Will inbreeding necessarily cause problems?

Inbreeding, as the name suggests, refers to the mating between two individuals with close bloodline or kinship, that is, the mating between two individuals with similar genes or close relationships.

From a genetic point of view, because they are close relatives, the incidence of various genetic diseases will be greatly increased, because the couple obtained more identical genes from their common ancestors, which can easily lead to the encounter and homozygosity of harmful genes that are not conducive to the survival of the offspring, thereby increasing the degree of harm of harmful genes to the offspring and easily giving birth to bad offspring. Therefore, all countries prohibit inbreeding, and my country's marriage law also stipulates that direct blood relatives and collateral blood relatives within three generations are prohibited from marrying. Even many science fiction novels mention avoiding inbreeding, such as how many people are needed for human immigration to maintain diversity, etc. However, is it really the truth to maintain diversity?

What I want to say today is that there is actually no need to worry about inbreeding. This may overturn many people’s existing cognition. . . Don’t worry, please listen to me patiently. . .

Why is inbreeding a problem no need to worry?

Because of inbreeding, for many people, the first thing they worry about is the diversity issue, which is just a diversity issue and they need to overcome a bottleneck.

Many people are troubled by simple biological knowledge and always think that inbreeding will lead to a decrease in diversity and then cause a series of problems.

I used to believe this truth.

It was not until later, as my studies and research progressed, that I discovered that, in fact, the problem of diversity is not particularly big.

Because even if the offspring of just one pair of individuals continue to reproduce, there will be enough diversity.

Let me give you a typical counterexample: inbred strain.

In biology, in order to keep the experimental subjects as stable as possible, it is necessary to specifically choose inbreeding, which is the opposite of sexual reproduction in nature.

Inbred animals refer to a group of animals with a degree of inbreeding equivalent to more than 20 consecutive full-sibling or parent-offspring matings, an inbreeding coefficient of more than 98.6%, and a population gene that is highly homozygous and stable.

Finally, the entire population will achieve high homozygosity and stability.

In order to achieve this, the requirements are very high, which is to keep inbreeding.

For example, brothers and sisters from the same litter can mate, or even parents and children can mate, and then continue inbreeding in this way.

Until in the future the level of inbreeding reaches a point where it cannot be further deepened.

Interestingly, animals do experience a bottleneck during the inbreeding process, namely: inbreeding depression.

That is to say, when inbreeding continues to occur for a certain generation, a lot of problems will appear. Deformities are just a small matter, but there will often be a large number of deaths. It is a bit like the bottleneck in the process of martial arts training, and many individuals will go astray.

The reason for inbreeding depression is that inbreeding increases the probability of homozygous harmful alleles, resulting in a decrease in individual adaptability.

For example, around 5-7 generations, some individuals began to show severe deformities:

Some individuals experience a decrease in fertility

Some individuals show decreased vitality.

But what is amazing is that after you have gone through so many mountains and rivers and thought there was no way out, you will find another village beyond the bends and flowers.

At this time, there are always a few particularly stubborn individuals who can survive, and then they actually get through this bottleneck, and then from then on, everything will be smooth sailing.

Marriage between close relatives is no longer a problem.

Sometimes I really feel that biology is the cure for all kinds of dissatisfaction.

The inbreeding bottleneck predicted theoretically was actually broken through by some individuals.

Let me put it this way, there is no practical difference between an inbred line of more than 20 generations and an ordinary hybrid.

In reality, the inbred mouse strain that began in 1910 is now 110 years old. In terms of generations, it has been hundreds of generations, and the breeding population is estimated to be in the billions.

The mice we often mention, such as C57 and Balb/c, are inbred strains.

Yet, these mice are used by major laboratories around the world without any problems.

It can be seen that the inbreeding problem is actually not a problem.

This is something I often reflect on. From an evolutionary perspective, many individuals can be traced back to the earliest individuals. For example, modern Homo sapiens can be traced back to a matriarch named Eve and a paternal named Adam (this is biological, not God). The former was about 200,000 years ago, and the latter was about 130,000 years ago.

Although theoretically, they may not be a single individual, but at least they are a group of sisters or brothers, and their descendants are all from them, yet they still have not become extinct.

Similar evolutionary issues hold true.

If the origin of species is a single origin, then the diversity problem is not a problem. Otherwise, how do we explain the diversity of the world today?

What's even funnier is that during the inbreeding process, strains will appear. That is, even if the offspring of a pair of parents are always inbred, differentiation will occur and eventually different strains will be formed. These are very stable, but different from each other.

What's even more exaggerated is that inbreeding can also lead to the emergence of mutant strains.

Some people may say that this is a special trait caused by the homozygous recessive gene.

However, some are really not, they are new variants. Because genes will mutate randomly during replication, the mutation frequency is always the same (that is, the molecular clock theory of neutral evolution theory).

Not to mention the variations caused by various other factors. In fact, even identical twins have different genes.

Of course, in reality, we still have to consider the inbreeding depression bottleneck.