Evolution

Independent Emergences#

Instead, the correct view of evolution is that animals radiated from common ancestors (Fig. 1c). Within these radiations, complex nervous systems and sophisticated cognitive abilities evolved independently many times. For example, cephalopod mollusks, such as octopus and cuttlefish, possess tremendously complex nervous systems and behavior (Mather & Kuba, 2013), and the same is true of some insects and other arthropods (Barron & Klein, 2016; Strausfeld, Hansen, Li, Gomez, & Ito, 1998). Even among nonmammalian vertebrates, brain complexity has increased independently several times, particularly among some sharks, teleost fishes, and birds (Striedter, 1998).

In particular, regarding brain

Early students of brain evolution had constructed rather grand but speculative theories which stated that brains evolved in a linear manner, from fish to man and from simple to complex. These speculations were soundly refuted, however, as contemporary comparative neurobiologists used powerful new techniques and methodologies to discover that complex brains have evolved several times independently among vertebrates (e.g., within teleost fishes and birds) and that brain complexity has actually decreased in the lineages leading to modern salamanders and lungfishes. Moreover, the old idea that brains evolved by the sequential addition of new components has now been replaced by the working hypothesis that brains generally evolve by the divergent modification of preexisting parts.