For a species whose numbers show no signs of collapsing, humans have a shockingly high mutation rate. Each of us is born with about 70 new genetic errors that our parents did not have. That's much more than a slime mold, say, or a bacterium. Mutations are likely to decrease an organism's fitness, and an avalanche like this every generation could be deadly to our species. The fact that we haven't gone extinct suggests that over the long term, we have some way of taking out our genetic garbage.
Epidemics have a way of making one wonder about death. To put it plainly, in the raw form it takes as it first rises from our hearts: Why? Why on Earth does it have to be this way? In The Plague, Albert Camus' novel of harrowing disease in an Algerian city, Father Paneloux, a faithful Jesuit, steps to the pulpit and offers his explanation. "This same pestilence which is slaying you," Paneloux says, "works for your good and points your path."
In 1944, a Columbia University doctoral student in genetics named Evelyn Witkin made a fortuitous mistake. When she returned the following day to check on the samples, they were all dead--except for one, in which four bacterial cells had survived and continued to grow. Somehow, those cells were resistant to UV radiation. To Witkin, it seemed like a remarkably lucky coincidence that any cells in the culture had emerged with precisely the mutation they needed to survive--so much so that she questioned whether it was a coincidence at all. Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.
Her reaction mimicked the befuddlement of countless anthropocentric minds who have puzzled over this discrepancy since scientists began comparing species' genomes more than 70 years ago. The decades that followed brought more surprises: flying birds with smaller genomes than grasshoppers; primitive lungfish with bigger genomes than mammals; flowering plants with 50 times less DNA than humans, and flowering plants with 50 times more; single-celled protozoans with some of the largest known genomes of all. Three decades later, the evolutionary biologist Richard Dawkins solidified this idea in his popular 1976 book The Selfish Gene; the theory was quickly adapted to explain genome size. In the late 1990s, Dmitri Petrov, then a doctoral student at Harvard University, began tracking small mutations in insects--random genetic changes of up to a few hundred base pairs that resulted from DNA damage, copying mistakes and poor strand repair.