The average litter size for a Western Lowland Gorilla is two. However, it is not unusual for them to have just one offspring or even three. In the wild, gorillas typically give birth every four to six years. This low rate of reproduction is typical of long-lived animals with a slow growth rate and low environmental stressors (such as gorillas). Newborn gorillas are underdeveloped and fragile. They are born copper-haired, with pink skin which darkens as they age. They weigh only 3-4 pounds (1.3–1.8 kg) at birth and are completely dependent on their mothers for the first few years of their lives.