origin of humans (Origins)

by dhw, Friday, April 14, 2023, 11:59 (587 days ago)

An article in today’s Times contains an extraordinary contradiction.The headline is:
Grassland theory uproots story of our first steps.

Researchers in East Africa have shown that on 9 sites a group of plants known as C4 grasses were an important part of the ecosystem about 21 million years ago, which “suggests that substantial areas of open grassland existed at least ten million years earlier than was thought.” This in turn suggests that Morotopithecus – an ape that lived then and is “regarded as one of the best representatives of the ancestors to all of the living apes and humans”- would have lived in open spaces. And this is where the article contradicts itself. It begins with the following:

“It was widely thought that ancient apes first adopted a vertical posture while living high in the canopies of dense forests, where the limbs of the tree would have met those of the next. Being upright, it was reasoned, would have made it easier for these animals to climb and to reach for fruit while balancing on branches. It was thought that only rarely, if ever, would they have set foot on the ground.”

But after explaining all the research, the article goes on to say: “Roughly speaking, researchers have often assumed that humans came to walk on two legs because dense forests receded and grassland environments opened up. Being upright would have allowed us to see for relatively large distances across a flat savannah and would have given us an efficient running gait. However, the idea that ‘shrinking forests made us human’ seems too simplistic.”

I didn’t know researchers had "widely thought" or "often assumed" both theories at the same time! It’s the latter that I think has held sway and certainly sounds to me far more convincing than the former, since even in dense forests, ancient apes would have continued to move through the trees as they do now. And I can see nothing in the new research that makes it sound “too simplistic”. The new research need not even change our views on the timetable of events. Morotopithecus “would not have walked on two legs like a human”, so it proves nothing about the timing of bipedalism. We should bear in mind that bipedalism could have originated in a single group of anthropoids. The researchers examined nine sites. How many sites would have to be explored in order to find what may have been the single original site where a shrinking forest gave way to grassland, and a single group of anthropoids adjusted to their new surroundings by standing upright? Convergent evolution might have resulted in more than one group making the same adjustments, but this still wouldn’t invalidate the second theory.