From zygote to you

Human development is a continuous process that begins when an ovum from a female is fertilized by a sperm from a male. Growth and differentiation transform the zygote, a single cell formed by the union of the ovum and the sperm, into a multicellular adult human being. Most developmental changes occur during the embryonic and the fetal periods, but important changes also occur during the other periods of development: childhood, adolescence, and adulthood... Although it is customary to divide development into prenatal and postnatal periods, it is important to realize that birth is merely a dramatic event during development resulting in a distinct change in environment. Development does not stop at birth: important developmental changes, in addition to growth, occur after birth... Most developmental changes are completed by the age of 25. (Moore, Keith, The Developing Human, Clinically Oriented Embryology, 1982, p. 1)