EVERYBODY has recessive conditions. It may just be a dumb gene that mutated 300 generations ago and that, since it never activated (maybe because present only in that family tree), it didn't affect the hosts and it was never subjected to natural selection and so it "survived".
That's why mostly animals try (when possible) to avoid inbreeding.
I will finish my participation in this discussion with this post, since it is going off topic:
Those who have been culturally indoctrinated to accept or reject consanguineous relationship, will support or attack incest purely based on their cultural views. Facts will be irrelevant. Those who are interested in the truth will take facts and what is scientifically proven as valid and just forget about cultural preferences. Well, here are the facts:
"EVERYBODY has recessive conditions" It is a wild speculation, not a fact. Otherwise our world, specially in the Middle East, North of Africa and Asia, would be full of monstrous mutants!
"That's why mostly animals try (when possible) to avoid inbreeding" This is true to some extent: It is better for the species if genes are mixed, so animals will naturally try to mix their genes. But inbreeding won't be a problem and also happens naturally. ("Sometimes, though, the incest happens by accident. As Gabriella told us:
'Brother and sister dogs sometimes go at it. Ninety-nine percent of the time they are caught in time. But, every once in a while, it's too late, and they get a litter.'" -
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Documented health risks of incestuous relationship:
First Cousins
(Third-Degree Relatives)
Risk above general population:
- 1.7% to 2.8% for significant congenital defects
Father/Daughter - Brother/Sister
(First-Degree Relatives)
Risk above general population:
- 6.8% to 11.2% for significant birth defects (extrapolated from first-cousin data)
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For comparison, when a man correctly wears a condom in a sexual relation, his level of protection against AIDS is about 85% meaning a risk of 15% of getting infected, and it is called "safe sex". In order to not use double standards, if incest has a risk of 11.2% for birth defects, it should be named "safe reproduction".
Recessive Conditions:
Cousins on average, their progeny will be homozygous at 6.25% (1/16) of gene loci
Thus (extrapolating from cousins data) siblings on average, their progeny will be homozygous at 12.5% (1/8) of gene loci
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Additional reading:
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