Kissin' Kousins

I'm rewatching the brilliant Arrested Development, and there's this ongoing subplot with the teen son who is infatuated with his lovely freckled cousin, but of can't do anything about it because she is his cousin.

Does anybody know: is inbreeding problems a great risk between first cousins, or is this just one more guilt myth?

I was hoping that Pascal, an MD, would weigh in, and he does not disappoint:

Consanguinity [blood relationship] increases the chance that harmful genes meet, and that recessive traits get expressed. Most genetic diseases are based on recessive genes. If there are any genetic diseases in your family (and usually there's always a few imperfect genes in each of us), like for instance mucoviscidosis or Huntigton's disease, you're taking a significant risk of having children born with it. But genetics are a lottery. It's unpredictable hit-and-miss.

Think of races. Genuine races do not exist in humans, simply because isolated populations that developed a "type" of appearance over the milleniae were never consanguinous, they were always large enough to maintain a genetic diversity (albeit less diversity than the original population from which they stemmed). If you look at Africans, and look beyond the dark skin, large lips and nose, and curly hair, you'll have to admit they have a MASSIVE diversity of facial features. A recent anthropology study measuring specific body, skull and face details in an objective manner found that Africa has by far the greatest diversity in physical traits, when compared to other human populations in Earth. (This tends to support the "out of Africa" theory about the origins of our species, to me there's very little doubt.) Other ethnies/populations diverged once they emigrated from the "mother land" at the dawn of Humankind and lived isolated for thousands of years, divergences probably due both to chance (like slanted eyes in Asians) and some environmental factors (like melanin levels), but as I've once explained on this very blog a good while ago, the significant majority of these differences are LITERALLY skin-deep.

Now back to true races. These are an artificial concept made real by animal breeders. In dogs, cats, cattle, horses, etc... they constantly selected over many generations some traits they wanted, essentially through in-breeding between "blood related" individuals. What you can expect of long-going consanguinity ensues: many genes and traits become exclusive in one lineage.
The positive result is the "qualities" looked for in a race: giving a lot of milk, mellow character towards humans, physical strength and resistance, "pretty" fur, a constant bigger or smaller size than the original species... (Amazing but true, there is VERY little difference between a chihuahua, an afghan greyhound, a saint-bernard and a great dane. One single gene, with its variants, has been proven to determine the size of all dogs.)
The negative result is that, in spite of constant vigilance from the breeders, "the races degenerate". You've all heard about some very sad and specific problems encountered when you buy a puppy with a pedigree, like German Shepherds with hip malformation that cannot walk when they grow up. Breeders are now working hard at "cleaning the races" of a problem that was caused by making races in the first place. (In fact, the term "varieties" would be far more adequate.)

Basically, that's the kind of chance one takes with a consanguinous marriage, at a smaller scale because, as I said, if you weren't involved in the Lebensborn experiment performed by the nazis, and aren't from a very-very-very isolated family community of caricatural rednecks, then there's no "pure lineage", only a statistic similarity in your genomes. In classic incest, brother-sister or parent-child, the genes that both prospective parents have in common amount to 50%. That's a big chance to be taking. (Although, to be fair, Pharaohs did this for generations, and the results were not always catastrophic. But they got lucky, and probably "purged the race" of the most unwanted and embarrassing traits like unsightly deformities, mental retardation, physically incapacitating birth illnesses... Common practice in ancient times.)
Now, between first cousins, how much is the common genes rate? Child-parent: one-half. Parent-sibling aunt/uncle: one-half. Aunt/uncle-child: one-half. So, between first cousins, the identity rate of genes is one-half at the cubic power. That's 1/8, compared to the 1/2 of incest. Only 12.5%.
Still significant. Yet much less reckless, close to reasonable.

My medical opinion, and I believe it meets the current scientific consensus, is that marrying your first cousin (or just having kids!) is unadvised, but not a guaranteed catastrophe by far. Only do it after some very careful thinking.

Also, there is the moral issue, which without making prude lectures I'll sum as follows:
- You wouldn't marry your sibling.
- You wouldn't marry a sibling with whom you've been separated at birth, because that's still incest.
- You wouldn't marry an adoptive sibling whom you've grown up with, becase literally you're like brother and sister, and it would very much FEEL like incest.
So, if you and your cousin grew up quite close, you need to ponder your concept of family. Nature very wisely gave us some caution instincts: it's not a fluke if we generally fall in love with complete strangers.
Or a childhood friend, I reckon that can work too. But adult physical and marital intimacy needs to be safely distant from educational intimacy. A childhood friend IS NOT like a brother or sister, no matter how close you were.
As a proof, how many of you got along with your siblings as harmoniously as you did with your best friend? :-)

BTW, there's another element to ponder when considering Romans: due to the way they made and stored wine, the aristocrats often suffered from chronic lead poisoning, which can cause sadistic dementia. That's what you get from closing your jars of acidic wine with lead seals, and then drinking lots of it.