Here’s what you’ll learn when you read this story:The molecular clock theory posits that genetic changes happen steadily and gradually, offering a reliable means for peering into the past and theorizing when complex life first emerged. But a new study published in the journal Systematic Biology takes issue with the molecular clock itself, and suggests that evolution doesn’t “tick” as steadily as we might expect. To simplify things, if there are six genetic changes between these two species and the molecular clock is constant, this suggests one genetic change per million years. However, the Covariant Evolutionary Tempo model suggests that when a big group of organisms appear, evolution actually speeds up. “While the speeding clock idea needs testing,” Telford wrote, “it could explain other mismatches between molecular clocks and the fossil record.”