Common animals on land have two nostrils? Because two nostrils are more suitable for animals to breathe than one nostril. It has evolved since ancient times, and it is also the law of evolution, and it is also a suitable and necessary condition for the survival of animals. So common animals on land have two nostrils.

Bilateral symmetric animals are higher than radiation symmetric animals. The latter, like jellyfish coral, is radiation-symmetrical, with only the upper and lower points, and there is no distinction between the front and the back, which is only suitable for floating and epiphytic.

Lower bilaterally symmetrical organisms, such as worms, nematodes and earthworms.

They can move directionally, laying a foundation for the further evolution of organs.

This bilateral symmetrical system model has also deeply influenced us. Eyes are left and right, ears are left and right, and upper limbs and even breasts are left and right.

But as for why there are two, not four, six or more, although it is reasonable to explain it by natural selection, it is best to explain it by the theory of * * *.

The true inner nostril animals started from amphibians (fish only have outer nostrils), while amphibians, reptiles and mammals are actually close relatives, so it is reasonable and logical to have the same number of nostrils.

It is worth pointing out that many biological characters are neutral (there is no difference between good and bad), but they are not screened out by selective pressure. The number of nostrils is two, which may be only the most direct state of organ origin and development, and has no special significance. If the number really changes greatly, it can be said that it is caused by natural selection, but in fact there is no such creature.