The ability of humans to walk on two straight legs may have evolved in trees rather than on the ground, according to scientists studying wild chimpanzees in Tanzania.
This contradicts the widely accepted theory that prehistoric human relatives evolved on two legs to walk because they lived in an open savanna environment, according to a study published Wednesday in the journal Science.
Researchers from University College London (UCL) spent 15 months observing the behavior of 13 adult wild chimpanzees in the Issa Valley in western Tanzania, which is home to a mixture of open land and dense forest areas. Known as the “savanna-mosaic,” this type of environment is similar to that in which our early human ancestors lived.
The team recorded every time that the chimpanzees were upright, and whether it happened on the ground or in the trees.
They therefore compared this with instances of standing on two legs from the chimpanzees that live in other densely forested areas of Africa, he found that the Issa Valley chimpanzees spent as much time in the trees as their forest cousins.
In this way they are not based on more earthly, as they think there should be opinions, which are more open to the environment where they live. In addition, more than 85% of the time that chimpanzees walked upright in trees, rather than on the ground.
Study coauthor Alex Piel, an associate professor of anthropology at UCL, told CNN that the theories largely followed a certain logic.
“It’s been a long-held assumption: ‘Less trees mean more time on the ground, more time on the ground means more straight weather,'” Piel said.
However, his team’s data does not support, but suggests, that more open environments are not the catalysts to stimulate bipedalism, Piel said. “This is not a nice logical story,” he said.
The next question for researchers is why Issa Valley chimpanzees spend more time in trees, even though they hang around fewer trees than other chimpanzee communities, Piel said.
One explanation may be that the food trees are encouraged to spend time there to eat, he said, although it could also be a time component.
During the rainy season, the grass in the Issa Valley grows to about 6.5 feet in height, Piel said, which means chimpanzees are more vulnerable to ambushes by predators, such as leopards, if they stay on the ground.
“It is possible that this signature time is dramatic,” he said.
According to Piel, the first humans also had predation in a similar environment.
“It’s a true analog system,” he said.
However, Piel emphasized that the study does not draw direct comparisons between chimpanzees and our human ancestors, but rather theories that need to be tested against fossil evidence to see what it tells us about the anatomy of early hominids.
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