Every human being begins life as a single cell, formed when father's sperm fertilises mother's egg. Fertilisation normally takes place in the mother's Fallopian tube, which connects the uterus (womb) with the ovary. The uterus is the size and shape of a large pear: it is made of muscle and it stretches to allow the baby's growth throughout the months of pregnancy.
A woman ordinarily has two tubes and two ovaries, one at each side of her uterus. Every month one of the ovaries in turn releases an egg (ovum) which passes slowly along the tube towards the womb cavity
If the egg is not fertilised within 12 hours or so of being released, it dies; it cannot develop further. But if the woman has sexual intercourse during the days of her monthly cycle just before or at the time when an egg has been released from the ovary, then many sperm cells released by her partner may travel up to the Fallopian tube and one may fertilise the egg. When fertilisation is completed and the nuclei of egg and sperm have combined, a new being comes into existence and is capable of further development. Because the parents are human - belonging to the species Homo sapiens - the new being is also human. Fertilisation (by which we mean conception) marks the beginning of the human lifespan.
A consultant specialising in the care of pregnant women writes: "Life does not begin with birth. When born, we are already nine months old... we have a responsibility to learn how to study the life in utero, and how to care for it"1
The cells of living beings contain DNA (deoxyribonucleic acid), the substance in the nucleus that enable cells to reproduce and transmit characteristics from generation to generation. When cells divide, the DNA takes the form of chromosomes - the units carrying the genes that pass hereditary features from parents to offspring. Different species have varying numbers of...