The sleeping beauties of biological evolution

By | April 24, 2023

Andreas Wagner writes:

What are the most successful organisms on the planet? Some people might think of apex predators like lions and great white sharks. For others, insects or bacteria might come to mind. But few would mention a family of plants that we see around us every day: grasses.

Grasses meet at least two criteria for spectacular success. The first is abundance. Grasses cover the North American prairies, the African savannahs and the Eurasian steppes, which span 5,000 miles from the Caucasus to the Pacific Ocean. A second criterion is the number and diversity of species. Since the time grasses originated, they have evolved into more than 10,000 species with an astonishing variety of forms, from centimetre-high tufts of hair grass adapted to the freezing cold of Antarctica to the towering grasses of northern India that can hide entire elephant herds, and to Asian bamboo forests, with “trees” that grow up to 30 metres tall.

But grasses weren’t always so spectacularly successful. For tens of millions of years – most of their evolutionary history in fact – grasses barely eked out a living. Their origin dates back to the age of dinosaurs, more than 65m years ago. But for many millions of years, the fossil record suggests, they were not abundant. In fact, it wasn’t until less than 25m years ago that they became the dominant species that we recognise today.

Why did grasses have to wait 40m years for their proverbial spot in the sun? This mystery deepens once you know that, early on, evolution endowed grasses with multiple survival-enhancing innovations. Among them are chemical defences like lignin and silicon dioxide that grind down the teeth of grazing animals. These features also protect grasses against drought, as do sophisticated metabolic innovations that help them conserve water.

With these and other innovations, you’d think that grasses would have quickly become dominant. But their delayed success holds a profound truth about new life forms. Success depends on much more than some intrinsic characteristic of a new life form, like an enhancement or a novel ability bestowed by an innovation. It depends on the world into which this life form is born.

Grasses are among myriad new life forms whose success – measured in abundance or diversity of species – was delayed for millions of years. The first ants appeared on the scene 140m years ago, but ants did not begin to branch into today’s 11,000 or more species until 40m years later. Mammals with various lifestyles – ground-dwelling, tree-climbing, flying or swimming – originated more than 100m years before they became successful 65m years ago. And one family of saltwater clams had to wait for an astonishing 350m years before it hit the big time, diversifying into 500 species.

These and many other new life forms remained dormant before succeeding explosively. They are the sleeping beauties of biological evolution. They cast doubt on many widely assumed beliefs about success and failure. And these doubts apply not just to the innovations of nature, but also to those of human culture. [Continue reading…]