if procreating with close relatives causes dangerous mutations and increased risks of disease, how did isolated groups of humans deal with it?
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By getting more diseases and dying from it.
An increased chance of genetic disorders doesn’t mean that the entire population will become extinct. It simply means that some individuals in that population will have a smaller chance of survival.
Just because in has increased risks doesn’t mean it won’t work. If you went from a 5% chance of having a child with serious defects to a 50% chance of having a child with serious defects, you still have a 50% chance of bearing a child who doesn’t have serious defects. If a small group of isolated people gets lucky, they can still survive and prosper. Some isolated groups of humans died out, and some managed to survive.
Procreation with close relatives can increase the risks of genetic mutations and disease because it increases the likelihood of inheriting the same harmful genetic variations from both parents. This is known as inbreeding, and it can lead to a range of health problems and disabilities.
In isolated groups of humans, such as small populations on isolated islands or in remote communities, inbreeding may have been more common due to the limited gene pool and the lack of genetic diversity. However, these groups have likely developed mechanisms and strategies to mitigate the risks of inbreeding and the associated health problems.
For example, some isolated populations may have developed cultural norms and rules that discourage or forbid marriage between close relatives, in order to prevent inbreeding and the associated health risks. Other populations may have developed genetic adaptations or evolved mechanisms that protect against the effects of inbreeding, such as increased immunity or resistance to diseases.
Overall, while inbreeding can pose significant health risks, isolated populations of humans have likely developed strategies and mechanisms to mitigate these risks and maintain the health and wellbeing of their communities.
Some cultural practices promote this (eg some Arabic groups preference cross-cousin marriage). But humans don’t live in isolated groups. Foragers live in bands which meet regularly, and usually have rules about who you can marry (some West Australian groups have rules so complex that anthropologists needed algebra to map them). One purpose of the meets is to negotiate marriages. The minimum number needed to keep a language alive (language being the marker of who’s in ‘my tribe’) is around one thousand, which is more than enough to avoid the accumulation of genetic risks and probably the minimum number in regular contact (not all at once- but gatherings of 50-100 once or twice a year, each gathering connecting to another)
Inbreeding doesn’t cause mutations, it just makes it easier for those mutations to express themselves.
Simplified explanation:
Normally you get one copy of your genes from your father and another copy from your mother.
If one of those two copies contains an error your still have the other one.
If your mother and your father are sibling and inherited the faulty copy from the same parent. You may get the broken plan from both your parents and no clean unbroken copy.
In a group of closely related humans that keep having children with each other birth defects and genetic diseases thus become more common.
Of course populations can still survive with this handicap. Individuals not so much, but the group as a whole yes.
The ones with the biggest issues simply die and do not get to have children of their own.
One exception are stuff like royal bloodlines where they kept marrying each other and kept getting worse and worse birth defects, that a peasant would simply have died in childhood with but a noble had the resources to survive to have more inbred kids of their own.
Dealing with it is a bit of a trick to answer. How can we know? We know that some royal lines bred themselves into extinction.
Apparently primates actually have biological incest avoidance. Males and females of breeding age actually leave their families. Those that grew up together are more attracted to strangers. There might be something about being repulsed by the scent.
There was a custom in Taiwan, recorded in the 1800s, for unimportant marriages, the future wife would grow up in her future husband’s family. For important marriages, they wouldn’t meet until the wedding. Those important marriages tended to have more children born.
In a nutshell, because it’s a non-issue:
https://gizmodo.com/why-inbreeding-really-isnt-as-bad-as-you-think-it-is-5863666
A quick article on it but all verifiable facts. Basically inbreeding creates a very small increased chance of genetic defects – and many of those don’t manifest till well after sexual maturity anyways (MS for example).
Unless you’re basically *trying* to aggressively inbreed – Ie. dad has kid with daughter, then daughters’ daughter, etc – it’s not a massive threat. Just marginally sub-ideal.
When isolated groups of humans have to make babies with people who they are related to, they can have babies with people who are not as closely related as a brother or sister. For example, if two cousins wanted to have a baby, that would be less risky than if a brother and sister wanted to have a baby. This means that the baby would still have a chance of getting some of the same genes, but not as many as if the parents were more closely related.
Inbreeding does not cause dangerous mutations. Inbreeding has no effect on mutation rate. Instead, inbreeding increases the likelihood of someone inheriting two identical copies of a gene (homozygosity). A lot of dangerous conditions are recessive, which means you don’t get the disorder unless you have two copies of the “broken” version of the gene. If instead you have one “broken” copy and one functional one, you’re fine. Inbreeding makes inheriting two “broken” genes more common.
…. From my college biology (so take that as you may)…inbreeding doesn’t ALWAYS have adverse side effects. It can and sometimes does. You tend to get exaggerated genetics. So if two “bad” genes pair, you get really bad genetics. If two “good” genes pair, you get really good genetics. If none do, you are ok.
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