利用DNA给物种分类

解释分支分类学：生物是根据共有的衍征来分组的，而不仅仅是基于相似性；说明如何利用分子数据（DNA序列比对）和分子钟构建系统发育树；解释为什么鸟类在技术上属于恐龙的一个类群（冠群Avemetatarsalia）；区分趋同演化（不相关的物种演化出相似的特征）和平行演化；介绍水平基因转移，以及为什么生命之树更准确地说是生命之网；解释为什么随着新数据的出现，分类系统会不断变化。

Explain cladistics: organisms are grouped by shared derived characters, not just similarity; how phylogenetic trees are built using molecular data (DNA sequence alignment) and the molecular clock; explain why birds are technically a group within dinosaurs (crown Avemetatarsalia); distinguish convergent evolution (unrelated species evolving similar traits) from parallel evolution; introduce horizontal gene transfer and why the tree of life is more accurately a web; explain why classification systems keep changing as new data emerge

评估问题 / Assessment

{{name}}能否解释，为什么生物学家现在说鸟类就是一种恐龙——不只是它们的后代，而是真的处于恐龙家族谱系之中？这告诉我们科学家是如何对动物进行分类的？

Can {{name}} explain why biologists now say that birds ARE a type of dinosaur — not just their descendants but literally within the dinosaur family tree? What does that tell us about how scientists classify animals?