Evidence of Evolution

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Scientific Theory Noun

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[sy-en-tif-ik thee-uh-ree]

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Scientific Theory

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A well-substantiated explanation of the natural world, based on facts repeatedly confirmed through observation and experiment.

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Example: A scientific theory, like the theory of gravity shown here, is a powerful explanation for observable phenomena, such as the Moon's pull causing ocean tides.

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Biogeography Noun

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[by-oh-jee-og-ruh-fee]

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Biogeography

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The scientific study of where organisms live currently and where they and their ancestors lived in the past.

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Example: The camel family originated in North America. As ancestors migrated to different continents, they evolved into distinct but related species like llamas and camels.

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Radioactive Dating Noun

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[ray-dee-oh-ak-tiv day-ting]

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Radioactive Dating

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A technique used to determine the age of rocks and fossils by measuring the decay of radioactive isotopes.

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Example: This graph shows that after each 'half-life' passes, the amount of a radioactive substance decreases by half, a predictable rate used to date fossils.

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Fossil Noun

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[fos-uhl]

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Fossil

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The preserved remains, impressions, or traces of organisms that lived in the past, often found in rock.

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Example: This diagram shows that older rock layers at the bottom contain simpler fossils, while younger layers at the top contain different, more complex fossils, demonstrating change over time.

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Homologous Structures Noun

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[huh-mol-uh-guhs struk-cherz]

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Homologous Structures

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Structures shared by related species that have been inherited from a common ancestor, but may have different functions.

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Example: This image shows that the forelimbs of a human, cheetah, whale, and bat have a similar bone structure, suggesting they share a common ancestor.

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Analogous Structures Noun

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[uh-nal-uh-guhs struk-cherz]

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Analogous Structures

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Body parts that share a common function, but not structure, and were not inherited from a common ancestor.

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Example: This diagram shows that a shark's fin, a penguin's wing, and a dolphin's flipper have a similar function (swimming) but different internal structures and evolutionary origins.

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Vestigial Structures Noun

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[ves-tij-ee-uhl struk-cherz]

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Vestigial Structures

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Structures inherited from ancestors that have lost much or all of their original function due to evolutionary change.

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Example: This diagram shows a whale's skeleton, highlighting the small, unused pelvic bones, which are vestigial structures left over from its land-dwelling ancestors.

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Comparative Embryology Noun

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[kuhm-par-uh-tiv em-bree-ol-uh-jee]

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Comparative Embryology

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The study and comparison of early developmental stages of different organisms to reveal ancestral relationships.

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Example: This image shows that embryos of different animals, like sharks, chickens, and humans, look very similar in their early stages, suggesting they share a common ancestor.

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Genetic Code Noun

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[juh-net-ik kohd]

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Genetic Code

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The set of rules by which information encoded in genetic material is translated into proteins by living cells.

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Example: This diagram shows how the genetic code in DNA is first transcribed into an mRNA message, which is then translated into a chain of amino acids.

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Hox Genes Noun

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[hoks jeenz]

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Hox Genes

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A group of related 'master control' genes that determine the basic body plan of an embryo during development.

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Example: This diagram shows that the order of Hox genes on a chromosome matches the order of the body parts they control, from head to tail, in a fly.