The term “ape” refers to the Hominidae family, a group of primates that includes gorillas, chimpanzees, orangutans, gibbons, and humans. Apes are distinct from monkeys because they lack tails and generally possess larger bodies and brains. Investigating the body mass across different ape species reveals a profound biological diversity, ranging from the smallest, agile tree-dwellers to the massive, terrestrial giants. Comparing these weights offers insight into the varying evolutionary pressures that have shaped these closely related primates.
Defining the Ape Family Tree
The ape family is broadly separated into two major categories. The first group is the Lesser Apes, consisting solely of the gibbons and siamangs (family Hylobatidae). These species are known for their remarkable agility and relatively small stature.
The second group comprises the Great Apes, which are substantially larger and include the genera Pongo (Orangutans), Gorilla (Gorillas), and Pan (Chimpanzees and Bonobos). This division establishes that body mass varies widely across the ape lineage, and the size difference is a primary physical trait used for classification.
The Lesser Apes Body Mass
The Lesser Apes are the lightest members of the Hominidae family. Most gibbon species are relatively small, typically weighing between 5 and 7 kilograms (11 to 15 pounds). These weights are suited for their highly arboreal lifestyle, which relies on brachiation, or swinging through the trees.
The largest Lesser Ape is the siamang, found in Sumatra and the Malay Peninsula. Adult siamang males average approximately 11.9 to 12.8 kilograms (26 to 28 pounds), while females average about 10.5 to 10.7 kilograms (23 pounds). Sexual dimorphism is not strongly pronounced in Lesser Apes, as the sexes exhibit only a small difference in weight.
Comparing Great Ape Weights
The four genera of Great Apes demonstrate the full spectrum of ape size. Body mass differences are often pronounced between species and between the sexes within the same species.
Gorillas
Gorillas are the largest living primates, exhibiting the most dramatic example of size variation among apes. Wild adult male gorillas, known as silverbacks, can weigh between 136 and 227 kilograms (300 to 500 pounds). Females are considerably smaller, with an adult body mass typically ranging from 68 to 113 kilograms (150 to 250 pounds).
Orangutans
Orangutans, the only Asian Great Ape, display extreme sexual dimorphism. A fully developed male can weigh approximately 87 kilograms (192 pounds), while females are generally much smaller, weighing around 37 kilograms (82 pounds). The size range for wild Bornean orangutans is between 30 and 100 kilograms. This substantial weight difference is linked to the males’ secondary sexual characteristics, such as large cheek pads and throat pouches.
Chimpanzees and Bonobos
The two species within the Pan genus, chimpanzees and bonobos, represent the lightest Great Apes. Adult male chimpanzees typically weigh around 40 kilograms (88 pounds), with a general range for both sexes being 32 to 60 kilograms. Females are slightly lighter, averaging about 30 kilograms.
Bonobos are comparable in size to chimpanzees, despite their historical classification as “pygmy chimpanzees.” Bonobo males average approximately 39 kilograms (86 pounds), and females average about 31 kilograms. Both species exhibit only a modest size difference between the sexes.
Factors Influencing Ape Size
The wide-ranging body masses across ape species are rooted in their ecology, behavior, and evolutionary history. Sexual dimorphism is largely driven by intrasexual competition; in species where males compete fiercely for mating access, such as gorillas and orangutans, selection favors larger, dominant males.
An ape’s habitat and locomotion method also impose size constraints. Lesser Apes remain small because their survival depends on moving quickly through the thin branches of the forest canopy. Terrestrial species, like the gorilla, face fewer physical constraints and benefit from a larger body mass for defense and dominance.
Diet and Captivity
Diet and food availability also play a role in determining maximum body size. Apes in the wild must expend significant energy foraging for food, which is often less calorie-dense than human-provided food. Captive apes frequently exhibit a greater body mass than their wild counterparts because their diets are more energy-dense and lower in fiber, leading to a higher caloric intake and sometimes less physical activity.