Is This A Sensible View of Human Evolution?

[jimmydasaint]

OK, there are a number of different views on human evolution. This is a theory that is not new but seems quite attractive in terms of the hypothesis that is presented. I would like to stimulate discussion on this topic. Please read the following:

 

Humanity's earliest ancestors did not drag their knuckles along the ground before mastering life on two feet, but learned to walk upright while still living in the trees, according to a team of British scientists. The claim challenges the belief that humans evolved from chimp-like creatures that descended from the trees to roam the savannahs of east Africa, using their knuckles for support, before slowly rising to the upright posture of more modern humans.

 

The theory marks a dramatic twist in evolutionary thinking that suggests some of our earliest ancestors may have begun walking on two legs up to 24m years ago, rather than shortly after the human lineage split from chimpanzees around 6m years ago. It suggests early humans adapted rapidly to open landscapes by honing the basic walking skills they developed to move around the forest canopy.

 

The team, led by Robin Crompton at Liverpool University and Susannah Thorpe at Birmingham University, claim our tree-dwelling ancestors learned to walk on two feet because it helped them edge along outer branches while having their hands free to grasp ripe fruit. The tactic also enabled them to clamber between neighbouring trees without having to descend to the forest floor.

 

The scientists reached their conclusions after spending a year observing the movements of orang-utans in Sumatra. The great apes of the region are the only species to spend their entire lives in the trees. Footage of nearly 3,000 movements showed the apes consistently walked on two legs to reach the outer branches of trees, using their arms primarily for balance. Unlike gorillas and chimps, which bend their knees to walk on the ground, the orang-utans straightened their legs to adopt a more human-like gait.

 

Professor Crompton said such skills would have benefited early human ancestors enormously between 24m and 5m years ago, when eastern and central Africa experienced dramatic climatic cycles and the forests first thickened and then died back. "As the forests became sparse, the strategy of our human ancestors was more or less to abandon the canopies and come down to the ground, where they could use this bipedalism immediately to get around," he said.

(emphasis is mine - jimmy)

 

http://www.guardian.co.uk/print/0,,329958141-117780,00.html

[ecoli]

Doesn't seem too unusual or even that new, honestly.

[Mokele]

I actually had to wade through a lot of the primate locomotion literature while writing my first paper, and the article above isn't wrong, but it's not really right, either.

 

Basically, we've known for a long time that other primates will use bipedalism while in trees, sometimes for just moving about on level, wide branches, but also for reaching fruit and the like. This probably set in place the basic neurological motor patterns to allow bipedalism, but it wasn't really a hugely important mode of locomotion at the time - bipedalism in trees in extant primates is still very rare, vastly outweighed by lateral-sequence quadrupedal walks.

 

Based on anatomy and fossil evidence, as well as some modern experiments, it's likely that humans did have a chimp-like, knuckle-walking ancestor who, upon entering the savannah, switched to bipedalism (a recent study in nature shows that even modern chimps gain a small benefit in terms of calories per meter by switching to bipedalism).

 

However, the world of primate locomotion studies is....weird. They've spent the last ~20 years obsessing over the fact that primates walk with a *slightly* different gait from terrestrial mammals, while ignoring many other issues that are, frankly, much more interesting and fundamental. And they spend an inordinate amount of time defending very absolutist hypotheses ("THIS is the reason primates became upright, and NOTHING ELSE!"), when in reality they're just squabbling about the relative important of different factors. Basically, anything you hear about primates, turn down the rhetoric about halfway and you're probably about at where it should be.

 

Mokele