You might wonder at this point why evolution hasn’t selected for these incredibly buff creatures. Shouldn't they have (literally) crushed the competition and made more babies, thus skewing mammalian populations toward general swoleness? The reason these mutations remain uncommon is that more muscle isn’t always a good thing. Bully whippets, for instance, aren’t very good runners compared to closely-related dogs, because they’re essentially overburdened with muscle. Cattle fare a bit better, since they mostly just need to stand around and eat, but farmers aren’t rushing to breed them that way—they require an expensive high-protein diet and they’re unusually lean, meaning they can’t achieve a rich (and delicious) marbling of fat in their muscles. The massive size of their calves also makes giving birth dangerous, so c-sections are often required.