The females can start reproducing when they're six weeks old.

If bacteria make it past our immune systems and start reproducing inside our bodies, they cause disease.

It's like the rabbits, which were brought to Australia and started reproducing.

The rhinovirus gets into the cells lining your nose and starts reproducing.

By killing the cubs, the males bring forward the time when they can start reproducing.

But as the first human populations started reproducing independently from one another, each started to develop its own pattern of genetic differences.

But mice are prolific breeders and start reproducing just five weeks after birth.

Males will become sexually active after their first year of life and females generally take two years before they can start reproducing.

They will start reproducing after about seven years.

Females start reproducing at 12 months but, unlike males, probably do not survive to breed twice.