‘Zoobiquity’: What Animals Can Teach Us About Our Health
What can animals teach us about cancer and eating disorders? Carl Zimmer on 'Zoobiquity.'
Barbara Natterson-Horowitz’s world was turned upside down by a monkey with a heart attack. Natterson-Horowitz is a cardiologist at the David Geffen School of Medicine at UCLA. She’s also on the medical advisory board for the Los Angeles Zoo, where she goes from time to time to consult for the zoo veterinarians. One day in 2005, the vets at the zoo asked her to come by to take a look at a kitten-size emperor tamarin named Spitzbuben that was suffering from heart failure.
As Natterson-Horowitz examined Spitzbuben, she did what she usually does with her human patients: she gazed into Spitzbuben’s miniature eyes to put her at ease.
Immediately she felt the vet’s hand on her shoulder.
“Please stop making eye contact,” the vet said. “You’ll give her capture myopathy.”
Capture myopathy? Natterson-Horowitz was puzzled. She knew very well that myopathy refers to heart muscle damage, but in her 20 years as a cardiologist, she had never heard of capture myopathy. Later she did some research and discovered that it’s a form of heart damage experienced by many animals. It occurs when animals are chased or captured by predators. A surge of hormones floods their body and ravages the heart. Some species—including small primates—can even die as a result. Even the gaze of a predator can help cause capture myopathy. At the zoo, Natterson-Horowitz had thought that her gaze was saying, “I’m here to help you.” But to Spitzbuben, she was saying, “Prepare to die.”
Natterson-Horowitz felt a connection snap into place in her mind as she read about capture myopathy. It existed in humans, under the name of Takotsubo cardiomyopathy. Intense emotional stress can cause a hormone surge in humans, which can cause serious damage to the heart. Cardiologists discovered Takotsubo cardiomyopathy just a few years ago. But veterinarians knew about its animal version decades ago.
That experience opened Natterson-Horowitz up to all the things that doctors can learn from veterinarians. She’s spent the past few years exploring the many parallels between human and animal health—a phenomenon she likes to call “zoobiquity,” a mash-up of the words zoology and ubiquity. Now she’s gathered her many observations together in an engaging new book, Zoobiquity: What Animals Can Teach Us About Health and the Science of Healing, coauthored with science writer Kathryn Bowers.
It’s remarkable just how many examples of zoobiquity there turn out to be. Natterson-Horowitz once inspected a rhinoceros, for example, and discovered a type of cancer called squamous cell carcinoma under its horn. Rhino horns are made of keratin, the same protein found in our fingernails. And squamous cell carcinoma also develops under our fingernails.
The fact that we share so many ailments with animals is no coincidence. We evolved from a common ancestor, and inherited much of the same biochemistry—along with its weaknesses. Humans, rhinos, and all other animals are at risk for cancer, for example, because they all have bodies made up of huge numbers of cells. If a mutation makes a single cell deaf to the needs of its body, it can develop into a tumor.
Our common ancestry with animals is also the source of many dangerous infectious diseases. You may not think you have all that much in common with a chicken, but to an influenza virus humans and birds are promising hosts alike. Seventy percent of infectious diseases in humans got their start in animals. HIV evolved from a chimpanzee virus. It hopped over to our own species in the early 1900s by infecting West African hunters killing chimpanzees for meat. Chimpanzees and other primates carry many other viruses, one of which might well become the next HIV.
In each chapter of Zoobiquity, Natterson-Horowitz investigates a human disorder—obesity, addiction, heart disease to name a few—and presents its animal counterpart. She has plenty of great stories to tell, like the time that 80 cedar waxwing birds got drunk on fermented Brazilian pepper-tree berries and crashed into a reflective glass wall. But in each case, Natterson-Horowitz also finds provocative new ideas about human diseases. Pigs, for example, sometimes develop their own version of anorexia. One thing that seems to prevent pigs from becoming anorexic is keeping them warm. Natterson-Horowitz speculates that changing the thermostat works by affecting a gland in the brain called the hypothalamus, which is involved both in regulating body temperature and appetite. Perhaps a similar treatment may work on human anorexics too. In Natterson-Horowitz’s own practice as a cardiologist, she has become much more wary now about restraining patients with heart problems. The fear of being trapped may bring on a human version of capture myopathy.
Learning about animal health may also give doctors clues about new treatments for human diseases. Natterson-Horowitz points out that the risk of cancer should increase as animals get bigger. The more cells an animal has, the more tickets it has in the oncological lottery. But whales defy this expectation. The biggest whales often live more than 100 years, despite the fact that they should be dead from cancer long before then. Some scientists have speculated that whales have evolved some powerful anti-cancer weapons. No one knows what those weapons actually are, but we’d do well to find out.
It’s exciting to watch a doctor discovering just how much the animal kingdom has to teach her. But Zoobiquity also displays some common misconceptions about how evolution works. In her chapter on sex, for example, Natterson-Horowitz starts off her account of the male anatomy with invertebrates like barnacles. They experience what Natterson-Horowitz calls “proto-erections,” or “Erection 1.0s.” Human males, by contrast, enjoy superior upgrades, because they have complex brains that control their libido.
This sort of account turns evolution into a simple march of progress, which it’s not. We didn’t evolve from barnacles; we’re their cousins. After our lineages split apart 600 million years ago, the ancestors of barnacles evolved just as much as we did, producing penises admirably adapted to a life spent attached to wave-battered rocks. A barnacle’s erection unfurls a penis up to eight times the length of its whole body. It thoughtfully probes its neighbors for a receptive mate. If a barnacle grows up in particularly violent tides, it develops a stouter, shorter penis that will be less likely to snap off. “Erection 1.0” does barnacles a grave injustice.
Natterson-Horowitz then explores the animal kingdom for some clues to why some men experience premature ejaculation. She offers up a list of other species in which the males make quick work of sex. Chimpanzees take 30 seconds to do the deed. Some birds can transfer sperm in a fraction of a second. The zoobiquity of swift sex leads Natterson-Horowitz to conclude that human males are adapted for getting sex over and done with. Otherwise, they’d be left vulnerable to attacks from predators or ambushes from other males.
Just because some species benefit from quick sex doesn’t mean that they all do. In fact, some males mate for a very long time. Water striders, those insects that flit across the surface of streams, can have sex for hours, even as female water striders try to throw the males off.
To see whether a behavior really does boost the reproductive success of a species, scientists have to dig deeper. Male water striders are clearly adapted for marathon sex: they have hooks and barbs to keep them attached to females. And experiments on these insects shows why that equipment has evolved: the longer a male holds onto a female, the harder it is for the females to mate with other males. Understanding human sexuality demands the same close examination.
I don’t mean to single out Natterson-Horowitz with these criticisms. As a journalist, I’ve encountered a number of doctors whose eyes have been opened to the importance of evolution, and I’ve heard these misconceptions and many others from them. The trouble, I think, lies in the fact that doctors tend to develop their fascination with evolution well into their careers. Pre-med students don’t have to study evolutionary biology, and until recently, medical schools offered no courses at all in evolution.
Fortunately, that’s starting to change. Leading medical schools such as Harvard and Johns Hopkins are building evolution into their curriculum. The National Academies of Science are urging that MCATs include many more questions about evolution. Natterson-Horowitz herself is doing her part, organizing conferences where doctors and veterinarians can come together to share their experiences and observations. We can only hope that future generations of doctors won’t have to wait until they happen to be gazing into the eyes of a monkey to understand that medicine is not just about humans.