Did we start walking because there were fewer trees? If you look at chimpanzees, it’s not obvious

It is so obvious that many take it for a fact. Our ancestors moved from the forest to the savannah, where the distance between the trees is greater and where you are easier prey for predators. This different “us” environment required us to walk on two legs, which is simply a more efficient way of moving on the ground. It could have been so, but new research clearly shows that the explanation is not as obvious as it seems.

In the absence of fossil evidence for or against such a hypothesis, biologists often examine the behavior of living related species in similar situations. The same goes for Rhianna Drummond-Clarke’s team at the University of Kent. They found a colony of chimpanzees in western Tanzania with a perfect living environment: half forest, half savannah. Do these animals walk more often on two legs in the savannah zone than in the forest zone?

They studied the chimpanzees remotely for 15 months and peated their poses: still or moving, and whether they were doing it on all fours or on two. Chimpanzees were found to be no more bipedal in open terrain than they were in forest. It was even reversed before.

The life of the trees remains useful

In addition, another hypothesis also turned out to be wrong: as the landscape opened up, these chimpanzees no longer often moved on the ground. Instead, they stayed longer in the same tree. True, large productive trees with a wide crown of branches, as in the photo, are an ideal place for great apes. They are safe from predators on the ground and there is enough food for a longer period of time, which avoids the number of tiring journeys on the ground to the next tree.

And in this tree, they moved remarkably often on two legs. It’s an effective way to grab fruit from the end of a branch, the researchers note. Moving on two legs can therefore be seen as an adaptation to the life of trees.

These remain hypotheses, but these observations have given researchers another idea. The fossils we have, especially the wear on the teeth, seem to indicate that our ancestors ate a lot of tree food, more than you would expect from a savannah walker. If the strategy of chimpanzees in the Issa Valley is any indication of how primates cope with a transition to savannah, then early hominids may well have spent a long time in the same tree before moving on to the next. Whether you can really learn to walk in a tree like early hominids could undoubtedly be debated for a long time. But it’s at least an interesting possibility that their ancestors made the transition to soil life in a much straighter way than previously believed.

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