Costly signals:

Zahavi & Zahavi:

>We believe that natural selection encompasses two different, and often opposing, processes. One kind of selection favors straightforward efficiency, and it works in all areas except signaling. This selection makes features - other than signals - more effective and less costly; we suggest calling it "utilitarian selection." The other kind of selection, by which signals evolve, results in costly features and traits that look like "waste." It is precisely this costliness, the signaler's investment in the signals, that makes signals reliable.<