The reproductive system is the reason for existence. It is the perpetuation of the species. There are two genders, male and female. Usually the two sexes are separate however some animals are both male and female.
In most cases, without mating and giving birth a species will die out. Many factors contribute to healthy reproduction, proper environment and clean food and water are major factors. When an animal’s environment is lost the tendency to mate is curtailed. Tainted food and water sources contribute to ill health and interfere with the reproductive cycle.
The male of any species contributes the sex of the offspring. The reproductive system includes testicles where the sperm is produced, the scrotum, which holds the testicles, and the penis which delivers the sperm into the female reproductive system. These are the basic parts of the male mammalian reproductive system. Testosterone is the driving male force though males do have some estrogen, the female hormone, in their bodies
The female of a species is the nurturer of the zygote which becomes the fetus. The basic female reproductive organs are the egg or ova, where the female sex hormones estrogen and progesterone is produced, the ova is fertilized by the sperm and becomes the zygote, the fallopian tubes funnels the ova into the uterus. The sperm is injected into the female's entrance called the vagina which connects to the cervix, the lower part of the uterus where fertilization takes place. Once fertilized the zygote moves up into the uterus or womb where it develops into a complete organism. Then it moves back through the cervix and the vagina which is known as the birth canal.
Testosterone and estrogen trigger mating urges. In canines, the penis enters the vagina and swells locking it into the female. He then throws his leg over the back of the female and they copulate anus to anus. This might take as long as half an hour. Stallions and male lions bite the neck of the female to reach a climax.
Hermaphrodites have both male and female organs like earthworms. When they mate they exchange both sperm and ova. Some insects can reproduce without mating. The female walking stick can lay unfertilized eggs that hatch as females. Honey bee eggs that are fertile become female and, in the spring, the unfertile eggs become males.