PRINCIPLE 3: SIZE MATTERS In general, the bigger the brainarea, the more neurons are present in it, and the more complex theintegration that occurs there. Thus mammalian brains, with tensof billions of neurons, perform more complex integration than doinsect brains with tens of thousands of neurons. By the same token,the massive enlargement of the cerebral cortex in the courseof mammalian evolution (as a result of the developmental proliferationof greatly increased numbers of neurons) attests to majorincreases in processing capability of mammalian, and especiallyprimate, brains. Primate brains are not “more evolved” than thebrains of fish and amphibians, because fish and amphibians havehad as long a time to evolve and can be considered to be as welladapted to their ecological niches as primates are. Nevertheless, thegreat expansion of cerebral cortex in primates has allowed types ofneural function (e.g., language, culture) not found in brains withfewer neurons.