GB Lil' Pixel Pals: A socio-evolutionary Experiment on the DMG-01

A tiny machine learning experiment, written for the hardware of 1989.

Pixel Pals are small, round and fluffy, with eyes far too big for their faces and an appetite far too big for their size. Eight of them live on a meadow inside a Game Boy. They are young, curious and keen to explore every corner of it, and they spend most of the day looking for berries. They are also about to find out what it means to share a meadow with seven others.

Which is where the trouble starts. There is a berry in the grass, and two Pals have spotted it at the same moment. Neither of them is in the mood to be polite about it.

What happens next depends on who they are, what they remember about each other and how hungry they feel. Sometimes a small heart appears above both of them. Sometimes a little storm cloud does, and one of them walks off with a full stomach while the other one stares at the place where lunch used to be.

That small stand-off over a berry is the whole idea behind GB Lil' Pixel Pals. The cartridge plays it out across a meadow of eight creatures, step after step and generation after generation, and lets the player watch how the little society sorts itself out.

It joins the other cartridges built for this collection. Among them is the GB Museum, a reference work about the DMG-01 ecosystem in the manner of the InfoGenius titles, and GBuddy's Escape, in which a small robot learns its way out of a maze.

Take a tour 

For anyone who is new to Lil' Pixel Pals, TAKE A TOUR tells the story in four short chapters. The tour's animations are staged and marked as such. They explain the ideas without running a simulation, and the real experiments wait in the Playground.

Eight Pals and a very small meadow

The entire world of the Lil' Pixel Pals is a meadow, which is only ten fields wide and seven high. There are lovely trees, cosy grass to walk on and now and then tasty berries. But not everything is as fluffy and cosy as it seems at first sight. Rocks block the way, and there are dangerous patches of ground a Pal should not step on. Now and then a fire breaks out, after a polite warning. All in all, it is not a perfect world to live in.

Every Pal starts with 50 points of energy out of a possible 80. Each step costs a little, a berry provides energy, and stepping on dangerous ground costs extra. A generation's life ends after 200 steps, or earlier if the Pals are unlucky, which on a stingy meadow happens more often than one would like.

Nobody holds the controls

The player does not steer anybody. That takes some getting used to on a Game Boy, where the D-pad usually means somebody is about to steer the carts main character. Here it means following one particular Pal and quietly hoping it spots the berry two fields to the left.

What the player can do is change the conditions: make food scarce, normal or plentiful, and switch the social rules on or off. And at any moment START opens a small window on the Pal of choice, with its energy, its berries so far and the genetic traits it was born with.

Game Boy evolution, one generation at a time

Each Pal carries eight inherited traits, shown as little bars. Vision decides how far it can spot food, Caution how much it dislikes the painful ground, Learning and Memory how strongly experience changes it and how long that lasts. The other four are social, and they come into play further down.

When a generation comes to its end, the cartridge looks at who did well, counting food and survival and frowning a little at anyone who walked into a fire. The two most successful Pals go into the next generation unchanged. The other six places go to their offspring, and offspring come with small random changes, which is the whole point.

Nothing guarantees that the next generation does better. Sometimes it does, sometimes it goes backwards, and sometimes a trait that looked splendid turns out to be useless once the berries move. A longer bar is a stronger tendency, not a better Pal.

Learning is not inheriting

There are two quite different kinds of change on this meadow, and the cartridge is careful to keep them apart.

During its own life, a Pal learns. A berry makes it keener on berries, a burnt foot makes it warier of fire. That experience changes what it does next, and slowly fades again if nothing reminds it.

Its genes, on the other hand, never change while it lives. When it has offspring, they inherit its traits but none of its memories. A Pal that has learned the hard way about fire passes on its caution, not its story. Every new generation has to burn its own feet.

Share or grab

Back to the berry. When two Pals reach the same one, each decides on its own whether to share or to grab. If both share, each gets an equal share of energy. If one grabs while the other shares, the grabber gets the full energy and the polite one gets nothing. If both grab, they get just a tiny bit of energy each, and a lot of the berry is lost in the scuffle.

Anyone who has met game theory will recognise a small prisoner's dilemma. Grabbing pays for the individual in the moment, sharing pays for both of them together, and nobody can be sure what the other one will do. Hearts above the heads of the Pals mark a shared berry, a storm cloud marks a grab, and a sad face marks the Pal who came away with nothing. Every one of those symbols follows a real event in the simulation.

Grudges, second chances and a helping hand

Pals can remember how a particular neighbour treated them last time and answer in kind. The cartridge calls that Reciprocity. It is loosely related to the famous strategy of returning kindness for kindness and a shove for a shove, with a fair amount of chance mixed in.

Forgiveness lets a Pal share again despite a bad memory. And Helping lets a well-fed Pal give a very hungry neighbour five points of its own energy. The helper really loses those five points, the receiver gains exactly five, and no energy appears out of thin air.

These are model rules, not feelings. Whether a Pal is a saint or a scoundrel depends on a handful of numbers, which is either reassuring or slightly worrying, depending on the day.

Ready for an experiment?

The Playground has a section called TRY AN EXPERIMENT, and it asks two questions. Have the inherited traits helped, compared with the very first Pals? And do the social rules help the current Pals, compared with the same Pals grabbing everything and helping nobody?

Both groups run under matched conditions, and the player's own family is left untouched. The first answer comes after a single start per group and is called a FIRST IMPRESSION, because that is all it is. More runs can be added for a sturdier answer.

The cartridge has no favourite outcome. Cooperation is allowed to lose, and a generation is allowed to be worse than its parents. A small difference is shown as a small difference rather than a law of nature. It is a meadow on a Game Boy, after all, not a study of humankind.

Everything on the Game Boy

All of it happens inside the ROM: every decision, every lesson, every selection and mutation and every comparison run. There is no internet connection, no external AI and no calculation on a PC. And no, there is no language model in there either. What runs is a handful of small, understandable methods: agents on a shared meadow, a genetic algorithm across generations and a very simple kind of learning from experience.

That is rather the charm of it. A machine from 1989, with eight kilobytes of working memory, keeps eight little lives, their genes and their grudges in its head, and still finds time to draw a butterfly.

Try it

GB Lil' Pixel Pals is a beta. It works but you might stumble upon some glitches. It will keep growing whenever I find some time to provide the Pals a bit more attention. It is written for an original Game Boy DMG-01, and with a flash cartridge that has battery-backed memory the family survives being switched off. I did my testing with an EverDrive, as always. In a browser, the simulation still runs inside the emulated ROM.

Try it yourself: Lil' Pixel Pals runs in your browser, and the ROM is free to download for a real Game Boy. You find it on our Homebrew Collection page.

Anyone who watches for long enough ends up with a favourite. Which one is yours? Let me know in the comments below, as well as every glitch you stumble upon and every idea about making the experiment better.