Gorillas do not possess tails. This absence is a distinguishing feature of all great apes, including gorillas, and reflects a significant evolutionary divergence in their lineage.
Apes Versus Monkeys
A fundamental biological distinction between apes and monkeys lies in the presence or absence of a tail. Most monkey species have tails, which serve various functions depending on their lifestyle. For many arboreal monkeys, tails provide balance as they move through trees, while some New World monkeys even possess prehensile tails capable of gripping branches like an extra limb. In contrast, all apes, including gorillas, chimpanzees, bonobos, orangutans, and gibbons, naturally lack external tails.
Beyond the tail, other physical differences exist between these primate groups. Monkeys typically have narrower chests and often move on all fours, either running along branches or on the ground. Apes, however, are generally larger, with broader chests and shoulder joints that allow for a wider range of arm movement. This anatomical difference supports their distinct modes of locomotion, whether it is swinging through trees or moving across the ground.
The Evolutionary Advantage of Taillessness
The absence of a tail in apes is a result of evolutionary adaptation, likely linked to changes in their locomotion and lifestyle approximately 25 million years ago. As ancestral apes transitioned towards more upright postures and modes of movement such as brachiation—swinging through trees using their arms—a tail would have become less necessary for balance and potentially even a hindrance. Their specialized shoulder joints and longer arms provided the necessary adaptations for navigating arboreal environments without the need for a tail.
Furthermore, as some ape lineages began spending more time on the ground, a tail offered little to no advantage and could have been cumbersome. The transition to terrestrial locomotion, including knuckle-walking in gorillas and chimpanzees, or bipedalism in humans, rendered the tail functionally obsolete. The genetic basis for this loss involves specific mutations, such as the insertion of a DNA sequence called an Alu element into the TBXT gene, which plays a role in tail development. This genetic change is thought to have contributed to the sudden evolutionary shift towards taillessness in apes. Though they lack an external tail, apes, including humans, retain a tailbone or coccyx, which is a vestigial remnant of their tailed ancestors.
Other Tailless Primates
The absence of a tail is not unique to gorillas; it is a defining feature shared across the entire ape lineage. This includes all great apes: chimpanzees, bonobos, and orangutans, alongside humans. Additionally, the lesser apes, which comprise various gibbon species, also do not possess tails.
These diverse species, ranging from the large, ground-dwelling gorillas to the agile, arboreal gibbons, all demonstrate this shared characteristic. While they exhibit a wide array of sizes, behaviors, and habitats, their common evolutionary history as apes is underscored by their tailless anatomy. This commonality reinforces that tail loss was a significant evolutionary event for the entire group of primates classified as apes.