Learning is a function that has always been precious to humans. In a way, it allows us to believe the fallacy that we can revolt against our evolved, basal tendencies, and forge our future as a species through intellect, as opposed to natural selection.
We value the capacity to learn in ourselves, but also in other species. It's why we take so much delight in teaching a dog new tricks, and yet feel threatened by the possibility of sentient, non-human beings.
Today, French scientists took a poke at humans' intellectual hegemony by demonstrating, for the first time ever, that a single-celled organism without a brain or nervous system is capable of learning. The study, published in the Proceedings of the Royal Society B, could force us to reconsider the primordial origins of learning that occurred long before the evolution of lifeforms with brains.
A team of biologists from the Centre de Recherches sur la Cognition Animale observed a type of slime mold (Physarum polycephalum) adapting and changing to a series of repetitive challenges—exhibiting a form of learning called "habituation."
Two groups of slime mold were presented with two separate obstacles to cross: a bridge impregnated with quinine or caffeine, and a bridge free of any substance. Once the experimental group realized the bitter quinine and caffeine were harmless, it passed through the substances with the same ease and swiftness as the control group crossed over the non-impregnated bridge. According to the study, this learning process took six days to encode.
"What's interesting about slime molds is they appear to be simple, because there is only one cell, but they are capable of amazing stuff, things that we thought were only possible with nervous systems or brains," lead author Romain Boisseau told the Los Angeles Times. "These guys are very cool."
It took approximately two days for the slime mold to revert to its distrust of the substances after becoming habituated to them. And the test group demonstrated a separate suspicion toward both the quinine and the caffeine, suggesting it was able to identify each substance by its individual properties, and not just its bitter qualities.
Slime molds are protists, which means they're neither plant, nor animal, nor fungi. These primitive eukaryotes first appeared 1.5 billion years ago, and are credited with giving rise to the evolution of multicellular life on Earth.
Scientists became fascinated by slime molds in particular after noticing rudimentary patterns of decision-making in their natural behavior. For example, some of these molds have been known to cooperate with one another, change their appearance based on their surroundings, and even reattach themselves when split in half.
"Slime molds are redefining what you need to have to qualify as intelligent," said biologist Chris Ried.
In the lab, other researchers have demonstrated the existence of primitive intelligence in slime molds. Japanese biophysicists proved the amoeba could memorize things and anticipate events. And scientists in Australia found the mold could navigate mazes using a technique akin to a breadcrumb trail. But none of these past experiments suggested a drive or mechanism for learning.
"That's what is exciting here, because maybe this mechanism appeared really early in the history of life," Boisseau said to the Los Angeles Times. "Probably learning abilities evolved first, before the evolution of neurons and nervous systems."
What the authors of this new study hope to uncover is how, exactly, learning functions managed to predate the evolution of nervous systems in early life—and what this means for modern viruses and bacteria that have shown adaptability, but have not yet exhibited learning capabilities.
One of the most profound faults in human intelligence is our tendency to project our own species as the paragon of evolutionary sophistication. If it doesn't look and behave like us, then it must not be that smart.
But what if intelligent life on Earth—and even other worlds—evolved sideways to everything we currently know about the phylogenetic tree? One day, we might discover something that forces us to completely reevaluate our hierarchy in the universe, and this is a good place to start.