Adult orangutans of opposite sex tolerate each other’s company for one purpose only. After a brief tryst, including copulation that lasts about 15 minutes, the male and female go their separate ways. If a pregnancy results, then the mother, who weighs about 40 kg, will carry the fetus for 8 months giving birth to a 1-kg baby, nurse it for about 3 years, and continue to protect it until it reaches the age of 7 or 8. For the father, who weighs about 70 kg, the beginning and end of parental investment is a few grams of semen, which he can replace in a matter of hours or days. In their pattern of parental investment, orangutans are typical mammals. In more than 90% of mammal species, females provide substantial parental care and males provide little or none.
Evolutionary Analysis (4th ed.) by Scott Freeman and Jon C. Herron