Through the course of evolution, the brain has undergone considerable changes. In many invertebrates, such as worms, the nervous system consists of no more than a net or bundle of nerve cells. In fish, amphibians, and reptiles, the brain is a well-developed organ consisting of several distinct structures, such as the cerebellum, tectum, and basal ganglia. These structures are specialized for different basic functions, such as detecting visual patterns, generating walking or swimming movements, generating reflexive responses, and so on. Mammal brains also contain many of these primitive structures, so scientists can understand many aspects of our own brain function by studying these areas in other animals.
Mammal brains have undergone dramatic evolutionary changes which are thought to be responsible for their increased thinking capacity. One striking aspect of mammalian brain evolution is the development of neocortex (pink shaded region in the rat, monkey, chimpanzee & human brain). Compared to other mammals, higher primates such as humans and chimpanzees have disproportionately larger neocortices. In some primates, the neocortex has expanded at such a rate that it has folded in on itself. Scientists believe that it is this development of neocortex, and in particular, of the frontal region, that is responsible for our increased intelligence and capacity for problem solving.