EVOLUTION & EVOLUTIONARY THEORY

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 18^thCentury "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