Descent with modification occurrs at every level, from bears to bacteria, and it's all so simple a six-year-old can understand it...
Sammy strep was a bacterium who lived with lots of other Strep family cousins in the left upper lobe of Homeless Homer's lung. But s/he was not happy.
Even though the economy was booming, and everyone had all s/he needed, and everyone was having lots of children, Sammy had no friends.
Sammy was a little different. S/he was always sweating, and his-her cousins would tease Sammy: "Eeewww! -- you smell like penicillinase!" Nobody ever wanted to play with Sammy.
One day Homer went to the Emergency Room of UNM hospital, complaining about coughing and shortness of breath. The Doctors there gave him a terrible magic pill.
After Homer swallowed the pill, Sammy's world began to fall apart, and so did his-her friends -- literally.
A strange poison began to cover everything. Almost everyone who touched it fell apart. Their safe, cozy shells became soft and their insides leaked out. All of Sammy's friends died.
But, for some reason, Sammy did not fall apart. Sammy slogged through the poison, but remained perfectly healthy.
With all his-her cousins gone s/he had plenty to eat, and plenty of room. Sammy began to have children of his-her own. All of them were just like him-her -- sweaty.
Soon Homer's left upper lobe was full of Sammy's' sweaty Streptococcal progeny. They even migrated into Homer's right middle and left lower lobes
Soon, Homeless Homer was coughing up blood, and went back to the hospital, and the Doctors gave him more magic pills, but Sammy did not care. Their magic pills had no effect on his family!
Homer was very ill, and his friends were concerned about him. They gave him some nice blankets and a cozy spot under the I-25/I-40 overpass, but Homer did not get better.
One morning Homer did not get up. Sammy's family's imperialistic, green revolution, Friedmanist lifestyles had dstroyed Homer's lungs.
Homer stopped breathing, and he never got up again. But Sammy Strep did not care. He and lots of his family had moved into Homer's friend's lungs.
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The economy was booming, everyone was very happy, and everybody was very secure, knowing that magic pills would have no effect on Sammy's new naturally selected sweaty streptococcal family.
[Tune in next week for the story of Billy and Betty Blowfly's discovery of poor Homer...]