Why is DNA sometimes a better tool than appearance for telling species apart?
01 · Text difficulty by level / 各级别文本难度
同一篇文章提供五档写作目标；本文继续保留 PDF 中“从短句到长句、从常用词到正式词汇”的渐进逻辑。
Specialist vocabulary 专业术语
Taxonomic (about classifying organisms), amphibians and specimens belong to biology. Their meaning is often guessable from word parts: taxo- (arrangement) + -nomic (law). 学科术语常可从词根推测。
Stacked participles and appositives 分词与同位语层层叠加
One noun (comparison) is followed by a relative clause; inside it a second clause without “that” (differences [that] … had masked). 注意省略 that 的定语从句。
Hedged numbers 带限定词的数字
“only about … known” narrows the claim three ways: small number, approximate, and only species already named. 读数字时要看清限定词。
Evaluative, ironic wording 带评价色彩的反思语气
“Apparent” means seeming but possibly misleading, and “limited comfort” signals that the writer disagrees with the cheerful reading. 注意作者态度，不要只看字面。
02 · Long-sentence breakdown / 长难句解析
- To untangle the group：不定式表目的；主句 the team analyzed genetic material …。
- alongside = 与…一起；extracted from … 和 collected roughly a century ago 都是过去分词短语，分别修饰 DNA 和 specimens。
- a comparison that exposed … and allowed …：同位语，两个动词 exposed / allowed 共用主语 a comparison。
- differences (that) the animals’ outward appearance had masked：省略 that 的定语从句，过去完成时表示“更早就已存在的遮蔽”。
- allowed the frogs to be sorted：allow sb to be done（被动不定式）。
- 主干: A … analysis concluded that …。
- the fastest rate on record：同位语，补充说明数字的意义；on record = 有记录以来。
- while estimating that …：while + -ing，表示“同时还估计…”，前后主语相同（analysis）。
- go extinct = become extinct（go + 形容词表变化）。
- Yet = but，句首转折。
- apparent = 看起来的（未必真实）；limited comfort = 有限的安慰。
- since = because；the question of how many species may vanish … ：of + 疑问词从句作同位语。
- before they are ever documented：ever 加强语气，“究竟有没有被”。
03 · Vocabulary & sentence usage / 词汇与句型用法
tell apart / distinguish between
Lower levels say “tell the kinds apart”; the original says “distinguishing the different kinds”. Distinguish between A and B and tell A from B mean the same. 区分的几种说法。
go extinct / become extinct / die out
Go + adjective shows a change of state (go bad, go missing, go extinct). Die out is the plain phrasal verb.
on record
“the fastest rate on record” = the fastest ever written down or measured. Also “since records began”.
describe a species (technical)
In biology, to describe a species means to officially name it and publish its features. So “describing 16,000 new species” is about naming, not about writing descriptions in general. 生物学里 describe = 正式命名并发表。
past perfect for earlier states
“had masked” and “had frustrated” show that the hiding and frustration happened before the research result. 过去完成时表示“在此之前已经…”。
04 · Vocabulary / 词汇卡片
正文中的 A2 以上重点词用半透明色块标出；PC 端悬停、移动端长按即可查看中文释义。
05 · Background knowledge / 背景知识
How a new species is officially named 新物种如何正式命名
To name a species, scientists compare it with the “type specimen”, the museum specimen that carries the official name. When names were given long ago, only old specimens exist, so researchers extract DNA from them. That is why century-old museum collections matter for today’s discoveries.
给物种命名时，科学家要与“模式标本”比对，即带有正式名称的博物馆标本。很多名称是很久以前确定的，只剩老标本，因此研究者要从中提取DNA。这就是百年前的博物馆藏品对今天的发现仍然重要的原因。
Cryptic species 隐存种
Cryptic species look almost identical but are genetically distinct. DNA analysis has revealed many of them, especially among frogs, whose bodies can look alike even when the animals are separate species that do not interbreed.
隐存种在外形上几乎一样，但在遗传上截然不同。DNA分析揭示了许多隐存种，青蛙尤其如此：即使是互不杂交的不同物种，外形也可能十分相似。
Why Madagascar? 为什么是马达加斯加？
Madagascar broke away from Africa about 160 million years ago and from India about 88 million years ago. Long isolation let its animals evolve into forms found nowhere else, and most of its frog species are endemic, meaning they live only there.
马达加斯加约1.6亿年前与非洲分离，约8800万年前与印度分离。长期隔离使岛上的动物演化出别处没有的类型，大部分蛙类是特有种（endemic），即只生活在那里。
How many species are there? 地球上到底有多少物种？
About two million species have been described so far, but estimates of the true total run into the millions more. Amphibians are among the most threatened animals: roughly four in ten species are at risk of extinction, according to a global assessment by the IUCN.
迄今已被描述的物种约有200万种，但对真实总数的估计还要多出数百万。两栖动物是受威胁最严重的动物类群之一：根据世界自然保护联盟（IUCN）的全球评估，大约十分之四的物种面临灭绝风险。
06 · Sources / 来源
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