It is the patchiness of the record that makes each new find look so sudden and distinct from all the others. If we had tens of thousands of skeletons distributed at regular intervals through the historical record, there would be appreciably more degrees of shading. Whole new species don't emerge instantaneously, as the fossil record implies, but gradually out of other, existing species. The closer you go back to a point of divergence, the closer the similarities are, so that it becomes exceedingly difficult, and sometimes impossible, to distinguish a late Homo erectus from an early Homo sapiens, since it is likely to be both and neither. Similar disagreements can often arise over questions of identification from fragmentary remains— deciding, for instance, whether a particular bone represents a female Australopithecus boisei or a male Homo habilis.
记录方面的不完整性使得每一次新的发现看上去都十分突兀，与所有别的化石大相径庭：假如数万块化石是按年代顺序均匀地分布的话，其相互之间的细微差异就会一览无余。正如化石记录所显示的，所有新的种类并不是突然之间就出现的。越是接近分界点的地方，其相似之处就会愈加明显。因此，要想把晚期智人和早期直立人区分开来是十分困难的，有时甚至是不可能的，因为他们彼此之间太相像了。类似的问题在区分支离破碎化石时经常出现——比如，一块骨头究竟是一个女性南方古猿鲍氏种，还是一个男性能人，这是很难确定的。
With so little to be certain about, scientists often have to make assumptions based on other objects found nearby, and these may be little more than valiant guesses. As Alan Walker and Pat Shipman have drily observed, if you correlate tool discovery with the species of creature most often found nearby, you would have to conclude that early hand tools were mostly made by antelopes.

有关古人类化石的研究是如此具有不确定性，科学家不得不根据附近所发现的其他物证作出假设，这种假设也许不过是大胆的猜测。正如艾伦·沃克和帕特·希普曼所客观描述的那样，如果你把附近经常与化石一起发现的工具联系起来，你会不得不作出这样的结论，早期手工工具大多是羚羊的杰作。

Perhaps nothing better typifies the confusion than the fragmentary bundle of contradictions that was Homo habilis. Simply put, habilis bones make no sense. When arranged in sequence, they show males and females evolving at different rates and in different directions—the males becoming less apelike and more human with time, while females from the same period appear to be moving away from humanness toward greater apeness. Some authorities don't believe habilis is a valid category at all. Tattersall and his colleague Jeffrey Schwartz dismiss it as a mere "wastebasket species"—one into which unrelated fossils "could be conveniently swept." Even those who see habilis as an independent species don't agree on whether it is of the same genus as us or is from a side branch that never came to anything.
也许最令人困惑的，莫过于支离破碎的能人化石中所出现的矛盾现象。单独放置，能人化石并没有任何意义。但是，如果把它们依次摆放在一起，就会发现男性和女性在进化的速度和方向方面存在着明显的不同——随着时间的推移，男性与猿的区别越来越明显，越来越具有人的特征，女性在相同的时期却似乎在由人类向更具有猿的特点的方向转变。一些权威认为根本没有理由将能人单独归类。塔特萨尔和他的同事杰弗里·施瓦兹认为，它只能归人“字纸篓种”——即互不关联的化石“可以被随手扔进”的那个种类。即便是那些将能人看做是独立种类的人也不能确定，它究竟是与我们同属一属，还是属于另外一种已经消失得无影无踪的旁支。