There’s a difference, though, between disorders that are caused by gene defects or undesireable interactions between genes (generally the result of inbreeding in a small population, or disorders rare enough not to significantly affect reproductive fitness), and a genetic subceptibility to viruses or bacteria. Sure, various poxes and plagues killed off a majority of the New World Aborigonies, but it wasn’t because the Eurpeans were “naturally” more resistant to infection. The difference was that the Eurasians, who had been participating in animal husbandry for thousands of years (by which the diseases passed from domestic animals to humans) and had gone through a gradual sifting process by which weaker and less adapted infectious organisms had already killed the “weaker” members of the population. The ones that were left, and especially those hardy enough to survive a perilous ocean voyage and attendent hardships were far better able to resist infection.
By the time the Europeans landed in the Americas, human bacteria/virus genes had been engaged in a several millenia-long arms race of virulence and resistance; a race in which the Clovis people unintentionally opted out of by emigrating to the New World. Being less prepared to resist the now-well-adapted microbio invaders, infection raged like a California wildfire in October.
The differences in nuclear genes between different “races” are almost slight, not only because the short amount of time (tens of thousands) of years for genetic divergence, but also because of the interbreeding that occurs whenever human populations encounter each other. With the exception of extremely isolated populations that could more easily be destroyed by more conventional means, there just isn’t (generally speaking) enough difference to make a clear distinction between races. We may look a lot different, but so does a Great Dane from a Pomeranian, yet both are more alike than either is compared to a coyote.
On the other hand, if you could figure out a mechanism to link your hypothetical selective plague to a particular genotype, you might be able to target all (or most) people who exhibit a certain phenotype. For instance, you might be able to target all blue-eyed people (or at least those whose gene for blue eyes comes from the same population.) But most racial identification is due to phenotypical expressions (hair color and form, skin color, et cetera) that are the result of the confluence of a number of different genes.
One method that might work, again assuming some kind of discriminating mechanism which can target any particular gene sequence, is to use the mitochondrial DNA which are passed down directly from mother to child, and therefore are identical for all members of a lineage accounting after accounting for random mutation. This is one of the ways in which bioanthropologists track the divergence of human populations. (Given a constant mutation rate, you compare samples for differences and back-calculate the time needed for divergence.) You’d still pick up mulattos whose traits from the “undesired” population aren’t predominate or are dilluted (and there’s a lot more of them than you think, especially in the Americas) but you’d be limited to a single lineage.
I don’t know how you’d do this, though…or why. People seem to be pretty effective in acting on their cultural xenophobia with guns, machetes, gas chambers, napalm, and any other number of horrors without needing to bring in the eggheads.
I’d forgotten about “Sixth Column”. Heinlein seemed to have a burst of xenophobic output for a while (see “Farnham’s Freehold” for another example) before settling down to attempt at integrating every story he ever wrote into his increasingly tenuous “Future History”.
Stranger
:eek: