In The Descent of Man and The Expression of the Emotions in Man and Animals, Darwin argues for evolutionary continuity between the minds of man and higher animals, stressing that higher animals share with us many complex mental capacities:

In one form or another, the continuity thesis is accepted by all evolutionary biologists. Even when a large mental gap between the minds of animals and man is recognised, the interpretation of this gap is based on the assumption that there is an underlying genetic and evolutionary continuity. However, notice how Darwin framed his statement: he did not claim that we are psychologically and cognitively simpler than we believe we are – that we are psychologically more like ‘lower’ animals. On the contrary, Darwin believed that ‘lower’ animals are more complex than is usually thought – that they are more similar to us, possessing more sophisticated capacities than we usually grant them.

In this book, we have followed Darwin's approach, emphasising the learning capacities of higher animals, particularly their ability to learn from others.