REVIEW Virulence evolution and the trade-off hypothesis: history, current state of affairs and the future

How and why parasite virulence (terms in bold font are in the Glossary) evolves are arguably some of the most important questions addressed by evolutionary biologists. The 1990s saw rich and abounding research in this area, mostly based on the ‘trade-off hypothesis ’ (Anderson & May, 1982), which states that virulence is an unavoid-able consequence of parasite transmission (see Box 1). In this review, we first briefly outline the seldom-discussed history of virulence evolution. Then, we expose the current debate in the field, which can be summarized as a challenge to the trade-off hypothesis. Finally, to answer this challenge, we discuss the advances made in the past decade and we argue that, in the light of these advances, we need not abandon the trade-off model. Instead, we argue that these new insights ought to b