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Evolution
in biology
Evolution is the change in characteristics of
populations of species over time.
Species – closely related organisms that can mate and reproduce
Population – a group of organisms of the same species that live in a
specific geographical area
Evolution is the product of two
opposing forces: processes that
introduce variation and processes that
make those variants become more
common or more rare.
Variation is produced by :
1) random mutations – errors in genetic
material (rarely advantageous)
2) gene flow- migration between
populations
3) recombination – an exchange of
genetic material during meiosis or
between species
Two mechanisms determine if variants
become more common or more rare in
a population:
1) natural selection
2) genetic drift- change in allele
frequency over generations because
alleles in offspring are a random
sampling of in the parent
genetic drift
CHARLES DARWIN is considered
to be the father of modern
evolution theory.
He proposed that individuals with favorable adaptations or
traits would survive and reproduce more successfully than
individuals without these favorable traits.
Also called “survival of
the fittest”, this
mechanism of evolution is
known as natural selection.
An example of a favorable
trait would be camouflage
or antibiotic resistance in
bacteria.
Darwin developed this theory
based on a huge amount of
data that he collected on the
HMS Beagle, a British ship on
which he served as a
naturalist from 1831-1836.
His voyage involved collecting
and identifying species from
Australia, Africa, South
America, and islands such as
the Galapagos.
http://evolution.berkeley.edu/evolibrary/home.php
http://evolution.berkeley.edu/evolibrary/home.php
www.darwinday.org/englishL/life/beagle.html
www.darwinday.org/englishL/life/beagle.ht
Used by permission of Darwin Day
Celebration (at DarwinDay.org), 2006
I have called this principle, by which
each slight variation, if useful, is preserved,
by the term Natural Selection.
—Charles Darwin from "The Origin of Species"
http://evolution.berkeley.edu/evolibrary/home.php
Life Sciences-HHMI Outreach. Copyright 2006 President and Fellows of Harvard College.
Evidence for Historical
Evolution
FOSSILS – evidence of
organisms that lived on Earth
in the past. Fossils show
change in species diversity
over geologic time. Fossils
are dated using carbon
radiometric dating up to
50,000-80,000 years. Other
isotopes are used for dating
older fossils.
Most fossils are found in
sedimentary rock. Where would
the oldest fossils be located?
STRUCTURAL ADAPTATIONS– these are adaptations
that allow an organism to survive in its
environment. (Ex: tooth structure in carnivores vs.
herbivores; beak shape in Darwin’s finches)
Mimicry–organism mimics or resembles a
harmful species.
Camouflage–organism blends with its environment.
ANATOMY COMPARISONS
1) Homologous structures – structures that are so
similar they may point to a common ancestor.
2) Analogous structures– structures that are similar
in function possibly due to similar environmental
pressures.
Biogeography
Gene distribution patterns across
geographical regions.
Example: Malaria is unable to grow
in sickled cells. The sickle cell trait
is more common in areas near the
equator where malaria-harboring
mosquitos are common.
BIOCHEMISTRY – all organisms on Earth share
the same genetic code. The more similar the
genetic sequence, the more closely the species
are related to each other.
Origin Theories
ARCHAEA
•Ancient prokaryotic
organisms
•Genetically more similar
to eukaryotes than to
bacteria
•Many live in extreme
environments and use
alternate energy sources
BACTERIA
•Prokaryotic organisms (no
nucleus)
•Most are helpful, but some can
be harmful to eukaryotes
•Examples: cyanobacteria, E.
coli, Lactobacillus
Endosymbiotic Theory
– This theory suggests
that the first eukaryotic
cells evolved as
prokaryotic cells began
to live together in
symbiotic relationships.