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For decades, researchers have observed that rates of evolution seem to accelerate over short time periods—say five million years versus fifty million years. This broad pattern has suggested that "younger" groups of organisms, in evolutionary terms, have higher rates of speciation, extinction and body size evolution, among other differences from older ones.

Evolutionary processes appear to operate at different time scales, perhaps necessitating the need for a new theory linking microevolution and macroevolution. The larger question has tantalized scientists: why?

There are plausible explanations. A new species may inhabit a new island chain, allowing for more variation as it spreads into new niches. An asteroid may hit the Earth, increasing extinction rates. Perhaps species evolve to an "optimal" trait value and then plateau.

A paper published in PLOS Computational Biology now proposes an entirely new explanation for understanding this evolutionary pattern: statistical "noise." The paper, "Noise leads to the perceived increase in evolutionary rates over short times scales," was written by Brian C. O'Meara, a professor in the Department of Ecology and Evolutionary Biology at the University of Tennessee, and Jeremy M. Beaulieu, an associate professor of in the Department of Biological Sciences at the University of Arkansas.

The authors note that "by employing a novel statistical approach, we found that this time-independent noise, often overlooked as inconsequential, creates a misleading hyperbolic pattern, making it seem like evolutionary rates increase over shorter time frames when, in fact, they do not. In other words, our findings suggest that smaller, younger clades [groups with common ancestors] appear to evolve faster not due to intrinsic properties but because of statistical noise."

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