Animals try to avoid backcrossing. Why do humans deliberately let dogs backcross?

Backcrossing is a type of inbreeding, and inbreeding usually makes offspring unhealthy and even causes offspring to die. Therefore, in nature, organisms have evolved strategies to actively avoid backcrossing.

For example, beavers will leave their original populations and start families in distant places when they are adults; koalas will show a strong interest in the opposite sex from far away; roosters will especially love hens they don’t know, Even more sperm are secreted during mating.

The strategy adopted by these animals is to avoid inbreeding as much as possible, so as not to produce deformed offspring.

However, humans have broken this natural law. In the past few hundred years, in order to cultivate more docile, cute and lovable dogs, humans have deliberately made dogs inbreeding, or even backcross breeding.

So what's going on here?

First of all, we need to know that backcrossing is not uncommon in nature, many plants have to backcross, for example: plants have difficulty spreading seeds, so that three generations of grandparents and grandchildren may be located in the same place, and when they bloom, it may appear phenomenon of backcrossing.

Plants do not have pain nerves, and even backcrossing will not affect their survival, but continuous backcrossing will lead to a decrease in their genetic diversity, as well as dwarf plants and low competition, so plants will try every means to make their own Seeds spread farther.

For animals, backcrossing is even more terrifying, because animals have a pain-sensing system, and they need to avoid predators or hunt all the time to survive, and the offspring of backcrossing are less competitive and are easily affected by natural selection. disuse. Under the action of natural selection, individuals who like backcrossing will gradually die out, while individuals who avoid backcrossing and inbreeding as much as possible may stay.

It is because of this that backcrossing is avoided in nature, whether it is plants or animals. Only under unavoidable circumstances will backcross breed offspring.