A new discovery may change the way we understand evolution to progress.

Natural selection, or "survival of the fittest," refers to the serendipitous emergence of a genetic mutation that puts an organism at an advantage over its peers, allowing it to adapt to its changing surroundings. This evolutionary model has traditionally been thought to rely on a single, crucial change that alone alters the trajectory of the species.

Now, researchers at Princeton University have found that the process is not driven by a single mutation, but rather by a group of co-existing, disparate mutations divided between two groups - "drivers" and "hitchhikers" that each contribute to the organisms survival over millennia. While the mutations in the former set improve the organism's general fitness, those in the latter are simply "along for the ride," and may instead become relevant farther down the line.

"Our study indicates that evolution is more of a group effort," said Gregory Lang, first author on the paper. Their findings are published in the journal Nature.

In the study, the team observed 1,000 generations of adaptation in 40 yeast strains reproducing asexually. Rather than developing isolated, beneficial mutations and passing them on to their offspring, the thriving yeast colonies all contained the same group of five to seven simultaneous mutations.

"We found that small groups - which we call cohorts - of mutations were associated with increased survival. No single mutation is driving adaptation. The whole group, which includes hitchhikers, drives adaptation together," said Michael Desai of Harvard University.

David Botstein, a professor of Genomics at Princeton University, noted that the results add to our understanding of evolution as a complex event.

"We've shown that this first component, the genetics, involves not just one gene mutation but several that need to co-exist before evolution can happen," he explained.

A more sophisticated knowledge of the mechanisms behind genetic mutations may deepen our understanding of how tumors and bacteria become resistant to treatment methods.

"By following genomic changes across cell populations over time, this study allows a rare glimpse of evolution in progress," said Stefan Maas of the National Institute of Health's National Institute of General Medical Sciences.

"This systems biology approach yields insights that could help us understand how mutations spread through other evolving systems, such as cancer cells or disease-causing microbes," he continued.

Future research will focus on determining how the mutations are split between the two categories, and whether the "hitchhikers along for the ride" eventually assume the driver's seat, or otherwise contribute to the organism's fitness down the road.


Gregory I. Lang, Daniel P. Rice, Mark J. Hickman, Erica Sodergren, George M. Weinstock, David Botstein & Michael M. Desai. "Pervasive genetic hitchhiking and clonal interference in forty evolving yeast populations." in Nature. doi:10.1038/nature12344