not all animals walk on four legs, not all animals even have legs. whales have flippers, centipedes have a hundred legs, kangaroos have two legs, cats have four. it varies depending on the creature because we are built to do different things. if a bird didn’t have wings it couldn’t fly, if a shark didn’t have its fins it wouldn’t be able to swim. just because humans are technically an animal does not mean we are exactly like other animals.