According to a theory proposed by Amotz Zahavi (formulator of the so called Handicap Principle), and others, sexual selection can be seen as a subtype of signal selection, which in it's turn is a subtype of natural selection.
The well known example of a signal that is selected for is the tail of the peacock, which signals the high quality of it's owner. The interesting thing is that to maximise fitness it would be better for the peacock to have a smaller and less colorfull tail. Signal selection and efficiency selection (for want of a better word) hence often work in opposite directions!
Some quotes from the abstract of the article "The Logic of Analog Signaling and the Theory of Signal Selection" by Amotz Zahavi & Avishag Zahavi:
... evolution by natural selection is a consequence of two selection mechanisms: the selection for efficiency on the one hand, and signal selection that reduces efficiency in order to provide reliability on the other hand.
The fundamental difference between signal selection and efficiency selection is that
when the investment required for signalling is reduced to the extent that everyone can signal alike, the trait loses its value as a signal. This loss of value is unique to biological analog signals
For example, lace used to be a signal of wealth, but it's effect as a signal diminished once lace machines took over manual production.
The exciting thing about this approach is that it could explain the evolution of features that would be hard to explain by efficiency selection only:
We further suggest that the interaction between the selection of signals and the selection of other traits enabled the evolution of new traits that require the accumulation of many mutations that reduce efficiency before they can start contributing to new efficient adaptations e.g. antlers and feathers.