It's often said that we humans share 50 percent of our DNA with bananas,80 percent with dogs,and 99 percent with chimpanzees.Taken literally,those numbers make it sound like we could pluck one cell from a chimp and one from a human,pull out the tangle bundles of DNA known as chromosomes,unroll each on elike a scroll,and read off two nearly identical strings of letters.
人们常说 人类DNA与香蕉DNA的相识度50%，与狗的相似度80% 与黑猩猩相似度99%。这听起来就好像 我们可以从猩猩和人类身上各取一个细胞，拖出染色体上缠成一团的DNA，展成卷轴状，然后读取出两列几乎一样的字母排序。
But in reality,the human and chimp scrolls don't sync up so easily.In the six to eight million years since we split from our last common ancestor,chance mutations and natural selection have changed each of our genomes in radical-and unique-ways.
Two human scrolls fused,leaving us with 23 pairs of chromosomes to chimps' 24.Other large mutations revised huge sections of text-duplicating a chunk of a human DNA here.erasing a chunk of chimp DNA there-while throughout the scrolls,tiny mutations swapped one letter for another.When researchers sat down to compare the chimp and human genomes,those single letter differences were easy to tally.
人类卷轴的两段融合，使我们只剩23对染色体 而黑猩猩有24对。其他大量的突变则改变了大段的遗传信息 在这儿复制一大段人类DNA。在那儿删除一大段黑猩猩DNA 个别字母替换这种小差异则遍布整幅卷轴 研究员着手比较黑猩猩和人类基因时，可以轻松找出这些小差异。
But the big mismatched sections weren't.For example,if a genetic paragraph-thousands of letters long-appears twice in a human scroll,but only once in its chimp counterpart,should the second copy as thousands of changes,or just one?And what about identical paragraphs that appear in both genomes,but in different places,or in reverse order,or broken up into pieces?
但是大的片段差异...则不然例如，一段含有几千个字母的基因片段 在人类卷轴里出现了两次。而在黑猩猩卷轴里只出现了一次。那么多出来的这段基因应该视为几千个差异 还有一个？再例如 相同的片段在两者基因组中都出现，但是位置不同。或顺序变化，或变成分散的片段 又该怎么算呢？
Rather than monkey around with these difficult questions,the researchers simply excluded all the large mismatched sections- a whopping 1.3 billiion letters of DNA-and performed a letter by letter comparison on the remaining 2.4 billion,which turned out to be 98.77% identical.So,yes,we share 99% of our DNA with chimps-if we ignore 18 percent of their genome and 25 percent of ours.
与其对着这些难题瞎忙活，研究人员干脆删除了13亿 差异较大的DNA序列 然后对剩余的24亿进行逐字比较，得出了相似度98.77%的结论。是的 我们的DNA跟黑猩猩相似度高达99% 前提是忽略18%的黑猩猩基因和25%的人类基因。
And there's another problem:just as a small tweak to a sentence can alter its meaning entirely or not at all,a few mutations in DNA sometimes produce big changes in a creature's looks or behavior,whereas other times lots of mutations make very little difference.So just counting up the number of genetic changes doesn't really tell us that much about how similar or different two creatures are.
还有一个问题:句子中一个小小的停顿 就可能完全改变句子的意思 也可能毫无影响，有时 一点点的DNA变化 会令生物的外观或行为发生巨变，而有时大段的变化只会造成些微差异。因此只是数数基因变化的数量 并没办法说明 两个物种是否相似。
But that doesn't mean we can't learn anything by comparing their genomes.DNA contains a record of the evolutionary relationships between all organisms.It's a garbled record-but by reading closely,we've been able to glean enough information to refine the evolutionary trees we started drawing long before genome sequencing was around.
当然 这并不表示比较基因组的做法一无是处。DNA中记录着所有物种的进化关系。这些记录杂乱无章 但通过细致的研究。我们就能够收集到足够的信息 完善早在基因组测序出现前 就开始绘制的基因树。
We may not actually be 99 percent chimp,but we are 100 percent great ape...and at least a little bananas.