There were too many people. Something had to be done. All governments had failed. Those who might have been prime ministers or presidents were out gathering shoots of grass and trapping sparrows and mice to feed their children. It was not recognized, but the death rate was now in uneasy balance with the birth rate. And it was not just starvation that killed. Now armed gangs were eating all the children they could find. There was no beauty left on earth.
In a sub basement lab, below two layers of underground tenements filled with hungry, bickering people, two geneticists studied their computer screens. They had modeled the human genome and they were tweaking it this way and that. After years of failure they thought that their new model of the genome might save the problems of humanity.
As the scientists worked, all over the world buildings were collapsing from the weight of human flesh they carried. People rushed into the space provided by these disasters and took up habitation among the bodies of the dead and soon they joined the the dead as disease swept through.
The two scientists worked day and night, stopping only to sip artificial water and nibble on nutrition bars.
They knitted together an instruction code and they shared it with a virus that took to the winds and currents of the earth and was absorbed by all.
No one thought much when babies started getting smaller. They'd been getting smaller anyway. The first generation reached maturity at four feet tall, the second at three, the third at two and the fourth at just twelve inches or thirty centimeters. That's about where the average adult height stabilized.
It was a very good height really. Cows and rats and carrots were still the same size, which of course resulted in a new set of difficulties, but the benefits were obvious. It seemed that the problems of the human race were over, at least temporarily.
It was really very sad that this delicate and sophisticated gene combination, so carefully locked in place by the best of human minds, could not withstand the random mutations that began to occur. Great ones began to appear, killing their tiny mothers at birth, persons who grew to five foot six inches by the time they were twenty. And when there were enough of them the Great ones formed groups and stomped under foot all the tiny people and their hopeful, tiny new governments and buildings, until no trace of them remained.
``The earth is back where it should be!'' the Great ones said, and they were contented in their villages on the new green land and they gave birth to many children.