Download Evolution - WHS Biology

EVOLUTION NOTES
Evolution
o Change in gene frequency / species over time
o Unifying theory of biology based on scientific
observation
o Occurs in populations – not individuals.
Microevolution
Change in a population’s alleles over a period of
time (small scale) still the same species.
Macroevolution
Large changes recorded in the fossil record (large
scale) and gives rise to new species.
Associated Theories and Concepts:
Catastrophism – successive changes in species was
caused by major catastrophes
Gradualism – Evolution in slow gradual steps
Punctuated equilibrium – short periods of rapid species
formation followed by long periods of little evolution
Lemarck’s theory
o Organisms develop new organs or change their
structures to meet changes in their environment
(use it or lose it)
o Inheritance of acquired traits – traits acquired
during a lifetime could be passed on to next
generation
Darwin’s theory
o all species reproduce in excess of the numbers
that can survive
o all organisms compete for limited resources
o variations exist within a species
o environment selects for the more advantageous
variations
Needed for evolution to occur
1. Means of increasing Variation
 Mutations – changes in nucleotide
sequence of DNA
 Recombination – reshuffling of genetic
material during meiosis
 Gene flow – gene frequency changes due to
immigration from other populations
2. Means of decreasing variation
o Natural selection – organisms with more
advantageous traits (genes) will survive
more often to produce off-spring. Those
without those traits will be naturally selected
not to survive. This process drives
evolution.
o Genetic drift – random events cause change
in gene frequency (small Populations)
o Gene flow – gene frequency changes due to
emigration
Speciation:
When a group of one species is cut off from the
rest of the population and gene flow is stopped.
Each group is acted on by local selective
conditions.
Observations that led to, and support evolution
Fossils
Any preserved remnant or impression left by
organisms that lived in the past.
o Relative dating – superimposition of
sedimentary rocks tells the relative age of
fossils
o Absolute dating – dating using radioactive
isotopes (Potassium 40, Rubidium 87, Uranium
238, Carbon 14)
o Transitional forms – Archeoptryx and similar
bird-like reptiles. Absence of some forms can
also be used as an argument against evolution.
Homologous structures
Structures that share a common ancestry. Modified
versions of the same structure.
Vestigial structures
Remnants of an organism’s evolutionary past. The
structure serves no purpose at this time.
DNA comparison
Protein comparison