Written by Guan Zhenhua (Southwest Forestry University)
Rui Min (Kunming Institute of Zoology, Chinese Academy of Sciences)
Photo by Guan Zhenhua Xiong Shiming Liu Yekun
This article is an excerpt from the magazine Knowledge is Power
The gibbon's long arm is as striking as an elephant's nose, and it is this gibbon that makes the gibbon very well adapted to forest life. This extremely remarkable feature constantly arouses people's curiosity, and children will ask when they see gibbons: "Why are gibbons so long?" ”
01
What are the long arms for?
The naturalist David Attenborough gave the answer, describing gibbons this way: "A branch of the great ape spreads eastward into the tropical forests of Asia. There, they live permanently in trees, forming their own unique way of life. Their tails disappear, their arms extended, and they move by swinging rather than crawling, and the skill and speed of their actions are astonishing. This is gibbons. ”
Male western black-crowned gibbon
In fact, the gibbon's long arm is a morphological trait adapted to arboreal life that helps them move quickly through the canopy, capturing arboreal small mammals or avoiding predators. But at the same time, we've also found that many arboreal primates (such as monkeys) have long tails that can also help them maintain balance as they live in trees. So why are gibbons long-armed and not long-tailed?
Although they are all characteristics of adapting to arboreal life, two differences can be found through comparison: the long tail of the monkey can maintain balance, but it affects the rapid movement, while the long arm of the gibbon can achieve rapid movement; the long-tailed monkey can live in the tree, but also has a lot of time to live on the cliff face, and can also move flexibly on the ground, while the gibbon mainly lives in the tree, if it moves on the ground, it must raise the long arm, reduce the movement speed, so it is not suitable for ground life.
Therefore, the long arms and long tails that are both adapted to arboreals are obviously conducive to more pure arboreal life, and the long tails allow monkeys to adapt to more complex environments.
The grey langur has a long tail
02
How are long arms formed?
We all know that apes evolved from trees to the ground, so did gibbons evolve from apes that descended to the ground and then returned to trees? Or did it not go through the process from the tree to the ground, and the gibbon was formed directly by the long-tailed monkey through the long process of shortening the tail and extending the arm?
From the history of human evolution, apes originated in Africa and have degenerated their tails. One of the apes arrived in Southeast Asia, and due to the degradation of its tail, it formed another trait adapted to arboreal life - the long arm. If the evolutionary route of gibbons returning from the ground to life in trees is to be established, fossil evidence is needed to support it. We look forward to finding primates in transitional form in the future – with relatively long arms, but strong leg bones because they have not yet fully adapted to arboreal life; but if we find a monkey with a long arm and a short tail, this kind of monkey camp arboreal life, then we have to think about whether the evolutionary route of "the ape goes to the ground and then returns to the tree" is correct.
Knowledge points today
Secondary School Biology | Biological evolution