To make sense of the fact that adaptation can happen quickly and yet true evolutionary change seems to take forever, biologists suggest that evolution runs on two very different clocks
15 June 2022
BY THE YARDSTICK of a human lifetime, time itself is dizzyingly long. If you condensed the entire 4.5 billion years of Earth’s existence into a 24-hour period, more than 3 million years would pass each minute. The dinosaurs would go extinct at 11.39 pm and 48 seconds. Human history would begin two-tenths of a second before midnight.
The vast timescales at play in the universe’s past are counter-intuitive. Even when the early pioneers of geology and evolutionary biology had proved beyond doubt that Earth was very, very ancient, it was still widely believed to be no more than a few tens of centuries old. Some people still cling to that belief today.
Charles Darwin, as usual, was ahead of his time. He realised that a few thousand years were nowhere near enough to incrementally transform, say, a primitive fish into a bird of paradise or a tiny weed into a mighty oak. Aeons were in order. As he wrote in On the Origin of Species, “we see nothing of these slow changes in progress, until the hand of time has marked the long lapse of ages”.
That was the dominant view for a long time, says Matthew Pennell at the University of British Columbia in Canada. Indeed, biologists fretted that the rate of evolution was too slow to account for the riot of biodiversity they observed in the world. Now, however, the problem has flipped on its head. “We basically found over the last 30 years that evolution over small timescales is way too fast to explain patterns of diversity at longer timescales,” says Pennell. “Many of the great …