Entikayrus: A Live Simulation of Evolution by Natural Selection

 

What would it take for a leaf-eating, house-cat-sized animal on a quiet island to turn into a monkey hunter? I built a small world to find out, and you can watch the answer unfold in your browser.

Entikayrus (The creature's name is a play on my intitals: NTKrus) is invented, but the factors in the process that transforms it are real: variation, inheritance and natural selection, climbing, leaping, diet,  Nobody tells it to climb, grow fangs or change its diet. It happens because some animals eat, escape and breed better than others.

The idea

Evolution by natural selection takes thousands of generations, but this computer simulation compresses 6000 generations into a few minutes. Basically, animals which have slightly different physical attributes that enable them to find more food, or avoid being eaten, will be more successful in breeding and passing on their genes. The young inherit their parents' differences. Repeat for a few thousand generations , and we will have creatures that are increasingly successful at finding food and breeding.

Meet Entikayrus

Entikayrus is about the size of a house cat, weighs around 4 kg, and eats leaves, fruit and shoots. It lives on a forested island with no rivals for its food and nothing that hunts it. In the low branches above live a troop of small, agile  monkeys, at ease because nothing has ever hunted them either.

I took the outline from a real animal, the fossa of Madagascar: a cat-like hunter that evolved on an island and preys on lemurs in the trees.

 

Our model shows 5 stages in the evolution of Entikayrus. 

1. Browser. It eats only plants and lives entirely on forest floor. 

2. Opportunist. Some Entikayrus discover that if they climb the low branches of the forest canopy, they can find birds' eggs and chicks to add to their plant diet. Better climbers eat better, so grip and claws spread. Up in the trees, they meet monkeys.

3. Omnivore. Young and injured monkeys become easy meals, and longer legs and sharper claws start to pay.

4. Arboreal hunter. Healthy monkeys are now on the menu. The animals that are better at leaping from branch to branch out-eat the rest. So Entikayrus with longer legs, stronger haunches and binocular vision for better leaps evolve.  

5. Specialist. Most of Entikayrus energy now comes from monkey meat , and its body shows it: bigger, heavier and stronger. Long legs, a long tail, forward-facing eyes, sharp teeth and claws, a redder coat.

The monkeys fight back

Entikayrus is not the only one evolving. Monkeys that are faster, warier, live in bigger groups or sleep in safer places are more likely to survive. The monkeys' defences average about 23% of their maximum at generation 3,000, and about 79% by generation 6,000.

Biologists call this coevolution: each side's improvement raises the bar for the other. It is sometimes called the Red Queen effect, after the character in Through the Looking-Glass who must keep running just to stay in the same place.

Here is the model in html. You can tweak Entikayrus' evolution by pplaying with the sliders.

https://claude.ai/artifact/TXx2GBWTjD77TNCMoSQQgg

The model starts running as soon as you scroll to it. Here is how to read it:

• Left and right. On the left is the 4 kg ancestor, unchanged. On the right is the average animal of the current generation, drawn from its genes.

• The stage labels. They light up as the diet shifts toward meat. The stages are read from the simulation, not from a timer.

• The charts. Populations, diet, body mass, 12 Entikayrus traits and the monkeys' defences. Click a name under a chart to hide or show that line.

• The seed. It picks the run's luck. The same seed gives the same history every time; "Random seed" gives a new one.

• Pause and "+1 generation". Stop the run and step forward one generation at a time.

Three things worth trying.  Change the slider, then press Restart.

1. Scarce plant food accelerates switch to meat. Set "Plant food on the island" to 40. Entikayrus is pushed toward meat sooner: in six test runs, every one reached the Specialist stage. Set it to 240 and the animal stays stuck at Omnivore or Arboreal hunter.

2. No easy meat. Set "Easy meat (eggs, chicks, carrion)" to 0. Entikayrus still learns to climb, but the evolution slows badly: in 12 test runs, none reached the Specialist stage within 6,000 generations.

3. Plentiful fruit. Set "Fruit for the monkeys" to 700. There are far more monkeys, and their defences evolve later and weaker, because each one is less likely to be hunted.

What is real, and what is simplified

This is a teaching toy, not a prediction. Here is what it is:

• Real: variation, inheritance, competition and selection. Nothing about the outcome is scripted. Body size is not fixed either: it settles wherever the model's trade-offs put it, usually between 5 and 10 kg, not far from the fossa.

• Simplified: Each Entikayrus has 12 numbers for its genome and each monkey has 6. Food is the same every generation, with no droughts or disease.

• Compressed: a run covers a few thousand generations with an exaggerated mutation rate. Change of this size would really take tens of thousands of years.

Different seeds give the same broad story with different details, like rerunning history with different luck.

Press start, then watch the diet line climb, the ancestor and the average animal drift apart, and the monkeys begin to answer back. If you find a run with a surprising story, tell me its seed in the comments.