1) Suppose that the microbial community living inside us have a sufficiently long relationship with our own cells such that the microbes have an important role in a large majority of physiological functions, not just digestion.
2) As human societies have evolved, the variety of microbes that live in our environment have undoubtedly changed. Once humans wandered grasslands on bare-foot and ate raw food without even washing them. Now we buy processed food from supermarkets and even walk inside our houses with socks. The result is that the community of microbes that interact with and enter/exit our bodies has changed.
Combining (1) and (2) above leads to the possibility that the human physiology has indeed changed of the past several centuries, even though the change the human phenotype "appears" unchanged. The extent of evolution depends on the extent to which the microbial communities influence human physiology. If there are long-distance signaling molecules that are released by microbes which enter the blood and if the microbes are capable of receiving our signals, then...
2) As human societies have evolved, the variety of microbes that live in our environment have undoubtedly changed. Once humans wandered grasslands on bare-foot and ate raw food without even washing them. Now we buy processed food from supermarkets and even walk inside our houses with socks. The result is that the community of microbes that interact with and enter/exit our bodies has changed.
Combining (1) and (2) above leads to the possibility that the human physiology has indeed changed of the past several centuries, even though the change the human phenotype "appears" unchanged. The extent of evolution depends on the extent to which the microbial communities influence human physiology. If there are long-distance signaling molecules that are released by microbes which enter the blood and if the microbes are capable of receiving our signals, then...
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