Project Goal

The Less-than-Holy Grail

Every science has a dream. Physicists want the Grand Unified Theory; computer scientists want Artificial Intelligence; and in silico biologists want Open-Ended Evolution.

In Open-Ended Evolution, simulated creatures evolve indefinitely, becoming ever more interesting and complex–just like they do in the real world. But nature doesn't like complexity: why should a creature become complex if it's living in a simple ecosystem? Simulated ecosystems are not nearly as complex as the real world, so artificial creatures get complex up to a point, and then stop evolving.

In Narjillos, we're not even aiming for that holy grail of Open-Ended Evolution. We'll be happy if we reach a more humble goal: the creatures become complex enough that we go "wow". Let's call this goal the Wow Factor.

To get the Wow Factor, the first thing that we needed was obviously that all-important triplet: Phenotypic Variation, Selection and Mutation, the three together resulting in Evolution. We did reach that goal, as we explain on the project's home page. However, the resulting creatures are not yet complex enought to be wow-inducing. They can evolve to become snake-like or bipedal swimmers, but they barely ever get any more interesting than that.

To make the creatures more interesting, we could make the system ever more complex, which would mean more and more simulation code. That's not a feasible strategy. The alternative, as ever, is to look at nature.

Getting to Arms Races

Creatures in nature become increasingly complex because they're living in an increasingly complex ecosystem–one made up of other creatures. This triggers something called an Evolutionary Arms Race: creatures become more complex and specialized by competing with other creatures, that are themselves becoming more complex.

There are two kinds of arms races. In a Symmetrical Arms Race, the creatures compete with other creatures of the same species, like the pines in a forest growing higher than their neighbors to catch some extra sunlight. In an Asymmetrical Arms Race, creatures compete with other creatures of different species–like cheetas and gazelles.

Narjillos already engage in symmetrical arms races: bipedal swimmers develop slimmer bodies and larger feet for the same reason. This fratricide arms race is the force that shapes the creatures' bodies. Triggering symmetrical arms races is easy. The hard problem is getting an Asymmetrical Arms Race, which could result in more interesting, very specialized creatures that have that Wow Factor.

To get an arms race between species, we need two things.

1. We almost certainly need Complex Interactions between the creatures, because they can't compete asymmetrically if they don't interact. Right now, all they do is steal food from each other. That doesn't cut it–you won't make us go "wow" by getting slightly longer feet that get you to the food one fraction of a second earlier. So, Complex Interactions come early in our to-do list.
2. Oh, and we also need to have species. Doh! As it turns out, Speciation is its own challenge.

Getting to Speciation

"Species" are (to simplify my biology) pools of genomes where each genome is similar to others in its pool, and different from genomes in other pools. When different species evolve out of a shared ancestor, that process is called Speciation. Guess what–Speciation is one more hairy problem in Artificial Life. Most systems (including the current version of Narjillos) quickly converge on a single species. This dominating species takes over the world and drives everyone else to a quick extinction. So, how do simulations get those species to diverge?

Many simulations encourage Allopatric Speciation, that is speciation driven by geographic isolation: essentially, you build a wall in the world, and watch different species evolve on the two sides of the wall. However, you might remember that our ultimate goal is an Asymmetric Arms Race. For that to happen, we need Complex Interactions, so we probably need the separate species to come back together at some point and interact the hell out of each other. But here is a problem: in the early simulations, the newly reunited species wouldn't stay separate. Instead, one of them would take over the world–just like at the beginning of a simulation, when different randomly generated creatures quickly go extinct to make space for one dominating species. So we needed something better than Allopatric Speciation–we needed species to diverge and stay distinct while sharing the same geographic environment. That's called Sympatric Speciation.

Now, that's where it gets interesting. It seems that you can get long-term Sympatric Speciation in silico if you have two things:

1. An environment that supports Ecological Niches. If there are no niches that force creatures to specialize, then there is no reason not to have a single generalist species.
2. Once the creatures start specializing, you need some mechanism to discourage the diverging species from merging again. This is particularly critical if you have Sexual Reproduction, because sexual reproduction re-shuffles the genes and prevents them from drifting apart. A good mechanism to keep genomes separate in the presence of sexual reproduction is Assortative Mating: a creature must be more likely or willing to mate with another similar creature, rather than a different one.

Narjillos don't have Sexual Reproduction (at least not yet), so we didn't need a mechanism like Assortative Mating. However, there was little doubt that we needed Ecological Niches. In the very beginning, all the creatures made their living the same way, by swimming to food. If all the species compete for the same prize, then the winner takes it all. We needed an ecosystem that supported different prizes for creature that choose different specializations.

To define Ecological Niches, we introduced a Self-Regulating Ecosystem: different creatures can consume and produce various elements in the atmosphere, so one species benefits from the presence of another species that produces the right element. That was the moment where multiple species finally emerged.

The Grand Plan

To wrap it all up, here is the current plan of Narjillos:

• Phenotypic Variation, Selection and Mutation, all together resulting in Evolution. We reached this goal already.
• A Self-Regulating Ecosystem, that creates Ecological Niches, and hence, hopefully, Speciation. It took a lot of work, but we finally reached this goal as well.
• If the previous point doesn't trigger Speciation, then we might need Sexual Reproduction, and then Assortative Mating. As it turns out, we got Speciation without having to implement this. Yay!
• Complex Interactions between the creatures to promote progressively more specialized creatures, hopefully triggering an Asymmetrical Arms Race.
• The result of the Asymmetrical Arms Race should be creatures that have that elusive Wow Factor.

The last two points are still open, and they will certainly require a lot of work.

(All that being said, this is just a plan. It will keep changing as we groom, pivot, or abandon this project. The real, short-term goal of Narjillos is to have fun. In that respect, it's working great.)