The Sonic Hedgehog Gene ∞

The Violinist's Thumb (★★★★★), Sam Kean’s 2012 book about genetics is jam-packed full of quirky, fascinating science goodness. It’s hard to pick a favourite, but this is a good candidate:

Be warned: before you dash to the health store for megadoses of vitamin A for a special pregnant someone, you should know that too much vitamin A can cause substantial birth defects. In fact the body tightly caps its vitamin A concentration, and even has a few genes (like the awkwardly initialed tgif gene) that exist largely to degrade vitamin A if its concentration creeps too high. That’s partly because high levels of vitamin A in embryos can interfere with the vital, but even more ridiculously named, sonic hedgehog gene.

(Yes, it’s named for the video game character. A graduate student—channeling those wacky fruit fly names—discovered it in the early 1990s and classified it within a group of genes that, when mutated, cause animals to grow spiky quills all over, like hedgehogs. Scientists had already discovered multiple “hedgehog” genes and named them after real hedgehog species, like the Indian hedgehog, moonrat hedgehog, and desert hedgehog. Robert Riddle thought naming his gene after the speedy Sega hero would be funny. By happenstance, sonic proved one of the most important genes in the animal repertoire, and the frivolity has not worn well. Flaws can lead to lethal cancers or heartbreaking birth defects, and scientists cringe when they have to explain to some poor family that sonic hedgehog will kill a loved one. As one biologist told the New York Times about such names, “It’s a cute name when you have stupid flies and you call [a gene] turnip. When it’s linked to development in humans, it’s not so cute anymore.”)

One more selection from The Violinist’s Thumb. The nugget: “we’re four times more virus than human.”

The name Human Genome Project even became something of a misnomer, because it turned out that 8 percent of our genome isn’t human at all: a quarter billion of our base pairs are old virus genes. Human genes actually make up less than 2 percent of our total DNA, so by this measure, we’re four times more virus than human. One pioneer in studying viral DNA, Robin Weiss, put this evolutionary relationship in stark terms: ‘If Charles Darwin reappeared today,’ Weiss mused, ‘he might be surprised to learn that humans are descended from viruses as well as from apes.’