Today, more than half of the human population lives in hive-like warrens called cities. Does this mean we are on the tipping point of becoming colony animals the way bees and ants did? It's not entirely impossible. We talked to scientists to find out whether urban humans are evolving into superorganisms.
Illustration of hive world Titanicus via EA
What Is an Individual?
Before we consider whether humans could form hive minds or colony societies, we first need a working definition of what it means to be an individual. But the whole idea of an "individual organism" is a lot messier than it seems. Washington University biologist Joan Strassmann, who has published papers on this topic with colleague David Queller, pointed out that it's incredibly hard to define an individual life form.
What, for example, makes a tree an individual? "Say it's an oak from an acorn — that's one organism," Strassmann said. "But if it's an aspen, the tree may not be separate. All the aspens in a grove may well be the same clone all coming up from the same root system with connections. Or those connections may be severed." She's referring to the way aspens grow from the same root system, the way many plants and slime molds do. Is your aspen an individual who shares a root system with its neighbors, or are all the trees who share the root system part of one "individual"? And this is just the beginning of the kinds of complexity you run into when trying to define life forms.
Plus, every person whom we think of as an individual actually evolved from simpler organisms that work cooperatively. Your body is a society of cells that function together to make you walk, clean your blood, and digest your food. And even the cells in your body are actually a collection of organelles, or tiny organs, like the energy-producing mitochondria. Scientists believe mitochondria were once single-celled creatures absorbed by larger cells that eventually became the familiar animal cells we know today, with their nuclei, organelles, and cytoplasm all wrapped up in a nice fatty membrane.
Strassmann and Queller use the term "evolution" to describe the process of becoming an individual organism. They emphasize that even our individuality is the result of a "social process" where many organisms that were previously individuals came together to make our multicellular sense of self. In a sense, we are already hives. Our bodies are comprised of millions of cells and microbes that work together selflessly, living and dying for the colony.
The Daughters Who Don't Leave Their Mothers
The origin of colony organisms, then, lurks in our own bodies. What led those first single-celled individuals to join up and become multicellular?
University of Minnesota biologists Mike Travisano and Will Ratcliff have been doing experiments that hint at the answer. They managed to turn single-celled yeast into multicellular organisms in just a few months, by breeding the yeast for what they call clumpers. First they put ordinary, single-celled yeast in a liquid medium where the cells that clumped together fell to the bottom more quickly. Then they bred these clumpers exclusively, and found that after 60 days — roughly 400 generations of yeast — they had simple multi-cellular organisms.
"Clustering is the first step," Ratcliff said. But what makes a single celled creature suddenly become a cluster? It's all about children who refuse to leave the nest. Yeast reproduce by "budding," forming a new daughter cell attached to the mother cell wall. "Normally when the daughter is mature it makes an enzyme that releases it," Ratcliff explained. "It looks like what happens is that daughter cell release is inhibited. The mothers remain attached to their daughter cells. That has the effect of making each cluster genetically identical." Multicellular organisms are, generally, packed with genetically identical cells — that's the case in your body, where every cell contains exactly the same DNA.
What Ratcliff and Travisano discovered was that eventually these clusters started behaving like individual organisms, with some cells committing suicide in a process called apoptosis. This seemingly grisly process is actually how multicellular organisms typically maintain their integrity. Older cells who aren't functioning optimally kill themselves off while younger ones continue to divide. Once a cell is willing to accept the death sentence from another in its cluster, you could argue that it is placing the survival of the organism over its own. Now, you have a colony organism that behaves like an individual.
Ratcliff and Travisano called their multicellular yeast individuals "snowflakes" due to their shapes (see image, with dead cells in red). When these snowflakes got big enough, one would break off from another. Eventually, the researchers found, these yeast were evolving as snowflakes rather than as single-celled organisms.
Through single-celled cooperation, new individual organisms had begun to form. Ratcliff and Travisano are continuing their experiments, trying to figure out whether the yeast snowflakes show other signs of organismality beyond apoptosis. They're trying to create multicellular green algae too.
Welcome to the Hive Mind
Now for the real question: What would inspire a group of multicellular organisms like ants or humans to form a superorganism? In their book The Superorganism, biologists Bert Hölldobler and E.O. Wilson argue that it's a complex process involving genetic evolution and environmental pressures. Generally a group of insects like bees will move from behaving as individuals to forming colonies when they are storing food (like honey or pollen) that comes from multiple sources. At that point, a colony has a better chance of surviving than an individual.
But the big transition moment from individual to colony — like the yeast snowflake moment — comes when two bees engage in a division of labor. Hölldobler believes the first division of labor is probably when one insect becomes a reproducer and the other takes care of her babies instead of reproducing herself. She sacrifices her ability to reproduce for the greater good of the burgeoning colony.