alt Hacker News> Harmful mutations can accumulate through inbreeding. Yet somehow Neanderthals managed to survive across most of Eurasia for nearly 400,000 years
It is also true that inbreeding for extended periods weeds out both dominant and recessive bad genes very effectively. As long as at least one good or not-so bad alternative is maintained.
So not as surprising that small groups can last a long time, once they reach a threshold, as implied by the article.
It’s a brutal way to improve the stock, as lots of individuals suffer until (and in service of) a debilitating gene going “extinct”. And every new maladaptive mutation restarts the process, but it works.
On the upside, any adaptive mutation can just as quickly become pervasive.
The biggest downside in the long term is a lack of genetic diversity as a shield against new diseases.
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I wouldn't single out the concern new diseases if the population is small. Most diseases co-evolve intra-population. The lethal ones are the ones that suffer a mutation and are suddenly able to be passed to a different 'species'. So, if they already survived on a 'knife's edge', immune variety is of comparatively low concern (but still existential) on the list of things that can end your species (climate change, competition, demographics - 2-3 infertile females in a group of 20, say bye bye to tribe).
In captive breeding, it's a brutal way to "improve stock" but in wild populations this is pretty normal for large mammals. It also generally happens more slowly... so isn't that different from every other ambient process that selects some genes and culls others.
Fwiw... something similar also occurs with outbreeding/hybridization. Novel gene combinations can be maladaptive, just like double recessives.
These are all pretty normal population dynamics.
There are billions of us now... but that's not normal for a large animal, especially predators. How many leopards, or bears, or elephants are there at any given time?
These tend to be sparse, structured populations.