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Imagine the heartbreak of learning that your unborn baby has a genetic disease that will make her deaf, severely intellectually disabled and limit her life expectancy to around 20 years.

But your doctor offers you a solution – called CRISPR – that can rewrite the stretch of DNA causing all those problems. With a single injection, your baby’s DNA would be “fixed.” She would develop normally and healthily, with no possible chance of remission, and no chance of passing those problems on to her own children. Do you get the shot?

Oh, the genetic scan also revealed a 30 per cent chance that your child will develop Parkinson’s disease by the age 60, but another CRISPR shot can bring that probability down to the usual 1-2 per cent. Do you want that one, too?

And you’re fine with brown eyes, are you?

Very soon, those will be real decisions parents can make. As an experimental tool for geneticists, CRISPR isn’t even a decade old, but what it promises is staggering, and there’s really nothing but ethical arguments to stop geneticists from using it on humans next. Suddenly, we are on the precipice of a Brave New World.

Carl Zimmer’s just-released book about heredity, She Has Her Mother’s Laugh: The Powers, Perversions, and Potential of Heredity (Dutton), explores the context and implications of CRISPR and other advances in genetics. Carl is one of the most well-respected science writers working today. His work appears in The New York Times, National Geographic, and elsewhere. This is his 13th book.

The Globe and Mail reached Zimmer by phone.

Beyond humans, where do you think CRISPR will have its biggest impact?

Food. I think that CRISPR is going to allow scientists who are tinkering with crops and livestock to make some really dramatic changes. If you have a particular idea about how to make some plant grow more fruit, you can zero in on that precise little bit of DNA and tinker with it – and you don’t make any other changes.

The other big impact CRISPR could have would be in conservation. Imagine you have an invasive species; potentially eradicating it by using CRISPR to spread a gene around that causes sterility or infertility or so on. It could be dangerous though, because those genes might spread to a closely related species that you actually want to save, and nobody knows how easy it could be to pull back CRISPR once you release it into the wild like that.

In addition to CRISPR, you talked about recent research where scientists take skin cells from mice, make them into stem cells and then in turn make those into sperm or eggs. If I understand this correctly, that could mean a homosexual couple could make sperm and eggs to have babies just like heterosexual couples do. How close are we to that happening?

I think we’re pretty close, as strange as that sounds. Something we would have thought was profoundly mysterious and defied the laws of nature turns out to be just a matter of finding the right chemicals to dunk your cells into. There are still a lot of obstacles for them to overcome but the fact that they’ve gotten so far already is pretty mind-blowing.

I think that that kind of technology could unsettle our ideas about heredity much more than CRISPR. Imagine one man takes a cheek scraping, turns them into stem cells, turns some of those cells into sperm and eggs, fertilizes the eggs with the sperm, and that turns into an embryo. That’s a one-parent embryo! Theoretically that’s possible!

Now imagine that you pluck a cell from that tiny little embryo, when it’s just a clump of cells, and you then grow eggs or sperm from that. Remember this is an embryo that has never turned into an adult. Then you fertilize another egg created this way, and you do that for a few generations. If an embryo that develops from that is now implanted into a woman and is able to grow into a person, that person has no parents… has no grandparents! That family tree is pretty much impossible to draw. So when I think about that possibility it just seems like we could really be going into a science fiction future.

Okay, so the future looks complicated. You also said something about the past in the book that I found really counterintuitive – that anyone alive 5,000 years ago, who has any descendants alive today, must also be an ancestor to every other human on Earth. That would mean any ancestor of, say, Aborigines in Australia must also be an ancestor to all of the Hasidic Jews. That seems impossible!

It does seem impossible, however that’s just because we have the wrong picture of genealogy in our heads. When we think about her own ancestry we think about our self, and then you draw two branches that go up to your mother and father, and more branches to grandparents and so on, and you have this tree that’s sort of branching out over and over and over again. But the problem with that is that it’s based on the idea that somehow all of your ancestors are completely unrelated to each other, and that’s just not true – they’re cousins… maybe sixth, seventh, who knows? That means that the tree is not infinitely branching, but sort of folds back in on itself. So I agree it’s astonishing but if you talk to geneticists and mathematicians, they just shrug their shoulders and say “Look, that’s just how it is.”

As part of the research you did for this book you had your entire genome sequenced. What did you learn from that process?

If you go to 23andMe or, they are going to decode about 0.1 per cent of your whole genome. If you want to really see all your DNA down to the very last letter, you need to go to whole genome sequencing. It’s incredibly cheap compared to what it used to be, but it’s still around $1,000, and the problem on top of that is that you need to make sense of this huge amount of raw data. So once I got my hands on my genome I went to a number of scientists and asked them if they could help me make sense of it. And it was an amazing experience.

One of the exciting things was being able to see all my Neanderthal genes. It was interesting that some of them were involved in the immune system which might mean that I inherited genes from Neanderthals that help me fight certain diseases. But there are other Neanderthal genes that I just don’t understand. There’s this one gene with a particular mutation that comes from Neanderthals, and that mutation is linked to a risk of nosebleeds! I don’t think of myself as someone who bleeds out the nose more than anyone else, and also I can’t really think of a reason that Neanderthals would have evolved to be prone to nosebleeds. So it’s just a mystery that is very tantalizing, and I just have to sort of be content with that.

A lot of people don’t want their DNA scanned because they’re afraid of what they’re going to find. Did you find anything in your genome that scared you?

No, I didn’t find anything that scared me. I would say if you’re just searching for individual mutations that on their own can make you really sick or make you at risk of serious diseases, most people are going to get boring results. A small percentage will get some bad news, and from a public health perspective that could be really important. But even then, if you know that you have a gene that’s been linked to a particular kind of very risky heart disease, there are things you can do about it! So I think that on the whole it’s a good idea to overcome your fear and just take a look.

People love to debate whether a person is just born a certain way, or if they’re a product of the environment they live in. Obviously there’s truth to both sides. After doing all the research for this book, where do you sit on that continuum?

I came away really scratching my head over the paradox of nature versus nurture. I mean the whole world is much taller now than it was a hundred years ago, and that has nothing to do with genes at all. Height is like one of the most heritable traits that we know of, and yet we’ve changed height in a way that doesn’t have anything to do with genes. What I came away with was appreciating how hard it is to balance those two things in your head at the same time, and I think it’s still going to take a while to master that.

This conversation has been edited and condensed.

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