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The Human Animal

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By Mary Daily

Published Oct 1, 2019 8:00 AM


Professor of Medicine Barbara Natterson-Horowitz studies animals to make better sense of humans. One thing she knows for sure: Adolescence is dangerous for both.


“There are some tragic but fascinating parallels [between adolescence in animals and humans] that are important for physicians and parents to recognize,” says Professor of Medicine Barbara Natterson-Horowitz. Photo by Christina Gandolfo.

Cardiologist Barbara Natterson-Horowitz believes in crossing lines.

A professor of medicine in UCLA’s Division of Cardiology and visiting professor in Harvard University’s Department of Human Evolutionary Biology, Natterson-Horowitz co-directs the UCLA Evolutionary Medicine Program. Her bestselling 2012 book Zoobiquity: What Animals Can Teach Us About Health and the Science of Healing, co-authored with Kathryn Bowers, makes the case for a species-spanning approach to health. One of the courses Natterson-Horowitz teaches at UCLA is “Coming of Age on Planet Earth,” which uses an evolutionary frame to better understand humans’ developmental transition from puberty to adulthood. It’s also the topic of her new book, Wildhood (again co-written with Bowers). Natterson-Horowitz was a keynote speaker at the Nobel Conference in Stockholm in September.

When did you start studying the connections between human and animal health?

I came to UCLA in 1988 for residencies in internal medicine and psychiatry [at the UCLA Neuropsychiatric Institute] following medical school at [the University of California, San Francisco,] and undergraduate and graduate school at Harvard, where I had studied evolutionary biology. During my cardiovascular fellowship at UCLA, I became focused on cardiac imaging. I was imaging lots of patients with a range of cardiovascular conditions, helping to develop imaging technologies for our cardiac arrhythmia group. Then a phone call changed my life.

What was the call?

The call came from a veterinarian at the Los Angeles Zoo. One of their chimpanzees, Pandora, had symptoms that were neurological, and they wanted me to do an imaging procedure to rule out a cardiac cause. It was something I had done on thousands of human patients, but that day I performed it on my first nonhuman patient. Over the years, I imaged her many times and got to know her well. Then [the zoo] started asking me to image their gorillas and other primate patients. Eventually, I was working on a whole range of animals — a bear, a tapir, a lion, a California condor with a heart murmur. It was a magnificent experience.

Where did that experience lead you?

It led me to think deeply about how to take the information I was getting from veterinary medicine and bring it to human medicine. And I started conducting systematic reviews on a range of health challenges in humans, looking for their spontaneous occurrence in animals — both captive and wild — from breast cancer and diabetes to atherosclerosis and infertility. That led to more research, my partnership with Kathryn, our book Zoobiquity and the Zoobiquity conferences.

Did you see a need for more connection between veterinarians and physicians?

I was learning so much from veterinary cardiologists, veterinary oncologists and animal behaviorists who deal with eating problems, self-injury, anxiety, depression and compulsion in their patients. I realized we could accelerate innovation, and we started the conferences to bring physicians and veterinarians together.

Can you give some examples?

At the Zoobiquity event at the Nobel Conference, for instance, we brought together giraffe veterinarians and medical doctors to explore how giraffes’ heart muscles get very thick from having to pump at a high pressure without the tissue getting stiff, as a human heart muscle does when it thickens from high blood pressure. We asked why hibernating bears who don’t drink anything [and don’t] urinate for four or five months avoid becoming uremic. So, turning to the natural world to identify adaptations becomes nature’s massive R & D project.

What led to your new book, Wildhood?

One chapter in Zoobiquity about comparative adolescence was an eye-opener. Animals of all species transition from being juveniles to mature adults. We knew human adolescence was dangerous. Annual mortality increases at least sevenfold between the ages of 12 and 19, mostly due to car accidents. Is it also dangerous for birds? For fish? We conducted large systematic reviews and found that it is remarkably similar from one species to another. There are some tragic but fascinating parallels [between adolescence in animals and humans] that are important for physicians and parents to recognize.

Many forms of mental illness occur during adolescence, and we learned that self-injury and eating disorders may occur in animal adolescence. I knew that victims of sexual assault are disproportionately adolescent, and we found that sexual coercion between animals is more likely to occur when there is a power gradient — which means young [low-status] adolescents are at risk. We had learned so much about cancer and heart disease; now here was an opportunity to learn about this destiny-shaping phase of life. It’s no coincidence that Kathryn and I both had adolescents at that time. If we had written Wildhood sooner, I know I would have parented differently.

How does that look in the animal world?

High mortality relates to inexperience. When birds reach a certain size, they leave the nest. They are no longer protected by parents and also lack experience. They’re what wildlife biologists call “predator naïve.” Those first few days out of the nest are the most dangerous of their lives. But every week they live, the likelihood of living another week goes up. Experience with danger makes them safer. Unfortunately, that experience can be deadly. Some adolescent animals will move toward a predator instead of away. The hypothesis is that [the animals] are learning what’s dangerous, getting information about how to tell whether a predator has fed or not, because they’re more dangerous when they’re hungry.

Animal parents use progressive teaching techniques to help offspring eat safely. Meerkats like to eat scorpions. But scorpions can kill them if [not killed correctly]. The adults know how. They kill the scorpion first and bring it to their young pup. As the pup gets older, the parent captures the scorpion, injures it and presents it to the pup. Finally, the parent brings the almost-adult pup a live scorpion and supervises while the pup kills, then eats the scorpion. The other way they learn is from peers, and the peer learning is so powerful that animals will deliberately eat food that can sicken them if all their peers are doing it. We can understand human adolescent risk-taking in this kind of comparative context. The idea is to offer this kind of comparative understanding of this period. I think we can also apply it to later life.

Is that your next book?

Well, there is a lot of research on orcas and menopause. But for now, my focus is on adolescence. My mission is to understand the human animal in a deeper way. Teaming up with veterinarians is a great way to make this happen. This younger generation of doctors is more collaborative and connected to the natural world. So I am optimistic.

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