Not yet mentioned: Collectively, the human gut evolves. Over quite a short timespan! Climate is basically rock solid by comparison. For example, a new type of

Not yet mentioned: Collectively, the human gut evolves. Over quite a short timespan! Climate is basically rock solid by comparison. For example, a new type of food may become quite popular over the course of like five to ten years. In that time millions upon millions of people will undergo a change in their gut flora from eating that food--even if only on occasion! Who TF knows what the long term impact of such an evolutionary change could be? 90% of the time it's probably nothing but 10% of the people might develop IBS later in life because their gut bacteria suddenly evolved in such a way as to throw off the "balance of power" (as it were... The many zillions of gut bacteria are constantly at war with each other to process food faster and more efficiently).