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explainer: Answers to your questions about the news.

Will Cockroaches Inherit the Earth?What Wall-E gets wrong about the apocalypse.

By Daniel Riley
Posted Tuesday, July 8, 2008, at 3:23 PM ET

Wall-E's roach companion

Pixar's post-apocalyptic love story Wall-E finished No. 2 at the box office over the Fourth of July weekend after hauling in $65 million the weekend before. The film depicts a future Earth abandoned by humans, blanketed in garbage, and nearly devoid of life. At the outset, Wall-E, a robot, has but one companion: a friendly cockroach. How did we come to believe that cockroaches will outlive everything else on Earth?

The cockroach survival myth seems to have originated with the development of the atom bomb. In The Cockroach Papers: A Compendium of History and Lore, journalist Richard Schweid notes that roaches were reported to have survived the blasts at Hiroshima and Nagasaki, leading some to believe that they would inherit the Earth after a nuclear war. This idea spread during the 1960s, in part due to its dissemination by anti-nuclear activists. For example, a famous advertisement sponsored by the National Committee for a Sane Nuclear Policy and referenced in a 1968 New York Times article read, in part, "A nuclear war, if it comes, will not be won by the Americans … the Russians … the Chinese. The winner of World War III will be the cockroach."

There is at least a modest scientific basis for the myth: Cockroaches are more resistant to radiation than humans and nearly all other noninsect animals. This is because they are relatively simple organisms with fewer genes that might develop mutations. Roach cells also divide more slowly than human cells, which gives them more time to fix problems caused by radiation, such as broken strands of DNA. Whereas a person will certainly die from a radiation dose of 1,000 rads, cockroaches can withstand more than 10 times that amount. (For comparison, a full-body CT scan gives a dose of 2 or 3 rads.)

In 1962, H. Bentley Glass, a Johns Hopkins geneticist, told the New York Times that in the event of nuclear war, "the cockroach, a venerable and hardy species, will take over the habitations of the foolish humans, and compete only with other insects or bacteria." But studies over the last half-decade, such as those conducted by the United Nations Scientific Committee on the Effects of Atomic Radiation, have found that these "other insects" are more likely to reign in the age after humans; the cockroach might, in fact, be one of the first bugs to go. More recently, the television show MythBusters tested the effects of radiation on several kinds of insects and discovered that tiny flour beetles were the hardiest—with some surviving a dose of 100,000 rads. (Click here to watch the MythBusters segment.) Organisms that aren't classified as animals are even better-equipped to handle a nuclear fallout: certain bacteria, protozoa, mosses, and algae might thrive long after roaches and flour beetles bite the dust.

In any case, the cockroach is a proven survivor. Most researchers believe the roach's fossil record dates back to approximately 300 million B.C., a period predating dinosaurs by nearly 70 million years. Additionally, the roach knows how to get by during tough times: It can survive on dead or decaying organic matter and can even live without its head for more than a month.

Got a question about today's news? Ask the Explainer.

Explainer thanks George Beccaloni of London's Natural History Museum, Grzegorz Buczkowski of Purdue University, Andrew Karam of Rochester Institute of Technology, Joseph Kunkel of the University of Massachusetts-Amherst, and journalist Richard Schweid.