What makes a good theory?

1. What makes a good theory? In defence of evolution

2. It’s only a theory A common criticism of evolution is that it’s just a theory What merit is there to this argument?

3. There is nothing ‘just’ about theories • All of science is ‘just theories’….yes all of it!! • Other theories include: gravity, the existence of atoms, and the idea that babies grow from eggs fertilised by sperm • Task: • Write three other things you have come across in science that are just theories

4. What makes a good theory? • Explanatory power – can it explain observed reality • Consistency – does it fit with other things we hold to be true (be careful here) • Falsifiability – can it in principle be shown to be wrong? • Predictive power – can it make testable predictions? • Simplicity – often simpler theories are correct? • Occam’s Razor – of two competing explanations for an event, the one which makes fewer and simpler assumptions is likely to be true • Comprehensiveness – it explains a wide range of phenomena without special exceptions

5. What makes a good theory Explanatory power Consistency Falsifiability Predictive power Simplicity Comprehensiveness • Task: • Produce a table to make a side-by-side comparison of evolution with a competing theory for the existence of complex life (us included) • Which do you think is the better scientific theory?

6. Summary Evolution is a theory but there is no ‘only’ about it! As a theory, evolution survives all the tests of what makes a good theory There are other theories but they can not be called science as they do not fit with observed reality