Culture, Natural Selection and the Human Brain

Section 8: Culture, Natural Selection and the Human Brain

Consider how culture has influenced our behavior and particularly our biology? For example, treating childhood diabetes allows these children to grow up, have children and pass the gene on to their offspring, also in the gene pool. A hundred years children would die of diabetes and never reproduce, thereby never contributing the trait to the gene pool and reducing the number in the gene pool. Because of our ability to keep these children alive longer, we have changed our gene pool and subsequently, our biology. Now, use your own examples.



Brain size or encephalization

Does size matter?

-Einstein had an average sized brain and we can certainly say that made little difference.

-Mozart was a microcephalic. A genetic disorder that usually means mental deficiencies.

-Modern male humans have approximately 10% larger brains than do female humans…and we all know that means nothing.

image6.png Hominid Brain Evolution

-Encephalization or the measure of brain size relative to body size

-Notice the changes in the brain organization in the images from A. africanus where the brain is located behind the eyes and remains there until Homo sapiens, even in Neandertals, who happen to have a larger brain, the image7.pngfrontal lobe is relatively small compared to humans.

Why the Hominid Brain Enlarged

The Radiator Hypothesis:

-brain= 25 of body mass

-brain =uses 25% of O2

-brain uses 70% of glucose

Higher energy metabolism produces higher heat production. Therefore, brain size is limited by the Ability of the organism to cool the brain. Hominids have more diffuse blood flow through passages through the skull than do Australopithecines.

Brain/Body Mass Ratio

image8.pngLargest brains found in the largest animals ) Elephant and Blue Whaleimage9.png

Overall, mammals have larger brains per body mass. Modern humans are at the apex of brain mass to body mass ration

Human brain = 2.3% of body weight

Elephant brain = 0.2% of body weight


Here you see the gradual increase in brain volume over time. Notice the incredible jump in the last million years.

With the increase in brain size, reorganization and particularly the development of the prefrontal region and neocortex also came culture.


Brain Reorganization

Olfactory bulbs

Prefrontal region

Primary Visual Regions


image10.pngReorganization and reduction in the olfactory bulbs resulted in the decrease in the sense of smell. This trend started in the early primate radiation with the reduction in the snout and wet nose.

image11.png Large prefrontal region

The prefrontal region is the area for forming goals and making plans…imagine going to 2 minutes without thinking of the future.

Why do humans have an expanded visual cortex?


image13.pngThe primary visual cortex is the area where sensory information from various sources is processed and synthesized.

The expanded visual cortex is an “ancestral” characteristic.

Why do primates have a neocortex?image3.png

image14.png …because all primates are mammals.

The neocortex occupies a larger proportion of the brain volume in humans than it does in any other species.

The neocortex is an “ancestral” characteristic. Meaning that it is a feature that has been around a long time.

image15.png The Neocortex

Neocortex is divided into four lobes that process different types of information:

Frontal lobe: assimilates information relayed from “lower” brain areas concerned with movement. Plans and executes complex movements. Also an integral part of personality.

Parietal lobe: higher processing of sensory information from other brain areas and the spinal cord. Orientation in 3-dimensional space. Proprioception.

Temporal lobe: processes auditory information. Concerned with the production of speech and understanding spoken language (and music).

Occipital lobe: Visual processing

Theories to account for brain expansion in humans.

-Your brain is a Swiss Army knife

-Your brain is a scheming despot

-Your brain is a culture medium

-Your brain is a Las Vegas hotel suite

image16.png Your Brain is a Swiss Army Knife

-this is the predominant view of evolutionary psychologists

-your brain is a collection of specialized cognitive devices that are designed to solve specific problems

-problems may be difficult to recognize and processes may be co-opted for other means.

Steven Pinker popularized this view.

Problem: Many of the things that we do with our brains are hard to reconcile with the kinds of tools needed to find food or flee lions.

Your Brain is a Scheming Despot

image17.pngPrimates are distinguished from all other animals by their scheming, Machiavellian politicking, thieving, lying and murderous deception.

