On Heredity

Carl Zimmer’s She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity is an essential read in our present moment. Genetic essentialism and ignorance; fundamentalism and fascism; the revival of eugenic racist thought and strategy by the Republicans; all these combine in the vital necessity of a history and understanding of biological and cultural heredity today.

The perversions of the title are grim indeed. You must know that American anti-immigration, eugenics, “scientific racism,” bogus histories of “feeblemindedness,” and forced sterilization programs, aroused by the robber barons and given impetus by philanthropists and museums like the American Museum of Natural History, were the direct precursors of the Nazi exterminations. The Nazis were frank in their admiration and emulation of these American notions.

Meanwhile, genetic essentialism, the notion that genes are destiny, crowds the minds of the ignorant. Did you know that at least one sperm bank lets you pick the astrological sign of the donor?

Unsurprisingly, too, racists still fall back on bogus genetic determinism for their beliefs. The white supremacist fantasists extolling a kind of white Euro-putinesque nonsense are clueless about the actual history of the waves of migration into what we now call Europe. (Isn’t it sick irony, too, that people of Irish, southern European, and eastern European ancestry, barely considered white a century ago, now Trump-et themselves the saviors of a nonexistent white race?)

“If you go back far enough in the history of a human population, you reach a point in time when all the individuals who have any descendants among living people are ancestors of all living people.”

There is so much in this book, it’s impossible to summarize. But in addition to the historical material, I was particularly taken with the discussion of CRISPR, which has both amazing and terrifying potential, and the following.

I’ve been using the term chimera for a while now to refer to both the human/microbiome mixture and the more basic mitochondria-cellular fusion, but there is actually another biological sense as well. First discovered in cows, later humans: fetal twins can share their mother’s and each other’s cells, resulting in all sorts of fascinating mixtures.

We used to think the placenta was an iron wall between mother and fetus, but “about half of mothers still carry fetal cells in their blood decades after carrying their children.” These can include Y chromosomes (females, remember, have XX chromosomes). Meanwhile, an estimated “42% of children end up with cells from their mothers.” Girls can end up with Y chromosomes because their mother had previously given birth to a boy. Writes Zimmer, “We use words like sister and aunt as if they describe rigid laws of biology. But despite our genetic essentialism, these laws are really only rules of thumb. Under the right conditions, they can be readily broken.”

Beware of rules and laws. They were made to be broken.

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