Sexually selected signals are not similar to sports handicaps.

The handicap principle is a simple but powerful metaphor that has had a major impact on how biologists study and understand sexual selection. Here, I show that its application to signalling in sexual selection is not a valid generalization from its roots in economics. Although some signalling systems, with additive costs and benefits, have solutions that resemble sports handicaps, the signalling in sexual selection has multiplicative costs and benefits, and solutions that do not resemble sports handicaps. The sports analogy is technically incorrect, metaphorically misleading and a poor guide for empirical research on the signalling in sexual selection. The evolution of sexually selected signals is not a missing piece of Darwin's puzzle; it is an integral piece of the process of evolution by natural selection, and it should be approached with the same tools that we bring to bear on the evolution of other correlated traits involved in social interactions.