-much of this notion is driven by observations of primate behavior

-there are no better schemers than us

-theory is that our great cerebral hemispheres (especially perhaps the frontal lobes) have evolved help us with “social intelligence”.

– a euphemism for Machiavellian scheming.


Your Brain as a Culture Medium

At some point in our evolutionary history, we crossed a threshold when we had enough cerebral ‘stuff’ to produce culture.

Culture can be thought of as a kind of unit of mind that is independent of bodies (memes).

Culture and the brains that support it entered a kind of positive feedback cycle – brains better at propagating memes succeeded. E. O. Wilson was the originator of sociobiology, the forerunner of evolutionary psychology.

image19.png Your Brain as a Las Vegas Hotel Suite

Sexual selection

-it’s no good surviving if you don’t have sex

-to have sex you need to attract a mate

-if there is variability in mating success, then the traits that promote that success will be strongly selected for what if many of the things that we consider to be uniquely human were sexual ornaments like the tail of the peacock?

-this would mean that such traits would not have to have direct relationships with finding fruit or fleeing lions.

Geoffrey Miller is a strong proponent of sexual selection particularly as it relates to evolutionary psychology. His book “The Mating Mind” details his theories.


In apes and early hominids, the pharynx is high, and the larynx is low, restricting the range of possible sound production. In humans, the larynx is high, accessing a large space in the pharynx, in which a wide range of sounds can be produced.


Three major reorganizational changes in hominid brain evolution relevant to language:

1. reduction of the relative volume of primary visual striate cortex area, with a concomitant relative increase in the volume of posterior parietal cortex, which in humans contains Wernicke’s area.

2. reorganization of the frontal lobe, mainly involving the third inferior frontal convolution, which in humans contains Broca’s area.

3. the development of strong cerebral asymmetries of a torsional pattern consistent with human right-handedness (left-occipital and right-frontal in conjunction), localization of language skills in the dominant (generally left) hemisphere of the brain.

Darwinian Theories on Language Evolution

Early hominids developed symbolic communication as

a way to establish social contracts permitting stable

family and group structures, which otherwise would

not have permitted hunting and scavenging for meat

as a systematic source of supplemental food during

times of drought.

This set the state for nearly two million years of

evolutionary adaption for improved symbolic

communication, probably due to sexual selection

(crudely, females preferred males who could make

more convincing promises).

Dunbar’s studies suggest that language in fact evolved in response to our need to keep up to date with friends and family. We needed conversation to stay in touch, and we still need it in ways that will not be satisfied by email, or any other communication technology. In a segment of “This American Life” the discussion is all about the importance of gossip ( As Dunbar shows, the impersonal world of cyberspace will not fulfill our primordial need for face-to-face contact. Evidence of this can be seen in recent increases in violence against strangers like the shootings in Aurora and others. The need to be a part of a social unit is imperative in humans denying this need has terrible results. Games and long distance communication with other gamers does not have the same effect as physical contact. I don’t mean just sex, I mean touch. image20.pngWhen a stranger touches your arm for example it could feel like a breach of space, but can quickly turn into a positive perception of that person. Try this, the next time you are in a line that is taking a bit too long, make a joke that is loud enough for a few people to hear or engage in a conversation with the person in front or behind you. The reaction you get will be positive in turn though it will seem awkward. In days past, it was usual to greet people or smile to each other on the street. These days it is acceptable behavior to ignore people. In France today you would usually acknowledge people when entering a room or say a small shop by saying “Monsieurs, Madames” sort of a general greeting to everyone present. Of course, the obligatory kiss on the cheek. In fact, I remember being scolded by my mother-in-law because I should kiss every single person on each check, yes even if there are 15 people in the room. Actually, if you are in the north of France its three kisses, left cheek, right cheek and left again. Who thinks up these social rules? In any case, not being a social can have immediate results in depression, and a simple smile or positive comment from a stranger can make a big difference in someone’s attitude.

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