Jane Galt asks
I'm not sure whether [the idea that second wives are less intellegent than first wives] is true on average, or whether it's just folk wisdom that appeals to our envious streak (sure, she may be younger and prettier, but boy is she stupid!) Nor can I imagine there's much data on it, but maybe I'm wrong. What do y'all think?
I don't know of much data but my hunch is that they are on average less intellegent. Whether people admit it or not estimates of you are your future spouses combined income feature prominetly in the marriage decision.
When marrying for the first time men are generally less wealthy. Having a wife who has earning capacity can be important simply for making the household finances add up. The second time around the man is better situated and likely doesn't put as much of a premium on spousal income.
Since intellegence is major factor in earnings as well as attractiveness its double counted when choosing a first wife. When a wealthier man chooses a second wife the earnings criteria is diminished and so intellegence counts only as far as it contributes to attractiveness.
For men who really find intellegent women attractive the difference between the first and second wife will be small. However, for men who don't care as much about attractiveness per se the difference will be large. The large differnce for the second category of men should tend to drive the average down.