“Air Pollution, Evolution, and the Fate of Billions of Humans: It’s Not Just a Modern Problem. Airborne Toxins Are so Pernicious That They May Have Shaped Our DNA over Millions of Years”, 2020-01-13 (; similar):
Scientists are still figuring out how air pollution causes these ailments. They are also puzzling over the apparent resilience that some people have to this modern onslaught. Some researchers now argue that the answers to these questions lie in our distant evolutionary past, millions of years before the first cigarette was lit and the first car hit the road.
Our ancestors were bedeviled by airborne toxins even as bipedal apes walking the African savanna, argued Benjamin Trumble, a biologist at Arizona State University, and Caleb Finch of the University of Southern California, in the December issue of the Quarterly Review of Biology. Our forebears evolved defenses against these pollutants, the scientists propose. Today, those adaptations may provide protection, albeit limited, against tobacco smoke and other airborne threats. But our evolutionary legacy may also be a burden, Dr. Trumble and Dr. Finch speculated. Some genetic adaptations may have increased our vulnerability to diseases linked to air pollution. It is “a really creative, interesting contribution to evolutionary medicine”, said Molly Fox, an anthropologist at the University of California, Los Angeles, who was not involved in the new study. The story begins about seven million years ago. Africa at the time was gradually growing more arid. The Sahara emerged in northern Africa, while grasslands opened up in eastern and southern Africa. The ancestors of chimpanzees and gorillas remained in the retreating forests, but our ancient relatives adapted to the new environments. They evolved into a tall, slender frame well suited to walking and running long distances. Dr. Finch and Dr. Trumble believe that early humans faced another challenge that has gone largely overlooked: the air. Periodically, the savanna would have experienced heavy dust storms from the Sahara, and our distant ancestors may have risked harm to their lungs from breathing in the silica-rich particles. “When the dust is up, we’re going to see more pulmonary problems”, Dr. Finch said. Even today, Greek researchers have found that when Sahara winds reach their country, patients surge into hospitals with respiratory complaints. The dense foliage of tropical forests gave chimpanzees and gorillas a refuge from dust. But the earliest humans, wandering the open grasslands, had nowhere to hide. Dust was not the only hazard. The lungs of early humans also may have been irritated by the high levels of pollen and particles of fecal matter produced by the savanna’s vast herds of grazing animals. Dr. Finch and Dr. Trumble maintain that scientists should consider whether these new challenges altered our biology through natural selection. Is it possible, for instance, that people who are resilient to cigarette smoke have inherited genetic variants that protected their distant ancestors from cave fires?
…“Most traditional people live in a highly smoky environment”, Dr. Finch said. “I think it has been a fact of human living for us even before our species.” Smoke created a new evolutionary pressure, he and Dr. Trumble believe. Humans evolved powerful liver enzymes, for example, to break down toxins passing into the bloodstream from the lungs. Gary Perdew, a molecular toxicologist at Penn State University, and his colleagues have found evidence of smoke-driven evolution in another gene, AHR. This gene makes a protein found on cells in the gut, lungs and skin. When toxins get snagged on the protein, cells release enzymes that break down the poisons. Other mammals use AHR to detoxify their food. But the protein is also effective against some of the compounds in wood smoke. Compared to other species, the human version produces a weaker response to toxins, perhaps because AHR protein is not the perfect protector—the fragments it leaves behind can cause tissue damage. Before fire, our ancestors did not need to use AHR very often; in theory, their bodies could tolerate the limited damage the protein caused. But when we began breathing smoke regularly and needing the AHR protein constantly, the gene might have become dangerous to our health. Dr. Perdew believes that humans evolved a weaker AHR response as a way to find “a sweet spot”, a compromise that minimized the damage of airborne pollutants without causing too many side effects. These adaptations were never perfect, as evidenced by the fact that millions of people still die today from indoor air pollution. But evolution doesn’t seek perfect health.