The Evidence for Evolution (or, “Why evolution is almost certainly true.”)

Biogeography

Living things show patterns of geographic distribution consistent with the view of common ancestry in one place, followed by dispersal and change in adjacent places. These patterns make no sense except in light of evolution.

Fossils

The fossil record provides literally thousands of examples of older forms differing slightly from similar younger forms, which is what we would expect if evolution is true. Such patterns make no sense except in light of evolution.

Comparative anatomy

All organisms are adapted to their local environments, but all organisms also display numerous features that are not adaptive. Evolution explains such features as inherited from ancestors, which might have acquired them as adaptations for very different functions in very different environments.

Observable small scale changes

Evolution can be observed occurring every day – in the bacteria that make us sick and which often develop resistance to antibiotics; in insects that develop resistance to pesticides; in the plants and animals we develop through selective breeding for agriculture or domestication; and in natural populations which change in response to changing environmental conditions. If we extrapolate these processes to longer lengths of time, we can reasonably conclude that they explain much of the pattern and history of all life.

Classification

Living things are classifiable into a hierarchy of groups within groups. This is not entirely a human construct, but clearly reflects the hierarchical structure of the features that organisms possess. This structure is explicable only if organisms share a common ancestor and have changed through time.

Genetics

All life on Earth shares the same basic structure for its genetic material, and the same mechanism – the genetic code – by which that material instructs cells what to do. This is explicable only if life has a single common ancestor and has changed through time.

Natural selection

Natural selection – the phenomenon of organisms that possess heritable features which enhance their ability to survive and reproduce leaving more offspring – is in the view of most evolutionary biologists the most important cause of evolutionary change. Natural selection can be seen abundantly in nature and in the laboratory.