Squares are men.
Circles are women.
Green circles are food.
As the men and women age, they get greyer.
The younger the person, the smaller they are.
Food grows, and appears randomly from time to time.
The people move towards food they can see.
If they can't see any food, they try to huddle together.
If there is not enough food, the people begin to fight.
When a man and a woman come close, they often produce a child.
In the end, each person dies.
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The source.