Male and female are terms we can use only for more advanced animals, like insects, fish, reptiles, birds, and mammals. Simpler creatures, such as the earthworm and sponge, usually do not exist in two different sexes, or genders.
But among all animals that do exist as male or female, the numbers of males and females are amazingly equal. Just as the odds that a newborn baby will be a boy (or a girl) are about 50-50, so most animals produce offspring of both genders in equal numbers.
The animal that shows the greatest imbalance in the number of male and female offspring is the greyhound, with about 110 males born for every 100 females!
