The relationship between domesticated ungulates and humans and between certain ungulates and microorganisms demonstrate a remarkable harmony in the universe. With respect to the microorganisms, most of the even-toed ungulates have developed a mutually beneficial symbiotic relationship with various microorganisms. This has benefits for both parties. The microorganisms digest hard-to-digest cellulose and convert it into a form the plants can use. In some cases, they can also allow the mammals to consume normally poisonous plants, since the microorganisms can break down the plant toxins. On the other hand, the microorganisms receive food and a place to live and reproduce. This reflects the view of Lynn Margulis, who reasoned that life took over the planet more through cooperation than through a Darwinian competition.
With respect to the relationship between humans and ungulates, some species also have a long history together. This is no more evident than in the case of humans and horses, which often have a strong bond of heart. Some species of even-toed ungulates have prospered and filled the earth due to domestication by humans, despite many non-domesticated species passing away into history. However, in many cases, the relationship between humans and domesticated ungulates has also been an ugly history of exploitation and mistreatment by humans, revealing the darker side of the character of some humans.