How well certain trait tokens work varies among individuals of a species. At some point we clearly consider a trait to be working so poorly that it is pathological. But what determines where the line between the healthy and the pathological is to be drawn? In this seminar I will provide an account of this. I will also show that the suggested account proves better than Christopher Boorse’s biostatistical theory with regard to the problem of goal conflict, the problem of trait levels, and the problems of healthy populations, common diseases, and normal aging.