To understand the Twenties, you have to understand the unusual orbit that Anvhar tracks around its sun, 70 Ophiuchi. There are other planets in this system, all of them more or less conforming to the plane of the ecliptic. Anvhar is obviously a rogue, perhaps a captured planet of another sun. For the greatest part of its 780-day year it arcs far out from its primary, in a high-angled sweeping cometary orbit. When it returns there is a brief, hot summer of approximately eighty days before the long winter sets in once more. This severe difference in seasonal change has caused profound adaptations in the native life forms. During the winter most of the animals hibernate, the vegetable life lying dormant as spores or seeds. Some of the warm-blooded herbivores stay active in the snow-covered tropics, preyed upon by fur-insulated carnivores. Though unbelievably cold, the winter is a season of peace in comparison to the summer. For summer is a time of mad growth. Plants burst into life with a strength that cracks rocks, growing fast enough for the motion to be seen. The snowfields melt into mud and within days a jungle stretches high into the air. Everything grows, swells, proliferates. Plants climb on top of plants, fighting for the life-energy of the sun. Everything is eat and be eaten, grow and thrive in that short season. Because when the first snow of winter falls again, ninety per cent of the year must pass until the next coming of warmth. Mankind has had to adapt to the Anvharian cycle in order to stay alive. Food must be gathered and stored, enough to last out the long winter. Generation after generation had adapted until they look on the mad seasonal imbalance as something quite ordinary. The first thaw of the almost nonexistent spring triggers a wide-reaching metabolic change in the humans. Layers of subcutaneous fat vanish and half-dormant sweat glands come to life. Other changes are more subtle than the temperature adjustment, but equally important. The sleep center of the brain is depressed. Short naps or a night's rest every third or fourth day becomes enough. Life takes on a hectic and hysterical quality that is perfectly suited to the environment. By the time of the first frost, rapid-growing crops have been raised and harvested, sides of meat either preserved or frozen in mammoth lockers. With this supreme talent of adaptability mankind has become part of the ecology and guaranteed his own survival during the long winter.