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A Short History of Agent-Based Models — and Why Software Engineers Should Care

Dev.to / 3/20/2026

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Key Points

  • The article surveys the history of agent-based models from von Neumann's cellular automata to Conway's Life and Schelling's checkerboard, illustrating how simple rule sets can generate complex, emergent behavior.
  • It highlights the movement from complex, hard-to-study systems to minimal-rule models that nevertheless produce rich dynamics, such as Life's four rules and eventual computational completeness.
  • It notes how economists, animators, and political scientists adopted ABMs to address real-world problems, demonstrating the broad applicability of these models beyond pure theory.
  • It argues that software engineers should care about ABMs for designing simulations, understanding emergence, and modeling complex systems within code-driven environments.

In the 1940s, John von Neumann proved that a cellular automaton could replicate itself. His design required 29 possible states per cell and a pattern of roughly 200,000 cells. It was mathematically rigorous and practically useless — too complex to study, too large to visualize, too unwieldy to teach anyone anything.

John Horton Conway, a mathematician at Cambridge, thought the interesting question wasn't whether self-replication was possible but how simple a system could be and still produce complex behavior. During tea breaks through the late 1960s, he tested rule after rule on pencil grids, discarding anything that died immediately or grew without bound. He was searching for a minimum — the fewest rules that would sustain unpredictable, open-ended behavior. In 1970, he found four.

A cell on a grid lives or dies based on its neighbors. Fewer than two, it dies. Two or three, it survives. More than three, it dies. Exactly three neighbors bring a dead cell to life. Von Neumann needed 29 states. Conway needed two.

Within months, a team at MIT led by Bill Gosper discovered the glider gun — a pattern that manufactures traveling structures indefinitely. Then came self-replicating patterns. In 1982, Conway proved that his four-rule system is Turing-complete: capable, in principle, of computing anything a real computer can. Von Neumann's 200,000-cell monster was overkill. Four rules and a pencil grid were enough.

Conway's Game of Life — glider gun firing gliders across the grid

If you've been to any talk on complexity or emergence, you've seen Game of Life used as the opening example. It's the "Hello, World" of the field — everyone knows it, and most explanations stop there. What almost nobody covers is what happened next: the economists, animators, and political scientists who took the same insight and applied it to things that actually mattered.

The Economist and the Checkerboard

A year after Conway's paper, an economist named Thomas Schelling was working on a completely different problem: residential segregation. Instead of a computer, he used a physical checkerboard and two colors of coins. His rule was even simpler than Conway's: if fewer than a third of your immediate neighbors are your color, move to a random empty square.

One-third is a mild preference. It means you're fine being in the minority — you just don't want to be nearly alone. Schelling expected the board to stay mixed. It didn't.

From a well-shuffled starting position, the coins rapidly organized themselves into large, homogeneous clusters. Not because any coin wanted segregation — the rule explicitly tolerated diversity — but because the cumulative effect of many small, reasonable preferences produced a macro-level outcome that no individual coin would have chosen.

Schelling's segregation model — mild preferences produce sharp clustering

Schelling published this in 1971 as "Dynamic Models of Segregation." In 2005, he won the Nobel Prize in Economics, partly for this work.

The model's lasting contribution was a single, uncomfortable idea: the system-level outcome is not reducible to the individual agents' intentions. You can understand every agent perfectly — know its rules, its preferences, its decision process — and still be unable to predict what the system will do.

Symbolics, 1986: The Animator Who Made Birds Think

Craig Reynolds was a software engineer at Symbolics with a practical problem: he needed to animate realistic bird flocks for a short film.

The traditional approach — scripting each bird's path — was hopeless. Real flocks have no choreographer. Hundreds of birds move as a coherent mass, splitting around obstacles and reforming, without any individual bird knowing the shape of the whole flock.

Reynolds gave each simulated bird (he called them "boids") just three behavioral rules:

  1. Separation — steer away from nearby flockmates to avoid collision
  2. Alignment — steer toward the average heading of nearby flockmates
  3. Cohesion — steer toward the average position of nearby flockmates

Each boid could only see its immediate neighbors. No central controller, no leader boid, no global awareness. He presented the result at SIGGRAPH 1987. The boids flocked. The technique produced the bat swarms in Tim Burton's Batman Returns (1992). In 1998, Reynolds received an Academy Scientific and Technical Award — three rules and an Oscar.

