Although each egg cell produced by a woman carries a single X chromosome, the sperm cells produced by a man carry either an X or a Y. This means, in very simple terms, that the sperm cell determines a baby's sex.

Biology is far from understanding exactly how a single cell develops into a baby, but research suggests that human development can ultimately be explained in terms of biochemistry and molecular biology. Most scientists would make a similar statement about evolution.

Man comes not from an egg but from an animalcule that is found in male sperm.

It's only a mature sperm that can fertilize an egg and eventually produce a baby.

For each chromosome contributed by the sperm there is a corresponding chromosome contributed by the egg, there are two chromosomes of each kind, which together constitute a pair.

So, unlike in humans, every chimp male's sperm has to fight really hard to fertilize a single egg.