Chimpanzees, like all other ape species, do not possess external tails. This is a common point of curiosity, as many other primates, such as monkeys, are known for their prominent tails. The absence of a tail in apes is a distinguishing characteristic that reflects a unique evolutionary journey and adaptations to different ways of moving and living.
Chimpanzees and Tails
Instead of a visible tail, chimpanzees possess a structure called the coccyx, commonly known as the tailbone. This small, triangular bone is located at the very end of their vertebral column, tucked internally at the base of the spine. The coccyx in apes, including humans, is considered a vestigial remnant of a tail, meaning it is a reduced and non-functional version of a structure that was present and functional in their distant ancestors.
The coccyx typically consists of three to five fused or partially fused rudimentary vertebrae. It does not project externally from the body and serves no role in balance or locomotion, unlike the tails of many monkeys. The presence of this internal tailbone highlights the evolutionary link to tailed ancestors, even though the external appendage has been lost over millions of years.
The Evolutionary Path of Apes
The absence of a tail in apes is a result of evolutionary adaptations linked to changes in their locomotion and lifestyle. Around 25 million years ago, the ape lineage diverged from monkeys, and the tail was gradually lost. This loss is connected to the development of new forms of movement that did not require a tail, or where it might have been a hindrance.
Apes developed methods of movement such as brachiation, swinging through trees using their arms, and knuckle-walking, moving on all fours with their knuckles. The upright body posture and broader chests seen in apes facilitate these movements and would not benefit from a tail for balance. Recent research suggests the tail loss was influenced by a genetic change involving an insertion of a repetitive DNA element, called an Alu element, into the TBXT gene, which plays a role in tail development. This genetic alteration led to a different protein formation, resulting in shorter or absent tails.
Apes Versus Monkeys
A key distinction between apes and monkeys lies in the presence or absence of a tail. Most monkey species possess tails, which can be long and used for balance, or even prehensile, allowing them to grasp branches as a fifth limb. In contrast, all ape species, including chimpanzees, gorillas, orangutans, and gibbons, are tailless.
Apes typically have larger body sizes, broader chests, and a more upright posture than monkeys. Apes also tend to have larger brains relative to their body size, contributing to more complex cognitive abilities and social structures. While monkeys often move quadrupedally across tree branches, apes exhibit more varied locomotion, including swinging, knuckle-walking, and upright walking.