Evidence for Evolution

Evolution - descent with modification or changes in the genetic population over time (across generations)

Evidence for evolution: evidence of change over time and evidence of common ancestry

Microevolution: Small-scale evolutionary changes occur in gene frequency and trait distributions that occur in populations and species

Macroevolution: large-scale evolutionary changes, evolution on a species level (speciation and extinction), and at a higher taxonomic classification (appearance or disappearance of genera, families, orders, etc). Typically refers to the evolutionary differences among a population usually in morphology.

Evidence of Microevolution: Change over Time

Vestigial Structure - a functionless or rudimentary version of a body part that has an important function in a closely related species; structure with no apparent nor predictable function (unusable organs). Eye sockets on a blind cave fish, rudiments of a pelvis and hind limbs on snakes, wings on flightless birds, flowers in self-pollinating plants. In humans, ear wiggling muscles, and tails are present in all humans and vertebrate embryos, appendix, and wisdom teeth. Rudimentary organs can often be detected in the embryo, but are lost later during development. The ancestor had an organ that was fully functional and developed. Each feature in an organism tends to be inherited, even if they aren’t used by descendants. Experiment with Mexican Terra Fish (cave population has a vestigial eye socket) (surface population has normal eyes) when surface and cave fish are bred, the offspring had small eyes (inherited trait). Transplant lens tissue of surface fish to cavefish and the cavefish grow eyes (the cavefish has a degenerative optic nerve and retina). Therefore blind cave populations are descended from the eyed, surface-dwelling population; they lost their eyes recently. Vestigial features are of great importance, which may reflect inheritance. Mechanism 1: disuse. Mechanism 2: Natural selection (an organ useful in some conditions might be injurious in others (beetles on islands)).

Pseudogene - a sequence of DNA similar to a functional gene but nonfunctional, probably the remnant of a once functional gene that accumulated mutations. Common in the human genome (~6,000/40,000). Might come from an early stop codon or other loss of function mutation. Hemoglobin pseudo-alpha is similar to HGB alpha but with a mutation. Olfactory receptor (OR) genes: humans have over 1000 (70% pseudo) sense of smell correlates with loss of genes, mice have over 1500 (20%) and a more accurate sense of smell, dogs have more than 800 (pseudo 18%) and olfactory sensitivity is 100x that of humans. Dolphins have many OR genes, but all are pseudo (they don’t need to smell underwater).

Change through time evidence: soapberry bug ate the fruit of host plants, prior to 1925 it was the Southern Florida balloon vine which has thick fruit, since 1926 it has been the central Florida flat-podded golden rain tree which has thin fruit. The difference in the bugs’ beak size decreased in response to the new food introduced.

Evidence of Macroevolution - evidence of fossil record (fact of extinction), transitional forms, and the law of succession.

A fossil is any trace of an organism that lived in the past.

Extinction is the complete elimination of all individuals in a species from the earth. A common occurrence based on the fossil record (>99% of all species that have lived are extinct). Example: Irish Elk (neither Irish nor elk nor moose nor reindeer) is an extinct species a relative to a living species, evolved during glacial periods, unable to adapt to subarctic conditions of the last glaciations, the last one died ~11,000 years ago.

Law of succession: Fossil types are succeeded in the same geographical area by a similar fossil and or extant species. This close relationship between fossils and extant holds over a wide range of geographical areas and taxonomic groups. Example: similarity in marsupials fossils in Australia and the marsupials currently living there.

Transitional Forms - Ancestor → transitional form → descendant. Examples: reptile → archeopteryx → bird. The archeopteryx had modern feathers but a dinosaur-like skeleton. Fossils of dinosaurs also have bristly structures, filamentous structures, and modern feathers.

Phylogenetic tree: a graphic representation of relatedness between species, genera, etc. Assumes that groups are related by descent from a common ancestor and that changes occur over time.

Taxon: any named group of organisms such as species or genus

Sister Taxa: two taxa share a more recent common ancestor with each other than either does with any other species on the tree.

Homology

Homology: the study of likeness, structural similarity between species despite the difference in function, the similarity between species the results from inheritance of traits from a common ancestor. Structural homology is the bones (forelimbs in vertebrates, different functions same sequence of bones). Developmental homology is the similarity in embryonic forms. Molecular homology has two forms, the conservation of the genetic code as well as the case of shared genetic flaws.