EVOLUTION & EVOLUTIONARY THEORY
- ORGANIC EVOLUTION
- Records the changes in populations (groups of individuals living together belonging to the
same species) over time.
- Several modes of speciation have been identified in the biological realm.
- ADAPTIONS
- Species are comprised of specialized features that perform one or more specialized functions
- adaptions.
- Adaptions function together, but are not perfect mechanisms specially designed to allow each
species to function optimally.
- The evolutionary feature is often constrained by the structure of the ancestor.
- POPULATION DISTRIBUTIONS
- Continuous or discontinuous species distributions
- Each discontinuous or isolated population interbreeds within its own gene pool (the
complement of genetic material held by the entire population).
- MODES OF SPECIATION I
- Reproductive barriers may prevent interbreeding (mating behavior, incompatibility, failure of
offspring to develop [abortive embryos])
- New species may form when members of once isolated populations interbreed upon contact.
- New Species May Form When Members of Once Isolated Populations Interbreed upon Contact
- Helianthus annuus -Sunflower
- Original population of H. annuus isolated in Mts. Of New Mexico and Arizona
- Confined to mud plains at high elevations.
- Small flowers and short stature.
- Helianthus petiolaris occurs naturally on the Great Plains, not exceeding 1 meter in height.
- Early 18th Century "Transplantation"
- Pioneers recognized economic use of plants and brought seeds of these (and other
Helianthus) species back to St. Louis.
- Hybridization of Discrete Populations
- H. annuus interbred with H. petiolaris resulting in fertile progeny
- F1 backcrossed (introgressive hybridization) resulting in the mutational Great Plains H.
annuus and the "camp-follower race."
- Wheat (Triticum) is a plant that is polyploid -that is it has more than the diploid number of
chromosomes. 30 species are recognized.
- Speciation by Generic Interbreeding
- Diploid (2n=14) species are known as the primitive "einkorn" that is a wild and cultivated
plant in the Mediterranean.
- Tetraploid species (2n=28) are also known in the wild and have been cultivated. These
plants are known as "emmers" used in macaroni.
- Tetraploidy is the result of hybridization with the grass Aegilops.
- Hexaploid species (2n=42) species are only known through cultivation. . These plants are
known as the "bread wheats" with an origination in Europe.
- Charles Darwin & Alfred Wallace
- Recognized change in biological populations.
- Both believed mechanism paralleled breeder selection.
- Darwinian Natural Selection
- Success due to survival of the individual and ability of individual to produce viable and
prolific numbers of offspring.
- Proposed that the progression of species occurred over a prolonged period of time, gradually.
- Concept termed Phyletic Gradualism.
- There is some evidence in the fossil record for gradual change in lineages particularly
of unicelled plankton.
- Punctuated Equilibrium
- Recognized the fossil record depicts the appearance of new groups suddenly in strata where
there is no evidence of any imperfection in the geologic record.
- New species originate instantaneously (in the geologic sense) at the periphery of the
population
- Species remain unaltered for millions of years.
- Rates of Evolution and Extinction
- Rapid expanses in species
- Ancestral adaptive condition radiates to new adaptive conditions in descendents
- New species functionally related to new ways of life.
- May be preceded by adaptive breakthroughs - appearance of a key feature along with
ecologic opportunities allow radiation to occur.
- Evolutionary Patterns
- Divergent - marsupial mammals show wide divergence
- Compare an Australian echidna, the thylacine ("marsupial wolf"), the koala, and
kangaroo
- Convergent - marsupials and placental mammals
- Compare echidna and porcupines; thylacines and true wolves; the koala and true bears
- Iterative - the development of a similar feature more than one time in the history of a group
-cephalopods
- EXTINCTION IS FOREVER
GE142