字幕表 動画を再生する 英語字幕をプリント When you think of the most dominant creatures on earth - what comes to mind? If considering sheer size, perhaps you immediately thought of the ocean - and the largest animal that's ever lived - the blue whale. Or perhaps thinking of strength and ferocity, you imagined lush forests full of fearsome big cats. Or maybe, quite sensibly, you thought of us - human beings- the most intelligent, and one of the most widespread creatures on the planet. But if you were to walk down the sidewalk, or lean against a tree, the first animal that you would likely encounter is something small - ants. Their total population is around ten thousand trillion, and when combined their total weight would be about the same as the weight of all human beings. in biomass and in impact on ecosystems, these small animals are arguably the most successful creatures to have ever lived. Ants have colonized almost every landmass on earth. Their presence is so significant that they have directed the evolution of countless other plant and animal species. Aggressive, warlike, but also cooperative, altruistic - ants living in colonies exhibit some of the most complex behaviors of all insects. And the colony is the only thing that matters in the lives of ants. Their loyalty to it is absolute. And in their service to it, they exhibit some of the most complex social behavior in the animal kingdom, giving rise to their nearly complete ecological conquest of the earth. How do ant societies work, and what is it about the colony that has made ants so successful? Is it as simple as “strength in numbers?” Or is it something more profound? Even though insects were among the first animals to colonize land, cooperative insect societies are a relatively recent development. The first insects emerged around 400 million years ago - but ants didn't emerge until much later, around 100 million years ago. They lived amongst the dinosaurs, and for a long time did not rule the landscape. This was the era of the giant dragonflies, cockroaches, and termites. It wasn't until 60 million years ago that they became the dominant insects. And since then, they have truly flourished. Today there are around 16,000 different species of ant, and they are found on every continent except Antarctica. The competitive edge that allowed ants to become a world-dominant group is their highly developed colonial existence and specialized social structure. Ant societies are broken up into two castes: a non-reproductive worker caste, and a reproductive royal caste. The queen is the only reproducing female of the entire colony, and the colony exists to serve her, and her alone. The birth of a colony begins with the birth of a queen. The life of a queen begins when its mother queen lays a special kind of egg, different from the millions of regular worker eggs the queen ant will lay in her lifetime. These special eggs are laid when the colony passes a certain size - and when they hatch, they produce ants that are larger than regular workers and have wings. These are the reproductive males and young queens. During what is called a nuptial flight these winged ants take to the air and mate with each other, after which the males die and the females drop to the ground, scrape off their wings and begin to search for a place to dig their nest. Few get far in this journey. Predators snag most of these young queens before they can establish themselves. Only around 1 in 500 new queens has a chance at success. But those that do succeed become the single egg-laying queen of their new colony. Over the course of her life, a queen ant can lay up to 300 million eggs, depending on the species of ant. And the vast majority of these eggs hatch into dedicated worker ants - female ants whose lives are devoted to the queen's welfare and reproductive activity. At any given time, there are millions of worker ants maintaining the colony. There can be many different types, and many different sizes of workers even within a single colony. Some care for larvae, others excavate tunnels, others build amazing structures, while others leave the nest and search for food, or go to war with neighboring colonies. And surprisingly, it is the ant workers themselves who ultimately decide the fate of the young, choosing which worker caste they will develop into. Larvae develop into different types of workers based largely on the nutrition they receive. Those fed more insects than seeds are more likely to become larger individuals. For leaf cutter ants, the polymorphism that exists among the workers is extreme. The largest workers, called soldiers, defend the colony, while the medium sized workers collect leaves, excavate tunnels, or collect garbage, and the smallest workers raise the young and cultivate and farm fungus - the only food source for the whole colony. The workers toil away in a flawless synchrony - in a flow that looks chaotic to our eyes, but is in fact based on a complex system of communication, a chemical and physical language invisible to us, but binds these societies together. For years, scientists knew that ants must have some way to talk to each other in order to organize their intricate societies. But ants have poor vision and hearing, so scientists knew that ant communication must work in a fundamentally different way to ours. It was a mystery for years, but in 1962 leading entomologist EO Wilson began to crack the code of ant communication. He started with the question of how ants tell other members of the colony the location of a new food source. He noticed that ants often tap their abdomen to the ground when travelling, so wondered if they were leaving some sort of chemical trail. He began painstakingly dissecting fire ant abdomens, crushing each of