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The Cultural Brain Hypothesis ...

Explanation

The cultural brain hypothesis is an attempt to explain the evolution of the brain across species with reference to environmental and social factors. The human brain is extremely large compared to other species (making birthing particularly difficult), and in the last few million years it has more than tripled in size. This is perplexing since brain tissue is particularly energetically expensive. The theory argues that the environment constrains brain evolution, rather than driving it. Our brains store and manage information that we receive from our environment through individual or social learning. Our brains expand in response to the availability of calories and information; and they expand in order to manage and store more information. Availability of information is affected by learning strategies, mating structure, group size, and the length of the juvenile period. Animals that rely more on social learning can use information acquired by others. So as the size of social groups grow, there is more information available to learn, making learning more efficient. In order to adapt to this overload of information, our brains have increased in size. The human juvenile period has also co-evolved with brain size, allowing us to ascertain how to learn more efficiently.

Origins

This theory is closely related to the social brain hypothesis, popularised by Robin Dunbar which correlates brain size in primates with social group size. Larger group size is something that necessitates more complex coordination and cognitive complexity. Dunbar’s number is a proposed cognitive limit to the number of people with whom an individual can maintain stable social relationships. Using average human brain size, Dunbar concluded that this number is 150. He argued that this limit is a function of brain size and this in turn, limits group size. The cultural brain hypothesis, constructed by Michael Muthukrishna, Maciej Chudek, Michael Doebeli and Joseph Henrich, integrates not just social group size but also the factors listed above.

Models

Personal identity and social identity are two modes of self-thought that allow us to survive both as individuals and as groups. We cooperate when we think of others as part of our group. Helping behaviour within animals increases chances of survival or reproductive capacity, and are categorised into cooperation and altruism. But we don’t just cooperate with others, we learn from them as well. We acquire norms based on our specific environments. This theory has been clarified using an analytical and computational model which specifies two pathways for acquiring information - individual and social learning. Muthukrishna et al. have carried out tests on cetaceans and compared this to tests carried out on primates in order to compare asocial and social animals and found that the results differ, with social animals having a more positive linear relationship between brain size and factors such as group size and juvenile period.

The cumulative cultural brain hypothesis

The cumulative cultural brain hypothesis is an expansion of the cultural brain hypothesis that posits that these processes, under specific circumstances, can lead to cumulative cultural evolution. It explains the parameters that can cause information to accumulate faster, forcing brains and social factors to evolve. These parameters display the evolutionary regime under which interaction between genetic and cultural inheritance is most likely to generate this take-off. They are: high transmission fidelity, low reproductive skew (more consistent with a monogamous breeding structure), intelligent ancestors and rich ecology where calories are in good supply. Humans have developed strategies in order to cope with large amounts of information and the effects of brain evolution, such as dividing up information and the division of labour leading to a ‘collective brain’, and expanding the juvenile period.

There are three key assumptions that regulate this theory. Firstly, larger and more complex brains decrease an organism’s fitness, since they require more calories, take longer to develop, are harder to birth and have organisational challenges. Secondly, larger brains have increased capacity or complexity that allows for the storage of more adaptive knowledge, which can relate to things like locating food and avoiding predators. Finally, adaptive knowledge which can be acquired either socially or asocially, through experience, causal reasoning or trial and error, increases an animal’s fitness by either increasing its number of offspring or reducing its probability of dying before reproduction.

Other points

Research has also suggested that evolutionary competition among males for females has allowed for males to evolve larger brains with learning abilities allowing them to acquire more effective strategies. It has also been suggested that offspring obtain similar genetic characteristics to their parents - including four specific genetic traits that are salient to this hypothesis, namely brain size, social learning probability, oblique learning probability and oblique learning bias. Large brains permit more adaptive knowledge which in turn exerts a selection pressure for larger brains. Bigger groups who rely on social learning obtain larger amounts of knowledge which exerts a selection pressure for an extended juvenile period, in which more adaptive knowledge can be created and learned. An extended juvenile period consists of reliance on oblique learning - learning from non-genetic others in the group which creates a selection pressure for learning biases better adapted to select individuals and knowledge to learn. Finally, oblique learning and learning biases lead to cumulative cultural evolution.

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References

{{BJORKLUND, D. GRAY, P. 2014. Psychology 7th ed. Worth: Duffield, UK.

CHUDEK, M, DOEBELI, M, MUTHUKRISHNA, M, HENRICH, J. 2018. The Cultural Brain Hypothesis: How culture drives brain expansion, sociality, and life history. Available online at: (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6224031/#:~:text=The%20Cultural%20Brain%20Hypothesis%20posits,through%20asocial%20or%20social%20learning.). Accessed 25th January 2023.

DUNBAR, R. 2016. The social brain hypothesis and human evolution. Available online at: (https://oxfordre.com/psychology/display/10.1093/acrefore/9780190236557.001.0001/acrefore-9780190236557-e-44). Accessed 25th January 2023.

MUTHUKRISHNA, M. 2018. The Cultural Brain Hypothesis: How culture drives brain expansion, sociality, and life history. Available online at: (https://michael.muthukrishna.com/cultural-brain-hypothesis-model/). Accessed 25th January 2023.

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