In this deck, we'll explore one of the most important ideas in all of biology: evolution by natural selection. We'll start by looking at why individuals within a species are different from one another, a concept called variation. Then, we'll break down Charles Darwin's famous theory, step-by-step, to understand how species change and adapt over time.

Look around at any group of people, or even a group of dogs or cats. You'll notice they aren't all identical. There are differences in height, hair colour, eye colour, and so on. In biology, these differences between individuals within a species are called variation. Variation is crucial because it provides the raw material for evolution to act upon.

So, where does this variation come from? There are two main causes. The first is genetic variation, which is caused by the different genes and alleles an individual inherits from its parents. Things like your natural eye colour or your blood group are determined by your genes. The second cause is environmental variation, which is caused by the conditions in which an organism has developed. For example, a scar from an accident or the accent you speak with are due to your environment.