So why isn't there a decline in appetite as the fat reserves grow? It won't matter while there are no side effects of adding more fat, but there seems to be a widespread belief that fat causes all sorts of health problems. At the least there is decreased mobility (more likely to be eaten by lions), earlier mortality (eg heart attacks) etc.

I wonder if there are any studies correlating obesity levels with reproductive success, and success of the offspring produced. That is what should end up controlling the genes and behaviour behind all this.