How can isolated matrilineal societies avoid loss of genetic variation?

Question

In this setting, the family unit is based around a clan system. An individual's wealth and status is related to the clan they are born in, and its ancestry is based on matrilineal lines. Due to certain environmental factors on the continent, travel between regional areas can be somewhat difficult and expensive. Therefore, most breeding takes place between clans in relative proximity of each other.

Marriage does not exist in the form we would recognize. Women remain in the clan they were born into, while men are the ones who leave the home to join other families. Men don't marry an individual, instead they marry into an entire clan. This leads to many offspring coming from the same group of fathers. A cultural belief system has developed in which boys are considered "sons of society" and raised in bulk while girls are "daughters of their mothers" and raised specifically by their mother.

How can this society avoid genetic inbreeding under these circumstances?

Answer 1

Due to certain environmental factors on the continent, travel between regional areas can be somewhat difficult and expensive.

Travel anyway. Do it in groups -- a traveling "meat market" where the men show themselves off in hopes of being chosen by the clan with the prettiest women -- during the the least-unfavorable time of the year.

A man doesn't marry an individual, but marries into an entire clan. This leads to many offspring coming from the same father.

There's a reason that most cultures are monogamous: polygamy leads to a lot of unmarried men with no sexual outlet, and that leads to violence (including rape).

Answer 2

The answer is in the question itself:

Women remain in the clan they were born into, while men are the ones who leave the home to join other families.

Humans are an XY sex determination species. So when a man joins a clan, he brings not only his Y chromossome - he also brings a X which adds variety to the the pool of X chromossomes in the matriarchy.

To improve genetic variation, you need to change the man who is fathering children every once in a while. You can either have a clan marry multiple men at the same time, or have marriages be temporary.

The animal I can think of with the behavior that most closely matches that are african elephants, and as a species they've managed it (until we started hunting them). Males don't stay with a band for long after they become adults. They will rover around alone or in small bands of males. When the females of a clan are in heat, a male will mate with them and then leave.

Answer 3

How can this society avoid genetic inbreeding under these circumstances?

This has happened even when travel is relatively easy throughout our history.

Inbreeding is mitigated against in a few ways.

With matrilineal societies ambitious men have few ways to upgrade their social status, and some will be displaced. Some of these will travel and spread genes. If there is conflict you may get mass displacement.

A lot would depend on whether their is any restriction on marrying outsiders whether outside the clan, region etc,. But with a large enough demographic you are unlikely to get dangerous inbreeding, human cultures have always culturally protected against that in broad strokes by various taboos unless under extreme pressure. So while you get regional traits coming from shared ancestry with a few exceptions like royalty who want to keep power within families you don't really have any danger of it getting dangerous unless the communities are totally isolated like Islands.

Humans have experienced several population bottlenecks with at least one being estimated at as few as 600 breeding pairs Worldwide, yet from that we have the huge diversity we have now. You don't need a huge influx of new blood every year, just a small intermittent supply of travelers would be fine and cultural taboos against close relatives getting too frisky.

Answer 4

Sperm peddlars.

This exists now, for people who raise animals.

https://www.swinegenetics.com

Swine Genetics International is an artificial insemination swine genetics company, also offering swine production related consulting.

Liquid semen is available from over 150 sires to help you meet your genetic needs. Boars representing the following commercial lines are housed at SGI: Purebred, Exotic, Terminal, Maternal, Meat Quality and Certified "Niche" Program animals. We also offer 40 sires that comprise our showpig program. Frozen semen is available on boars housed at SGI since 1981 - including sires currently on stud. SGI is very active in exporting both swine semen and live animals all over the world. Our current staff provides artificial insemination and production-related consultation for swine operations globally.

In your world, magic allows preservation of semen. The sperm peddlar comes around once or twice a year, when it is optimal to conceive. Her wares (and it will be her, because magic is involved) will have information about the sire and children he has produced.

I envision her arriving in a gypsy wagon. Travel is hard, but she knows ways and has skills. When she arrives, she can help with the whole process. If there are males in the village she might make some purchases as well.

Answer 5

Your society needs a taboo that encourages gene distribution.

The European one - "don't marry your close family" - won't work in your society, because in your society men have a clan, not a family. But that detail also points to another option.

A taboo for clan-based societies with no families could be "don't have sex with people born in the clan you were born in."

That doesn't quite fit your society either, but we're getting closer. Also it doesn't guarantee that genes get spread over a larger area than two neighbouring clans.

"Don't have sex with people born in the clans your parents were born in" is better. Genes get spread over three or more clans quickly, so the people are less inbred. But, in your society, it doesn't sound like people are always keeping track of who their father is. So that doesn't work.

A ring of clan taboos can spread genes around like that without people knowing who their father is. In Clan A sons are usually given to Clan B and sons of Clan B cannot join Clan A. And so on around a circle back to Clan F giving most of its sons to Clan A and never taking husbands from Clan A. In a few generations this can spread genes over a geographical area that's much wider than the distance that most individuals travel. If it's also forbidden to have sex outside your clan or have sex with boys who haven't switched clan yet, then nobody's having sex with their brother. These two sets of taboos should be enough to prevent extreme inbreeding.

So the anti-inbreeding rules for your society are: "I only have sex within my clan. I don't have sex with unmarried boys. Unmarried boys are forbidden from having sex with women. There is a clan that my clan cannot take husbands from. Most of my sons will marry into that clan." Breaking these rules isn't just illegal, it's widely thought to be disgusting, like how you would think marrying your uncle is disgusting.