There's enough DNA in the human body to stretch from the sun to Pluto and back. But don't confuse DNA with your genes, says writer Sam Kean.

"They are sort of conflated in most people's minds today but they really are distinct things," he tells Fresh Air's Terry Gross. "Genes are like the story and DNA is the language that the story is written in."

In The Violinist's Thumb, Kean goes inside our genetic code, looking at the stories written by the fundamental building blocks within us. The book explains things like why some people can't handle drinking coffee and why some human babies are born with tails. It also delves into the history and science of the story of DNA, a nucleic acid which contains the genetic instructions that form the basis for all living organisms.

Among the stories Kean shares is that of Tsutomu Yamaguchi, who survived the bombing of Hiroshima, took a train home that evening to Nagasaki and then survived a second atomic bomb blast.

"He ended up surviving for an amazingly long time, despite being close to both nuclear bombs," says Kean. "He actually lived until 2010. So he must have had inside his cells a very efficient way to repair DNA and to make sure any mutations he might have had got patched up."

All living things accumulate mutations as they age. Segments of DNA can get cut out or swap with one another or never stop forming.

"Cancer is really a DNA disease," he says. " ... We have these certain genes that prevent our cells from growing out of control at the expense of the body. And it's a pretty good, robust system. But if a couple of these genes fail, then that's when cancer starts and cells start growing out of control."

Interview Highlights

Sam Kean is also the author of The Disappearing Spoon, an investigation into the cultural history of the periodic table. (Courtesy of Little, Brown and Co.)

On genetic tests

"Genes work with probabilities; they don't work with certainties. So most things that you're looking at with these genetic tests, it's not like you're condemned to automatically get the disease or the syndrome. There's a lot of factors in play there."

On babies born with tails

"At some point in our past, we did have a tail. It was interesting to me that in some cases, we have the genetic blueprints to make these atavistic traits inside us like tails. Another famous example is human embryos. You can see our gill slits. So it's interesting to me that we have these remnants that never quite got pruned out. We don't use the DNA for much anymore but every once in a while it can pop up and you get things like a little baby with a tail."

On nature and nurture

"The more that I looked at DNA, the more I realized it was nature and nurture. It's how genes and your environment work together to produce the person you are. So I don't feel like I'm really hemmed in because of my DNA. Obviously there's some things that were never going to happen for me — I was never going to play in the NBA — because I'm not tall enough or bulky enough. But even now we're finding a lot of behavioral traits that have some sort of genetic influence or roots in DNA somehow. We're also finding that those things don't rigidly dictate who we are. Genetic determinism is an idea that really scares people and understandably so. But thankfully the more we find out about our DNA, the more we realize we're not determined by our DNA."

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