First, these are all just informed guesses. 第一、这些都仅仅是根据资料作出的推测。

Estimates for the number of animal species alive at the end of the Permian range from as low as 45,000 to as high as 240,000. 据估计，二叠纪结束的时候，活着的动物物种数量从45000-240000种不等。

If you don't know how many species were alive, you can hardly specify with conviction the proportion that perished. 要是你不知道有多少活着的物种，你就不大有把握算出灭绝物种的具体比例。

Moreover, we are talking about the death of species, not individuals. 第二，我们在谈论的是物种的而不是单个动物的死亡。

For individuals the death toll could be much higher — in many cases, practically total. 就单个动物而言，死亡的数量可能还要多得多——在许多情况下，实际上是全部。

The species that survived to the next phase of life's lottery almost certainly owe their existence to a few scarred and limping survivors. 存活下来进入生命下一阶段的物种，几乎肯定都要把自己的存在归功于几个受伤的和残疾的幸存者。

In between the big kill-offs, there have also been many smaller, less well-known extinction episodes, 在几次大屠杀之间，还有许多较小的、不大知名的灭绝事件，

the Hemphillian, Frasnian, Famennian, Rancholabrean, and a dozen or so others, 亨菲利世事件、弗拉尼世事件、法门尼世事件、兰乔拉布里世事件，以及10多个别的事件，

which were not so devastating to total species numbers, but often critically hit certain populations. 它们对物种总量的破坏程度不是很大，但对某些种群往往是个沉重的打击。

Grazing animals, including horses, were nearly wiped out in the Hemphillian event about five million years ago. 发生在大约500万年以前的亨菲利世事件中，包括马在内的食草动物差一点儿被一扫而光。

Horses declined to a single species, which appears so sporadically in the fossil record as to suggest that for a time it teetered on the brink of oblivion. 马只剩下一个物种，时而出现在化石记录中，表明它一度到了灭绝的边缘。

Imagine a human history without horses, without grazing animals. 请你想像一部没有马、没有食草动物的人类历史。

In nearly every case, for both big extinctions and more modest ones, we have bewilderingly little idea of what the cause was. 对于差不多每种情况，无论是大规模的灭绝还是中等规模的灭绝，我们都感到迷惑不解，不大清楚到底是什么原因。