I’m reading my first Carl Zimmer book, She Has Her Mother’s Laugh, which is about heredity. He’s a little too popular for my taste, and his presentation frequently exposes the fault line between scientist and science writer, not seismically, but enough to engender a small shudder. So I mostly skimmed the background and history stuff in the first 200 or so pages, until I reached Part III (of V).

It was an attentional cattle prod. There are so many ways to inherit so many things that reading about it undermines one’s sense of self.

The main takeaway of the book will probably be that the popular model of DNA, just like the popular models of memory, germs and microbes, cancer, fingerprinting, intelligence, and depression, is way too simplistic. Biology is super messy. Most non-geneticists think we know about genes in a sort of Mendelian way, but Humans are Not Peas. Peas are not even peas, for the most part.

You’ve probably been hearing about epigenetics, the shortest explanation of which is, It’s not the genes you have, it’s the genes you use, and you don’t have to have read my blog to know that an army of microbes in our gut controls what we eat and how we feel. This book discussed these and many, many more mesmerizing methods genetic material finds to mill around and reshape us in the womb, as we grow, and as we age. Mammals can even inherit learned phobias, across multiple generations.

Two of my favorite methods so far are mosaicism, when some clusters of cells have different DNA than others, and chimerism, when one person carries the complete genomes of two people, possibly of the opposite sex. Examples of the former are tri-color cats, port-wine stain, and the syndrome that plagued the Elephant Man.

A chimerism case in point is Lydia Fairchild, who applied for child support in Washington state after splitting up with her husband, while pregnant with her third child. The seeds of the Mean State were germinating even then, and genetic testing was required in order to qualify for aid. The genetic testing showed she was not the mother of her children. During the court case, the testimony of her obstetrician was not persuasive, and she faced removal of her children, whom it was assumed she had abducted, even though the paternity of her husband was not in doubt. Even Fairchild’s own mother expressed doubt.

The court decided to have a witness attend the birth of her third child, not because this was proof that she was the mother, but so the birth could be followed immediately by a genetic test of both, which again was negative.

That trick puts Houdini to shame.

Fairchild was saved when her lawyer learned about chimerism and insisted on some more extensive tests that finally substantiated her claim. Genetic testing showed that her mother was the grandparent of all three children, for example, and after sequencing genomes from cells in various parts of Fairchild’s body, a match was finally found: in her cervix.

Do you think this sounds Dickensian, or even like a real witch hunt, by which I mean an actual campaign of persecution of an innocent person by an irrational mob? It happened in 2003. Tens of people believed a diagnostic test over the actual emergence of a baby from a woman’s body, including highly-educated people and close relatives. We have a real passive-aggressive thing going with science in this country, don’t we? No wonder we can’t grasp complicated models.

And don’t, don’t, don’t let your DNA get into the national database. If live birth isn’t a good enough alibi to overturn DNA findings, conventional criminal alibis are toast.