But the consensus against animal intelligence began to unravel with Darwin's Theory of Evolution

Aristotle believed that humans possess reason,while animals could only follow brute instincts for survival and reproduction.Almost 2000 years later,Descartes suggested a more extreme version of that idea,arguing that animals following instincts were indistinguishable from robots responding mechanically to stimuli in their environments.But the consensus against animal intelligence began to unravel with Darwin's Theory of Evolution.Darwin hypothesized that intelligence could evolve from simpler instincts.He had observed earthworms making choices about how to drag oddly shaped leaves into their boroughs,and was struck that a human might employ similar means to solve a similar problem.