In this talk I will provide an overview of the work I did for my PhD, which focused on the evolutionary genetics of clutch size and laying date in the great tit (Parus major), a small hole-nesting passerine. I will provide a brief introduction into some quantitative genetic concepts, and will outline how the recent application of statistical methods originally developed by animal breeders to data from natural populations has opened up a range of exciting new possibilities. I will illustrate these using long-term data from a number of Dutch great tit populations that have been monitored already for several decades. This will provide new insights into the role of selection and gene flow in shaping population structure, and into the capacity of natural populations to respond to selection.