33.5: The Evidence for Evolution
Genetic variations accumulating within populations over generations give rise to biological evolution. Evolutionary changes can result in the formation of novel varieties and entire new species. These changes are responsible for the diverse forms of life inhabiting the planet. The evidence for evolution suggests that all living organisms descended from common ancestors.
The collection of fossils within sedimentary rocks give a record of common ancestry and often depicts the history of evolution. The fossil record displays compelling evidence of the evolving levels of complexity in life forms, over generations. Fossil remains of more complex life forms are found higher up in the rock layers, while simpler ones found in lower ones, reflecting the succession of rock layers laid down over time.
A remarkable uniformity exists in the nature, assembly, and utilization of the basic molecular components of all living organisms. The degree of similarity in the genetic information stored within the DNA, biomolecules, metabolic pathways, and other cellular and biochemical processes point toward the genetic continuity and common ancestry of living organisms.
Several striking resemblances also exist in the anatomical organization of the diverse life forms. For example, homologies in the forelimb of vertebrates provide evidence for evolution. Evidence of structural similarity supports the inheritance of skeletal structure plans from a common ancestor that has been modified as organisms evolved and diversified while adapting to specific demands of their environments.
The biogeography or the geographic distribution of species also provides links to the patterns of past evolution. The geographical features like oceans, mountains, rivers, and islands act as barriers to populations allowing them to evolve separately from one another. As a result, several isolated land areas and island groups have distinct plants and animal communities—a result of the evolution in isolation through millions of years. Yet surprising similarities between species remain even when separated by some of these uncrossable barriers.