My blood type is A negative. I've heard this can cause pregnancy issues, so I Googled "Rh-negative blood" and ran across a bunch of weirdo sites with "theories" about the origin of negative blood types and some online communities with seriously racist undertones. Where did all this crazy mythology surrounding blood types come from?
—Katrina
That sure is some netherworld of dodgy disinfo you inadvertently spelunked into, Katrina—no place you'd want to find yourself without up-to-date antivirus software, an airtight pop-up blocker and ideally a strong stomach. Many links concerning Rh-negative blood look kosher enough in your search results but when clicked release a flood of wide-eyed theories about ethnic migration, blood type-based dating tips and offers to trace your ancestry back to extraterrestrials, angels or lizards.
Various stalwart rationalists, bless 'em all, have labored above and beyond to debunk this stuff. But I'll go out on a limb here and assume that none of my readers actually suspects some randy E.T. begat great-grandpa. Instead, as you say, the question is where these crypto-hematologists emerged from and what their deal is. On examination, they generally seem to be people who had certain theories about how the world worked long before they learned of Rh negativity. And then? Well, they smelled blood.
Now, blood can seem like a loaded concept, I guess—essence of life, symbol of tribal identity, beverage of vampires, etc.—so maybe even the otherwise level-headed get weird about it sometimes. But come on—this is science. The term "Rh factor" is commonly used to refer to the presence of a certain protein, the D antigen, on the surface of an individual's red blood cells. If you've got it—and most of us do—you're Rh-positive. The slim minority of humans without? Rh-negative. It's always good to know your blood type, but particularly when you're pregnant. Things can get tricky when an Rh-negative mother is carrying an Rh-positive fetus—if she's been exposed to Rh-positive blood before (typically via a prior pregnancy), she'll produce antibodies that can attack her helpless kiddo like it's an infection.
As with most of our species' biological oddities, scientists believe that Rh-negative blood initially resulted from a DNA mutation that evidently served some sort of evolutionary purpose that research hasn't quite yet nailed down. Having the gene for Rh negativity seems to improve resistance to the parasitic condition called toxoplasmosis, which might hint at an answer, but no one knows for sure.
No one knows for sure: five magic words that will forever summon swarms of crackpots from dankest cyberspace. Some try to tell you that the children of the Nephilim, an antediluvian race of fallen angels and/or giants casually mentioned in Genesis, still walk among us—ye shall know them by their Rh-negative blood. Others will list the "reptilian" physical characteristics Rh-negative folks possess, including extra vertebrae and lower-than-normal body temperature. Yet others want to talk about the AB-negative blood supposedly found on the Shroud of Turin. But two major sets of opportunistic cranks stand out, each armed with their own theories about Rh negativity.
The first crew is relatively benign, of a type familiar to all battlers against pseudoscience: those who for more than half a century have recast the divine beings of the world's religions as "ancient astronauts," crediting extraterrestrials with constructing the pyramids and inspiring the stone heads of Easter Island. You've seen their paperback bible in thrift stores, or on your favorite hippie uncle's bookshelf: Chariots of the Gods?, by Erich von Daniken. (Who, the blood-type fans excitedly insist, was Rh-negative himself!) But for some scholars of this ilk, aliens weren't here just to jumpstart our civilization. They manipulated us on a cellular level, creating, according to UFO-centric author Nick Redfern, "a slave race to dutifully mine gold." The evidence? You guessed it: Rh-negative blood.
You're more likely, though, to encounter the suggestion that Rh-negative blood makes its possessor superior to others.
Unfortunately, this viewpoint attracts far nastier sorts, too. Forever on the lookout for some minor genetic distinction between ethnicities to bolster their worldview, certain white supremacists are tickled a melanin-deficient pink about the fact that about 15 percent of people of European descent will tend to be Rh-negative, while less than one percent of Africans, Asians and Native Americans will. Thus, predictably, you'll see assertions that Rh-negatives have a higher IQ and that the fair-skinned Caucasian traits of Northern Europeans were caused by the mutation. Stray far enough into the muck and you'll find "proof" that Jesus was Scandinavian—with AB-negative blood, natch.
Back here in reality, I've got good news for Rh-negative moms-to-be: As long as you discuss potential Rh-factor issues with your OB-GYN early enough, complications can usually be avoided.
Send questions to Cecil via StraightDope.com or write him c/o Chicago Reader, 350 N. Orleans, Chicago 60654.
