Procreating with a relative is taboo in most human societies for many reasons, but they all stem from avoiding one thing in particular — inbreeding increases the risk of genetic disorders that can seriously compromise a child’s health, life prospects, and survival.
While we all inherit potentially harmful mutations from our parents, the effects of these mutations are often partially or completed masked if we possess two alternative variants of a gene — one from each parent. However, the children of closely related parents are more likely to inherit the same copies of harmful mutations. This is known as ‘inbreeding depression’.
But inbreeding depression can happen in any species, with the risk increasing as populations become smaller. Because many species are rapidly declining in abundance and becoming isolated from one another predominantly due to habitat destruction, invasive species, and climate change, the chances of inbreeding are also increasing.
Not only are such populations more susceptible to random disturbances, they are also victim of reduced population growth rates arising from inbreeding depression. This produces what is generally known as the ‘extinction vortex‘ — the smaller your population, the more you inbreed and produce sub-optimal offspring, leading to even more population decline and eventually extinction.
One emergency intervention that can ‘rescue’ such inbred populations from extinction (at least in the short term) is to introduce unrelated individuals from other populations in an attempt to increase genetic diversity, and therefore, the rate of population growth. While somewhat controversial because some fear introducing diseases or eroding local-area specialisation (so-called ‘outbreeding depression’), the risk-benefit ratio of this ‘genetic rescue’ is now widely considered to be worth it.
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