The ancient concept is that we humans are human because we are composed of human cells.
The emerging modern concept is radically different, even something not yet in the textbooks.
That new, emerging, modern concept resembles nothing your mother and father told you about yourself when they taught you to say "foot", "arm", "leg", "head", "eyes", or "me".
Before we tie these new concepts about what it means to be human together, later in this post, let's get a feel for the magnitude of the issue we are dealing with:
... the fields of medical and environmental microbiology have begun to merge. The resulting hybrid discipline embraces the complexity of a larger system; it’s integrative rather than reductive, and it supports the gathering view that our bodies, and the bodies of other animals, are ecosystems, and that health and disease may depend on complex changes in the ecology of host and microbes ...
(The Body Politic, Seed Magazine, emphasis added). A singularity is at the core of the way we see ourselves, not a community, but that concept is now outdated:
“We’ve all been trained to think of ourselves as human,” he says. Bacteria have been considered only as the source of infections, or as something benign living in the body. But now, he says, it appears that “we are so interconnected with our microbes that anything studied before could have a microbial component that we hadn’t thought about.” It will take a major cultural shift, says Karasov, for nonmicrobiologists who study the human body to begin to take microorganisms seriously as a part of the system.
(ibid, emphasis added). This is a challenge to some of our western notions, so it will need to be handled gingerly, so as not to confuse some of us:
Equally challenging, though in a different respect, will be changing long-held ideas about ourselves as independent individuals. How do we make sense of this suddenly crowded self? David Relman suggests that how well you come to terms with symbiosis “depends on how comfortable you are with not being alone.” A body that is a habitat and a continuously evolving system is not something most of us consider; the sense of a singular, continuous self is a prerequisite for sanity, at least in Western psychology.
(ibid, emphasis added). A new sense or definition of sanity comes with this new foundation, this new psychology of self as a community, a concept of self as an ecosystem within the Earth's global ecosystem, which in turn is part of a larger cosmic community which we call the universe.
The modern concept will also have an impact on our vision of government.
Some nations have already made inroads into that vision via advanced legislation, based upon modern environmental understanding.
International gatherings fostered by The United Nations, and other organizations, work to coordinate environmental protection, recognizing the reality that ecocide is not a sane way for mature, properly functioning nations to behave.