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现代科学调查已基本确认了地球上还有多少种生物 ,凡是被宣布灭绝了的生物 ,如果某一天突然复活或重出江湖 ,毫无疑问 ,人类必将睁大惊恐的眼睛。有一些我们长期以来一直认为已经灭绝、只在化石标本中认识的动物 ,可能仍在深海里生存着。在那些使地球上大量生命灭绝的无法解释的大灾难中 ,海底动物往往幸存下来 ,因为深海的生态环境相对稳定。空棘鱼就是一例。空棘鱼发现始末1938年 12月 2 2日 ,正是印度洋的捕鱼季节。这天早晨 ,在南非东南靠近东伦敦几海里的洋面上 ,有一条奇怪的鱼落进了“涅尼雷”号渔船的拖网。这条鱼的外表很像鲑鱼 ,… 相似文献
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来沙漠之前就听人说,沙漠深处有人家,当时的第一反应”太苦了!”,在那一个没有一切现代文明元素(公路、电、自来水、煤气、电视、网络、医院)的地方生活是不可想象的,心中暗想,到时一定要跟他们好好聊聊,也好帮他们向上反映反映。 相似文献
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人类是从370多万年前的森林古猿进化来的已成为学术界公认的历史事实 ,即由森林古猿经过西瓦古猿〈sivapithecus〉、南方古猿〈Australopithecus〉进化为人类。人类起源的原因 ,即由森林古猿进化为人类的原因 ,迄今仍众说纷云 ,莫衷一是 ,笔者认为森林古猿进化为人类的原因固然很复杂 ,很多 ,至今尚无充足的证据将其证实 ,但森林古猿下地生活 ,是其进化为人类的最关键、最重要的一步 ,森林古猿下地生活在人类起源中具十分重要的意义。一、森林古猿下地生活 ,有利于其向直立行走方向进化人与古猿的重要区别之… 相似文献
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<正>进入若尔盖县后,路边常常可见层层堆叠着的水泥井圈,标示着该地区打井之普遍。随后在对多家牧民的询问中也证实了这一点:除了居民自挖的土井,也有不少政府打的机井。我们在路边的草场上看到这样一幅情景: 相似文献
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肉食类恐龙在6500万年之前已经绝灭了 ,它们如何捕猎 ,如何打发闲暇时光 ,它们的群栖生活行为及繁殖等习性 ,人们均可通过了解化石记录去寻求答案。在描述肉食类恐龙的生活方式时 ,我不以为研究爬行动物的生理学可以推断出恐龙是变温动物还是恒温动物。然而这个曾经有争议的问题 ,现在很快获得了认可。肉食类恐龙有三种基本类型 :胫骨龙、原蜥脚类、和兽脚类。前两类是四趾型的 ,他们在地史时期的发展较局限。兽脚类是三趾型的恐龙 ,为数较多 ,延续时间较长 ,其中有较著名的霸王龙、跃龙和腔骨龙。因为有类似鸟的运动特性 ,这群生物从三… 相似文献
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Scott Atran 《American anthropologist》1985,87(2):298-315
Original work by Brent Berlin, Eugene Hunn, Cecil Brown, and other ethnoscientists has produced significant findings pertaining to claims of universality for folk-biological ranks, in general, and folk-botanical life forms, in particular. These findings implicitly call into question conventional wisdom in the history of biology, which tends to consider life forms as the outworn vestiges of scholastic tradition or as merely socially practical ways of carving up the living world. Unfortunately, however, ethnobiologists continue to rely on faulty analytical schema for assessing the nature of life forms which philosophers and historians of biology have developed in their ignorance of the popular conceptual foundations of folk taxonomy. The error is compounded by the adoption into ethnosystematics of the most empiricistically reductionist, and logically confused, interpretation of such schema that derives from the neo-Adansonian, or pheneticist, school of modern system-atics. This interpretation confounds (1) meaning and reference, (2) the semantics of cognitively distinct object domains, and (3) the conceptual differences between common sense and science. These points are challenged, and it is concluded that life forms, though anthropocentrically biased, are no more "artificial" or "special-purpose" than higher-order scientific taxa. Finally, the problem of so-called "unaffiliated" and "ambiguous" generics is addressed and a new analysis offered. 相似文献
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TOSHIKAZU KOSAKA 《The Journal of eukaryotic microbiology》1991,38(2):140-148
ABSTRACT. Studies were completed on the natural population density of Paramecium bursaria syngen 1 and on the life cycle stages to which the individuals belonged. Green paramecia were collected from two streams once every 20 days for over one year: 413 individuals on 26 collection dates in Mikumarikyo stream and 83 individuals on 23 collection dates in Momijidani-gawa stream. Individuals in nature did not maintain at a steady density but fluctuated greatly depending on the month. It seems that conjugation occurred from April to June in the Mikumarikyo stream and from May to June in the Momijidani-gawa stream. The appearance of individuals with mating ability might be related closely to increasing population so that sexual reproduction probably occurred near the peak of the population density. The 413 individuals from Mikumarikyo stream were examined to determine their position within the life cycle; 309 (74%) were immature, 55 (13%) were adolescent, and 49 (12%) were mature. No senile individuals were observed. The fraction of individuals with mating ability was generally less than 30% at any collection. Four mating types were observed occurring with about equal frequencies in mature individuals. The results show the frequencies of the recessive genes for mating types (a and b) are higher than for dominant genes (A and B). Of 83 individuals from Momijidani-gawa stream, 44 (52%) were immature, 21 (25%) were adolescent, and 18 (21%) were mature. Again, no senile individuals were observed. Because only two mating types were found, II and III (genotypes aaB- and aabb), it seems possible that the dominant gene A was rare or absent in the Momijidani-gawa population. 相似文献
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Biophysics - Questions about the nature of life and the ability of living things to evolve are still attracting attention of scientists from different backgrounds. The idea that all living... 相似文献
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M. W. Gillman 《BMJ (Clinical research ed.)》1996,313(7060):765-766
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贵州雷公山自然保护区秃杉天然种群生命表 总被引:7,自引:1,他引:6
运用相邻格子法,对雷公山秃杉种群进行生态学调查,采用空间代替时间的方法,编制秃杉种群的生命表。结果表明:秃杉种群结构存在波动性, 成年阶段的个体较丰富, 种群趋于Deevey Ⅱ型;秃杉种群死亡率和消失率曲线变化趋势基本一致, 均出现2个高峰, 一个出现在第6龄级阶段, 另一个出现在第12龄级阶段;秃杉种群的生存率单调下降, 累计死亡率单调上升, 生存率下降趋势前期高于后期, 累计死亡率则相反;生存函数曲线表明,秃杉具有中期稳定和后期衰退的特点。 相似文献