the organs with an applicator stick. He would then spread the ant juice on a piece of paper in front of other fire ants, to see if they would react. As he worked through each of the known organs, the ants showed no interest. But then he stumbled upon an organ that had never been studied before - something called Dufour's gland. When he crushed this gland and spread it across the paper, the ants went wild. They followed the trail immediately and completely. Over time, scientists have discovered over 20 different pheromones that ants use to communicate. And by combining different signals, ants have created a complex pheromonal language. African weaver ants, in particular, have the most sophisticated pheromone communication system ever studied in animals. Some of their thoughts are expressed by spreading pheromones on the ground, like previously mentioned, combined with physical gestures. When a worker wishes to say 'follow me I have found some food' she deposits a trail from the rectal gland, while running from the food back to the nest. When she encounters other workers, she waves her head and touches the other ant with her two antennae. Or when a worker wishes to raise the alarm about an enemy, she lays short looping trails around the intruder with secretions from the sternal gland. Other signals are sent through the air. When an African weaver ant worker encounters an enemy in her own territory, she releases a mixture of four chemicals that not only convey a message but elicit a response from all other workers in her vicinity. The first tells the other ants to 'be alert'. The next one tells them to search for the trouble. The next one tells them to come closer and bite anything in their path, and the final compound tells them to go nuts and attack. Scientists believe that the combination of these signals very closely resembles syntax that we see in human language. A main reason ants are so successful in the world then, is the same reason that humans are. Like us, communication gives ants the amazing capacity to cooperate. Of all ants, weaver ants are among the most impressive. They dominate the forests in Africa and Australia, in large part due to their complex and efficient chemical communication. But perhaps more remarkable than their ability to communicate so effectively, is what they can achieve with it. Weaver ants are a species of ant that do not live in or on the ground, but in the trees. And to keep their huge populations safe there, they construct their own housing. They weave branches and leaves together to create an architectural feat, full of a network of different rooms complete with roofs, walls, and floors. To begin the process, a single ant searches for a nice, bendy looking leaf. It will pull on the edges, testing to see if the leaf will curl. If the ant has some measure of success, other ants will be attracted to the endeavor, and begin pulling the edge as well. As the leaf bends more, more workers arrive. They line up in precise rows, gripping the edge, pulling it towards another leaf. If the gap is too large for a single row of ants to seal, they perform an impressive acrobatic tactic: they chain their bodies together to form a bridge. Workers climb down the bodies of others, until the chain can reach the other leaf edge, up to 10 workers long. Once the leaf edges are within reach, the workers move into position to seal the leaves together. But what looks like glue on the finished structure is something more surprising. Once the bent leaves are ready to be sealed, the workers will collect larvae who are in their final stages of development, and use their threads of silk to bind the leaves together. Holding the larvae in their mandibles, the workers move the larvae back and forth across the leaf edges - using their babies like a hot glue gun. The larvae seem okay with this, as they respond to this motion by exuding thousands of threads of silk. This silk becomes a sheet between the edges, and works as a powerful adhesive. Structures like this speak to ants capacity to organize their labor effectively, millions of individuals combining their abilities into something much greater. It's easy to assume, then, that their effectiveness comes down to a strength in numbers, along with the communication to orchestrate the work. But this can't account for all of their behavior, and all of their success. There is something more unifying in the world of the ants. And the individual ant's cooperation with one another is so profound, that it makes scientists rethink the idea of individuality. The power of a group is evident - with more ants working together, they can find food more quickly, build more impressive structures, and defend against enemies more effectively. And working together is common in nature - birds in flocks, or bison in herds live longer when they live in groups. But in cooperative animal groups like these, individuals still look out for their personal interests. For them it's not just about the group. But this is not the case for ants. Worker ants die young, and usually don't create offspring. Their existence is sacrificial. They have no self interest. Certain ants have been found to suffer a death rate of 6% per hour when outside the nest, due to fighting with neighboring colonies. On average each forager survives for only a week. But during that time, she manages to collect 20 times her own body weight in food for the colony - all to support the group, and ultimately, the queen. This unwavering loyalty to the queen, and the self sacrifice to her cause, becomes more evident when a queen dies. Logic would assume that when the queen dies the workers would raise another queen to replace her. But this is not at all what the workers do. In most cases, the colony fails to produce a royal successor, and it declines until the last worker dies. They simply do nothing until there is no one left. This level of altruism and self sacrifice is so rare in the animal kingdom, that it has made scientists rethink what it means to be an individual. If ant individuals in a colony are not competing against each other, if they are bound tightly by communication and a caste-division of labor, if they cannot survive out of the colony for very long - does the concept of the individual break down? The idea of the superorganism is one that has been debated for decades. With ants, it's the idea that the colony is the organism, where the queen is the reproductive organ, the workers the supporting brain, heart, and gut. The exchange of food among the workers is like the circulation of blood.  