Pandas are notoriously picky eaters: they only eat bamboo. But a recent study has found that pandas are actually poorly adapted for their diet. Pandas apparently evolved from omnivorous bears. Whether as a consequence of a decrease in the availability of prey or an increase in bamboo, however, they shifted to an exclusively vegetarian diet about two million years ago. But they did not evolve the kind of digestive apparatus usually seen in herbivores. They have a carnivore’s digestive system, and they lack the gut flora required for extracting the maximum amount of energy from plant-based sources. Hence, perhaps, the fact that they spend so much of their time eating.Why didn’t pandas evolve a more suitable digestive system? There are at least two possible explanations. One is that evolution can only work with the mutations that happen to occur: it can’t select for genetic changes unless they happen, by chance. The second reason is that evolution will only occur if there are pressures favoring one trait over another. Pandas had few predators and the strategy of eating all day worked well enough for them. There was no selection pressure in favor of greater efficiency.
Why is this interesting? I happen to think it’s intrinsically interesting, but it has some relevance for broader issues too. It is quite common these days to come across claims about the kinds of activities or lifestyle to which human beings are adapted. You come across these claims in the popular media and in academic contexts too.
A prominent example in the popular media concerns the ‘paleo’ diet.
The views, opinions and positions expressed by these authors and blogs are theirs and do not necessarily represent that of the Bioethics Research Library and Kennedy Institute of Ethics or Georgetown University.