33.6
趋同进化
Bats and most birds share the ability to fly by flapping their wings. At first glance, it may seem that these two groups evolved from a common ancestor with wings.
In fact, bats and birds are not closely related, and their last common ancestor was a ground-dwelling animal with four limbs. The evolution of wings is an example of convergent evolution, where similar features evolve independently to perform similar functions.
The ability to fly evolved multiple times. We can see this when we look closely at the structure of wings in birds and bats.
The hand and wrist bones of birds are fused, and feathers create a large surface area that helps generate lift during flight.
Birds keep their hindlimbs tucked under their bodies during flight, which reduces drag.
On the other hand, the finger bones of bats are elongated and support a large membrane of skin that forms the wing. A membrane connecting the hindlimbs and tail also helps with flight control.
Another example of convergent evolution appears in whales and fish.
Whales are warm-blooded mammals that nurse their young and breathe air using lungs, while most fish are cold-blooded animals that lay eggs and use gills for gas exchange.
Life in water placed similar demands on whales and fish. This led to the evolution of similar, or analogous, features. Both groups have fins and streamlined bodies that help them move easily through water.
Whales and fish do not share a recent common ancestor with aquatic body plans, yet they have analogous features with similar functions because of convergent evolution.
进化会随着时间的推移塑造生物体的特征，确保它们适合它们所生活的环境。有时，选择压力导致类似但无关的适应在生物中兴起，这些生物最近没有共同的祖先，这个过程被称为融合进化。
收敛演产生的结构称为类似结构。它们在功能上相似，即使它们的结构不同。此外，结构可以相似，同时也包含同源特征 - 那些从共同祖先继承。鸟类和蝙蝠的翅膀相似，但翅膀内的前肢骨骼是同源的，它们改编自遥远的四肢祖先。另一方面，蝴蝶的翅膀与鸟类和蝙蝠的翅膀相似，但它们不是同源的。
有时，当两种生物体作为融合进化的结果而共享特征时，情况很明显，例如鸟类、蝙蝠和蝴蝶翅膀，但在其它时候，这种特征就不那么明显了。为了确定特征是否相似，从而产生收敛进化或同源的结果，以及共同祖先的结果，科学家可以检查有关生物体的DNA序列。
海豚和许多蝙蝠使用回声定位来导航和狩猎。DNA序列数据表明，在哺乳动物耳蜗中编码一种蛋白质的基因普雷斯廷（Prestin）在具有高频听觉的假设下，在关系较少的蝙蝠之间以融合的方式进化，在海豚中也以类似的方式进化。
不同物种中结构相似的毒素和毒液提供了另一个例子，其中DNA序列数据对于确定特征是相似还是同源性至关重要。
Bats and most birds share the ability to fly by flapping their wings. At first glance, it may seem that these two groups evolved from a common ancestor with wings.
In fact, bats and birds are not closely related, and their last common ancestor was a ground-dwelling animal with four limbs. The evolution of wings is an example of convergent evolution, where similar features evolve independently to perform similar functions.
The ability to fly evolved multiple times. We can see this when we look closely at the structure of wings in birds and bats.
The hand and wrist bones of birds are fused, and feathers create a large surface area that helps generate lift during flight.
Birds keep their hindlimbs tucked under their bodies during flight, which reduces drag.
On the other hand, the finger bones of bats are elongated and support a large membrane of skin that forms the wing. A membrane connecting the hindlimbs and tail also helps with flight control.
Another example of convergent evolution appears in whales and fish.
Whales are warm-blooded mammals that nurse their young and breathe air using lungs, while most fish are cold-blooded animals that lay eggs and use gills for gas exchange.
Life in water placed similar demands on whales and fish. This led to the evolution of similar, or analogous, features. Both groups have fins and streamlined bodies that help them move easily through water.
Whales and fish do not share a recent common ancestor with aquatic body plans, yet they have analogous features with similar functions because of convergent evolution.
From Chapter 33:
