Tonyblack said:
People have problems with wisdom teeth because their dental care is too good. In past times enough teeth would have fallen out so that when the wisdom teeth arrived there would be no problem with them erupting.
I should think that the case here is the same as for cancer - it has no effect on reproduction, so there's no evolutionary pressure. Probably the jaw shortened as the diet changed, which also meant that there was no need to replace teeth, but they just never went away. If you go back to before we discovered sugar, teeth were a lot better anyway. Also, a lot of people would have died before their wisdom teeth grew (and not everyone gets them).
From an evolutionary point of view, once you've made babies your work here is done.