字幕表 動画を再生する 英語字幕をプリント The human brain is one of the most sophisticated organs in the world, a supercomputer made of billions of neurons that processes and controls all of our senses, thoughts, and actions. But there was something Charles Darwin found even more impressive: the brain of an ant, which he called one of the most marvelous atoms of matter in the world. If you find it hard to believe that something so tiny could have a complex brain, you're not alone. In his project to classify and describe all living things, Swedish naturalist Carl Linnaeus assumed insects had no brains at all. He was wrong, but understandably so. Insect brains are not only miniscule, but in many respects, they function differently than our own. One of the most noticeable differences is that an insect that loses its head can still walk, scratch itself, breathe, and even fly. This is because while our nervous system works like a monarchy, with the brain calling the shots, the insect nervous system works more like a decentralized federation. Many insect activities, like walking or breathing, are coordinated by clusters of neurons, also known as ganglia, along their bodies. Together with the brain, these local ganglia form the insect nervous system. While an insect can do a lot with just its local ganglia, the brain is still crucial for its survival. An insect's brain lets it perceive the world through sight and smell. It also chooses suitable mates, remembers locations of food sources and hives, regulates communication, and even coordinates navigation over huge distances. And this vast diversity of behaviors is controlled by an organ the size of the head of a pin, with less than one million neurons, compared to our 86 billion. But even though the insect brain is organized very differently from ours, there are some striking similarities. For example, most insects have smell detectors on their antennae, similar to those found in human noses. And our primary olfactory brain regions look and function rather similarly, with clusters of neurons activated and deactivated in precise timing to code for specific scents. Scientists have been astonished by these similarities because insects and humans are not very closely related. In fact, our last common ancestor was a simple worm-like creature that lived more than 500 million years ago. So how did we end up with such similar brain structures when our evolution took almost entirely different paths? Scientists call this phenomenon convergent evolution. It's the same principle behind birds, bats, and bees separately evolving wings. Similar selective pressures can cause natural selection to favor the same evolutionary strategy in species with vastly different evolutionary pasts. By studying the comparison between insect and human brains, scientists can thus understand which of our brain functions are unique, and which are general solutions to evolutionary problems. But this is not the only reason scientists are fascinated by insect brains. Their small size and simplicity makes it easier to understand exactly how neurons work together in the brain. This is also valuable for engineers, who study the insect brain to help design control systems for everything from self-flying airplanes to tiny search-and-rescue roach bots. So, size and complexity are not always the most impressive things. The next time you try to swat a fly, take a moment to marvel at the efficiency of its tiny nervous system as it outsmarts your fancy brain.