【摘要】 <正> 达尔文的《物种起源》以人工选择为契机,确立了生存斗争和适者生存两个原理,从而创立了自然选择学说。根据自然选择的理论,提出物种起源和生物进化过程中的一些基本规律。其中之一,即种属进化是一个由少到多,复而又少,以至灭绝的缓慢渐进过程。同时,认为灭绝的原因是,优越类型的物种在数量上的增加,就不免使比较不优越的类型减少,使之成为稀有。稀少是灭绝的前驱。只有少数个体的生物物种,当遇到季候性质起大波动的时候,或者在敌害的数量暂时增多的时候,就很可能趋于完全灭亡。所以达尔文的主要结论是物种经自然选择导致灭绝。更多还原

【Abstract】 This paper intends to deal with the causes of rarity of the giant panda.According to the size measurements and characteristics of fossil and present skulls of Ailuropoda microta, A. baconi, A. fovealis and Ailuropoda melanoleuca, some authors (Pei 1965, 1974; Wang 1974) tried to expound the causes of extinction of the giant panda was in line with the phylogenetic roles of development of diminution in body size of Quaternary mammals-small-large- smaller-extinct-Pei’s modification of Deperet’s law. They consider that Ailuropoda made its first appearance in Early Pleistocene, it began by a small sized species, Ailuropoda microta, and adopted the bamboo diet. Coming to Middle and Late Pleistocene, Ailuropoda became well developed, and its body-size increased, Ailuropoda baconi, A. fovealis, a great sized species, and they were maintained up to Neolithic time. After it, they lived in a limited region and with limited food-stuffs, diminishing in size and finally became almost extinct at present day and are in a natturally declining situation of its histiry.But based upon the further studies on comparative morphological characteristics andmeasurements of fossil and present skulls and teeth of Ailuropoda (tab. 1), we have foundout the body size of the present population of the giant panda is not in reduced phase. Ourresults assure that there was no any indication of physical regression of the present popula-tion of the giant panda.Fossil records from 14 provinces and ancient literatures indicate that the giant panda widely distributed in the most eastern pait of China in the geographical and historical period (fig. 1, tab. 2). Even in the centre part of China Ailuropoda distributed until one and two hundreds years ago (fig. 2). The giant panda has a wide food spectrum too, which includes more than 50 species of plants and animals as we record (tab. 3). The reproductive of present population of the giant panda studied in the field shows normally at the present time (tab. 4). So the population of the giant panda becoming rarely or surviving is not as a result of natural decline in the evolution.Otherwise, the natural environment was and are subjected to the increasing of human various activities, so the area of distribution and the habitat of the giant panda had been shrunk. The present area of the giant panda’s distribution has been now divided into six nearly seperate parts, which cover a total area of 29,500sq. km. (tab. 6). The population of the giant panda has been threatened in a disadventage condition. We are of the opinion that the rapid and severe change of natural environment influenced by human various activities is the main threaten factor to the giant panda.For living organism the influence of human activities on nature is another kind of artificial selection, just as a pattern of changes of environoment in natural selection, and plays an important role in the evolution of nature. It is also of very important to predict the general trend of evolution and the consmervation of sustained survival of species for future.更多还原