Gorillas move around by knuckle-walking, although they sometimes walk bipedally for short distances
while carrying food or in defensive situations. Wild male gorillas weigh 135 to 180 kg (300 to 400 lb)
while adult females usually weigh half as much as adult males at 68–113 kg (150–250 lb). Adult
males are 1.7 to 1.8 m (5.6 to 5.9 ft) tall, with an arm span that stretches from 2.3 to 2.6 m (7.5 to 8.5
ft). Female gorillas are shorter with smaller arm spans. Adult male gorillas are known as silverbacks
due to characteristic silver hair on their backs reaching to the hips. Occasionally, a silverback of over
1.8 metres (5 ft 11 in) and 230 kg (510 lb) has been recorded in the wild. Obese gorillas in captivity
can weigh as much as 270 kg (600 lb). Gorilla facial structure is described as mandibular
prognathism, that is, the mandible protrudes farther out than the maxilla. Adult males also have a
prominent sagittal crest.
The eastern gorilla is more darkly colored than the western gorilla, with the mountain gorilla being
the darkest of all. The mountain gorilla also has the thickest hair. The western lowland gorilla can be
brown or grayish with a reddish forehead. In addition, gorillas that live in lowland forests are more
slender and agile than the more bulky mountain gorillas. The eastern gorilla also has a longer face
and broader chest than the western gorilla.
Studies have shown gorilla blood is not reactive to anti-A and anti-B monoclonal antibodies, which
would, in humans, indicate type O blood. Due to novel sequences, though, it is different enough to
not conform with the human ABO blood group system, into which the other great apes fit. Like
humans, gorillas have individual finger prints. Their eye color is dark brown, framed by a black ring
around the iris. Similar to humans, the leading cause of death in gorillas is cardiovascular disease