GeneTank

The idea

Two kinds of games

In Finite and Infinite Games (1986), James P. Carse splits play into two kinds. A finite game is played to be won; it has agreed edges, a clock, and a moment when someone is declared the winner and it ends. An infinite game is played so that play can continue. Its players change the rules when the rules threaten to stop the game.

Evolution is the oldest infinite game there is. Nothing in it wins. Lineages persist by changing, and every change rewrites the conditions for everyone else. Gene Tank tries to make that something you can hold in your hands for thirty seconds at a time.

You don't win the tank. You become one of the forces it adapts to.

Six ideas, built in

How the tank takes them seriously

The chromosome

Grown, not drawn

Each fish carries 37 genes. One of them, body plan, decides whether it grows as a finned fish or a long ribboned eel; the eels swim in the same gene pool and can crossbreed back. Eight of them are tokens that build an L-system: a rewrite rule applied to the letter F a few times over, then traced by a turtle that turns at the gene's branch angle. The trace is mirrored into fins and a tail that ripple as the fish swims. Tap any specimen below to read its rule, or grow a fresh plate.

And the genome can grow. Mutations duplicate stretches of a rule, invent new rewrite symbols that start as copies of old ones and then drift, and duplicate body segments into chains. Each new symbol takes on a job: spines that make predators let go, frills for sharper escapes, lures that feed a fish at night but glow, and ornaments that win mates but catch every eye. A pickiness gene sets how much a fish cares about a partner's ornaments. Every part costs upkeep, so complexity only builds where it pays. The Evolution panel charts it and spotlights the most complex creature alive.

Tap a specimen to see its rule.

The tank

Hide in plain sight

The far water is one seamless fractal that drifts between smooth washes, streaks, and mottled blotches, softened and hazed so it reads as distance. A row of faint plants, grown from the living flora's own genomes, stands in front of it. A fish's visibility is the distance between its colors and whatever lies behind it, eased when its stripes or spots match the texture and by the darkness of deep water. Rock spires, boulders, and the plants themselves sit in front of the fish, so cover is real.

Predators hunt whatever stands out. So do you. Over generations, the survivors drift toward matching colors, faster bodies, deeper water, and the habit of tucking into plants.

The predators evolve too. Each carries its own chromosome: the hue its eyes are tuned to, acuity, speed, size, night vision, and stamina. The hunters that eat best breed, so their eyes follow whatever colors the fish are wearing. Their eye color shows what they hunt.

And the light turns. Over a few generations the tank passes from day to dusk to night and back. In daylight, a fish hides by matching the color behind it; after dark, color barely matters and only brightness gives a fish away. Long nights favor dim fish and predators with night vision, whose eyes glow in the dark.

How to play

Net. Multiply. Let go.

1. Explore. Drag, scroll, or use WASD to swim the camera. Pinch, ctrl-scroll, or + − to zoom. The map in the corner shows the whole tank. M toggles the music.

2. Choose who breeds. Each round lasts 20 seconds by default. Net fish to pull their genes out of the pool. Multiply the fish and plants you like: each tap spawns three young fish from a parent and a nearby mate, or two seedlings. Tap a predator to stun it and spare the fish it's chasing.

3. Watch it go dark. The lights fade, one or more generations pass, and the tank comes back up on the descendants. A short note tells you who was born, eaten, and netted.

4. Read the drift. Open Evolution to see the population's traits change over time, or use Look on any fish or plant to read its whole chromosome.

In Tank settings you can lengthen rounds, run up to 25 unwatched generations between them, set up to eight predators, change the length of the day, and raise the mutation rate.

The series

Infinite Games

Classic arcade and table games with the ending taken out.