answer:In those cases, the ability to make tools would probably allow us to adapt to many more environments, thereby allowing more children to happen. As far as diseases, a lot of the ones that kill us off now are old-age ones like cancer, which tend not to happen until you’ve had kids anyway. If it doesn’t kill you before you breed, it matters less, evolutionarily speaking. One thing I notice, though, is that the number of children a family has seems to decrease as the education level rises. (I like to think of it as the “too smart to have kids” factor… I am childless, yet some drunk teenager who gets knocked up has won a place in the next generation and I have not.) This would seem to be detrimental.