Symbiosis, or How We All Get Along

Hermit crab and anemone, protection in exchange for food (
Hermit crab and anemone, protection in exchange for food (

Competition has long been regarded as the main dynamic in the way that humans and other living things interact with one another. It was a familiar concept early on for those living in the capitalist economies of Europe and America. When Darwin published On the Origin of Species in 1859, he put the stamp of science on a belief that people harbored, then and since, in their daily struggles.

Cooperation, by comparison, has barely acquired a foothold with the public as a fundamental feature of organic life. Our countless daily cooperations among family and colleagues, along with the huge synchronization of goods and services that is modern society, appear to most people as unremarkable. In the late 1800s, Social Darwinists promoted Darwin’s work as a justification for intensifying capitalist exploitation, but early research on mutual biological interactions was viewed as subversively Marxist and was ignored. Today, competition—political, economic, athletic, social—makes headlines, while successful collaborations make the human interest pages.

Mutualistic symbiosis, the term that biologists use for cooperation, refers to close interactions between organisms that benefit both parties. It is what we sometimes call a “win-win.” (Competition is a “win-lose.”) In their many forms, close, mutually beneficial interactions are pervasive throughout the living world and are as crucial to its continuity as competition. Here is a scan of such relationships, ranging from human cooperation, through mutual assistance between members of different species, down to the integration of one organism into another.


  1. We humans are thoroughly wired to connect with other people whenever we think we can do so safely. And when we’re not actually engaged with others, we’re almost always looking back on an exchange or planning a new one. Some of that thinking is competitive, but much of it is collaborative.
  2. Many other animals are also intensely social and cooperative, from ants and bees to rats, starlings, gorillas, killer whales, and even vampire bats.
  3. Mutualistic interactions extend from members of the same species, as in the above examples, to interactions between different species. Radically different types of living things that live closely with each other for a long time often give each other regular and vital assistance. One example: bees fertilize flowers and find food in return.
  4. Such interactions can amount to full-time or almost full-time partnerships. Humans and our cats and dogs are good examples. More exotic are the hermit crabs that carry a pink anemone on top of the shell that the crab has housed itself in. The anemone’s poison darts keep predatory fish away from the crab and the anemone feeds on the crab’s meal leftovers. When the growing crab moves to a larger shell, it even brings its anemone with it.
  5. Sometimes such mutually beneficial relationships take place with one organism inside the the other. Consider the three or four pounds of bacteria inside your body that gain a home while digesting your food.
  6. Helpful sharing takes place even at the cellular level. Cells can actually give a copy of their genetic material to the cell next door. A notorious example are bacteria that are immune to antibiotics. One of several paths by which such resistance is acquired is that a resistant bacterium transfers a copy of its genes to an adjacent, non-resistant bacterium. Bad for our health, but good for the bacteria.
  7. Finally and most profoundly, certain parts of the ordinary cell, the building block of life, turn out to be the descendants of independent bacteria that long ago were absorbed into other bacteria and have continued to pursue their particular functions there ever since. Two such cell components are chloroplasts, which carry out photosynthesis, and mitochondria, which process oxygen to create energy. Around two billion years ago, these were free-floating bacteria. Some of them were “swallowed” by primitive, simpler bacteria. Today they provide the photosynthesis in plant cells and the energy of animal cells. In exchange, they enjoy a protected environment. Evolution might well have stalled without these mergers.


We living things are cooperative ventures at every level, in addition to being fierce competitors. Cooperation and competition are our yin and yang, complementary forces that constrain and generate each other, whose result—thriving life—seems much more than the sum of the parts.

A useful source on mutualistic symbiosis and the ongoing debate about its place in evolutionary theory is Darwin’s Blind Spot: The Role of Living Interactions in Evolution by Frank Ryan.


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