[Alneyan]

Now that was an old thread (January 2001). As found in the FAQ, Environmental Resistance affects both Reproduction and Happiness: every five points in ER corresponds to one point of Reproduction and Happiness.

ER is pretty much worthless because of that, except to get more points: you can lower Environmental Resistance and increase Reproduction to compensate (and Happiness if you really want, but that characteristic has very few actual effects).