Entitled “Chimpanzee Locomotor Energetics and the Origin of Human Bipedalism,” by Michael Sockol, David A. Raichlen and Herman Pontzer, the article will appear in the July 17 edition of PNAS (which at the time this article was written still not published at the PNAS site which is showing the July 10 edition as the most current).

Nevertheless, the findings have been foreshadowed by a press release issued through the Eureka Alert service and also widely reported by the Associated Press.
 
Anthropologists have long theorized that early humans began walking on two legs as a way to reduce energy costs, giving early upright walking hominids an evolutionary advantage of making the gathering and hunting of food a much less energy intensive process, thanks to a big saving in energy and caloric expenditure of not having to use arms and legs to ‘knucklewalk’.

A study was done in 1973 to compare energy usage, but strangely only looked at juvenile chimpanzees and they way they walked with their arms and legs, instead of studying adult chimpanzee walking and movement. Juvenile chimps have different locomotor mechanics and costs than adults.

The need for a new study was clear to the researchers, who used treadmill trials to analyze walking energetics and biomechanics for adult chimpanzees and humans.

Conducted by Herman Pontzer, Ph.D., assistant professor of Anthropology in Arts & Sciences at Washington University in St. Louis; Michael Sokol of University of California, Davis; and David Raichlen of University of Arizona, the report significantly puts the energy saving of two legged upright walking at 75% over kuncklewalking apes.

Pontzer said that: “Walking upright on two legs is a defining feature that makes us human. It distinguishes our entire lineage from all other apes.”

Eureka reports that the team examined the early hominin fossil record, which they found to include predicted changes consistent with lower energy cost- longer hind legs compared to body mass and structural changes to the pelvic bone allowing for more upright walking.

Analysis of these features in early fossil hominins, coupled with with analysis of bipedal walking in chimpanzees, indicate that bipedalism in early, ape-like hominins could indeed have been less costly than quadrupedal knucklewalking.

So, where here through God, evolution, both or something else, for humans at least, two legs aren’t just good, they’ve turned out to be just right, while we can be pretty sure four-legged animals and multi-legged insects are all quite happy too with the way they’ve turned out too.

For more information, do some fancy footwork and leg your way over to the report itself, when PNAS gets around to publishing it shortly!