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Smithsonian National Museum of Natural History
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Artist’s reconstruction of a new fossil species Hemignathus vorpalis (bottom), based on its probable resemblance to adult males of its genus: H. wilsoni (Akiapola’au, above) and H. lucidus hanepepe (Kauai Nukupu’u, middle). Illustration © J. Hume


Artist’s reconstruction of a new fossil species Hemignathus vorpalis (bottom), based on its probable resemblance to adult males of its genus: H. wilsoni (Akiapola’au, above) and H. lucidus hanepepe (Kauai Nukupu’u, middle).

Illustration © J. Hume

 

Burgess Shale fossil. Photo by Chip Clark (c) Smithsonian Institution
This Burgess Shale fossil, Waptia fieldensis, was a small shrimp-like creature from the Middle Cambrian (~510 million years ago) and was discovered in the Canadian Rockies in 1909. It can provide clues into the evolutionary relationship between insects and crustaceans.

Simply put, evolution is change. It is change in groups of living things over time, a process that connects all forms of life to one another. Charles Darwin called evolution “descent with modification” from a common ancestor.

The evolution of living things has been occurring for billions of years and is responsible for the dazzling diversity of life on Earth. That is a fact. Details of the mechanisms of evolutionary change, such as mutation and natural selection, are still being studied and explained.

Individuals Don’t Evolve, But Populations Do.


Evolution refers to changes in groups—populations—of living things over time. Individual members of a population grow and develop, but they don’t evolve.

What does "Theory" mean?


The scientific meaning of “theory” is the most logical, best-tested, and best-substantiated explanation for an observed phenomenon. The theory of evolution by natural selection explains how species of living things—plants, animals, microbes—change over time.

A scientific theory is also predictive—it can tell what is likely to happen.

A scientific theory is different from a hypothesis, which is a scientific “concept” that has yet to be fully tested

 

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