Excerpts from Darwin's 'On the Origin of Species' describing 'natural selection' and 'survival of the fittest' as terms which denote that some animals survive to breed and some don't. Animals with a slight advantage have a better chance of survival. Footage shows a gazelle that is fast and strong enough to evade a cheetah.
Darwin suggested that natural selection is a constant process; a lot of favourable differences add up over time to produce a new species.
Ask students what the differences might have been between a gazelle that was eaten and one that got away. Ask students to determine how this links with evolution and why this process is slow.