Making Evolution Happen

By looking at fossils of different ages we can see that animals, plants, fungi and bacteria have changed - very, very slowly - over time. We say they have 'evolved', and we call this slow process of change 'evolution'. So how does evolution happen?

Well, imagine two tigers racing to catch an antelope. The one that is the better hunter - maybe the one that runs faster - will get to it first and then have some food for its cubs. It is more likely to survive and raise young. At least some of the cubs will be like the parent - they'll be successful hunters. Gradually more and more of the surviving tigers will be faster runners. Over time they may become so different from the original tigers that they no longer breed with them, and so a new species evolves.

Similarly, fish with teeth and jaws evolved from the earliest fish that had neither. Teeth made these later fish more successful at catching their prey.

This has happened for other animals, and plants as well. The ones best equipped to get food or avoid being eaten are the ones best suited to their surroundings, and so they survive and multiply. The English scientist Charles Darwin was the person who worked out how evolution happened. He called it 'natural selection'.

But how would some tigers evolve more powerful legs? How did fish teeth change from being tiny, harmless bumps to the massive fangs of a great white shark?

The tigers did this by growing legs or teeth a little faster or for a little longer, and ended up bigger and more powerful. The fish did it much the same way with their teeth. These changes were then passed on from parents to offspring over many generations.

In the 1930s scientist realised that what we look like and how fast we grow was determined by chemical messengers in our cells, called genes.

So three things make up evolution: natural selection; changes in how fast and for how long we grow; and genes that pass these changes on to the next generation.

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