Over the past 50 million years, a group of small, hoofed mammals gradually evolved into today’s whales and dolphins. In the process, they gained much: a watery, planet-wide habitat and bountiful sources of food. But they lost a lot, too. Surrounded by endless blue, they became color-blind. Immersed in water, their sense of smell disappeared. And for some reason, they lost a gene called PON1.
PON1 helps humans and other mammals process fatty acids and cholesterol, but whales—and other marine mammals like manatees and seals—seem to have lost the need for it. For most of their existence, the gene’s absence was inconsequential.
In the 1940s, humans started intensively studying a new class of chemicals called organophosphates, which attack the nervous systems of animals. Researchers harnessed these substances to create chemical weapons like sarin gas, and insecticides like chlorpyrifos. Today, organophosphates are widely used as pesticides, and they occasionally become environmental pollutants. And as it happens, our main defense against these chemicals is a gene that can break them down—PON1, the same gene that whales have lost.
For millions of years, the loss of PON1 was just another quirk of evolution. Now it’s a tragic vulnerability. It means that whales and other marine mammals are uniquely susceptible to toxins that have only existed for a few decades. “It’s a bit of a strange coincidence,” says Nathan Clark from the University of Pittsburgh.