Evolution is change in heritable traits of biological populations over successive generations. Evolutionary processes give rise to diversity at every level of biological organisation, including the level of species, individual organisms, and at the level of molecular evolution.Another definition: the development from chimpanzees to "thinking man", i.e. "homo sapience". This development is due to development of working tools, including the mastery of fire and speech. As we have improved our mastery of nature, through the improved tools, we've changed ourselves, both physical appearance and the mental make up.