Evolution of microbial digestion in mammals

Abstract

Microbial digestion surely arose long before mammals evolved, but very little is known about it in other vertebrates. There is, however, an extensive literature on invertebrates12,13; many arthropods, in particular, harbour micro-organisms in their gut that make essential contributions to vitamin supplies, nitrogen metabolism and cellulose digestion. This association seems likely to have arisen more than 300 million years ago13, but its relevance to microbial digestion in vertebrates is uncertain, since the two lines probably diverged at least 200 million years earlier. This account is limited to a discussion of mammals and their gut microbes.