The most advanced ant societies, like weaver ants, driver ants, or leafcutter ants, fall into this category, where their workers do not compete amongst themselves at all, and do not reproduce outside of royalty. This capacity of the colony to act like a single superorganism has made scientists reconsider evolutionary theory as a whole. In the 1960s and 70s, the conventional way of thinking about evolution was centered around genes, and genes alone. Largely popularized by Dawkin's book The Selfish gene, it follows that the more two individuals are genetically related, the more sense it makes for them to behave selflessly with each other - that all altruistic group behavior comes down to each individual's competitive desire to improve chances of their kin's survival. But some ant biologists, like EO Wilson, believed that this couldn't be the whole story. Instincts from social species like ants go far beyond the urge to protect their immediate kin. The group must also have a role in evolution, whether or not the group members are related to each other. And this idea gave rise to the theory of multi-level evolution, or group selection, where natural selection acts at the level of the group, instead of at the more conventional level of the individual. The way ant societies function, in their daily lives and within evolution, has entranced us as humans for decades. They have created heated debates among the world's top scientists, and been the focus of every kid's backyard curiosity. Their world operates in ways our brains can barely conceive - with chemical signals painted on the ground, instincts that drive them to fatal endeavors - and yet, their sociality, cooperation, and complexity in many ways mirrors our own. Studying ants will continue to reveal answers about the nature of evolution, and in turn, will reveal answers about our own society, and our own individuality. Studying the animal kingdom gives insight into our world, and brings researchers on all sorts of journeys - both intellectual and physical. Some of the research about ants happens in the field, in the steamy tropics or the frigid parts of northern Finland. And some of it is done in the lab, with complex apparatuses engineered to study ant's chemical trails or their inclination to go to war with each other. Hearing about what it takes to carry out research like this is often just as interesting as the science itself. I love hearing the human stories behind the science - and this is why we decided to start a podcast. Modulus - hosted by me, and Brian from Real Engineering, is a podcast about the people behind the science we explore here on YouTube. We talk to the scientists who are on the cutting edge of research, and the people who are affected by the topics we discuss. The second episode of Modulus is out now. It's an episode where I talk to two pioneers of the ocean: some of the world's first saturation divers. They discuss what it's like to live at the bottom of the ocean, and how it affects both your body and your mind. Their personal accounts of the effects of the immense pressure on their bodies very much makes you realize that the profession of deep sea diving is not for the faint of heart. This episode is available now on Nebula, the streaming platform made by me and several other educational YouTube content creators. It's the place to watch and listen to our videos and podcasts ad free, along with original content that is not available anywhere else like the Real Engineerings' the Logistics of D-day, or Sam from Wendover's new trivia show - which features creators like Brian competing in sometimes silly tasks and trying not to make fools out of themselves. We can take more risks and have more fun on Nebula, where we don't have to worry about the YouTube algorithm. There is so much original content there, with more being added all the time. And to make it even better, Nebula has partnered with CuriosityStream, the streaming platform with thousands of high budget, high quality documentaries. There are loads of the best nature films, like David Attenborough's Ant Mountain - which explores one of the largest animal societies in the world - a supercolony of ants, with more than a billion members, nestled within the Swiss Alps. It dives into a whole new area of ant biology that I never knew, and since it's a David Attenborough film you know it's going to be good. And for a limited time, CuriosityStream is still offering 26% off their annual plans, making a yearly subscription just 14.79. So by signing up at curiositystream.com/realscience, you will get a subscription to CuriostyStream and a subscription to Nebula, for just $14.79 for the entire year. Signing up is also the best way to support this channel, and all of your favorite educational content creators. Thanks for watching, and if you would like to see more from me the links to my instagram, twitter, and patreon are below.