[sgylfg]

Without all the modernity, the anthropoid and protohuman had lived under the same conditions as the common wild animals. Back to that time, the physique of human beings enjoyed the common characteristics of wild animals: strong, powerful, attack-resistant, strongly immune to diseases, resistant to cold and heat, and excellent at hearing and vision. The superiority and inferiority of all these traits are a matter of life and death and withstand the harsh tests. In the past 10,000 to 20,000 years, the development of wisdom has brought a lot of application technologies and has greatly improved the living conditions, which makes those excellent physical qualities are less and less important and nearly “useless". As mentioned earlier, the useless traits are inevitable to decline, herein "useless" means that the survival will not be endangered in absence of these traits, rather than the common meaning.

In ape era, people spent their day and night in the wild, from spring to winter, facing all kinds of weather of wind, frost, rain and snow while without any equipment like coat, quilt, house or stove. Same with the other wild animals, their bodies could fully adapt to the natural environment, and even until today, this is the still case for the livestock and poultry such as cattle, sheep, etc. After the mankind invented the heating methods and anti-cold items, the cold-resistance trait became "useless", kept degrading, and basically lost by so far. Modern people in the winter without coat, stove and house will die, which is unique in the biology world. In nature, whether it is the giant homothermal animals, or the tiny heterotherm creatures, none of them have to rely on heating to resist cold and to survive. Modern people’s ability of heat-resistance is much stronger than that of cold-resistance; it is because for a long time, the popularity of heat-prevention/cooling technology and equipment are falling far behind heating and cold-resistance. The use of the refrigerating machine just starts recently. After the popularity of the refrigerating machine, given enough time, people will die from heat without air-conditioning just as the case in winter without coat and stove.