One of the things that scientist Charles Darwin noticed was how living things are usually similar but not identical. That is each living thing varies from every other one. You can see that in the picture above as well as in the video below.

The importance of this is that it shows how living things can all change - known as evolve - as a natural part of life. Because all things are different, some will change one way, others will change another. So, for example, some will change to resist a kind of illness, others won't. Over time the ones that have evolved to resist an illness might live longer.

Another example is that some living things might change to stand up to frost better than others. You can think of a great number of other examples, I am sure.

We can also select those variations that we think are useful. For example, we breed dogs to be calm and gentle by selecting those which are calmer in the first place. That is why domestic dogs are very different from wild dogs. We select the best seed from a field and grow that next year to get a better yield, and so on.

As you can see, natural variation is the foundation of living.