It seems we're always learning something new about slime molds, the bizarre roaming cell-colonies where countless biological principles can be found writ in miniature. Here's a point-by-point breakdown of why the slime mold deserves your respect.
Slime molds fascinate biologists because they're essentially swarms of single-celled creatures that can coalesce to act as one larger organism. Your basic slime mold is a one-celled unit, not very different from an amoeba. However, when activated by a chemical signal, the individual cells can come together to form a supercell—a largish, sometimes meters-long mass that creeps across the ground in search of nutrients. In their multicellular states, slime molds can look like mushrooms, puddles, and any number of other things. When mobile, they've been observed to move at more than a millimeter per second—not bad for a team of cells just looking to satisfy their hunger.
But slime molds aren't just interesting for the "wandering slicks of goop" factor; they have much to teach us, too. In January, we discovered that slime molds are at least as good at urban planning as the civil engineers who designed Tokyo's subways. Here are some more surprising things we've learned from slime molds in recent years.
They reflect systems the world over. Whatever the laws that let masses of slime-mold cells respond as one to changes in their environment, Ted Cox believes they apply to cells in countless other places, including our bodies. "It's a unifying theory of excitable systems," Cox, a biologist at Princeton, told Wired recently. Slime molds linked in a supercell can communicate with each other in the same way that our brain cells collude to release neurotransmitters, in the same way that nutrient levels are regulated in the womb, in the same way that communicable diseases jump from person to person. If we figure out the exact mechanisms by which slime molds talk to each other, it could explain vast amounts about life at the higher levels.
They can control robots. In 2006, a team at the University of Southampton grew a slime mold on top of a circuit in the shape of a six-pointed star. The circuit was then mapped to a small six-legged robot that sat a few feet away. Once that was done, the movements of the slime mold were echoed in the movements of the robot. Slime molds avoid light if they can, so when the slime mold was exposed to light and tried to move away, the robot scrambled around, mimicking the slime mold's attempt to find a comfortable dark space.
They have brains, sort of. In 2008, scientists at Hokkaido University had slime mold cells crawl across a petri dish. For ten minutes at the top of every hour, the scientists generated cold, dry conditions in the lab, causing the slime cells to slow down until the dish had warmed up again. After three hours of this, the researchers stopped changing the lab temperature, but the slime molds continued to slow down on their own, right on schedule, in anticipation of the cold. The scientists then kept conditions stable for a few hours, and the slime molds eventually adjusted, maintaining a steady pace. But when the researchers dropped the temperature again, the slime molds remembered and resumed the ten-minutes-every-hour pattern. The report concluded that the slime molds were demonstrating "a primitive version of brain function"—impressive for organisms without a brain.
They can't be stopped. A 2007 gardening column at the Chicago Tribune notes that "there is no way to prevent slime molds; the spores are all over the place, just waiting for the right conditions to become active." Pattern-learning, robot-controlling mobile slime units that can form at a moment's notice? We don't know about you, but this is the best news we've heard all day.