Martin Evans, University of Edinburgh
The Fisher equation describes the spread of a population and exhibits travelling wave solutions. A selection mechanism for the speed of these waves has been established some time ago. I shall review this selection mechanism which has appeared in many physical contexts. I shall then go on to consider two coupled Fisher equations representing two populations e.g. sub-populations of bacteria which are susceptible or resistant to antibiotic. We show that a subtle coupling between two population waves gives rise to a novel velocity selection mechanism.