[求助] LSAT-2-2-21 为何逆命题也可以INFER?

claudius77

21. One method of dating the emergence of species is to compare the genetic material of related species. Scientists theorize that the more genetically similar two species are to each other, the more recently they diverged from a common ancestor. After comparing genetic material from giant pandas, red pandas, raccoons, coatis, and all seven bear species, scientists concluded that bears and raccoons diverged 30 to 50 million years ago. They further concluded that red pandas separated from the ancestor of today’s raccoons and coatis a few million years later, some 10 million years before giant pandas diverged from the other bears.

Which one of the following can be properly inferred from the passage?  

(A) Giant pandas and red pandas are more closely related than scientists originally
thought they were.

(B) Scientists now count the giant panda as the eighth species of bear.

(C) It is possible to determine, within a margin of just a few years, the timing of
divergence of various species.

(D) Scientists have found that giant pandas are more similar genetically to bears than to raccoons.（D）

(E) There is substantial consensus among scientists that giant pandas and red pandas are equally related to raccoons.

确实相比之下，D是最合理的infer，但是我觉得并不严谨。原文说：

more genetically similiar -> more recent diverging from a common ancestor

genetically simiilar是后者的充分条件，但没有提到逆命题。换句话说：如果giant pandas are more similiar genetically to bears than to racoons, 我们可以籍此推出the diverging of giant pandas and bears from a common ancestor is more recent than the diverging of giant pandas and racoons from a common ancestor。然而，原文只告诉我们giant pandas diverged from bears是最recent的，因此D选项是上述逻辑的逆命题，并不能确定的推导出。

请问各位前辈这样的理解正确吗？还是说infer只是讲一个大概的可能性，不要求非常严谨呢？

非常感谢！

[此贴子已经被作者于2005-10-13 7:53:21编辑过]

snowjing

不是前辈. 我觉得你的思路有点偏.

文章并没有比较giant pandas和bear是否是genetically similiar,(即giant pandas和bear不是同一级, 而是祖先和后辈的关系),且文章最后一句话明确说明giant pandas是from bears.

个人理解这题完全没必要按照"more genetically similiar -> more recent diverging from a common ancestor"这一命题做. 因为下文的几个年代告诉你更准确的信息.

而且文章也没如你所说是recent-->more genetically. 因为10 millions years > a few years. 肯定是a few years 相对recent了.

文章其实想说明giant pandas不是在 a few millions years 时和red pandas 一起从raccoons分离出来的, 而是在10 millions years前就从bear分离出来了.

个人理解, 欢迎讨论!

claudius77

不是前辈. 我觉得你的思路有点偏.

文章并没有比较giant pandas和bear是否是genetically similiar,(即giant pandas和bear不是同一级, 而是祖先和后辈的关系),且文章最后一句话明确说明giant pandas是from bears.

个人理解这题完全没必要按照"more genetically similiar -> more recent diverging from a common ancestor"这一命题做. 因为下文的几个年代告诉你更准确的信息.

而且文章也没如你所说是recent-->more genetically. 因为10 millions years > a few years. 肯定是a few years 相对recent了.

文章其实想说明giant pandas不是在 a few millions years 时和red pandas 一起从raccoons分离出来的, 而是在10 millions years前就从bear分离出来了.

个人理解, 欢迎讨论!

非常感谢你的回复。我也觉得之前自己的那个理解似乎有点牵强，但不这么理解，似乎也存在一个问题。倘若没有genetically similiar -> recent这层逻辑关系的话，那原文提供的就仅仅是一组几个动物分化时间的数据，那这时候我们又如何根据这些数据来推出giant pandas和bears比较similiar呢，难道仅仅因为他们在时间上是比较靠近的祖先和后辈吗？这样不是等于加入了文章之外的知识？况且隔代的物种更接近也是完全有可能的。

谢谢！

claudius77

而且文章也没如你所说是recent-->more genetically. 因为10 millions years > a few years. 肯定是a few years 相对recent了.

原文说：

....... scientists concluded that bears and raccoons diverged 30 to 50 million years ago.

They further concluded that red pandas separated from the ancestor of today’s raccoons and coatis a few million years later, some 10 million years before giant pandas diverged from the other bears.>>

我的理解是：

科学家们认为bears和racoons在3千~5千万年前分化。他们进一步得出结论，又过了几百万年之后，red pandas从今天的racoons和coatis的祖先分化出来，而这个时间要比giant pandas从bears那里分化早了大约1000万年。

所以说giant pandas分化在后，比较recent。而且原文暗示的这层recent的概念是相对于racoons和bears从共同的祖先分化的时间来说的。

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[此贴子已经被作者于2005-10-13 8:32:55编辑过]