Flowers Flower

Plant revolution
130 million years ago

This may sound strange, but flowers are a quite recent invention. There have been land plants for 465 million years, yet there were no flowers for over two-thirds of that time. Flowering plants only appeared in the middle of the dinosaur era. The equally-familiar grasses appeared even more recently. The oldest fossil grasses are just 70 million years old, although grass may have evolved a bit earlier than that.

See other: History of Life

The Cambrian Explosion

Evolutionary leaps
535 million years ago

Soon after animals evolved, evolution went through two major growth spurts. In the Cambrian Explosion, it seems almost every group of modern animals appeared within tens of millions of years. This apparent ‘explosion’ may be partly down to better fossilisation, as many animals now had hard shells. Then 489 million years ago, each animal group expanded in the Great Ordovician Biodiversification Event.

See other: History of Life

Evolution 101

‘Consider Darwin’s original phrase natural selection: everything from Cuckoo Birds that lay their eggs in the nest of other birds, to giraffes whose long necks are good for reaching food in high trees, to humans whose brains make up for their fragile bodies, are selected for, naturally.

An even better phrase would be non-random selection or maybe even non-random elimination. While all genetic mutations are generated by a random copying error or random variation completely beyond the animal’s control, the selection of those traits is not random.

Successful variations that allow you to survive and reproduce are determined by the very specific circumstances of your environment, where elimination – death – might not be far away.

So, the selection of your traits is done by a very specific and sometimes brutal list of criteria. This is why people who say that they don’t understand how all animals could have “evolved by chance” don’t really understand how evolution works.

Here’s another phrase that doesn’t get it right: “evolution is just a theory”. In everyday speech, theory means guess; but in science, a theory is something that was tested time and time again, explains many different observations and is backed up by a mountain of evidence.

Evolution is a theory like gravity is a theory, and you don’t go jumping out your window because gravity is “just a theory”.

Why are we so certain? Emily knows:

Evolution is one of the most tested, most utilised and most widely accepted theories in science. It’s backed up by literally tonnes of fossil evidence which can show us shared traits with species that no longer exist, and help us map out lines of descent for creatures that are around today.

DNA sequencing further tells us about lines of descent and you can measure the commonality of the DNA possessed by two animals to tell how closely related they are, and when they may have split off from a common ancestor.

Radiometric dating allows us to assign dates to various fossils, further helping us map out lines of descent.

Then there’s the simple fact that extinct species are always found in the same rock layers you’d expect to find them. Which is why you don’t see a bunny skeleton in Cambrian rock layers from half a billion years ago. That’s also how we know that Dimetrodon is not a dinosaur.

Closely related species are often geographically distributed near one another. That’s not to mention that we can see evolution happening before our very eyes: whether it be the discovery of a new species that recently moved into a different environment, the development of newly adapted bacteria into superbugs, the evolution of new breeds of rapidly reproducing insects, or the almost constant changes in gene distribution in animal populations all over the world.’

– Green. H., Graslie. E. (2014, October 29) The Evolutionary Epic: Crash Course Big History #5