Estimates are that only ten percent of living cells in a human body are human. 90 percent of the living cells in a human body are described as non-human microbes, many of which can live nowhere but inside a human body. These microbes often help us, complementing our nutritional intake and warding off pathogenic intruders.
What makes these microbes nonhuman, if they make up most of our bodies and are involved in our physiological functioning? Our mitochondria have separate DNA lineages from what’s in our cell nucleus, but we still refer to the mitochondria as human. Why don’t we do the same with the other microbes in our bodies? Because they’re not lodged in cells?
Is there a reason not to think of human beings as communities of organisms with multiple genetic lineages?