Learning is a biological adaptation, and like any other adaptation is the outcome of evolution by natural selection. Because it is acted on by natural selection, learning in different species of animals exhibits both descent with modification and specialized adaptations. Many properties of learning, like the formation of associations, are widely shared among animals. The molecular mechanisms of learning are also remarkably similar among animals as different as sea slugs, honeybees, and rats. But, in addition, learning exhibits specialized adaptations, modifications of learning which differ between species. Evolutionary adaptation in learning is usually investigated using comparative methods to examine similarities or differences among animals in how or what they learn. Learning can also have a reciprocal effect on the process of evolution. Animals can learn to exploit new habitats and new resources within their habitat and thus change the selective pressures they are exposed...