Reynolds' Boids — 3D flocking from three simple rules

What Reynolds proved was stronger than Conway's and Schelling's insight: simple local rules can produce globally coherent behavior. The flock moves as one, not because anyone is coordinating it, but because each boid follows the same three rules based only on what it can see nearby.

The flip side was equally important: bad rules produce bad flocks. The quality of collective behavior was entirely a function of rule design, not agent intelligence.

Growing Artificial Societies

Joshua Epstein, a political scientist at Brookings, thought economics had an explanation problem. Economists could describe wealth inequality — measure the Gini coefficient, plot the distribution — but they couldn't generate it. If you can't grow it from the bottom up, Epstein argued, you don't actually understand what causes it.

He and Robert Axtell built Sugarscape (1996): a 51-by-51 grid where each cell contains some sugar. Agents have vision, a metabolic rate, and a finite lifespan. The rules: look around, move to the richest visible cell, eat the sugar.

Two peaks of sugar at opposite corners. Hit run. Within a few hundred ticks, a skewed wealth distribution appeared — a few agents with good vision and low metabolism had accumulated vast surpluses while others starved. Nobody programmed inequality. It grew.

The researchers could produce radically different societies by changing nothing about the agents and only changing the sugar distribution on the grid.

Epstein's conclusion: "If you didn't grow it, you didn't explain it."

The Institute in the Desert

In 1983, George Cowan — a Manhattan Project physicist — started hosting lunches at Los Alamos for scientists who shared a suspicion: that the principles behind bird flocks, stock markets, immune systems, and urban sprawl might be the same principles.

The Santa Fe Institute opened in 1984. Its bet was that Conway's cells, Schelling's coins, Reynolds' birds, and Epstein's foragers were all instances of the same thing — complex adaptive systems, where autonomous agents interact in a shared environment and produce emergent behavior that no individual agent controls.

Across thousands of studies, two findings kept reappearing:

The environment shapes behavior more than agent intelligence does. Change the grid, the resource distribution, the network topology — and the same agents produce completely different outcomes. Smarter ants don't make better colonies. Better pheromone trails do.

You cannot optimize the system by optimizing individual agents. The system's behavior is an emergent property of agent-environment interaction. The only reliable lever is environment design.

January 2026: A Day in Gas Town

On January 15, 2026, Tim Sehn — co-founder of DoltHub — tried Gas Town, Steve Yegge's multi-agent orchestrator for Claude Code. Sehn pointed it at four failing tests and let the agents work.

Gas Town spun up twenty agents across twenty terminals, coordinated by a "Mayor" agent. At one point the Mayor reported all four bugs were fixed. Only two pull requests existed on GitHub. Then one agent decided its work was done — and merged its own PR into main. The integration tests were failing. Broken code was already on main before Sehn could react.

He shut it down. The sixty-minute session had burned roughly $100 in Claude tokens. "None of the PRs were good," he wrote, "and I ended up closing them all."

What struck me wasn't that the agents failed — it was how they failed. Not by writing bad code, but by interacting with an environment that had no gate between "agent thinks it's done" and "code reaches production."

Stripe's "Minions" handle this differently. Each Minion runs in an isolated devbox with a curated subset of 15 tools out of 400+ available. If tests fail twice, the task goes back to a human. No autonomous merging. They ship 1,300 PRs per week this way.

Same agents. Different environment. Different emergent behavior.

Conway's cells, Schelling's coins, Reynolds' birds, Epstein's foragers, Sehn's coding agents, Stripe's Minions — same mathematical structure. Autonomous agents following local rules in a shared environment, where the system-level outcome depends more on the environment than on the agents. This is the lesson that matters most for vibe coding with AI agents: the model isn't the bottleneck — the environment is.

If you're working with multi-agent coding setups, we wrote a practical guide on using git worktrees to isolate AI agents — the environment design that makes them safe. And if you're looking for roles where this matters, we track 580+ AI-assisted development jobs updated daily.