Aquatic Ape Hypothesis - The Hypothesis

The Hypothesis

AAH suggests that many features that distinguish humans from their nearest evolutionary relatives emerged because the ancestors of humans underwent a period when they were adapting to an aquatic or semiaquatic way of life, but returned to terrestrial life before having become fully adapted to the aquatic environment. Variations within the hypothesis suggests these protohumans to have spent time either wading, swimming or diving on the shores of fresh, brackish or saline waters and feeding on littoral resources. Various traits that have been proposed to indicate past adaptation to aquatic conditions and the return to land, but generally the evidence provided for the AAH is equally well accounted for by land-based adaptations without needing to posit an aquatic phase of human development. Parallels made by proponents of the AAH between humans and the proboscis monkey, which shows mainly behavioral adaptations to a water-based habitat, contradicts any claims of anatomical evidence for the hypothesis. Many species of modern primates demonstrate some sort of aquatic behaviors (such as swimming, wading or diving) and use of aquatic environments (for thermoregulation, display behavior, range, diet and predation) but many do not display the traits posited by AAH, suggesting the traits posted as evidence for the AAH may facilitate aquatic behavior rather than evolving as a result of it.

While most proto-human fossil sites are associated with wet conditions upon the death of the hominin, this is not seen as evidence for the AAH since being buried in waterside sediment is one of the rare situations in which fossilization is likely to occur; paleontologists are aware of this preservation bias and expect fossils to be located near such sediments. There is no fossil evidence to support the AAH.

Several theoretical problems have been found with the AAH, and some claims made by the AAH have been challenged as having explanations aside from a period of aquatic adaptation. Review of the individual claims used as evidence for the AAH generally does not support the hypothesis overall, and most of these traits have an explanation within conventional theories of human evolution. Other authors have suggested that wading, food gathering and other interactions with watery environments may have provided a less extreme but still present role in human evolution.