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Scientific evidence for evolution

Know the name of the evidence AND

how it shows evidence

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http://www.pbs.org/wgbh/evolution/library/11/2/e_s_3.html

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• Biogeographical Evidence

• Compares species (biological) in different places (geographical areas)

• Darwin realised that a)Species could look similar but live in different parts of the world, Designed same body part for same reason• e.g dry habitat so preserve water by reducing size of

leaves to needles

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Euphorbia sp (left)and Cactus sp (right)

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Or b)

• Darwin noticed that animals on islands look more similar to animals on nearby islands, and different to animals on faraway islands.

• (More likely to have a common ancestor with closely related islands)

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• Different shaped tortoise, depending on how high up they reach for food, live on different islands.

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• Mainland iguana, island iguana

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Fossils • Show changes in a species over time,

e.g • horse fossils show trend over time• Ammonite fossils show how some animals are extinct now.

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Comparative anatomy

• The study of similarities and differences in body structure,

• It was what scientists used to make connections in family trees before DNA.

• The idea is that if species share a common structure, they probably have a common ancestor.

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• Vestigial organs are also part of Comparative Anatomy,

• They are organs that are present, because the ancestor had them, but are not needed for the species lifestyle today,

• e.g hips in snakes, • ear moving muscles in humans.

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• Snake hips and ear muscles – not useful now but show evidence of what used to be

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Comparative embryology

• The developmental stages of embryos show the relationship between different species, where there are common stages of development are likely to have had a common ancestor.

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• The vertebrate embryos all go through similar stages, no matter whether they are a fish, bird, reptile or mammal, which suggest they have a common ancestor.

• The next slide shows bird, pig, reptile and human embryos at similar stages.

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Molecular Biology

• DNA for all species is based on the same 4 letter code.• How similar two whole codes of the different

species are suggests how closely related two species are.

• DNA for Humans and for chimpanzees is 97% the same.

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• DNA code controls the proteins we make, • So if the proteins are similar in our bodies

then species probably have a common ancestor in the recent past.

• The strength of the similarity tells how closely related they are.

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Proteins are built up by joining Amino Acids, if they are the same species

are closely related.

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Year 13 examples

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• Scientists can study fossils and anatomy of current species to work out how animals evolved bones to help them fly.

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Analogous structures• Comparing structures that have the same purpose but did not

come from a common structure , they did not have a common ancestor with a similar structure,