from Entangled Life: How Fungi Make Our Worlds,
Change Our Minds, And Shape Our Futures
The biological identity of most organisms can’t be pried apart from the life
of their microbial symbiotes. The word 'ecology’ has its roots in the Greek word oikos, meaning 'house’,'household’, or 'dwelling place’. Our bodies, like those of all other organisms, are dwelling places.
Life is nested biomes all the way down.
We can’t be defined on anatomical grounds because our bodies are shared with microbes,
and consist of more microbial cells than our own - cows can’t eat grass,
for example, but their microbial populations can, and cows’ bodies have evolved
to house the microbes that sustain them.
Neither can we be defined developmentally, as the organism that proceeds from the fertilization
of an animal egg, because we depend, like all mammals, on our symbiotic partners
to direct parts of our development programs.
Nor is it possible to define us genetically, as bodies made up of cells that share an identical genome
—many symbiotic microbial partners are inherited from our mothers alongside our own DNA,
and at points in our evolution art history, microbial associates have permanently
insinuated themselves into the cells of their hosts: our mitochondria have their own genome,
as do plants’ chloroplasts, and at least 8 per cent of the human genome originated in viruses
(we can even swap cells with other humans when we grow into 'chimeras’,
formed when mothers and fetuses exchange cells or genetic material in utero).
Nor can our immune systems be taken as a measure of individuality,
although our immune cells are often thought of as answering this question for us
by distinguishing self from 'non-self’.
Immune systems are as concerned with managing our relationships with our resident microbes
as fighting off external attackers, and appear to have evolved to enable colonization
by microbes rather than prevent it.
Amanita muscaria photo by Tim Colman
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