人为啥有五个手指头脚趾头，五这个是咋进化出来的
四足动物的默认模板就是5个趾头。不是五个趾头的四足动物都是在演化过程中慢慢退化掉几个趾头的。所以大多数的四足动物都是五个趾头。也就是说鱼类演化成两栖类的时候就是五个趾头了，我们只是继承下这个性状而已。The condition of having no more than five fingers or toes--in this context, \u0026#39;most species\u0026#39; means a subgroup of jawed vertebrates--probably evolved before the evolutionary divergence of amphibians (frogs, toads, salamanders and caecilians) and amniotes (birds, mammals, and reptiles in the loosest sense of the term). This event dates to approximately 340 million years ago in the Lower Carboniferous Period. Prior to this split, there is evidence of tetrapods from about 360 million years ago having limbs bearing arrays of six, seven and eight digits. Reduction from these polydactylous patterns to the more familiar arrangements of five or fewer digits accompanied the evolution of sophisticated wrist and ankle joints--both in terms of the number of bones present and the complex articulations among the constituent parts.
【人为啥有五个手指头脚趾头，五这个是咋进化出来的】 Early evolutionary experiments in hexa- or octodactyly (that is, creatures having six or eight digits) were associated with rather simple limb skeletons, much like those present in the flippers of modern whales and dolphins. This might provide a functional clue about one of the reasons for digit number reduction, which is related to the functional demands of simple "walking" limbs. Unlike paddles, such limbs have to provide purchase on a range of substrates, provide the platform for an efficient push-off and allow some rotation relative to the lower and upper limb bones as the rest of the body travels onward. In the very few instances of secondarily evolved polydactylous limbs from the fossil record, the phenomenon is associated with aquatic taxa. The classic instance of this is in the paddles of ichthyosaurs, extinct fishlike marine reptiles that lived more than 65 million years ago.
Is there really any good evidence that five, rather than, say, four or six, digits was biomechanically preferable for the common ancestor of modern tetrapods? The answer has to be "No," in part because a whole range of tetrapods have reduced their numbers of digits further still. In addition, we lack any six-digit examples to investigate. This leads to the second part of the answer, which is to note that although digit numbers can be reduced, they very rarely increase. In a general sense this trait reflects the developmental-evolutionary rule that it is easier to lose something than it is to regain it. Even so, given the immensity of evolutionary time and the extraordinary variety of vertebrate bodies, the striking absence of truly six-digit limbs in today\u0026#39;s fauna highlights some sort of constraint. Moles\u0026#39; paws and pandas\u0026#39; thumbs are classic instances in which strangely re-modeled wrist bones serve as sixth digits and represent rather baroque solutions to the apparently straightforward task of growing an extra finger. Patterns of six (or more) digits can be achieved by laboratory-based developmental manipulations, some of which concern changes in gene activity that probably reflect transformations involved in the fin-to-limb evolutionary transition. Here might lie another part of the reason for the prevalence of five: pleiotropy, or the multiple effects of genes upon more than one physical characteristic. For instance, Hand-Foot-Genital syndrome is a rare condition in which, as the name implies, the genito-urinary tract and the limbs are malformed. Crucially, the genes responsible are within the set of those involved in digit number and patterning. Therefore, although this tells us nothing directly about the significance of digit number, it indicates something important about developmental stability: the mechanisms involved in patterning the tips of our limbs include those involved in our reproductive success. Thus, tweak at your perilWhy do most species have five digits on their hands and feet?我就不翻译了。当然古尔德对这个所有四足动物都有个五个手指的祖先的学说有所质疑。写了一篇THIS VIEW OF LIFEEight (or Fewer) Little PiggiesB16: The History of Life: Source Book
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五个指头是前因，不是后果，这只是自然界的先决条件而已。但是说后果，就有很多，比如：一，指头的数量决定了表达数字的文字表达方式，个位数因此而来；二，因为有五个指头，才会产生十进制。如果是六个指头，可能人类社会常用的就是十二进制了。
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分形几何。
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其实四五六个指头从功能上讲并没有很大差别。之所以是五个指头很可能只是巧合。
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手指脚趾的形成也符合图灵生物花纹理论--中国科技网
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食指是指别人，主语，大拇指好，小拇指坏，中指鄙视，无名指。。也有没有情绪的时候，对吧，为了更好的表达情绪，哈哈哈五指可以更好的将手掌覆盖，比较有力气，可以更好的实现抓，握的动作，我猜的。。
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祖先吃了一颗海星。海星把DNA注入了祖先的DNA
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