Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

This comic personifies Charles Darwin as a ghostly figure who represents the evolutionary drive to survive and reproduce, constantly urging a cat to "Eat, F*ck, Fight!" -- the primal biological imperatives. The cat initially obeys these instincts with ferocious energy, shown through increasingly wild and aggressive panels.

However, when the cat is neutered (has its testicles removed), it tells Darwin that he no longer has any hold over it. Darwin warns the cat that without biological purpose, the cat will have no purpose in life. But the final panel, captioned "Soon...," shows the cat enormously fat and blissfully happy, purring on its owner's lap. The joke is that the cat has achieved a state of pure contentment precisely by being freed from evolutionary drives -- a humorous inversion of Darwin's warning. Rather than being purposeless and miserable, the neutered cat has found its own version of paradise: eating without restraint and lounging in comfort.