Built collaboratively with Claude Opus 4.7 via Claude Code.
A browser-based artificial life simulator inspired by Tierra, the seminal digital evolution system created by Thomas Ray in the early 1990s. Self-replicating programs written in a 32-instruction virtual machine compete for CPU time and memory; bit-flip mutations and natural selection drive open-ended evolution — parasites, hyper-parasites, and degenerate replicators all emerge unprompted.
The implementation is plain HTML / CSS / ES modules — no bundler, no npm install.
🔗 Live demo: asari-mtr.github.io/tierra
Tierra was originally designed by Thomas S. Ray to study Darwinian evolution in a digital substrate. A 61-byte ancestor placed in a shared memory "soup" replicates by finding its own code, allocating memory, and copying itself. Random bit flips during copying and "cosmic ray" noise in idle memory provide variation; the Reaper culls older, error-prone creatures when memory fills up.
References:
- Ray, T. S. (1991). An Approach to the Synthesis of Life. Artificial Life II, SFI Studies in the Sciences of Complexity, 11, pp. 371–408.
- Tomray.me — Tierra publications
- Wikipedia — Tierra (computer simulation)
This implementation faithfully reproduces the core dynamics (template-based addressing, the Slicer for proportional CPU time, the Reaper, parasitism via host copy machinery) but is deliberately simplified for visualization and accessibility, not for research. Notable differences:
| Aspect | Original Tierra | This implementation |
|---|---|---|
| Instruction set | 32 ops, addressed by 5-bit templates | Same — 32 ops, 4-bit templates (NOP0/NOP1 pairs) |
| Memory size | Configurable (typ. 60k+ bytes) | Fixed 144 × 128 = 18,432 bytes (toroidal) |
| Mutation | Copy bit-flips + cosmic rays + flaws | Copy bit-flips + cosmic rays only |
| Viability check | Implicit | Daughter must contain at least one DIVIDE (prevents trivial degenerates) |
| Genebank | Disk-based archive of long-lived genomes | In-browser localStorage "Hall of Fame" |
| UI | Custom analyzer (x11 clients) |
Single-page HTML with canvas + DOM panels |
| Stagnation rescue | None | Auto-cull + ancestor re-injection if no births for N ticks |
| Comparison view | None | Side-by-side LCS-diff between any two genomes |
| Distribution | Compiled C, multi-process | Plain HTML + ES modules, runs entirely client-side |
- Live memory visualization — every byte of the soup is rendered as one pixel, colored by instruction. Owned regions are bright, unowned (free) regions are dimmed. Click any pixel to inspect the creature occupying that cell.
- Hue-shifting palette — the instruction color palette slowly rotates over time, just for visual flavor.
- Creature list — grouped by genome and category (self-replicator / parasite / degenerate), sorted by population.
- Inspector panel — selected creature shows category, parasitism ratio (cycles spent reading memory outside its own region), full register state, IP, lineage (child → ancestor), and disassembled genome.
- Genome comparison — click rows in the lineage list to add them to a side-by-side comparison view; for two genomes, an LCS-based diff highlights insertions, deletions, and substitutions in
git diffstyle. - Hall of Fame — auto-records long-lived, prolific genomes (lifespan ≥ 300 ticks, reproductions ≥ 5, length ≤ 55) to
localStorage. Re-inject them into a fresh soup at any time. Export/import as JSON. - Custom genome injection — paste a JSON array or comma-separated OP-name list to add your own organism, or seed a fresh simulation with a single custom genome.
- Adjustable rates — copy-error rate, cosmic-ray rate, and execution speed are all live sliders.
- Bilingual UI — switch between English and 日本語 from the header.
Each cell stores a 5-bit opcode (0–31). Template-based addressing uses NOP0/NOP1 pairs as bit patterns that other instructions search for. All arithmetic uses three integer registers (ax, bx, cx), a destination register (dx), and a small operand stack.
| Code | Mnemonic | Effect |
|---|---|---|
| 0 | NOP0 |
No-op, also acts as template bit 0 |
| 1 | NOP1 |
No-op, template bit 1 |
| 2 | ZERO |
cx = 0 |
| 3 | OR1 |
`cx |
| 4 | SHL |
cx <<= 1 (shift left, single-bit constant builder) |
| 5 | INC_A |
ax++ |
| 6 | INC_B |
bx++ |
| 7 | INC_C |
cx++ |
| 8 | DEC_C |
cx-- |
| 9 | IFZ |
execute next instruction only if cx == 0 |
| 10 | IFNZ |
execute next instruction only if cx != 0 |
| 11 | SUB_BA |
cx = bx - ax |
| 12 | MOV_AB |
mem[bx] = mem[ax] — the copy primitive, subject to bit-flip mutation |
| 13–16 | PUSH_A/B/C/D |
push register onto stack |
| 17–20 | POP_A/B/C/D |
pop stack into register |
| 21 | JMP_F |
search forward for a complementary template, jump there |
| 22 | JMP_B |
search backward for a complementary template, jump there |
| 23 | CALL |
push return address, jump (template-addressed) |
| 24 | RET |
pop return address, jump to it |
| 25 | ADR_F |
search forward, write template position to ax |
| 26 | ADR_B |
search backward, write template position to ax |
| 27 | MAL |
allocate cx bytes of free memory, write start to dx |
| 28 | DIVIDE |
release allocated region as a new creature |
| 29–31 | NOP_X1/X2/X3 |
reserved no-ops (mutation absorbers) |
Templates are short NOP0/NOP1 sequences; the search instructions (JMP_*, ADR_*, CALL) look for the complementary template, so a creature can find references inside its own code by reading the local template pattern.
No build step, no dependencies. Because the code is split into ES modules, it must be served over HTTP rather than opened via file://:
python3 -m http.server 8000
# then visit http://localhost:8000/index.html Markup only (no inline CSS / JS)
css/styles.css All styles
js/main.js Entry point — wires DOM events and runs the main loop
js/constants.js Opcode table, VM/world configuration, ancestor & sample genomes
js/state.js Shared mutable simulation state (mem, owner, creatures, ...)
js/i18n.js ja/en dictionaries + translation helpers
js/colors.js Instruction palette + hue-shift logic
js/vm.js VM core: templates, memory allocation, step, reaper, tick
js/creatures.js Creature lifecycle: birth, classification, genome registry, lineage
js/render.js Canvas rendering
js/ui.js Stats / creature list / inspector / legend
js/comparison.js LCS-based genome comparison view
js/inject.js Custom genome parsing & injection
js/hall.js Hall-of-fame storage and UI
MIT — see LICENSE. Use it, fork it, mutate it.
- Thomas S. Ray for inventing Tierra and publishing it openly.
- Built collaboratively with Claude Opus 4.7 via Claude Code.