Sir,
Drs. Smith and Mogie (BioEssays 22.3) criticise Robin Holliday for ``Taking an inductionist stance'', and later in their letter consider an argument in favour of induction in order to dismiss it. But surely it is a bit odd to dismiss induction. Without it we would be groping in total darkness, not only in science but in every aspect of our everyday lives. All knowledge of the world depends on it. There is indeed a place for deductive logic, but it only discovers what was implicit in our previous conclusions, which could only have been based on empirical observation and induction.
We never needed Popper to tell us that it is possible to make mistakes. The use of his refutations is in demolishing claims to have discovered Laws of universal application. But whatever may be the case in Physics, there are no such Laws in biology. We have only a lot of useful generalisations, some attracting a great deal of confidence but none guaranteed to rule everywhere without exception. We are certainly not going to throw away a generalisation of broad validity because we have found an organism that operates a somewhat different system. So I agree with Holliday that Popper is no great help.