Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent. Nowhere on Earth do we find, for example, mammals in Devonian (the age of fishes) strata, or human fossils coexisting with dinosaur remains. Scientists have learned a lot about evolution by comparing living organisms. They have compared body parts, embryos, and molecules such as DNA and proteins. Comparing body parts of different species may reveal evidence for evolution. For example, mammals may have front limbs that look quite different and are used for... Show more Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent. Nowhere on Earth do we find, for example, mammals in Devonian (the age of fishes) strata, or human fossils coexisting with dinosaur remains. Scientists have learned a lot about evolution by comparing living organisms. They have compared body parts, embryos, and molecules such as DNA and proteins. Comparing body parts of different species may reveal evidence for evolution. For example, mammals may have front limbs that look quite different and are used for different purposes. Bats use their front limbs to fly, whales use them to swim, and cats use them to run and climb. However, the front limbs of all three animals—as well as humans—have the same basic bone structure. The similar bones provide evidence that all four animals evolved from a common ancestor. An embryo is an organism in a very early stage of development. Embryos of different species may look quite similar, even when the adult forms look very different. For example, the embryos of chickens, turtles, pigs, and human beings look so similar that it is hard to tell them apart. Such similarities provide evidence that all four types of animals are related. They help document that evolution has occurred. Scientists can compare the DNA or proteins of different species. If the molecules are similar, this shows that the species are related. The more similar the molecules are, the closer the relationship is likely to be. When molecules are used in this way, they are called molecular clocks. This method assumes that random mutations occur at a constant rate for a given protein or segment of DNA. Over time, the mutations add up. The longer the amount of time since two species diverged, the more differences there will be in their DNA or proteins. Show less
Perhaps the most persuasive fossil evidence for evolution is the consistency of the sequence of fossils from early to recent. Nowhere on Earth do we find, for example, mammals in Devonian (the age of fishes) strata, or human fossils coexisting with dinosaur remains.
Scientists have learned a lot about evolution by comparing living organisms. They have compared body parts, embryos, and molecules such as DNA and proteins. Comparing body parts of different species may reveal evidence for evolution. For example, mammals may have front limbs that look quite different and are used for different purposes. Bats use their front limbs to fly, whales use them to swim, and cats use them to run and climb. However, the front limbs of all three animals—as well as humans—have the same basic bone structure. The similar bones provide evidence that all four animals evolved from a common ancestor. An embryo is an organism in a very early stage of development. Embryos of different species may look quite similar, even when the adult forms look very different. For example, the embryos of chickens, turtles, pigs, and human beings look so similar that it is hard to tell them apart. Such similarities provide evidence that all four types of animals are related. They help document that evolution has occurred. Scientists can compare the DNA or proteins of different species. If the molecules are similar, this shows that the species are related. The more similar the molecules are, the closer the relationship is likely to be. When molecules are used in this way, they are called molecular clocks. This method assumes that random mutations occur at a constant rate for a given protein or segment of DNA. Over time, the mutations add up. The longer the amount of time since two species diverged, the more differences there will be in their DNA or proteins.
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