Well, they do have trouble both with fertility and simply having sex as it's pretty hard for two hamplanets to get tab A into slot B.    Then you also see them not really taking care of their kids.  Every time I see a kid running around near a road or other place that is not good for a kid to be running around, the parent is a ham.  Most often clutching a beetus drink of some sort.    It is also very much like an STD.  You pretty rarely see a couple where one is fat and the other not turn into two normals.  Much, much more often the normal one turns into a ham.