What makes aliens stronger?

What exactly makes aliens stronger?

Is it based on the in-game time, the technologies, the overall pollution or other factors I didn't mention?

Solution 1:

There are a few factors that go into the evolution of enemies. From the Wiki, they include:

• The passage of time very slightly increases the evolution factor.
• The global Pollution Production increases the evolution factor.
• Destroying the enemy spawners significantly increases the evolution factor.

You can type in one of these commands into the console to find out the current evolution factor:

/c game.player.print(game.evolution_factor)

or

/evolution

According to the Wiki, the /evolution command will not deactivate achievments, but the other one will. The evolution number can be between 0 and 1, where 1 is fully evolved. Currently, evolution does not go down ever.

The break down of evolution is as follows:

• One game tick - 0.0004%
• 1,000 pollution Units - 0.0015%
• Destroying a Spawner - 0.2%