Evidence for Evolution

The theory of evolution is supported by many independent lines of evidence drawn from different fields of biology and geology. Because these separate sources converge on the same conclusion, evolution is one of the best-supported ideas in science. This lesson surveys the major categories of evidence.

The fossil record

Fossils are the preserved remains or traces of organisms from the past. When fossils are arranged by the age of the rock layers containing them, several patterns emerge:

• Simpler organisms appear in older rocks, while more complex forms appear later, matching the expected sequence of descent with modification.
• Transitional fossils show intermediate features linking major groups. For example, fossils with a mix of reptilian and bird-like traits document the origin of birds, an