All kinds of animals come from eggs. It's called being oviparous, and it includes all reptiles, all birds, all fish, all amphibians, and even a special group of mammals known as monotremes. That latter group covers species like the echidna and also the platypus.
Some egg-laying species use internal fertilization, in which the egg is fertilized while it is still within the female, while others use external, where the male fertilizes the egg after the female lays them. Different approaches are then used to bring the egg safely through to hatching. In the case of many birds, they will sit on the nest in order to warm the eggs, leaving them only to seek food. Some species, like frogs, ants, and many kinds of fish, take more of a scattershot approach and just have millions of eggs in the hope that some percentage of them will survive. Other species, like the penguin, lay only a single egg and thus tend very carefully and lovingly to it, carrying it with them to keep it off the freezing ground. Still further species bury their eggs for safety, and then there's the seahorse, which, in common with the penguin, has the male tends the eggs -- in this case, by carrying them around in his belly!
We'll never know which came first, the chicken or the egg -- but as long as we can tell which egg we've got handy, we'll know what's coming next. Let's find out!
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