The koala is perhaps the cutest of all marsupials, but it appears to have received the short end of the evolutionary stick. The koala lives mainly in the eucalyptus tree and almost exclusively eats the eucalyptus leaf. The eucalyptus leaf, on the other hand, has made it clear that it doesn't want to be eaten by anyone. Aside from having very little nutritional value, it is poisonous, and very hard to chew and digest. To deal with this, the koala has evolved a very long hindgut, which ferments the leaves, sometimes for over 100 hours. A remarkable and complex adaptation that the koala could have avoided by eating pretty much any other ♥♥♥♥♥♥♥ thing. Baby koalas don't have the fully developed piping to do this hindgut fermentation, so instead, they eat their mother's faecal pap. Faecal pap is a predigested greenish goo, like you know how a cow regurgitates cud? Well it's like that, except out of your arse. And you feed it to your child. The diets of most herbivore marsupials pose another challenge. The course grasses and leaves wear down their teeth. Each has evolved a unique strategy to deal with this. The kangaroo has 4 sets of molars which move forward as the front pairs wear down. Wombats have rootless teeth that never stop growing. The koala's unique strategy is to have neither of these, so when its teeth wear down it just starves to death. Not only that, but the koala has the smallest brain to body mass ratio of all the mammals, and it has a smooth brain, which means that it hasn't evolved the thinky-thinky parts. For example, if you pick eucalyptus leaves, which it eats, off the branches and put them on a plate, the koala doesn't know what to do with them. Not a genius animal. However, this lack of brain gives the koala a discreet evolutionary advantage, in that it does not give a ♥♥♥♥.