Life on Earth began as a solitary enterprise. For the first half of our planet’s history — billions of years — every living thing was a single cell, floating alone, competing for resources, asking nothing of anyone. The transition from that world to the one we inhabit now, built from trillions of cooperating cells, is one of the most consequential stories in the history of biology. And the rules that govern how cells live together turn out to mirror, in striking ways, the rules that govern how we live together.
The Oxygen Problem
Rewind roughly 2.5 billion years to the Proterozoic age. Earth’s atmosphere contained almost no oxygen. Cells generated energy anaerobically — without it. Then photosynthetic organisms emerged, drawing energy from sunlight and carbon dioxide, and releasing oxygen as a waste product. Slowly, that oxygen accumulated in the atmosphere.
For the cells already living there, this was catastrophic. Oxygen, if not handled carefully, is toxic. Life had to adapt or perish.
Some cells found a way not just to tolerate oxygen but to exploit it. The mitochondria — those structures found inside most of our cells today — learned to use oxygen to metabolize glucose through a process called oxidative phosphorylation, or OxPhos. This produced energy far more efficiently than the old anaerobic methods, while simultaneously neutralizing some of the toxic oxygen. The result is that modern mammalian cells carry functional pathways for both aerobic and anaerobic energy production, shifting between them depending on demand.
A crisis became a capability. That pattern repeats throughout the history of life.
The Leap to Complexity
The next major transition was the move from simple prokaryotic cells — small, structureless, no internal compartments — to eukaryotic cells, equipped with specialized organelles including the mitochondria. This was an enormous evolutionary jump. Eukaryotes like yeast are vastly larger and more complex than bacteria, yet they are still single-cell organisms.
For the first half of life’s history on Earth, all living things were single-cell organisms. That is not a brief prologue. That is billions of years of evolution producing nothing larger than what fits on the head of a pin.
Then, around 1.7 billion years ago, something new appeared: multicellularity.
The Shift from Competition to Cooperation
A single-cell organism is, by nature, entirely self-interested. It lives, grows, and reproduces entirely for itself. Its prime directive is survival and replication. It competes with surrounding cells for resources without exception.
But cells working together have a decisive advantage over cells working alone.
Early multicellular life likely began as simple colonies of single-cell eukaryotes that discovered mutual benefit in proximity. Over time, collaboration enabled specialization. Specialization enabled division of labour. Division of labour, combined with intercellular communication, produced organisms of greater size, complexity, and capability than any single cell could achieve alone.
The human body is the result of that process taken to its current extreme — over two hundred distinct cell types, broadly organized into epithelial tissue, connective tissue, blood, nervous tissue, and muscle, all working in coordinated concert.
Think of the contrast this way. A single-cell organism is like a person living alone in the woods. They answer to no one. They can do whatever they want. A multicellular organism is like a large city. Rules must exist. Behaviour must be coordinated. Individual freedom is partially surrendered in exchange for the vastly greater capability the collective provides.
In a city, some individuals risk or sacrifice their lives so others may live — soldiers, firefighters, paramedics. In a multicellular organism, white blood cells of the immune system are expendable for the protection of the whole. The needs of the many outweigh the needs of the individual.
The Rules of Cellular Citizenship
For cells to coexist in a multicellular organism, certain behaviours that are perfectly natural for single-cell organisms must be strictly regulated — or prohibited entirely.
Growth. A single-cell organism like a bacterium or yeast grows and replicates without limit. That is its entire purpose. It does not stop until resources run out. Multicellular organisms cannot allow this. Uncontrolled cellular growth is not a feature — it is cancer. The body imposes tight control using oncogenes, which promote growth, and tumour suppressor genes, which restrict it. Cells may grow only when instructed, in the right place and at the right time. A liver cell cannot proliferate on the tip of your nose. Good fences, as the saying goes, make good neighbours.
Lifespan. Single-cell organisms are effectively immortal. A yeast cell can divide indefinitely. There are sourdough starters more than a century old, their yeast lines still alive and active. In a multicellular organism, this immortality is not permitted. Every time a cell replicates, its telomeres — protective caps on the ends of chromosomes — shorten slightly. When they reach a critical length, the cell can no longer divide. It has reached senescence. Old, worn-out cells are then removed through a controlled process called apoptosis: programmed cell death. Cells that have outlived their usefulness are eliminated for the good of the organism, just as a condemned building is demolished so it does not endanger its neighbours.
Movement. Single-cell organisms are natural wanderers. They have no obligation to stay anywhere. Bacteria propel themselves using flagella — long, propeller-like structures — or through twitching movements powered by organelles called Type IV pili. Yeast can enter a dormant spore state, be scattered by wind, and reactivate wherever conditions are favorable. Movement is survival strategy: stay in one place too long, exhaust your resources, and perish.
In a multicellular organism, this wandering instinct must be suppressed at the cellular level. The liver depends on the lungs to supply oxygen. The body depends on the liver to filter blood. Each cell must be where it belongs, when it belongs there. A lung cell cannot simply drift into the bloodstream and migrate to the liver. To prevent this, multicellular organisms have evolved complex adhesion molecules that anchor cells to their correct positions. The default state flips: where movement is the natural condition of a single-cell organism, staying put is the natural condition of a cell inside a multicellular one. Movement happens at the level of the whole organism — not at the level of the individual cell.
What Cells Teach Us About Societies
The parallels between cellular life and human social organization are not merely poetic. They reflect something deeper about the logic of cooperation itself.
Single-cell organisms compete. Multicellular organisms cooperate internally while competing externally. Individual cells surrender autonomy — the freedom to grow without limit, to move at will, to live indefinitely — in exchange for membership in something vastly more capable than themselves.
We did the same thing. Cities, nations, and institutions are built on the same trade: partial surrender of individual freedom in exchange for the specialization, protection, and complexity that only a collective can provide.
The cell that defects — that starts growing without permission, that refuses to die when its time comes, that breaks free and migrates where it does not belong — becomes a threat to the entire organism. We call that cancer.
The social equivalent is not hard to identify.
Life, at every scale, is a negotiation between the individual and the collective. Billions of years of evolution have not resolved that tension. They have simply revealed how much depends on getting it right.
Source : The Cancer Code: A Revolutionary New Understanding of a Medical Mystery by Jason Fung
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