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The Violinist's Thumb

by Sam Kean

Mendel studied genes with binary traits. But most traits are determined by multiple genes, and so organisms show gradations of traits. Some genes turn the 'volume' up or down, producing even finer gradations. But bc genes are discrete, a beneficial gene can survive undiluted, through generations. And even a small advantage conferred by a mutation could compound long enough to push species in new directions.

Most of science has boring, hard-to-rem labels. Not genetics. Mutant genes described as groucho, fear of intimacy, lost in space, faint sausage, tribble. Armadillo gives fruit flies a plated exoskeleton. Turnip makes them dumb. Tudor leaves males sterile (as in Henry VIII). Cheap date makes them very susceptible to alcohol. Ken and barbies have no genitalia. Dissatisfaction females refuse sex.

Tsuttoma Yamaguchi regarded as the unluckiest man in C20 - in both Hiroshima and Nagasaki when bombs dropped. He was late for work at Mitsubishi ship yard, so only badly burnt on arms. Managed to get himself home to Nagasaki where wife and child lived, and got bandaged up. Then went back to work at Mitsubishi. Boss listened to his story and called him a liar. "You're an engineer, do the calcs. How can a single bomb destroy a whole city?" "What's that noise .....?" BOOOOMB! He lived to 93. Probably other dual survivors but he was only one recognized by Japanese govt.

James Watson and Francis Crick unusual biologists for their time in that they synthesised the work of others rather than doing expts themselves. This got them into a bit of trouble with Rosalind Franklin, who took (but didn't recognize) the crucial xray photos that showed the double helix.

All insects and animals have same hoxgenes, which control map, front to back, left to right and top to bottom. So all have same basic plan - a cylindrical trunk with a head at one end and an anus at the other, with appendages sprouting in between. Invertebrates have one stretch of 10 genes, vertebrates have 4 stretches of virtually the same ones. And the position on that stretch corresponds to body map: the first hox does the head, the next one does next bit down the body, and so on in sequence. They don't do the building themselves; they are the instruction set to tell other genes when and where to produce proteins and when and where to stop.

DNA that appears in the same basic form in many species is described as 'highly conserved', in that creatures remain very conservative about changing it.

Toxoplasma gondi is a single-celled protozoan which was originally a parasite of cats, but has now infected mammals, birds (chickens) and amphibians. It infects about a third of all humans. One common effect in humans is inability to small cat urine, and in some cases, to actually enjoy the smell. There is evidence that toxo also interferes with the brain's fear circuits, converting them into ecstatic pleasure, which offers an explanation for the risk seeking behaviour of some individuals.

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All other primates have short, finger-nail hard spines studding their penises. Humans don't, bc sometime in the last few million years we lost about 60,000 letters of 'junk' DNA. We still have the same genes as chimps, but no longer have the regulatory DNA to activate them. Speculation that this reduces penis sensitivity so longer sex so improves pair-bonding.

Humans rely less on scent than other mammals. Throughout our evolution we've lost or turned off six hundred mammalian smell genes. But we still have the harware - an organ called the VNO that other mammals use to monitor pheromones, plus the nerves connecting the VNO to the brain. And we can monitor signals travelling up and down these nerves. But the VNO starts to shrivel soon after birth and by adulthood has almost completely vanished.

There are about 150,000 chimps and 150,000 gorillas alive today, vs about 7 billion humans. Yet humans have significantly less genetic diversity than either of those monkeys. This means that the worldwide population of humans has dipped far below the population of chimps and gorillas recently, perhaps multiple times.

One idea is that the eruption of the Toba supervolcano 70,000 years ago almost eliminated human species. Toba was a mountain in Indonesia before the top 650 cubic miles blew off. We can gauge the effects by comparing with the second largest known eruption - that of Tambora in 1815. After that eruption there was so much fine ash in the upper atmosphere that 1816 was 'the year without a summer' causing widespread crop failures and worldwide famine. Yet Toba erupted five times longer and ejected twelve times as much ash. It probably caused a six-year long dimming of the sun which drastically reduced food resources, and then worsened an existing ice-age. Studies suggested that the world population of humans may have dropped to a few thousand adults, in scattered populations.

DNA confirms our African origins. A species shows greatest genetic diversity near it's origins, where it's had the longest time to develop. And that's what we see in Africa. Africans have 22 versions of a particular stretch of DNA linked to the insulin gene, only 3 of which appear in other parts of the world.

Henri Toulouse-Lautrec's family traced their line back to time of Charlemagne, and the counts of Toulouse ruled southern France for centuries. They were famous for annoying Popes, who, down through the ages, excommunicated them ten times. Scheming to keep their estates intact, various T-Ls usually married each other. Henri's parents were first cousins, his grandmothers sisters. Henri had brittle bones and stunted legs - an adult torso on child-like legs left him around 4 foot 6 tall. Other cousins were also runtish and deformed.

His father was a tall and handsome throwback (famous aphorism a lament that 'the days have gone when the Counts of Toulouse could sodomizea monk and then hang him afterwards if it pleased them.') who wrote Henri out of his will when it became clear that he couldn't go hunting with him.

Worst inbreeding was infamous Hapsburg kings, the worst being the last Spanish Hapsburg, Charles II, whose father married his niece. There was so much incest in his family tree that his parents were even closer related than brother and sister.

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(New Scientist)

THE waitress stopped as she passed my table. "Is that a mystery you're reading? Cover looks like it." "No," I answered. "It's a fast-paced, breezy romp through history using DNA as a unifying theme - it's nerd-vana."

In truth, it's a wonder that I broke away for long enough to converse at all, given the wealth of engaging information contained in every paragraph of this book.

In it, science writer Sam Kean sets out to explain many human phenomena in the light of DNA, speeding from personality quirks of early geneticists to evidence for interbreeding between Neanderthals and humans.

The book's title refers to Kean's retrospective diagnoses of medical conditions in historical figures, in this case attributing Ehlers-Danlos syndrome to Niccolò Paganini, the violinist. One symptom is double-jointedness, which would help explain his virtuosic abilities.

There are a few problems. When explaining the transmission of leukaemia between a woman and her fetus, Kean asserts that maternal-fetal microchimerism does not happen. In fact, almost all of us have some of our mother's - and, if you are a mother, your child's - cells within us. Kean's example is just a tragic demonstration of the phenomenon, as cancer cells are among those that cross the placental barrier.

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