Match observations with common-ancestry explanations and compare multiple evidence types.
Evolution is supported by multiple independent evidence types. Fossils show organisms from past environments and patterns of change through time. In an undisturbed sedimentary sequence, lower layers are generally older than upper layers. Transitional fossils can combine features associated with different groups, helping test predicted historical relationships. The fossil record is incomplete because preservation is selective.
Homologous structures share an underlying inherited origin even when their present functions differ, such as related limb-bone patterns in mammals. Similar function alone does not prove close ancestry because similar environments can favour similar solutions. DNA comparisons provide another evidence source: under comparable methods, more similar homologous sequences generally support a closer relationship. Strong conclusions use several lines of evidence rather than claiming one short sequence proves every detail of a species history.
A human arm and whale flipper share a similar basic bone pattern but differ in function. What does this support?
The homologous pattern supports inheritance from a common ancestor, modified for different uses. Equal function is not required.
A supplied DNA comparison shows 98% similarity for A–B and 85% for A–C using the same region and method. Which pair is better supported as closer?
A–B has the higher comparable similarity, supporting a closer relationship for that evidence. Other evidence can strengthen or qualify the inference.
Watch out: Similar functions can evolve independently. Homologous origins and molecular evidence help distinguish relationships.