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

Evolution by Natural Selection

‘The keystone of our story is evolution by natural selection. In the 1830s, a young Charles Darwin travelled around the world on the HMS Beagle – inarguably, by the way, the most important beagle of all time; I apologise Snoopy but it’s true. Darwin had the rare and amazing opportunity to study a great variety of the world’s wildlife, and upon returning to England he discovered that a variety of Finches he had collected on the Galapagos Islands had beaks that were suddenly adapted to their different environments and food sources.

Darwin later combined this idea with the observation of how populations tend to overbreed and strain their resources; I mean, if there is competition for resources in an environment, animals with useful traits would survive and pass those traits on to their offspring; those who didn’t survive long enough to reproduce would have their traits wiped out from the evolutionary tree: natural selection.

We talk about someone who does “good science” and Darwin was a good scientist; he worked on his idea for two decades, systematically finding new evidence to support his case; and then, finally in 1859 he published On The Origin Of Species and it sent shockwaves around the world. The book offered an explanation for why so many species that seemed perfectly adapted to their environment could have been formed by a blind but elegant law of nature. Darwin’s theory was so elegant yet so effective that his colleague Thomas Huxley exclaimed “How extremely stupid not to have thought of that!”

Sidenote: if you ever read On The Origin Of Species, try to get a first edition because in later editions, Darwin made a bunch of revisions in answer to some critics but he got it actually more right the first time.

Speaking of which, a bunch of the phrases only included in the later editions and commonly attributed to Darwin was “Survival of the fittest”, but that phrase was actually coined by Herbert Spencer, father of the more troubling Social Darwinism which tried to apply nature’s rather harsh laws to human social orders.’

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