Causes of Bipedalism: Wading at the Seaside

Outline

Part of Alister Hardy's original, but inexplicably ignored, aquatic ape theory. Hardy wasn't too specific about bipedalism directly but wrote this in his New Scientist article 'Was man more aquatic in the past?' "My thesis is that a branch of this primitive ape-stock was forced by competition from life in trees to feed on the sea shores... I imagine him wading at first, perhaps still crouching almost on all fours, groping around in the water..." Hardy 1960

The aquatic ape theory, despite thirty years of work by Elaine Morgan, has been largely ignored and consequently there is a kind of blind spot around the idea of wading as a cause of bipedalism.

This specific seaside habitat is problematic in that fossil evidence is very unlikely to be found. There is, to my knowledge no early (> 3 mya) fossil evidence for a seaside-living ape that had bipedal traits.

Authors

Alister Hardy first published the idea in 1960 but conceived the idea some thirty years earlier.

Location

Unspecified coastal area.

Selection Pressure

The selection pressure here is quite strong in as much that an individual who waded on all fours would be more likely to get a face full of sea water and perhaps drown. However, an ape that could not wade bipedally would still be able to search for food in more shallow parts of the sea and would be able to avoid the sea altogether if necessary. Flooding from high sea levels would be rare and hardly life threatening.

Intermediate Steps

One of the strengths of the idea of a wading origin for bipedalism is that it makes the transition from four-footed to two-footed locomotion much easier to achieve and therefore, so the theory goes, much more plausible.

Both Sexes?

Applies to both sexes equally.

Explains Australopith Anomalies

Much of Australopith morphology seems to indicate a waddling gait that would be consistent with a wading form of locomotion.

Why not Pan? Observed in Pan?

Chimps have been observed wading in fresh water, but to my knowledge not in sea water. The idea of a group of apes becoming geographically isolated by a sea flooding is a very attractive explanation as to why only some apes became bipedal.

Links with other Theories

This theory is still quite compatable with most of the other theories - carrying, tool use etc. - however it is totally incompatible with Wheeler's thermoregulation theory.

Popularity

The aquatic theory is almost totally ignored. I only found one reference in my list of text books and even that took the form of one of those news items that producers put right at the end of a show as light relief. "Finally" Fleagle (1999) wrote "there is the fanciful aquatic theory..."

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