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
1. Evolution: Organisms change
through time.
2. Descent with Modification:
Evolution spreads through the
branching of common descent.
Sexual reproduction guarantees
offspring are unique from parents &
siblings.
3. Gradualism: Change is slow, but
given enough time, small changes
accumulate forming new species.
4. Multiplication: Evolution not only
produces new species, it produces
an increasing number of new
species.
5. Natural Selection: Evolutionary
change is not random; it follows a
selective process operating under 5
rules:
a. Populations increase
indefinitely in a geometric ratio:
2, 4, 8, 16, 32, 64, 128, 256…
b. In a natural environment
population numbers must
stabilize due to limiting factors.
c. There must be a “struggle for
existence” as members of a
population compete for
resources.
d. There is variation in every
species.
e. Those individuals with
variations best adapted for
survival leave behind more
offspring than those less well
adapted – this is differential
reproductive success.