The purpose of reproduction is to ensure the continuation of a species. Animals have evolved a number of mechanisms to ensure variability and assortment in a population. The most widespread of these is sexual reproduction between male and female gametes.

Fertilization may be either external or internal. Aquatic and amphibian animals usually fertilize externally, using water as a medium in which the sperm swims to the egg. Terrestrial animals normally fertilize internally.

The processes of spermatogenesis and oogenesis produce haploid sperm and eggs in specialized organs called testes and ovaries.

These gametes are produced from germ cells which are separated early in the development of the embryo.

The reproductive organs are designed to manufacture and store the gametes as well as to allow the act of mating.

Three sets of glands in the male add nutrients and enzymes to sperm that help the sperm move through the vagina into the uterus where fertilization takes place.

The uterus is the place where the egg will implant and grow into the embryo - and eventually the infant ready to be born.

Male and female reproductive systems are under the control of a group of hormones, and the hypothalamus is the main center for this regulation. The female reproductive system of humans and other primates follows a menstrual cycle.

Fertilization between male and female gametes occurs in animals from jellyfish to humans. The same basic mechanism of sexual reproduction applies in every case.

But we should also note that as animals have evolved into more complex forms, reproductive systems have also evolved into complex anatomical structures. Hormonal control has become a vital component of the processes involved in vertebrate reproduction, and is also the basis for the most reliable method of birth control.

Copyright 2006 The Regents of the University of California and Monterey Institute for Technology and Education