Similar organisms have differences that help them adapt to their environments.
Many organisms have similar body plans.
Horses', donkeys', and zebras' bodies are set up in pretty much the same way, because they are descended from a common ancestor. As organisms adapt and evolve, not everything about them changes. The differences, such as the zebra's stripes, show that each species adapted to its own environment after branching off from the common ancestor. The bodies of deer, moose, zebras, and horses are very similar, and these animals are very closely related. One major difference is that deer and moose have antlers and zebras and horses don't.