That is not clear. The brain is not differentiable as a whole, but you are certainly able to converge very fast when you smell where the cookies are! There is a lot of (mostly speculative) research on how the brain could realize local gradient descent.
Evolution requires a somewhat viable solution at every step, and derives the next one by mutating the previous one. That means that it cannot cross a chasm of unviability.
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Viability is a very loose metric. A mutation can be viable but be less fit than the previous generation. This is different from gradient descent where the next step is that of greater fitness.
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If you think about the evolutionary landscape as a mountain range, you don't always have to find a higher peak, but you also cannot cross areas that are under water. Nonviable phenotypes are under water, i.e. they don't have positive fitness and cannot reproduce.
End of conversation
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