Bigger than Manhattan, Earth’s largest living organism sways in the surf south of Australia: Posidonia australis — a species of seagrass that, unable to flower, clones itself. Older than mathematics and the written word, it has been cloning itself since before the pyramids were built — a kind of immortality. And while I kiss my lover on the fresh-cut grass under the Manhattan Bridge, it goes on cloning itself as we go on dying and passing between our lips the heat of our mortality.An organism is a mortal unit of matter distinct from other organisms by its genome — the possibilities encoded in its particular genetic makeup — and its phenotype — the set of traits expressed, the actualities summoned by adaptation and chance from its possibilities. Human beings are organisms encased in the hardest yet most vulnerable exoskeleton in nature: a self. A self includes but surpasses the organism to encompass its environment and its social context, the psychological terrain of memory and desire, the fingerprints left on it by the touch of other selves. An organism ends at the physical boundary of its body, but a self does not — we spend our lives negotiating where we end and the world begins. Card from An Almanac of Birds: 100 Divinations for Uncertain Days.Humans are the only animals, save perhaps the bowerbird, who can alter their phenotype by means of their own making — grow, cut, and dye their hair, tattoo and tan their skin, increase and decrease the size of various body parts with scalpel and silicone. We are also the only animal who can radically alter both its environment and its social context, building elaborate homes on faraway landmasses, reconstituting our families and friend groups, changing the labors by which we put food on our table. Our selves are not like our cells, replacing themselves with clones in the course of living, but like Russian nesting dolls, each prior self outgrown but contained by the next. (“We are well advised to keep on nodding terms with the people we used to be, whether we find them attractive company or not,” Joan Didion wrote.) Our lives a relay race, running from the selves we have outgrown or wish to outgrow towards the selves we try to become to or are unconsciously becoming, the baton of personhood passed from one to the next along the arrow of time, the track of our mortality. This puts us in a peculiar predicament: Each human lifetime is lived by a single organism that contains a multitude of selves, genetically continuous and psychologically discontinuous, making it impossible to define where and what the person is. What, then, makes you yourself across all those replaced cells and reconfigured selves? Organisms like Posidonia australis, which both conceal and reveal the nature of the self, may give us the best hint at an answer — one which evolutionary biologist Rowan Hooper articulates beautifully in his book Togetherness: Symbiosis and the Hidden Story of Life’s Greatest Collaborations (public library). Considering Earth’s largest living tree, he writes:The Pando aspen grove in Utah comprises 47,000 trees, all genetically identical, connected by a vast root system. Language immediately becomes limiting when trying to describe Pando. Do we call the forest an organism? An entity? It has been estimated to weigh nearly 6 million kilograms, or 6,000 tonnes. If it helps, that’s about thirty-five blue whales or 1,000 elephants. It is one of the oldest organisms on Earth. Its cells are living and dying over time, but the DNA remains pretty much unchanged. That is, the entity lives on, even as its parts die.Art by Meredith NemirovWith an eye to the Ship of Theseus — Plutarch’s timeless thought experiment about the nature of the self — he reflects:Pando is biology’s Ship of Theseus — is it the same tree as when it first sprouted? I think not. It’s more like a continuation of the idea of Pando… The 47,000 stems of Pando start off genetically the same, but grow phenotypically different; a forest, but also a mass of individuals.“The word for world is forest,” Ursula K. Le Guin wrote in her subtle insistence that symbiosis — the ultimate unselfing of the organism — is what made this rocky planet a living world. Rustling through the canopy of the Pando is the whisper of an answer to the unnerving question of what makes a body a person: You are not your roots, not the stem of your circumstance, not your branching choices. You are the idea of you, the forest of your selves in constant conviviality with other selves, called again and again to unself into who you really are.donating = lovingFor seventeen years, I have been spending hundreds of hours and thousands of dollars each month composing The Marginalian (which bore the outgrown name Brain Pickings for its first fifteen years). It has remained free and ad-free and alive thanks to patronage from readers. I have no staff, no interns, no assistant — a thoroughly one-woman labor of love that is also my life and my livelihood. If this labor makes your own life more livable in any way, please consider lending a helping hand with a donation. Your support makes all the difference.newsletterThe Marginalian has a free weekly newsletter. It comes out on Sundays and offers the week’s most inspiring reading. Here’s what to expect. Like? Sign up.