Human ancestors can walk with their legs but most still live on trees

This is probably the trade-off between muscle development and brain size during human evolution.

Our ancestors "Lucy" spent at least a third of their lives on trees around 3.18 million years ago, according to a new study that could help explain the process of our species developing the brain. How more than muscle?

Lucy (of Australopithecus afarensis) developed an extremely powerful upper part of the body but besides, it also went on two legs. This is the conclusion of a new study, published in the journal PLOS ONE.

"Lucy can go on the same ground as we are now, but the number of steps is more," said lead author Christopher Ruff, a professor of functional and evolutionary anatomy at John Hopkins College of Medicine. "This will cost more energy and may limit the ability to move far away on the ground".

Lucy gibbon, "grandmother" 3.2 million year old primate is considered a human ancestor.

Using the tomography machine, Professor Ruff and his team analyzed the internal structures of Lucy's arm and thigh bones. The rest of Lucy was found in the Afar region of Ethiopia 42 years ago, showing one of the most complete bone fossils found in human ancestors walking straight on two feet.

The researchers continued to compare the scanned images of Lucy with the scanned image of the Paleolithic and the modern people, who spent most of their time walking on the ground , and with primates that spend most of their time in the tree. When on the ground, primates often move with all four limbs.

Lucy's upper limbs were really hard-pressed because they often had to climb trees, Ruff and his colleagues concluded. Like our species, one side tends to develop the lower limbs, but at that time they also have a very strong upper body.

"Lucy will look not like modern athletes, although the strength of her hand and leg bones is almost the same as the athletes today," Ruff said.

May describe a day of Lucy that will take place as follows:

"Like modern African apes, it tends to spend a lot of time on the ground searching for food , resting and moving but only at short distances , " Ruff said. "Some kinds of food, including a lot of fruits, must climb trees to be able to get them. Plants are also a place to sleep, again this is similar to modern African apes."

To this day, the diet consists of a variety of plant-derived foods such as fruits and nuts that are often preferred by our species. And if you feel comfortable around the trees as well as with the products of this nature, it is not uncommon because our ancestors, or specifically the Lucy gibbons spent a lot of time. on tall branches.

However, Lucy's story does not have a happy ending. It is not dead by old age but by injury after falling from a tree. Therefore, it is very likely that our ancestors had a transition from ape to the ground and this was obviously a difficult period.

The rest of Lucy.

However, Ruff quickly pointed out that even for primates, it is thought that the species is well adapted to climbing, sometimes falling trees and causing death. He added, "If Lucy spent more time in the tree than it was, it was clear that the possibility of this would be higher than that it only lived on the ground."

He and some anthropologists suspect that a dry climate of about 2.5 million years ago in Africa may have led to a narrowing of forest areas, thus increasing the benefits of moving. on the ground to go back to the areas of our ancestors. The change of diet, ecology and even social organization could also be the cause of Lucy's next generation deciding to leave the trees.

This is probably the trade-off between muscle development and brain size during human evolution.

Ruff explains: "The brain is an organ that requires a lot of metabolism. Muscle tissue also requires a lot of energy to maintain and grow. Lucy has a fairly large muscle, a large bone strength but "It has a small brain. Decreasing the average muscle mass later in human evolution may have released resources to target a larger brain."