Evolution - the progressive change in the characteristics of organisms over time.
Current evolutionary theory rests upon the theory of natural selection theory proposed by Darwin.
Natural Selection - those individuals that possess superior physical, behavioral, or other characteristics are more likely to survive than those that are not so well endowed.
These physical, behavioral, or other characteristics are determined by genome of the individual. Darwin recognized the heritability of these traits, but not the mechanisms of heritability.
Those which are most fit to survive to reproduction age will pass their genes on to future generations. Those which are not fit do not survive & therefore do not pass their genome on to future generations. This results in a refinement of characteristics to “fit” the environmental stresses upon an organism.
Environmental stresses may change over time, but so might the genome of a population.
Environmental
climate
topography
disease
predator/prey relationships
Genetic
mutation
changes in expression(mutation or inbreeding)
migrant infusion (hybridization)
The key to the ability to survive a change in the environment is the presence of the genes necessary for survival before or as the change occurs, not after. Organisms are not able to consciously alter their genome.
Given enough time, response of a population to changes in it’s genome leads to speciation, or the development of a new species from past & related populations.
Species - a group of organisms that look alike and are capable of producing fertile offspring in a natural environment.
If time enables the development of new species from existing populations, then it stands to reason that all present species must share a common ancestor.
Evolutionary evidence - organisms have changed over time, developing or altering characteristics in that time, therefore increasing in complexity.
Fossils
dating techniques
stratification
isotopes
nuclear resonance
Relatedness of organisms (extinct & extant)
homologous structures
vestigial structures
analogous structures
biochemistry
metabolic & structural compounds
genome similarity
molecular clock (mutation)
Embryonic development
ontogeny through phylogeny
Evolution of populations
Microevolution
changes within individuals or species
Macroevolution
Speciation
Five Tenets of Evolutionary Theory
Ernst Mayer
Evolution: Organisms change through time.
Descent with Modification: Evolution spreads through the branching of common descent. Sexual reproduction guarantees offspring are unique from parents & siblings.
Gradualism: Change is slow, but given enough time, small changes accumulate forming new species.
Multiplication: Evolution not only produces new species, it produces an increasing number of new species.
Natural Selection: Evolutionary change is not random; it follows a selective process operating under 5 rules:
Populations increase indefinitely in a geometric ratio: 2, 4, 8, 16, 32, 64, 128, 256…
In a natural environment population numbers must stabilize due to limiting factors.
There must be a “struggle for existence” as members of a population compete for resources.
There is variation in every species.
Those individuals with variations best adapted for survival leave behind more offspring than those less well adapted – this is differential reproductive success.
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