The basics of evolution are so simple that they can be conveyed in five minutes, and with only common knowledge.
We all know that frogs lay their eggs in ponds, where the eggs hatch into tadpoles, and the tadpoles then develop into frogs. The eggs of some frogs hatch and develop a bit quicker than average, and some a bit slower than average. In both cases, the offspring tend to be like their parents: faster-hatching eggs generally develop into frogs that lay faster-hatching eggs, and so on.
Assume that there is a pond in a place where the weather gets a bit warmer every year, so that the pond dries up a little earlier each year. Eggs that take too long to hatch and develop will not produce frogs, while the quicker ones will. That is called “natural selection”. The quicker ones fit the environment better.
If this occurs year after year, even if the yearly changes are small, the average development time of the frogs will become shorter. That is, most frogs will be developing faster, since the ones that were too slow will not have survived.
When the average character of a population changes, that is evolution. In this example, a slower-developing population of frogs evolves into a faster-developing population.
To summarize what is needed for evolution to occur:
- inheritance – offspring are generally like their parents
- variation – offspring are not exactly like their parents
- natural selection – an environment that favors particular variations
Of course there are many other details, but those are the basics.