By Andrew Hendricks
Are humans and plants related? Your knee-jerk reaction may be “no, obviously not.” Plants and animals, flora and fauna, different things… right? Not so!
Humans and plants almost certainly share a common ancestor that was neither plant nor animal. And decades ago, that would have to be qualified with “We think. Probably. Maybe. Aren’t fungi weird?!” But now, with the sequencing of the human genome and a greater understanding of the place of genetics in evolutionary biology, it’s crystal-clear among most academics that Earth experienced abiogenesis once, not twice.
I’ve been on a bit of an interrogative kick lately. I used to have fun asking my favorite cocktail question to drunk parents: Which child is your favorite? And watching them struggle to answer with such earnestness that is obviously not expected.
My new favorite, though, is asking everyone I know “Are animals and plants related?” It’s not a smug question. I recalled documentaries I’d watched in the 90s about the primordial soup and vaguely remembered fungi and bacteria are “life” but distinct from plants and animals. But this question took me down a Wikipedia hole of remembering things we’ve now known as a species for decades. Yet so few of us care to consider how interesting it is! I mean, that you’re literally related to the tree in your backyard? That’s pretty nifty in my humble opinion.
When asking this question, I’ve found some people stick to their guns. Especially the homeschooled Earth-is-six-thousand-years-old-types. But more often when I’ve asked, I immediately see the gears turning behind the person’s eyes.
The Phylogenetic Tree of Life
“What about sponges” one might ask. Sponges may seem like sea plants, but as we’re reminded by everyone’s favorite anthropomorphized animal of the phylum Porifera that lives in a pineapple under the sea, sponges are the animal most like plants to many people. But they are actually animals.
A more illuminating question in response to this confounding one of plants and animals being related, is “what about mushrooms?”
Fungi and plants may look similar, but they are not closely related. In fact, fungi are more closely related to animals than plants. This makes me much more sympathetic to people who act like prima donnas about mushrooms on their pizza.
How we can share genes with plants?
Image is notable because it shows interconnected gene transfers between branches rather than clearly distinct divergent branches.
You’ve met Lucy, but what about LUCA?
National Geographic puts it best: “A Human and a grain of rice may not, at first glance, look like cousins. ... The genes we share with rice—or rhinos or reef coral—are among the most striking signs of our common heritage. All animals, plants, and fungi share an ancestor that lived about 1.6 billion years ago.”
So while there used to be a non-religious, Darwinian-evolution-accepting argument to be made for two separate instances of abiogenesis more than a billion years ago—I mean, it’s just intuitive that plants and animals are so different—now not only does that strain credulity from a timing and likelihood perspective, it appears downright preposterous from a genetic scientific perspective.
We don’t know specifically what chemical processes began life on Earth. We can’t even be 100% certain that life on Earth began on Earth. But based on the tiny amount of evidence we have on life existing in the universe (our one data point), it would be incredibly amazing if life originated SEPARATELY, TWICE.
But based on fossil evidence and our sequencing of the genomes of so many different organisms, it appears that bacteria, humans, other animals, plants, and fungi all go back to that same primordial soup 1.6 billion years ago, whatever its scientific origin was.