I think you have to be careful because there are two things that need to be separated:<p>1) the human digestive tract is adaptable -- this measures the amount of adaptation the individual is capable of.<p>2) evolutionary pressure selects individuals who are highly adapted to their environment (I.e. The others simply die off!) -- this measures the adaptations of a population towards diet.<p>Ex: Swedish ability to digest lactose in adults. Asian insulin response to high carb&#x2F;rice diets.<p>It seems that if we really want to crack this nut, we should be looking at DNA data as well. I.e. This population gets this response with this diet, while that population has a completely different response.<p>And yes, unfortunately adding DNA populations makes all of this research even more complex than it already was.