I intended to read Sam Kean’s new book The Violinist’s Thumb: And Other Lost Tales of Love, War, and Genius as Written by our Genetic Code just for fun. I was expecting a miscellany of trivia loosely gathered around the theme of DNA. But I found something much more worthwhile that I thought merited a book review to bring it to the attention of our readers. Kean interweaves entertaining stories into a somewhat disjointed but nonetheless valuable history and primer of genetics. The title refers to Paganini, whose DNA created the unusual joint flexibility that facilitated his unprecedented feats of virtuosity on the violin.
Kean details the discovery of genes, chromosomes, and DNA; not only with the well-known players (Mendel, Watson, Crick) but with more obscure researchers, weird fruit fly studies, womanizers, scientists who fought against the growing consensus, those who unraveled the complexities of how our cells read the genetic code, those who took some very wrong turns, and the complex politics that plagued the human genome project. His vignettes make the scientists come alive.
Along with the basics about inheritance and the G-T-A-C code, we learn about endosymbiosis, the incorporation of viral DNA into the human genome, jumping genes, viral DNA manipulation of host behavior, the complications introduced by the development of the X and Y chromosomes, how a person’s environment can alter the expression of genes in their children and even their grandchildren (epigenetics), gene reassortment, how genes are read and mis-read, how DNA ties itself in knots that have to be unraveled by canny proteins called topoisomerases, why identical twins are not truly identical, why we have fewer chromosomes than any other primate, how the box gene organizes development in the embryo, and how “junk” DNA is proving to be anything but.
Along the way, we learn about a couple who shared their house with 689 cats, an oddball piece of math (Zipf’s law) that applies to both linguistics and DNA coding, an unlucky man who fled Hiroshima after the bombing only to be bombed again in Nagasaki, explorers who died of vitamin A poisoning from eating polar bear liver because humans lack the genes that polar bears have evolved to protect themselves, a Russian scientist who tried to create a human/chimp hybrid by inseminating women with chimp sperm either with or without their consent, the postmortem peregrinations of Einstein’s brain tissue, the origin of funny names for genes like sonic hedgehog, and Darwin’s mysterious lifelong health problems.
We learn how DNA illuminates human history and evolution. The rate of mutation is steady enough to serve as a clock. In a bottleneck after the eruption of a monster volcano, the population of humans dropped precipitously, perhaps even as low as 40 adults. Because of that, we have far less genetic diversity than chimps and gorillas, even though our current population is 7 billion and theirs is only 150,000.
Gene sequencing is getting cheaper every day. We can only speculate what the future may bring. We may eventually have the technology to eliminate genetic defects in individuals and to direct the evolution of our species.
Kean’s colorful cast of characters is unending. We meet Craig Venter, the midwife toad, Stalin, Dolly the sheep, Toulouse-Lautrec, Neanderthal cannibals, a Cyclops, King Tut, and Kim Peek, the inspiration for “Rain Man” whose abnormal brain could perform astounding feats of reading and memory but couldn’t handle simple tasks of daily living. We meet a Victorian zoophagy enthusiast who thought moles were the worst-tasting animal until he ate a bluebottle fly.
A Lesson About Personal Genomic Testing
When his results were reported, the company gave him the option to not learn his risk of specific diseases. He opted not to know his risk of Parkinson’s, a disease he particularly dreaded because he had bad memories of his grandfather’s deterioration from it. When he read about Craig Venter publishing everything about his genome, he was inspired by that example to unseal his own results. He was relieved to learn he had no increased risk for Parkinson’s after all. His emotional relief was only minimally impacted by his rational understanding that “no increased risk” didn’t mean “no chance” of getting Parkinson’s. Later the company announced updates to the old results based on new scientific studies. A new study had looked at the DNA in a different spot on the genome and it showed he had a slightly greater than average risk of developing Parkinson’s. He felt as if he had been condemned, pardoned, and then condemned again.
His reaction was tempered by what he had learned during research for this book:
- Parkinson’s is complex, affected by many genes.
- Any one gene probably contributes very little.
- Slightly higher was defined as just 20%.
- Parkinson’s only affects 1.6% of men. (If the baseline risk is 1.6% and his risk is 20% higher, that would only raise it to 1.92%.)
- The new study was classified by the company as “preliminary.”
- Preliminary results are subject to amendments and reversals.
In short, genetic testing shows probabilities, not certainties. It seldom leads to useful preventive actions and it can lead to unnecessary anxiety or false reassurance for those who don’t know enough about genetics to appreciate the limitations of the findings. Scott Gavura said it well:
Our access to genetic information currently exceeds our understanding of what that information actually means.
Thumbs up to The Violinist’s Thumb. You will learn things you didn’t know and you will be heartily entertained in the process.
This article was originally published in the Science-Based Medicine blog.