Much work supports the idea that cognition has a monotonic evolutionary relationship with certain environmental factors. For example, complexity: the more complex the environment, the more complex the cognition favored by selection. This is supported by comparative data where across species complex cognition is associated with a “quality-over-quantity” reproductive strategy involving large body-size, slow maturation, long-lifespans and small litters. However, these patterns do not clearly hold outside of the mammals. Instead, I’ll present some data from ongoing work that suggests that cognition evolves in a sweet-spot in which the environment is neither too challenging nor too simple, where lifespans are neither too long nor too short, and where brain tissue is neither too cheap nor too costly. Collectively this suggests the conditions favoring the evolution of cognition may be less common than previously thought, thereby explaining why complex cognition is rare.

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