The man says to the cockroach, "This rock ain't big enough for both of us."

The cockroach feels the vibrations of the man's voice but the meaning is beyond its neuron count, beyond primitive fight or flight. Besides, unbeknownst to the man, the cockroach has already deposited its egg sack a few meters away.

Unbeknownst to the cockroach, the man has a can of insecticide.

Both species, man and cockroach, are limited by their genetics. In this case it means the man quickly pulls up the can of insecticide, quickly because that's our genetics when confronted by things we fear and disgust.

In the case of the cockroach, its neurons decide 'flight' and it scurries away.

Driven by reflex and genetics, the man sprays the spot where the cockroach was, around and under the rock, continuing until the can runs out.

There's a universal facial expression for disgust, recognizable to humans across all cultures. The man makes it now, then shrugs his shoulders and walks away from the rock.

Evolution is not linear, think of it more as a landscape. The cockroach lives at the address "keep it simple, stupid." Its eggs will eventually hatch.

The man lives at the address, "change with the times." It's a more complex, higher energy strategy, but at the moment, there's still enough energy for him and his descendants.

He walks back to his workshop, thinking about a revised formula for insecticide and other methods of delivery.

Under the dimming reddened sun, life goes on.