A Human Skeleton
How these trends are related, in what ways they have been adaptive, and what their role is in the evolution of complex social organization and culture, are matters of ongoing debate among physical anthropologists.
Although body size is highly heritable, it is also significantly influenced by environmental and cultural factors such as diet. The mean height of an American adult female is 162 cm (64 in) and the mean weight is 62 kg (137 lb). Males are typically larger: 175 cm (69 in) and 78 kilograms (172 lb). Humans vary substantially around these means, and the means themselves have varied depending on locality and historical factors.
Human children, typically weighing 3-4 kilograms (6-9 pounds) and 50-60 centimetres (20-24 inches) in height, are born after a nine-month gestation period. Helpless at birth, they continue to grow for some years, typically reaching sexual maturity at around 12-15 years of age. Boys continue growing for some time after this, often only reaching their maximum height around the age of 18.
Human life expectancy at birth is approaching 80 years in wealthy nations, with the assistance of science and technology. The number of people over 100 was estimated at about 50,000 in 2003. The maximum human life span is thought to be about 120 years.