Since the first living things appeared on the planet, the biggest among them have become increasingly bigger. Over 3.6 billion years of evolution, life’s maximum size has shot up by 16 orders of magnitude – about 10 quadrillion times – from single cells to the massive sequoias of today (below right). And no matter what people say, size does matter.
The largest of creatures, from the blue whale to the sauropod dinosaurs, are powerful captors of the imagination, but they are big draws for scientists too. Jonathan Payne from Stamford University is one of them, and together with a large team, he ambitiously set out to understand how the maximum size of living things has evolved throughout the entire history of life on Earth.
Taking each geological era and period in turn, the team scoured the literature for examples of the largest species alive at the time and recorded their size by volume. They also interviewed experts in the field of classification to get their side of the story. Payne’s full database is available online and it showed that the massive increase in life’s maximum size wasn’t a gradual process.
Instead, it happened in two main bursts, which took place in just 20% of the history of life but accounted for 75% of the increase in maximum size. On both occasions, the largest living things became about a million times larger. The first followed the evolution of more complex, compartmentalised cells and the second came after the advent of multi-celled creatures, and both coincided with dramatically rising levels of oxygen in the air. It was a case of environmental changes unlocking pre-existing evolutionary potential.