Millions of years ago, humans’ ancestors, monkeys, decided to climb trees. They may have been searching for food, escaping predators, or looking for a shady place to rest. Later, like those who climbed high into the forest canopy, our relatives also realized that getting down safely was not as easy as it seemed.
Its primate ancestors must have solved the problem, but scientists are wondering how what first rose was able to descend, and how that affected the evolution of our species. A lot of work has to be done to understand what is involved.
“Everyone focuses on climbing because it’s difficult to climb. Every human being can relate to this, for example, in the same way that climbing a firefighter’s pole is difficult.” Nathaniel Dominey, an evolutionary biologist at Dartmouth College. “No one bothers to study climbing or descending, because gravity doesn’t affect whether you’re climbing or descending.”
in research Published on Wednesday Dr. Dominey and colleagues write in the journal Royal Society Open Science that great ape and ancient human ancestors probably had flexible shoulder and elbow joints, or finely controlled descent from the body, to counter the effects of gravity on large bodies. discovered that they had developed a kind of braking system that wood. The researchers hypothesize that this adaptation persisted even when early humans replaced trees with grassland habitats, and that their versatile upper limbs now allow them to forage, hunt, and defend.
The discovery could shed light on the gradual evolutionary steps that led our ancestors to walk upright and free their hands to make and carry tools.
A key insight came from the study’s co-author, Mary Joy, who was an undergraduate at Dartmouth at the time. She was watching videos of sooty mangabeys from chimpanzees, humans’ closest living relatives, and Old World monkeys from West and Central Africa. The footage was collected by the study’s other authors, graduate student Luke Fannin and Dartmouth College paleoanthropology professor Jeremy DeSilva.
Joy noticed that the two animals were climbing the tree with the same effort. But going downhill was different.
Using software typically used to analyze the movements of human athletes, Joy found that when chimpanzees descend from trees, they extend their shoulders and elbows much further above their heads than smaller monkeys. I have confirmed that. Compared to the sooty mangabeys, the chimpanzees bent their shoulders about 14 degrees more and extended their elbows about 34 degrees more when descending the tree (compared to climbing it).
“Mangabey was making similar movements when climbing, and the way he held his arms was quite diagonal,” Joy said. For the chimpanzees, it looked like they were falling in a controlled manner, but using their full range of motion to move as quickly as possible.
This freer range of movement is consistent with what scientists already know about the anatomical differences between chimpanzees and mangabeys, and the researchers reaffirmed it by looking at the skeletal remains. DeSilva explained that while great apes’ shoulder joints are roughly ball-and-socket shaped, monkeys’ joints are more pear-shaped. Additionally, the elbow joints of great apes open more widely. Combining these allows for a wider range of motion.
DeSilva said humans have similar shoulder and elbow anatomy to chimpanzees, as did ancient hominins such as Ardipithecus and Australopithecus. Dr. Dominey estimates that the emergence of this adaptation is between 15 million and 20 million years ago.
Susan LarsonA professor of anatomical science at New York’s Stony Brook University, who was not involved in the study, likened the new discovery to a missing puzzle piece that scientists have been searching for, explaining how hominids moved from trees to land. provided important insights into evolution.
“Climbing up and down trees is very important when escaping from predators and exploiting resources,” Dr. Larson says. “I think this study gives us a way to think about why early humans retained these traits for so long, until they abandoned trees and became bipedal hunters.”
The researchers hope to confirm their findings in other great apes.
“Sometimes there are larger monkeys like mandrills and baboons that climb trees,” Dr. Dominie says. “It’s great to see how the larger monkeys cope with the ‘downhill’.”