play out so frequently in my own life. I live surrounded (thankfully) by considerate people, and it’s a constant exchange of polite encounters, in which one person is nearly always thinking of how the other person feels or what they think, and it’s amazing how successful a human can become at “guessing” what kind of a mood someone else is in or what they’re thinking based on a store of knowledge, conscious or not.

Evolution of the human brain

by Myra Barrett

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