In developed countries, infants are typically in weight and in height at birth. However, low birth weight is common in developing countries, and contributes to the high levels of infant mortality in these regions. Both the mother and the father provide care for human offspring, in contrast to other primates, where parental care is mostly restricted to mothers. Helpless at birth, humans continue to grow for some years, typically reaching sexual maturity at 12 to 15 years of age. Females continue to develop physically until around the age of 18, whereas male development continues until around age 21.