Given that the genetic underpinnings of most traits are still not known (Ellegren and Sheldon 2008 ; Mackay et al. 2009 ; Anderson et al. 2013 ) and that the accurate measurement of natural selection is difficult (Kingsolver et al. 2001 , 2012 ; Kruuk et al. 2003 ; Hersch and Phillips 2004 ; Morrissey and Hadfield 2012 ), obtaining hard evidence to conclusively demonstrate adaptive evolution in the wild represents a major and ongoing challenge.