Stomachs and Evolution

The closest relatives of humans are the chimpanzees and bonobos. Bonobos are almost identical to chimps yet have a very different social structure, temperament and diet. It almost looks like humans are a mix of chimp and bonobo with added intelligence thrown in. Chimps eat mostly fruit augmented with protein and fat from insects and any smaller animals they can lay their hands on. Bonobos eat a lot of vegetable matter much like gorillas do. This is because they live south of the Niger River where there are no gorillas. Not having to compete with gorillas has resulted in them developing quite differently to chimpanzees. A diet consisting mostly of vegetables with fruit has resulted in a society where the leaders are females and empathy and sexual orgies abound – one female bonobo was observed copulating fifty times in one day. Ok, I’m digressing now.

The digestive systems of primates vary quite markedly. Chimps, bonobos and gorillas have large colons whereas humans have smaller colons but more volume, proportionally, in the small intestine. The overall gut volume in humans, on average, is proportionally smaller than the other high primates. This implies that humans have adapted to eating higher caloric and easier digested foods. The digestive tracts of the other primates are adapted to eating more vegetable matter that requires a higher degree of processing. Humans have adapted to eating high quality food that is mostly absorbed by the small intestine. In the pre-agricultural era this food would have been meat and starchy roots augmented with nuts and fruits. Selective pressures resulted in an animal that had a smaller gut volume relative to body size. A smaller gut is probably advantageous when running down prey. Predators tend to have smaller abdomens than herbivores.

Today we have greatly increased the ‘quality’ of food. Fruits and vegetables bear little resemblance to their ancestral originals. Fruits and vegetables are packed with sugars that we also extract and refine to produce super foods. Unfortunately we still have a cave-man type of mindset that eats when food is available – especially high carbohydrate food that doesn’t elicit a full response when enough has been consumed. The reason for this is unclear however such foods are so unnatural that we probably haven’t had enough time to adapt to nourishing ourselves with them. The future may well see a human with very small intestinal volume that matches the quality of food taken. We are already starting to do this now with surgical intervention. Stomach reduction surgery is now a very common method of controlling obesity.

Perhaps we will need to consider reducing the gut volumes of new born humans in order to prepare them for an environment where food is available in lethal quantities. If we don’t evolutionary forces will do it for us anyway. Already the epidemic of diabetes and other diet related diseases are working on adapting the human body to the new diet regime by killing off and reducing the fertility of individuals who cannot control their eating impulses. Diabetes and obesity is inflicting individuals at ever younger ages these days and looks set to continue. The survivors will be those most able to optimally process the high caloric foods that abound today.