Overpopulation has never bothered humanity. What really got in the way, though, was an irresistible desire of individuals to gather together, cluster, and occupy one single point in space. That’s how the herd instinct worked—the legacy of ancestors—which once helped people’s pack fend off stones and sticks from dangers arriving in the night…
Over time, a human realized there was nobody around anymore—and the only danger was themselves. Because there was simply too many of them.
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Humanity solves the problem of overpopulation by splitting the life of the most numerous middle class into two shifts. Day people and night people sleep in the same apartments, work at the same jobs—but they never cross paths with each other, since their safety and right to personal space are regulated by a multitude of rules.
The main character, one day, in spite of strict laws, begins to write to his shift partner.