errata:
Owing to changing schools a few times I got a total of 4 weeks of biology in school, so this may be all wrong:
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Sorry, I really don't know much biology, but I thought I did OK filling in for a creationist
OK, I'll hold the fort for AppliePie until Friday
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The absence of Chromosomal defects means inbreeding is fine. This could also explain the long lives of the ancients.
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It turns out the cheetah has exactly that problem, down to about 7 individuals during the massive mammal die out 10,000 to 12,000 years ago.
And from the article on cheetah extinction (ABC news), and the one on cheetah skin grafts, I discovered that...
Genetic defects isn't the only problem -
lack of genetic variety means one disease could wipe out the entire population.
And for some reason no one has yet found, lack of genetic variety leads to skull asymmetry.
Humans have picked up diseases from all over the World and shared them, some like the plague killed most people who contracted them. Humans are very numerous and form a big enough reservoir of infected individuals for some diseases such as flu to mutate and evolve within our population.
Cheetahs have a small population and limited range and so have not picked up any lethal diseases.
Geneticists have shown there is a lot of variety in the human gene pool. Even just looking around reveals tall thin Africans, short (pygmy) Africans, muscular Africans, slightly built Celtic type Caucasians, Viking type Caucasians, Mongolians, Polynesians, Arabs and others. Hair can be coarse and straight or curly or fine and straight, some men go bald very young, others haven't at 85, some people can not distinguish between bitter and sour, others between red and green, some can curl their tongues...
I can't see how one father (Noah) and five women 4,500 years ago gave rise to the variety we now have, especially if all five women can from just one Adam and one Eve.
Anyway it looks like even if their alleles had no defects the human race would not have survived this far,
sorry about the mistake