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From brains to bears. understanding brain size evolution: causes, costs and benefits

Chambers, HR


HR Chambers


S Heldstab


Developmental and energetic costs result in brains being expensive organs to grow and maintain, yet large brains have evolved in many mammalian species. The adaptive value of increased brain size has come under scrutiny over the past few decades and despite considerable research effort, much uncertainty remains regarding: (i) the selective pressures responsible and (ii) the potential benefits that big brains provide. Here, both topics are investigated.
Firstly, the influence of social, ecological and life-history traits were assessed on whole and regional brain size in two well-studied orders: Primates and Carnivora. In primates, consistent associations are found between brain size and dietary factors, such as dietary breadth; however, evidence is also found indicating sociality as a selection pressure driving brain size. In carnivores, evidence suggests ecological variables, most notably home range size, is influencing brain size, whereas no support is found for the social brain hypothesis. Life-history associations reveal complex selection mechanisms counterbalance the costs associated with expensive brain tissue through extended developmental periods, reduced fertility and extended maximum lifespan.
Secondly, to better understand the proposed benefits afforded by encephalisation, the cognitive abilities of 17 captive European brown bears (Ursus arctos arctos) were tested via two behavioural problem-solving trials. Results revealed evidence of trial-and-error learning; however, two juveniles appeared to acquire an association between the latch and access to the box, suggesting some individuals have potential to adopt successful strategies and draw perceptive associations. Individual variation in motivation levels appears to be an important factor influencing cognitive performance. The bears failed to spontaneously use a tool but still managed to retrieve the food reward, instead using alternative techniques. Analyses revealed both age and sex (using female as the reference category) to be negatively associated with time-to-solve in our sample, indicating that younger male bears solved the task more quickly. Results suggest social dynamics of group-living bears to be influencing cognitive performance, as the collective nature of testing resulted in increased competition over a high-value reward. European brown bears are confirmed to be an excellent model species for testing the benefits of increased brain size, as well as theories of cognitive evolution.
The findings of the first study, together with other recent re-examinations of brain size evolution, are shifting long-standing viewpoints on the variables responsible for encephalisation. Meanwhile the second study is one of the first to explore the cognitive abilities of captive European brown bears; this approach is at the forefront of cognitive evolution research, since it seeks to test the benefits afforded by encephalisation.


Chambers, H. From brains to bears. understanding brain size evolution: causes, costs and benefits. (Dissertation). University of Salford

Thesis Type Dissertation
Deposit Date Oct 5, 2022
Publicly Available Date Oct 5, 2022
Additional Information Additional Information : The research titled ‘Why big brains? A comparison of models for both primate and carnivore brain size evolution’, which is presented and discussed in chapters 2 to 5, has been published as a research article in PLoS One (DOI: 10.1371/journal.pone.0261185).
Funders : Bears in Mind;Santander Universities Travel Award
Award Date May 3, 2022


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