33.5:
The Evidence for Evolution
Life on Earth is incredibly diverse. Many different lines of research provide overwhelming evidence that evolution produced this diversity.
For example, the evolution of antibiotic resistance in bacteria can be observed directly, in as little as a few days. Such rapid evolution is possible due to large population sizes and short generation times—only minutes to hours in many bacteria.
Comparisons of the development of organisms also provide evidence for evolution. The embryos of vertebrates, for example, all resemble one another very early in development, sharing structures that include the pharyngeal arches and a spinal column. Individuals only later develop the characteristics that define genus and species.
After development is complete, comparative anatomy can reveal remarkable similarities among organisms. Tetrapods—animals with four limbs—evolved from a common ancestor. Species as diverse as birds, humans and whales have similar forelimb bone structure.
Fossils provide evidence of the existence of extinct species as well as insight into the evolution of modern species. Fossilized tissues can sometimes be dated directly and their location within sedimentary rock layers also provides information about their age.
These data allow scientists to estimate when extinct species arose, when they died out, and how they were related to one another and to their modern descendants.
All living organisms use DNA to store and transmit genetic information. Comparisons of DNA sequences can show the relatedness of organisms to one another. Organisms with more similar sequences are more closely related.
Biogeography studies how organisms are distributed around the world. This distribution pattern is affected by factors like extinction and speciation.
The finches that reside in the Galapagos Islands are a well-known example of speciation, a process that occurs when one species splits into two or more species. Speciation occurs when changes to the physical characteristics and DNA prevent interbreeding between individuals from different populations.
Some of the populations of finches accessed new food sources, and over time they evolved traits such as specialized beak shapes to match the specific foods that were most abundant.
Taken together, observations from these diverse fields of research provide evidence that “Nothing in biology makes sense except in the light of evolution”.
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.
Suggested Reading
“Evidence Supporting Biological Evolution.” Science and Creationism: A View from the National Academy of Sciences: Second Edition. U.S. National Library of Medicine, January 1, 1999. [Source]