This article discusses causation regarding two core aspects of human evolution: bipedal movement and brain expansion. Rather than focusing on their retroactive adaptive benefits, the discussion revolves around typical causes of mutation, particularly metabolic changes fomented by climate shifts over the course of time.
The causal origins of two distinctly human traits; bipedal movement and brain expansion are unclear. With respect to upright walking, a number of theories have been put forth over time. So- called “savanna theory” (generically) is based on the premise that nature selected bipedal locomotion because it facilitated food carrying (Hewes, 1961) and provided heat resistance in the African flatlands (Wheeler 1991) and facilitate a throwing capacity for hunting and self defense. (Calvin 1990).
Another is the“generalist/fisherman” theory (my term) (Niemitz 2010) which holds that an upright posture evolved because it is readily supported by water and that early hominids spent considerable time by water’s edge in search of a plentiful, convenient aquatic food supply. Still another, free-hands theory, suggests that an upright posture allowed the first hominids to make tools (Darwin 1861) and/or throw objects to hunt or defend themselves (Young, 2003) (Kirschmann, 1999).
Meanwhile, aquatic ape theory provides a scenario in which homo sapiens became adapted to water environments. It is based on the fact that our species has tear ducts and other features seen in aquatic creatures. (Morgan 1997)
Each of these theories has merit but each has been subject to criticism. With respect to Aquatic Ape theory, Preuschoft has argued humans are biomechanically suited to life in the water, that too many of us are afraid of water and/or poor swimmers for this to be a species indigenous trait (1991). It begs the question of how competitive would we be in an aquatic milieu; for example vis a vis crocodiles and boas? Could we submerge without air for long periods of time as they do? Could we employ stealth in fleeing from predators? Even the most adept Olympic swimmers splash too much to rely on stealth in the water.