Causes of Bipedalism: Display Behaviour

Outline

One of the most commonly observed bipedal behaviours in extant chimpanzees and gorillas is the threat display. It was logical, therefore, that it should be included as a possible mechanism where full bipedality might have arisen. The weaknesses of the argument are that a) threat display is primarily a male behaviour whereas clearly both males and females are bipedal and b) why would this behaviour become fully habitual bipedalism only in one type of ape and not others?

Authors

Attributed to Livingston (1962)

Location

Terrestrial.

Selection Pressure

Assuming that the social group took on a Pan troglodytes structure more than the Pan paniscus model - where males dominate more than females, you could argue that the ability for the dominant male to make stronger threat displays would be selected for in male intra-sexual selection. It is hard to see how the trait would be of any benefit to females using this model on its own.

Intermediate Steps

As existing apes do often get up onto their hind legs to perform a  threat behaviour an advantage in the the ancient quadrupedal form can be envisaged. If the threats became more pronounced and longer at every stage of its evolution - in some kind of inter-tribal arms race - you could argue that this feature would be an advantage at every stage on the way.

Both Sexes?

Mainly male.

Explains Australopith Anomalies

Australopithecus morphology does indicate that their bipedalism was inefficient over long distances but might have been sufficient for short bursts of bipedal activity as would be expected in extended threat displays.

Why not Pan? Observed in Pan?

This is where the theory is at its weakest. If this was the only factor contributing to bipedalism why didn't other apes adopt it too?

Links with other Theories

This theory is very compatable with most of the other theories.

Popularity

Quite a popular theory. Listed in 4 out of 8 of my sample textbooks.

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