Evolution: Supporting Evidence

The following items demonstrate descent with modification, as well as common ancestry. (Darwin’s principle of common descent)

I -Fossil Evidence (descent with modifications) Horse fossils indicate changes in size, as well as the transition from toes to hooves.

I - Fossil Evidence: Continued These mollusk fossils show the development of torsion, the twisting of their shells.

II -Homologous Structures are fundamentally similar in their makeup, position and development, but are adapted to different functions. Animal Forelimbs:

The Galapagos finch beaks are said to be homologous The Galapagos finch beaks are said to be homologous. They originated in a common ancestor and have adapted to various environments.

Homologous v. Analogous What’s the Difference? Homologous structures are features that originated in a shared ancestor. They have different mature forms, but develop from the same embryonic tissue. They are inherited from a common ancestor.

Analogous Structures have features that have identical functions, and look somewhat alike, but they may be different in internal anatomy. The evolved independently after their point of common ancestry, so they were not inherited from a common ancestor. A bird’s wing and a moth’s wing are analogous. They allow the animals to fly, but They have greatly different development and internal structure.

Moth Wing Structure

Catoblepia berecynthia

Bird Wing Anatomy Bones & Feathers

Also Analogous: Insect & horse legs

III -Vestigial Structures which may have been functional in an ancestor, are functionless and underdeveloped in later generations Human tailbone (coccyx) Human Appendix

III - Vestigial Structures: Structures that are vestigial in one organism, may be functional in others. Nictitating membrane Ear muscles

III - Vestigial Structures (continued): Limb bones in snakes Pelvic bones in whales

III – Vestigial Structures: Continued Erector pili muscles which cause “goose bumps” in humans Human baby born with fleshy tail

Does the tail really exist?

Baby girl born in a hospital in Chile

IV -Embryological Similarities Various embryos in early stages show evidence of gills slits and tails.

V - Biochemical Evidence All organisms have DNA (& RNA) All organisms have ATP Similarities in cell respiration enzymes

V- Biochemical Evidence (Continued) All organisms have cytochrome c in the electron transport chain (The difference in A.A.s is proportional to the length of time that has passed since the two shared a common ancestor.)

VI – Homeotic Genes Homeotic genes (Hox genes): regulatory genes that determine where certain anatomical structures, such as appendages will develop in an embryo. “They seem to be master genes of development that determine the overall body organization.” Common ancestry is demonstrated because animals share many of these Hox genes, which may control the development of similar regions.

In Summary Scientists have continued to observe examples of common ancestry and descent with modifications since Darwin observed finches on the Galapagos Islands so many years ago.