The evidence for evolution

Fossils, archives of the past

Fossils are remains or traces of ancient organisms, preserved in rock. Like the pages of a history book, they allow us to reconstruct the succession of life forms over time. In increasingly recent geological layers, we can observe the gradual appearance of new characteristics: for example, the fossil lineage linking certain ancient reptiles to modern birds shows the gradual appearance of feathers and certain bones specific to birds.

Anatomical similarities

Another major piece of evidence: comparing the skeletons of different species reveals striking similarities, despite very different functions. The arm of a human, the wing of a bat, the fin of a whale, and the leg of a cat contain, in a comparable order, the same types of bones. This structural resemblance, called homology, is explained by a common origin: these species descend from the same ancestor, whose basic skeleton was then modified differently depending on their habitats.

Evidence from genetics

Over the past few decades, comparing DNA between species has provided additional, very precise evidence: the more recently two species share a common ancestor, the more similar their DNA. For example, human DNA and chimpanzee DNA are more than 98% similar, reflecting a relatively recent common ancestor on the scale of the history of life.

Three converging lines of evidence

• fossils, which show a gradual succession of forms;
• comparative anatomy, which reveals inherited common structures;
• genetics, which quantifies the relatedness between species.

It is these three independent types of evidence, all pointing in the same direction, that make the theory of evolution so scientifically solid.