Hand-feeding squirrels accidentally changed their skulls
Red squirrels fed peanuts showed signs of weaker bite force versus those getting their own nuts

Squirrels love peanuts of course, but peanuts may not love them back. Populations of red squirrels fed a supplemental diet of peanuts developed weaker jaws than those living on a natural, harder nut diet.
Simon Hind/500px/Getty Images Plus