Insemination is the introduction of sperm into a female’s reproductive system for the purpose of impregnating, also called fertilizing, the female for sexual reproduction. The sperm is introduced into the uterus of a mammal or the oviduct of an oviparous (egg-laying) animal. In mammals, insemination normally occurs during sexual intercourse or copulation, but insemination can take place in other ways, such as by artificial insemination. In humans, the act and form of insemination has legal, moral and interpersonal implications. However, whether insemination takes place naturally or by artificial means, the pregnancy and the progress of it will be the same. Insemination may be called in vivo fertilisation (from in vivo meaning "within the living") because an egg is fertilized inside the body, this is in contrast with in vitro fertilisation (IVF). In plants, the fertilization process is referred to as pollination. It is the process of transfer of pollen grains from one anther to stigma of other plants. Natural insemination Insemination of a woman by sexual intercourse is referred to as "natural insemination" (NI) (i.e., insemination by natural means). Natural insemination involves ejaculation during penile–vaginal penetration, with the erect penis inside the vagina. If an artificial lubricant needs to be used, care must be taken that it does not have spermicidal properties. During ejaculation, semen, containing male gametes known as sperm, is expelled through the penis into the moist and warm environment of the reproductive tract. In humans, semen is usually ejaculated into the posterior vaginal fornix in direct contact with cervical mucus, though sperm may swim from other areas of the vagina or vulva to the cervix. The average volume of semen produced at ejaculation is 2 to 5ml (about 1 teaspoon), containing an average of 182 million sperm. Only a small proportion of the sperm in each ejaculation reach the site of fertilization in the fallopian tubes, their numbers decreasing exponentially as they progress through the female reproductive tract. The majority of sperm either die in the acidic environment of the vagina or drip out with the semen. Prior to ovulation, the cervical mucus becomes thinner and more hospitable to sperm. Sperm swim rapidly into the uterus upon encountering cervical mucus, though many become lost in the cervical crypts where they either die or are delayed. Further attrition occurs in the uterus, where sperm are attacked by the female immune system. Only about 100-1000 sperm reach the fallopian