People consume significantly less energy than chimpanzees when walking - whether they walk on all fours or on two legs. Photo: Cary Wolinsky
The human forefathers developed the upright walk primarily because they were able to move more energy-efficiently than on four legs. This is what American scientists conclude from a study in which they compared the energy consumption of chimpanzees and humans while walking. Thus, a human needs only a quarter of the energy that a chimpanzee needs to travel. This difference is mainly due to the longer legs and the lower center of gravity of the human anatomy. The scientists ran five chimpanzees on all fours and on their hind legs on a treadmill. In doing so, they determined muscle activity, oxygen consumption, soil force, and the time animals' feet touched the ground, and compared the values ​​to those of four human volunteers. On average, did people use 75 percent less energy than chimpanzees? whether they went on two or four legs, showed the evaluation. However, there were large individual differences between the animals: two needed more energy for walking on two legs than four, with two values ​​being about the same and one consuming two legs less.

According to the results, two main factors determine the energy consumption: the stride length and the active muscle mass. The shorter the steps and the more muscle mass needed for walking, the more energy-consuming it was. In particular, he benefits from his long legs and his favorable center of gravity: he lies just above the hips and knees, so that the short muscles at the ankles are mainly needed for walking. In contrast, the chimpanzee with its center of gravity in front of the hip must activate the large thigh muscles and consume more energy.

Regarding the evolution of the upright aisle, the individual differences between the chimpanzees are particularly interesting, the researchers said: They showed that even small changes can have a big effect, because the chimpanzee with the favorable energy consumption on two legs only took longer steps than his conspecifics. Perhaps there were such deviations even in the last common ancestor of humans and apes, speculate the researchers. Those who consumed less energy when searching for food, for example, had advantages over the others, so that this peculiarity could have prevailed over time. They now want to use fossils of early humans to check whether their physique already had corresponding changes.

Michael Sockol (University of California, Davis) et al .: PNAS, DOI: 10.1073 / pnas.0703267104 ddp / science.de? Ilka Lehnen-Beyel advertisement

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