This was initially surprising. But it is obvious that the temperature of the balls matter. This is why we put it outside the body, have a special device (the b

This was initially surprising. But it is obvious that the temperature of the balls matter. This is why we put it outside the body, have a special device (the ball sack) to keep it at the right temperature, and then load the whole structure with sufficient pain signals that the man will be very protective of it. Given that the temperature matters that much, it isn't surprising that making it too warm anyways is likely to create infertility.