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A Conversation With

Texas Scientist With a Thing for Longhorns

David M. Hillis, an evolutionary biologist who studies how the Texas longhorn evolved horns that can exceed seven feet across, has a ranch with about 50 of the animals.Credit...Ben Sklar for The New York Times

Deep in the heart of Texas, cows with fearsome horns are everywhere — on bumper stickers and T-shirts, on the signs of auto dealerships and chain restaurants, grazing in broad pastures. The ubiquitousness of the longhorn, a symbol of the state and its flagship university’s mascot, might lead one to wonder: How did this animal get horns that can exceed seven feet across?

David M. Hillis, an evolutionary biologist at the University of Texas at Austin, has the answer.

Dr. Hillis, 56, and the recipient of a 1999 MacArthur “genius” fellowship, has been employing genetics, biochemistry and computation to figure out how this breed of cattle developed its trademark feature.

We spoke for two hours in Austin and later by telephone. A condensed and edited version of both conversations follows:

Q. How exactly did this hobby of yours begin: researching the evolutionary history of the Texas longhorn?

A. It started about 10, 15 years ago when my wife and I bought a ranch outside Austin. In thinking about what we wanted to do with the property, we hoped to connect it to some aspect of Texas history. That’s what led us to longhorns. These animals are not only a symbol of the state, they have an unusual biological history.

Like all cattle, they were domesticated about 10,000 years ago from the wild aurochsen. But they are special because they went wild a second time and were twice domesticated. There aren’t a lot of animals for whom this is true. We don’t really know a lot about how animals changed while being domesticated. It seemed we could learn a lot by studying this breed. The idea was to use the ranch as a kind of off-hours laboratory. We call the place the Double Helix Ranch. Originally, we had four longhorns — three cows and a bull. When I got the MacArthur, we bought some more. Today, we have about 50.

What have the longhorns taught you?

Where they came from and how they got to be like they are. There’d been all these myths and theories floating around: that they’d originated in Northern Europe. We used genetic testing and historic documentation, here and in Europe, to confirm that Texas longhorns appear to be directly descended from Iberian cattle brought to the New World by Spanish explorers.

We know that Columbus had cattle with him during his second voyage. But here’s the rest of the story: In the early 1500s, the Spanish introduced them into Mexico, where they broke free of captivity and eventually formed feral herds. It was those that migrated into what would later become the American Southwest and that lived in the wild for hundreds of years. Then, in the 1860s, Texans returned home from the Civil War, broke and starving. Because there was nothing else, they rounded up these wild animals. That’s when redomestication began.

How did the longhorns get their long horns?

From that feral period. Today’s longhorns have much longer horns than the animals brought over from Spain. In the wilderness, these animals, which had been bred for docility, were forced to contend with bears, wolves and coyotes. The mothers had to protect their young from predation. That’s when the principles of natural selection came into play. The females with the longest horns proved the best defenders of their young. Their offspring survived, and they were able to pass their genes on to the next generation, which is how you got selection for those long horns.

When you look at this breed today, you can actually see differences between what humans select for in cattle and what nature does. Farmers select for docility, high meat and milk production. Those traits are not necessarily an advantage in nature. However, because of their second bout in the wild, longhorns are usually far more resistant to disease, live longer, have more calves than domesticated cattle. They generally need less water and feed on more diverse types of grasses and brush.

Does this have any present-day implications for the breed?

Well, with increased health consciousness, there’s now a new market developing for range-fed beef. Thanks to their evolutionary history, longhorns are ideally suited for that, and that may encourage more ranchers to acquire and breed them.

Given their economic potential, are you discovering a new appreciation in Texas for evolutionary biology?

A lot of the economic basis of Texas involves things directly connected to evolution. The fossil fuel industry couldn’t exist if you didn’t know about billions of years of evolutionary history. Ranchers understand how evolutionary change comes because they are practicing artificial selection themselves in breeding.

Let’s talk about your day job. What do you do in your laboratory at the University of Texas?

We do phylogenetics, where we take the genetic information from organisms and use computational analysis to understand evolutionary relationships.

When I was in graduate school, in the 1980s, the techniques to do this were just beginning to come together. Since then, I’ve become especially interested in finding ways to apply all this new information to practical everyday problems. And indeed, the practical applications have gone up enormously — for instance, the SARS epidemic in 2003. We had this brand-new disease. Earlier, it would have taken decades to try to isolate the pathogen and figure out where it came from. SARS was figured out within months because of these tools. Recently, in my lab, we’ve been trying to figure out the roots of the viral diseases that are causing die-offs of amphibians around the world.

You’ve also shown that phylogenetics can be useful in criminal justice. How does that work?

Yes, I’ve worked on several high-profile cases. One of them set the precedent for the use of phylogenetic analysis in American courtrooms. This was in Louisiana, where a woman had an affair with a physician named Richard Schmidt. After she broke off the relationship, he injected her with something he said was “vitamin B-12.” She later developed H.I.V. The district attorney had me build an evolutionary tree of her virus. We were able to show that her pattern was similar to that of an H.I.V.-positive patient from whom Schmidt had drawn blood the same week this woman was injected. Schmidt was convicted of attempted murder.

I worked on another case here in Texas where a man was accused of infecting a lot of women with H.I.V. In that case, we had a whole series of blinded blood samples. We could see the same evolutionary patterns in the virus in all of them, and it was clear that it was all derived from the same source. He was convicted.

Are you gratified to see, because of phylogenetics, how practical the applications for evolutionary biology have become?

Oh, absolutely. In my lifetime, the applications have exploded. But the intellectual side is still compelling, because we are talking about the connections that stretch across all life.

I sometimes tell my students how fascinating it is to think about how I’m related to the cotton fibers in my shirt. Think about it: About a billion years ago, we had a common ancestor, and it began to diverge into two species, and one of them, a billion years later, ended up being a cotton plant and the other ended up being us!

A version of this article appears in print on  , Section D, Page 2 of the New York edition with the headline: Expert on Longhorns and Those Long Horns. Order Reprints | Today’s Paper | Subscribe

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