Humans, like all organisms, have a life cycle that is common to all members of the species. This cycle begins at the moment a sperm fertilizes an egg, and if it is allowed to continue it will end when the human dies of old age. There are many steps in between fertilization and death that all human beings will experience.

Development in the Uterus

The human life cycle begins when a human sperm fertilizes a human egg, resulting in a one-celled zygote. At about eight weeks, the growing ball of cells becomes an embryo. About two months after that, the human continues its development as a fetus until it is born.

Babyhood

All humans begin living outside of their mothers as a baby, upon being born. During babyhood humans are almost completely helpless and dependent upon their parents. They must learn to use their senses and to walk before any independence can be achieved.

Childhood

The childhood stage occurs from about ages 1 to 11. During this time the young human explores the world around him and learns the basics of safety and survival.

Adolescence

During adolescence, which occurs between between the approximate ages of 11 and 17, a human achieves sexual maturity and thus the ability to create another human with a member of the opposite sex. Adolescents tend to start to show independent tendencies during this time.

Adulthood

A human arrives at adulthood at around the age of 18. She will remain strong, healthy, and able to reproduce until the onset of old age.

Old Age and Menopause

The onset of old age for a human occurs at approximately 50 years old. At this time, physical stamina and strength, as well as organ function, will begin a steep decline and ultimately end in death. Females will experience a phenomenon known as menopause that signals the end of their reproductive years. Men can continue to reproduce until death.

Source:

Biology Reference.com: Human Life Cycle