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Natural selection

Natural selection

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True or false? Species are always the same; their characteristics don't change over time.

Natural selection

Can you see that bird? Barely visible, huh? Oh, there it goes! Some animals look almost exactly like the environment they live in. They resemble leaves, bark, sand, or moss.

This makes it easier for them to hide from their enemies - or... ... from their prey. All living creatures have characteristics that helps them fit their particular environment... ... or that enable them to compete with others. They have, for instance... ...

a beak that can break seeds ... teeth that are good for chewing meat. ... roots that can go deep, and find water and nutrients even in dry environments. ... or fur that protects from cold conditions. But how did this happen?

How can a species shape itself after its environment, and adapt to its needs like this? This is how it can happen: This is a butterfly, a peppered moth. There's a bright and speckled variant... ... and a dark one. So, among these butterflies there are different genes, giving them different nuances of colour.

The peppered moth is often found on birch trees, whose trunks are often light in colour. The light shaded moths are hard to spot, against the light background. The darker kind on the other hand, is far more visible. And this is dangerous. These moths are easily found by birds, who want to eat them.

As the birds find the dark moths more easily, those moths become rare. Most peppered moths are light in colour. Or, at least that's how it used to be. Because, at the end of the 19th century, something interesting happened, in England. People burned a lot of coal for heating, and from the chimneys came black soot, that made the tree trunks darker in colour.

Now it was suddenly the light moths that were easiest to see, and who were most often eaten by birds. The black peppered moths, with genes for a darker shade, became a lot more common. Nowadays, we don't release as much soot anymore, and the trees have become lighter again. So again, the lighter peppered moths hide themselves better. Today, lighter is again the most common shade.

So, the species peppered moth has changed over time... ... because the individuals with genes for certain characteristics have survived and reproduced, while others have been eaten. And it happened the same way when... This beak, These teeth, These roots, And this fur... ... developed, and became so well adjusted to the particular environments these particular animals and plants inhabit.

Within every species, there have been individuals that happened to be slightly better adjusted to their environment. These individuals have had a better chance to survive, reproduce, and to pass on their genes. Genes for characteristics that enhance the chance of survival, are spread. Genes that reduce the chances of survival disappear. It is as if nature selects the characteristics that suits the environment, and helps them to spread.

We call this natural selection. Natural selection is one of the processes in nature that form the basis for how new species can appear... ... and for how old species can divide in two... ... or go under and disappear. How species develop and change, we call evolution.

And natural selection is an essential part of evolution.