Evidence for the Theory of Evolution

A Common Ancestor… ► The theory of evolution suggests that animals have a common ancestor. There are five pieces of evidence (gathered by making observations) that support the theory of evolution: the fossil record, homologous structures, vestigial structures, embryonic structures, and deoxyribonucleic acid (DNA).

The Fossil Record ► Millions of fossils have been found of animals that no longer exist. Some estimates suggest that over 90% of organisms that once lived on earth are now extinct. ► Dating of fossil remains using carbon-dating supports a timeline beginning with less complicated organisms and culminating with more complicated organisms.

Homologous Structures ► Homologous structures are structures that show great similarity. For instance, the similarity between a human hand, cat leg, dolphin fin, and bat wing. ► The similarity points toward the idea of a common ancestor.

Vestigial Structures ► Vestigial structures are structures that serve no apparent reason. Examples might be the tail bone of a human or the appendix of a human, they might have been useful in some past form of what is now the modern human form. ► Another example is the hip bone in whales. They don’t need a hip bone to walk upright. ► Vestigial Structures also suggest a common ancestor might have existed.

Embryonic Structures ► An embryo is a developing baby that is still inside its mother. During the early stages of development, the embryos of vertebrates (animals with backbones) look very similar. ► For instance, embryos of humans, rabbits, and chicken have gill slits and a tiny tail. Some of these animals will develop these and others will not. ► The similarity between vertebrate embryos is also evidence that a common ancestor existed.

Deoxyribonucleic Acid (DNA) ► DNA, the genetic material that carries the information about an organism and is passed from parent to offspring, is in all living things. ► The greater similarities between two organisms, the greater the similarity in the amount of common base pairing of DNA. ► For instance, the DNA sequences of chimpanzees and humans are 98% the same.

Darwin’s Conclusion… ► Darwin pondered his experiences while traveling on the H.M.S. Beagle for 20+ years after he returned. ► The finches he observed were very similar in structure but had slight differences (like their beak shape and size) that helped them be better adapted to the island they were on.

► His observations of the finches and of other animals helped him develop the five evidences to support his Theory of Evolution (by Natural Selection).