Lobby of One

Last night’s Discovery Channel special on Ardipithecus ramidus (AKA, Ardi) was a bit disappointing. Perhaps I was half-asleep but the broadcast seemed to imply through omission that bipedalism evolved as a distinctively human trait. To the contrary, humans were not the first species to rely on bipedal locomotion.

There are many theories as to how bipedalism evolved. But what most of these theories do not take into consideration is that the selective pressures that led to the evolution of bipedalism as an exclusive or transient mode of locomotion is specific to each species that employed it.

Some animals, for example, use transient bipedalism in displays of aggression or to gain momentum during an attack. In other animals, bipedal locomotion confers additional speed in skirting danger. Avoiding danger would appear the most immediate advantage conferred. (Actually living has a tendency to prolong reproductive capacity.)

But, once employed as a strategy to avoid danger, bipedalism becomes useful in any number of ways – from thermoregulation (keeping the core furthest away from the hot ground) to the ability to carry more food longer distances.

While the literature is sparse in this regard, the biomechanics of bipedalism may also increase the likelihood of ventro-ventral (face-to-face) copulation. Such sexual behavior, taken together with the uncoupling of vaginal intercourse from the estrous cycle, produces in part the social organization seen in humans today.