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.