How did humans become bipedal?

Scientists have been discussing how humans became bipedal (walk on two legs) for ages. It’s been a mystery but it is at the root of our uniqueness as a species. There are several theories and perhaps the most recent one which is reported in The Times newspaper today Thursday, December 15, 2022, maybe the right one! Firstly, you have to agree with Darwin’s theory of evolution. If you don’t agree with that then you can stop here.

The most recent theory has emerged from a study of our closest living evolutionary relatives. Scientists studied the chimpanzees of the Issa Valley in Tanzania. These chimpanzees live in a “mosaic” landscape of forests and open grassland.

That’s important because it means they can live in the trees and they can live on the ground.

Chimps of Issa Valley
A young chimpanzee feeds on seed pods in the Issa valley, Tanzania. Credit: R. Drummond-Clarke/GMERC
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The scientists discovered that these chimpanzees live in trees about 75% of each day which is similar to other chimpanzees in Africa living in dense forests.

And when they live in the trees they walk on two legs. They are bipedal when they are arboreal to put it another way.

And when they come out of the trees to walk on the ground they seldom walked on two legs. They almost always walk on all fours.

The revelation is counterintuitive. You would have thought that when they were on flat ground they would stand tall so they could see further and travel faster but that wasn’t the case.

The researchers spent 15 months observing 13 chimpanzees. They recorded how they climbed, walked and swung through their forest environment.

This latest theory indicates that humans adopted bipedal walking when our ancestors still lived in trees and not when the began travelling on the ground.

Earlier theories specified that bipedalism in human started when our ape ancestors came out of the trees and lived on the ground. At that point they started to walk on two legs because walking and running became more efficient, it helped to minimise exposure of the body to the sun and it allowed them use tools with their hands.

The modern theory is that bipedalism first evolved because it was useful to travel through the forest canopy. When our ancestors came out of the forest trees and started to live on the ground permanently that early bipedalism in the forest became useful to them. It was a happy spin-off of an evolutionary process that had happened earlier in the forest.

That’s the difference. It wasn’t being on the ground which drove evolution to bipedalism. It was living in trees which evolved bipedalism.

Bipedalism. Image in public domain.

Dr. Alex Piel of University College London, who led the study, said:

“We naturally assume that because Issa has fewer trees than typical tropical forest, where most chimpanzees live, we would see individuals more often on the ground than in trees. Moreover, because so many of the traditional drivers of bipedalism – such as carrying objects or seeing over tall grass, for example – are associated with being on the ground, we thought we would naturally see more bipedalism here as well. However, this is not what we found. Our study suggests that the retreat of forests in the late Miocene-Pliocene era around 5 million years ago and the more open savanna habitats were in fact not a catalyst for the evolution of bipedalism. Instead, trees probably remained essential to its evolution, with the search for food-producing trees a likely driver of this trait.”

This, as you will no doubt see, is a complete departure from discussing cats! I hope you will forgive me but this is an important aspect of human history and evolution which may interest people.

It is somewhat linked to the domestic cat in that human evolution led to farming and farming led to the domestication of the North African wildcat in the Fertile Crescent probably more than 10,000 years ago. So without human evolution we probably wouldn’t have domestic cats. There is a connection. 👍😃

P.S. Is bipedalism at the root of a lot of our musculoskeletal health problems?

Below are some articles on human behaviour in relation to cat caregiving.

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