人是由猩猩进化的？ 2011-07-11

　　- 人类进化中的缺失环节有可能被找到吗？换句话说，人类的祖先是否可以找到？什么是缺失的环节？人类和黑猩猩之间有什么关系（关于这一点你得出了什么有趣的结论）？如何在进化历史中为人类定位？如何找到我们古老的家族和祖先？如果我们永远无法找到那些缺失的环节，那么连续寻找是否在浪费工夫？化石记录对发现缺失环节有何作用？

　　达尔文和华莱士的物竞天择理论都蕴含一个主要的观点：即所有现存和已灭亡的生命形式都起源于同一个共同的祖先。换句话说，所有的生物都彼此相关。考虑到现有生命体的形式千差万别，该观点有时令人难以接受，并引出一个重要的问题：不同的生物种群之间仿佛有不可逾越的鸿沟，弥合这一鸿沟的过渡形式——即生命树上的缺失的环节——在哪里？

　　首先，我们可以肯定地说，目前无法找到任何现存的缺失环节。这种情况值得我们思考。黑猩猩和倭黑猩猩是与我们最接近的现存亲缘物种，但我们并非由它们进化而来。（因此，我们日常所说的“人是由猩猩变的”其实是错误或不准确严谨的说法）相反，我们与它们在几百万年前拥有共同的祖先。从那时起，我们与它们就开始了不同的进化之路。我们从黑猩猩进化而来的可能性与黑猩猩是从人类进化而来的可能性一样小，即不可能。

　　因此，我们必须通过化石记录找到那些所缺失的环节。但是，我们可能找到自己的直系祖先吗？当发现某些新化石时，尤其当这些化石与人类起源有关联时，人们总是宣称找到了人类的祖先。最近有关灵长类化石“伊达”（Ida）的报道正是如此。我认为这过于乐观。现存物种的数量特别庞大（介于200万-1亿之间，其中的多数尚未被研究发现），然而这只占曾有物种总量的一小部分。在这些物种中，绝大多数的进化后代已分化：只有寥寥数种是现存物种的直系祖先。考虑到物种成为化石的可能性较低，不同地质过程将化石送回地球表面并被古生物学家发现的可能性更低，因此，发现我们直系祖先的几率是微乎其微的。

　　那么，如果缺失环节一直难以找到，我们应当放弃寻找吗？当然不！我们发现的每块化石都在生命树上有着相对应的位置，并使我们进一步了解到生命的进化过程。即使“伊达”化石不是我们的直系祖先（我打赌它绝不是！），它仍与我们共同拥有同一的祖先，并通过她与我们（而非我们的亲缘种群——猿和猴子）的相同之处来告诉我们关于这一祖先的情况。因此，从某个方面来讲，我们已发现自己的祖先，虽然无法观察它或拥有它，但我们能通过模拟推测重建它。发现的化石越多，我们能够重建的祖先就越多，进而更加了解它们的后代在成为人类或任何其他物种之前的进化与改变。

　　Is it possible to find the Missing Links ever in human’s evolution? In other words, is it possible for us to find our ancestors ever? E.g. what’s Missing Links? What’s the relation between human being and chimpanzees? How to locate human being in evolution history and how to find our ancient families and ancestors? If we cannot find the missing links ever, does it mean it’s a waste of time for us to keep finding them? What do the fossil records work in finding the missing links?

　　A major implication of Darwin and Wallace’s theory of natural selection is that all life forms, living and extinct, are descended from a single common ancestor. In other words, all living things are related to each other. Looking at the very different forms of life living today, this idea is sometimes difficult to accept, and raises an important question: where are the transitional forms that bridge seemingly insurmountable gaps between different groups of living things – the missing links in the Tree of Life?

　　Well, for a start, we can safely say that we won’t find missing links alive today. This is worth thinking about for a moment. Chimpanzees and bonobos are our nearest living relatives, but we did not descend from them. Rather, we share a common ancestor that lived a few million years ago. Since then, our evolutionary paths have been separate. We have as little right to claim that we evolved from chimpanzees as chimpanzees have to claim that they evolved from us!

　　So it is to the fossil record that we must look to find the missing links. But will we ever find them – our direct ancestors? This is often claimed to be the case when certain new fossils come to light, especially if they have anything to do with the origin of humans, such as the fossil primate ‘Ida’ that has been in the news recently. This is, in my opinion, outrageously optimistic. The number of living species is very large (somewhere between 2 million and 100 million, most of which haven’t been described), but this is a mere fraction of the total number of species that have ever lived. The vast majority of these had their evolutionary lineages cut short: only a few are the direct ancestors of species living today. Now consider the improbability of a member of a species being fossilised and the further improbability of various geological processes bringing that fossil back to Earth’s surface today, and the further improbability that a palaeontologist stumbles upon it. The odds against any one of our direct ancestors ever being found are astronomical.

　　So, if the missing links will always remain missing, should we give up looking? Absolutely not! Every fossil we find can be slotted into the Tree of Life, and can tell us a little more about how life evolved. Even if ‘Ida’ turns out not to be our direct ancestor (and I’ll bet any money that it isn’t!), it still shares a common ancestor with us, and can therefore tell us about that ancestor by what we (rather, our group – the apes and monkeys) have in common with her. So, in a way, we have found our ancestor, but we can’t see it or hold it, we can only reconstruct it. The more fossils we find, the more ancestors we will be able to reconstruct, each telling us a little more about the evolutionary changes that took place on the lineage leading to humans, or any other species for that matter.

　　(本文来源：网易探索 )

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