The human life cycle is similar to that of other placental mammals. New humans develop viviparously from conception. An egg is usually fertilized inside the female by sperm from the male through sexual intercourse, though the recent technology of in vitro fertilization is occasionallsy used. The fertilized egg, called a zygote, divides inside the female's uterus to become an embryo, which over a period of thirty-eight weeks (9 months) becomes a human fetus. At birth, the fully-grown fetus is expelled from the female's body and breathes independently as an infant for the first time. At this point, most modern cultures recognize the baby as a person entitled to the full protection of the law, though some jurisdictions extend personhood to human fetuses while they remain in the uterus.

Compared with that of other species, human childbirth is dangerous. Painful labors lasting twenty-four hours or more are not uncommon, and may result in injury, or even death, to the child or mother. This is because of both the relatively large fetal head circumference and the mother's relatively narrow pelvis, by way of natural selection. The chances of a successful labour increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and natural childbirth remains a relatively hazardous ordeal in developing regions of the world, with maternal death rates approximately 100-fold higher than developed countries.

The human life span can be split into a number of stages: infancy, childhood, adolescence, young adulthood, maturity and old age. The lengths of these stages, however—particularly the later ones—are not fixed.

The philosophical questions of when human personhood begins and whether it persists after death are the subject of considerable debate. The prospect of death causes unease or fear for most humans. Burial ceremonies are characteristic of human societies, often inspired by beliefs in an afterlife or immortality.