Free Zoobiquity by Barbara Natterson-Horowitz

animal lactators.
    It may also be that lactation is protective because it decreases the exposure to estrogen a breast receives with every menstrual cycle. An approach suggested to me by Chris Bonar, the chief veterinarian of the Dallas World Aquarium, could help clarify exactly what it is about breast-feeding that seems to be protective. He noted that female mammals have different numbers of reproductive cycles per year.Some wild bats, for example, have vaginal menstrual bleeding every thirty-three days, a monthly cycle similar to that of some primates, includinghumans. In contrast, sheep and pigs are polyestrus and ovulate only several times a year. Female ring-tailed lemurs, bears, foxes, and wolves usually cycle just once a year. But breast-feeding disrupts reproductive cycles in mothers. So by comparing breast cancer rates in female animals with different cycle frequency—and different hormone exposures—comparative oncologists could home in on an important distinction: how much breast-feeding’s power to protect comes from lactation itself and how much from disrupting the hormones that accompany reproductive cycles.
    Another thing we can learn from animal cancer is the extent to which it’s caused by outside invaders: viruses. Veterinary oncologists see this all the time. Lymphomas and leukemias among cattle and cats are quite frequently viral. Many of the cancers sweeping sea creatures from turtles to dolphins are rooted in papilloma and herpes viruses.
    As we know, cancer starts as a cell with mutated DNA. Few things in nature rival viruses for their skill at tinkering with DNA. But human physicians tasked with fending off and treating so-called lifestyle cancers, such as those caused by smoking, drinking, or overeating, tend to think “infectious trigger” only when it comes to a narrow range of malignancies. Every oncologist and many patients, for example, know that viruses are responsible for Kaposi’s sarcoma, some leukemias and lymphomas, and some liver cancers. “Cancer à deux” (cervical and penile cancers shared by sexual partners) is spread by the human papilloma virus.
    In fact, worldwide, about 20 percent of human cancers are viral. In Asia, the leading cause of liver cancers is viruses: hepatitis B and C.Across Africa’s “lymphoma belt,” ‡ the Epstein-Barr virus is a known driver of Burkitt’s lymphoma. Human papilloma virus and hepatitis B and C are on the NIH’s list of known carcinogens. The idea that cancers spread virally has led some epidemiologists to call for treating cancer as an infectious disease. This is something veterinarians already do.
    Peto’s paradox, Jews and jaguars, professional lactators, viral triggers—in these cases, a zoobiquitous approach can help us generate new hypotheses about the causes of cancer. But animals may be able to help us in amore urgent or timely way. They may be able to warn us of impending disease—before it actually strikes us.
    In 1982, dead beluga whales began drifting ashore along the St. Lawrence Estuary in northeastern Canada. The leading cause of death was a grim list of cancers. Intestinal. Skin. Stomach. Breast. Uterine. Ovarian. Neuroendocrine. Bladder.
    The St. Lawrence belugas, it turned out, were saturated with heavy metals, as well as other industrial and agricultural contaminants, including dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), and polycyclic aromatic hydrocarbons (PAHs). Researchers from the University of Montreal didn’t have to look far for the source of these artificial intruders. Lining the coast were aluminum smelters. Every year for decades, these factories pumped tons of PAHs into the water and released other contaminants into the air. Day after day, these compounds had drifted through the water and accumulated on the ocean floor. Mussels and other sea-dwelling organisms absorbed them. When the belugas scooped into the sediment to feed, they received a double dose of toxins—in the