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Family Resemblances

All living things, from people to butterflies to mushrooms, are related to one another. Closely related types of animals, such as dogs and wolves, look a lot alike. Even animals that look different have some similar features. Both humans and birds have eyes, for example. This is a homology--a feature that two different living things inherit from a common ancestor.

Look at the limbs

All three animal limbs--human, chimpanzee and goliath frog--have the same basic set of bones. Only the sizes and positions of the bones are different. The similarities among these limbs tell us that all these animals evolved from the same four-legged ancestor, which lived about 365 million years ago.

final_chromosomechart.jpg

© AMNH Exhibitions

Human, chimp and mouse chromosomes with color showing differences


Recipe for a limb

Why do the human and chimp arms look so much alike? The recipes for building arms, and every other part of the body, are written in a very long but very tiny recipe book inside the body, called DNA. Human and chimpanzee DNA, shown as bundles called chromosomes, look very similar. Yet mouse DNA looks very different. Human and chimp arms and eyes look alike partly because they have a very similar DNA recipe.

Look at the limbs

All three animal limbs--human, eagle and bat--have the same basic set of bones. Only the sizes and positions of the bones are different. The similarities among these limbs tell us that all these animals evolved from the same four-legged ancestor, which lived about 365 million years ago.

Many Ways to Fly

Both bats and eagles fly. So why do their wing bones look so different? There's more than one way to evolve a wing. The eagle evolved from a birdlike ancestor with light bones and feathers. The bat, more closely related to humans, evolved on a different pathway. Its recent ancestor was a small mammal that probably looked somewhat like a mouse. Over time the bat's fingers grew longer and developed webbing, eventually becoming wings.

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