How are species born

Federal Agency for Nature Conservation BfN

Most animal children hatch from an egg. Birds lay eggs anyway, but so do fish, reptiles, most amphibians, insects and mollusks. The eggs look different, but they serve the same purpose: They provide the young animals with nutrients and protect them from the outside world for a while. In principle, an egg does the same thing as a womb, only outside of the mother. And that has many advantages:

Practical egg laying

The females do not go through a pregnancy that robs them of energy. Many animal species do not even hatch their eggs, but rather dig them in and leave the rest of the sun. This means that the old animals are independent again immediately after they have laid their eggs. Egg-laying animals can also have many more offspring than animals that give birth to live young. For example, a single common toad lays up to 6000 eggs!

Lots of offspring

But that does not mean that all offspring of egg-laying animals survive. On the contrary: Especially the animal species that do not hatch their eggs lay so many so that in the end a few young animals can get through. Because the eggs and the newly hatched young animals are a welcome meal for other animals. Those who hatch their eggs and protect and care for the hatched young do not have to lay so many eggs. This explains why a toad lays 6,000 eggs while a robin only lays four.

And the mammals?

Mammals grow in the womb and are born alive. Because they are suckled, mammals are dependent on their mother for much longer than other juveniles. But they are also protected longer. In the long period of childhood and adolescence, they learn from their parents everything they need to know for their adult life. There are even mammals that have a similarly long childhood as human children: an elephant child does not grow up until it is almost 20 years old.