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How inbred are we?

Slightly odd question, I know. But seriously...

I make a lot of assumptions here, but this is more about an exercise in math and follow-up questions that may arise from the answer.

If we were to assume that the average person throughout human history was born to a mother aged 30 this would imply that 6,000 years ago (Not only did I have to go there, but it makes for a nice round number) there could have been as many as 2^200 discrete ancestors 200 generations ago.

Naturally, if you look at that number in on a piece of paper you can see that the very notion of that being true is absurd.

A fair estimate based on the most recent studies mapping the number of people alive at various points in history since 10,000BC (HYDE 2010), would be somewhere around 30-40 million. For the sake of tidier arithmetic, let's say 2^25.

So my question boils down to this:

Assuming we are not limited by geography (which we would have been), and that every generation was distributed evenly (which of course, it is not). What would the average genetic relation between my parents be that would result in having 2^25 ancestors 6,000 years ago instead of 2^200 potential ancestors?

Xoviat 4 Apr 16
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In the end I did the math.

Assuming a HEAP of things that are not true, like uniform genetics, no geographical limitations, that all the people alive 6000 years ago were genetically unrelated and capable of reproduction and a much,much more -> Anyone's parents would genetically be the equivalent to half-siblings on average. 😀

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I thinking inbreeding is how a species or races develop. This is how we breed cattle, dogs, cats, flowers to get a stable strain of something better. In tribal times I'm sure the chief would have sex with whomever he wanted. As to the detriment to the genetic pool, a study showed that inbreeding did lower the intelligence level for a few generations, but that it came back to normal after that. (back in the 70's with fruit flies).

True, the chieftain situation is more than acceptable. It is historically documented that Egyptian pharaohs had 100s of offspring. I suspect the same could be said for many in positions of power. Did the fruit-flies continue inbreeding for successive generations? or was this just the first generation?

@Xoviat I believe it was for 3 to 4 generations before the quantifiable level of intelligence rose to original levels. I doubt it continue beyond that -- the article didn't say.

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Actually, out of one human pairing, you are supposed to produce an average of 2,000 descendants, over 12 generations time. 12 generations is about 240 years.

That would be suggestive of 300 generations over the course of 6000 years. A 91-digit long number for the maximum amount of individual ancestors 300 generations ago..

@Xoviat Homo Sapiens Sapiens go back 100,000 years.

@davknight I am aware of this and I don't care 🙂. More interested in the age of the world according to creationists.

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Your supposition doesn’t quite make sense.
Homo Sapiens have been on around for about 300,000 years. We all started out in Africa. Was inbreeding common, probably but who knows??

I fail to see how it does not make sense. It is not a question handling actual makeup but an exercise in math.

If the world population is reasonably estimated at 2^25 people 6000 years ago and we could have potentially have 2^200 distinct ancestors 200 generations ago assuming that to be 6000 years ago, but we obviously don't. If we assume in a best case scenario that is also extremely improbable that we are direct ancestors of all of those 2^25 people. To me, 2^200 - 2^25 would represent all the ancestors repeated at least once 200 generations ago.

I THINK this means that my parents would on average have (2^200 - 2^25)/2 common ancestors, 199 generations ago that are repeated at least twice (Well, A LOT more than twice). This is where I get lost or may already be wrong. I'm curious how that would translate to how my parents are related to each other on average. Whether it's something like 1st cousins twice removed or something a lot further away. But I get lost in the math.

This has no bearing on reality and I do not look to impose this result upon reality. I'm just curious as I imagine that the big numbers would've been very confusing to any ancient culture contemplating the origins of man. They're confusing to me now.

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Here's a conflict between your number, 2^200 and the creation myth (historical fiction has to be based on actual historical events): at the beginning of the 6000 year period, there were only two people.

JimG Level 8 Apr 16, 2019

I will eventually post elsewhere. I'm theorizing that the need for these creation / mass extinction ideas may stem from someone being perfectly capable of multiplying 2 x 2 repeatedly and thinking "wtf? there should be more people / dead bodies around and there isn't.. I'm confused and I don't know how to justify this!". Therefore 2 people not that long ago then Noah's Ark once this idea also became problematic.

Problematic in the way that the children of Adam and Eve would have reproduced, so that tale made it socially acceptable to screw your sister and get her pregnant. After a while, when the kids start turning out as we would expect from sibling on sibling action, this was perhaps decided as a bad idea.

So let's try to forget all that and start again with 8 people. Possibly from experience of reproducing with immediate cousins producing some mixed results.

Actually, If I recall correctly, we're talking about Noah and his sons, so they still don't have any problems with cousins and neither does Leviticus.

Purely speculative of course...

The actual ages of Genesis / Leviticus as far as I can tell are unknown as a lot of the old testament was passed down by oral tradition. I see it as entirely plausible that Genesis was at first much shorter, then Genesis was expanded upon later once people considered the incest with Leviticus attempting to patch up that unfortunate angle with commandments telling you who not to screw.

I don't know. I just think of it that way and laugh at the thought of scholars 3000+ years ago hastily trying to patch that up with another book.

@Xoviat Much of Genesis came from older Sumerian or Assyrian myths, I believe. Damn, I am getting forgetful.

@JimG Yeah, there seems to be an ancient flood myths involving arks across many of the earlier civilisations. Mesopotamian, Ancient Greek, Hindu... I would have to look at translations of all of them and find out if it is mentioned how many people were said to be on these huge boats though (likely the same story spread orally and just written down by different cultures when someone literate thought that it was a good idea).

@JimG The common theme seems to be immediate family and livestock, or immediate family and a handful of important men.. who then went on to repopulate the world. Generally the male-female ratio and the incestual stuff involved wasn't really thought through. Could have also been that there were plenty of women there too but they weren't considered worthy of mention in the stories.

A side effect of reading up on all this was discovering that in Sumerian writings the gods had a good old-fashioned natural disaster or plague every 1200 years to keep the population numbers under control. To me, this suggests that someone gave the issue some thought and came up with some creative storytelling to tidy up the issue.

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