Watching Rats Shrink: A Glimpse of Our Own Future
When I was a child in the countryside, huge rats were everywhere. But in today's countryside, large rats have nearly vanished; only the house mouse, far smaller than the old rats, remains. Why? Did food shortage make rats smaller?Actually this is natural selection (or artificial selection, because the huge changes in rats over the last two to three decades relate closely to human activity). Rats have not simply grown smaller; rather, the larger black rat and brown rat are no longer suited to modern homes, so only the house mouse remains.Among house rats there have always been three common types: black rat, brown rat, and house mouse. Black and brown rats can reach 400–500 g; the house mouse is far smaller, about 1/20 their weight, averaging 10–30 g.As human housing improved, food storage changed, and rodent control multiplied, black and brown rats—which need much food—can no longer find enough to eat in human dwellings, so they gradually vanished from view.The formerly disadvantaged house mouse, being small, consumes little—a few food scraps suffice—and hides more easily to escape human killing, so it adapts to new environments far better than black and brown rats; eventually only these mice remain in our homes.House mice breed prolifically: they mate year-round, gestation about 21 days, 6–8 litters a year, 5–10 pups per litter; a mouse can breed at 2–3 months, producing 4–5 generations within a year. After hundreds of generations, a species changes morphologically a great deal. So our naked-eye observation of huge rat-population change over two or three decades is not strange.Thus we can easily imagine that our own past and future must differ from the present. One of our hominid ancestors averaged 200–300 kg; but as Earth's climate changed and food grew less abundant, we adapted, becoming our present shape.If humans reproduce hundreds more generations, while the climate crisis worsens, the environment grows harsher, and life-threatening diseases multiply, what will we evolve into? It depends on which people have better adaptability and reproduction in such an environment. Natural selection is objective; the living world is forever evolving. Not only rat populations will change; future humans will change enormously too.No need to over-mourn the deterioration of the natural and social environment—Earth's life has faced worse. Within our power, protecting the natural and social environment matters, but more important is developing our own adaptability amid constant change. On trends beyond our control, each individual's effect is limited, and even collective effort may be futile. Did the larger black and brown rats not wish to survive? But the trend swept past them beyond their control.From Earth's birth, this planet's environment has never stopped changing. For 700 million years after Earth formed, it was gray and lifeless. Life developed from simple microbes into today's complex forms through a long evolutionary journey.In that journey, the only law is survival of the fittest—only those who follow natural law and continually adapt to changing environments survive. Without natural-selection pressure, no evolution occurs.For a long time ahead, humanity will be in disaster mode, facing what house rats faced over the past two or three decades. Perhaps being less greedy and attached, less anxious and rushed, and learning to survive at low energy is our proper way forward in disaster mode.