What's the closet biological relationship for safe breeding?

[dstebbins]

There are scientific reasons to avoid incest. Morality and "ew" factor aside, children tend to have deformities if their parents are biologically related to one another.

 

But ... what counts as "biological?" Aren't we all biologically related to some degree? Even if you're not religious and don't believe in the whole "Adam & Eve" thing, it's highly improbable that evolution would just happen to create independent batches of homo sapiens in different spots around the globe. Even if you take religioun out of the equation, we almost certainly started out as a single tribe.

 

So ... how many generations need to seperate the parents, biologically speaking, before it's safe for them to mate?

 

And before anyone starts trolling ... no, I have no particular "reason" for wanting to know this! It's just curiosity!

[Ophiolite]

There is no "safe distance". My understanding is that the issue (excuse the pun, my paronomasia is genetic) is that there is a higher probability of defective recessive genes being possessed by two closely related individuals than by ones who are only distantly related. So it comes down, essentially, to a roll of the dice.

 

This is reflected in both law and practice wherein the marriage of first cousins is permitted in some jurisdictions, but not in others.

[StringJunky]

There is no "safe distance". My understanding is that the issue (excuse the pun, my paronomasia is genetic) is that there is a higher probability of defective recessive genes being possessed by two closely related individuals than by ones who are only distantly related. So it comes down, essentially, to a roll of the dice.

 

This is reflected in both law and practice wherein the marriage of first cousins is permitted in some jurisdictions, but not in others.

I could well be wrong but if we sequentially take the cousin-line - first with first cousin, second with second etc - and each degree of separation results in 50% gene dilution, wouldn't it take about 15 degrees of separation for any relation to disappear? I assumed the human genome contains 25000 genes.

Edited December 11, 2014 by StringJunky

[Ophiolite]

You used the word if. Since the if need not apply your conclusion would appear to be invalid.

[StringJunky]

You used the word if. Since the if need not apply your conclusion would appear to be invalid

 

IF x=2 then x+1=3. Is my conclusion invalid?

[Ophiolite]

It is invalid if X does not equal 2. And in the relevant example you will not necessarily see the dilution you describe. Chance is involved. Sometimes 15 comes up on the roulette table three times in succession.

[StringJunky]

It is invalid if X does not equal 2. And in the relevant example you will not necessarily see the dilution you describe. Chance is involved. Sometimes 15 comes up on the roulette table three times in succession.

Right ok. Got it now. I suspected it wasn't that simple.

[dstebbins]

Sometimes 15 comes up on the roulette table three times in succession.

Well of course. Gambler's fallacy.

 

But, each individual flipping of a coin does, in fact, yield a 50% chance of success. Sure, you can get three failures in a row; you can get three hundred failures in a row! But every coin-flip will always ... ALWAYS ... have a 50% chance of success, since each coin flip is entirely independant of any other coin flip coming before or after it.

 

What StringJunky is saying is that each generation apart the parents are, the likelihood of undesirable recessive genes is reduced by half, per generation (because there are two parents; if there were three parents, each generation apart would be 1/3 as diluted as the last). Sure, it's still a probability, but the odds are more heavily in your favor the more distant you get. The chances of undesirable recessive genes would never go away completely, since the division of a nonzero numerator can never yield a zero quotient (and since it's impossible to have a zero denominator in the first place, we need not worry about that), but it gets smaller and smaller with each division, to the point of being negligible.

 

My question in my OP was ... at what point does the odds of birth deformities become so small that it's practically (emphasis on that word) nonexistent?

[Strange]

This question was discussed very recently on the BBC program "More or Less"

we find out for our loyal listener how many individuals he will need to create a new race of people.

http://www.bbc.co.uk/programmes/p029cx8y

Edited December 11, 2014 by Strange