EVOLUTION
A SCIENTIFIC THEORY
I. The History
Carl Linneaus (18th century)– The
father of taxonomy. Used binomial
nomenclature, came up with the
hierarchical classification theme, used
visible characteristics to classify plants
and animals.
Thomas Malthus (18th – 19th century):
Attempting to justify the conditions of the
poor by stating that poverty and starvation
were merely a consequence of
overpopulation.

http://www.pbs.org/wgbh/evolution/library/02/5/l_025_01.html
 Lamarck (18th – 19th century) – First to publish a
reasoned theory of evolution: A) the idea of use
and disuse B) inheritance of acquired
characteristics
 Lyell (19th century) – natural processes form
geological formations over a long period of time,
erosion and other forces that shape rocks are
very slow processes that take millions of years,
so the earth must be older than previously
believed.
 Wallace (19th – 20th century): theory of evolution
by natural selection.
Charles Darwin (19th century) – theory of
evolution by natural selection.
II. What is a scientific theory?
A widely accepted explanatory idea that is
broad in scope and supported by a large
body of evidence.
http://www.pbs.org/wgbh/evolution/library/11/2/e_s_1.html
III. Natural Selection
Natural Selection: The process in nature
by which, only the organisms best adapted
to their environment tend to survive and
transmit their genetic characteristics in
increasing numbers to succeeding
generations while those less adapted tend
to be eliminated. As a result the
POPULATION EVOLVES – or changes
over time.
The five aspects (steps) of natural
selection:
Variation – individuals exhibit variation in a
population, they have a unique set of traits.
Some of these traits improve their chances of
survival while others are less favorable.
Overproduction – populations produce too
many young, many must die.
Struggle for existence – food, water and other
resources are limited, organisms are compete
with one another for these resources.
Differential reproductive success – those
individuals that have the most favorable
characteristics in an environment, has higher
chance of reproduction.
Descent with modification – the varying
reproductive success result in a change in the
population – the more successful traits become
more common


http://www.pbs.org/wgbh/evolution/library/01/6/quicktime/l_016_08.html
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html
IV. Evidence of Evolution
 The fossil record – remains or traces of previously lived
organisms (shells, amber, prints, skeletal remains).
Mostly found in sedimentary rocks
 Their age can be determined by radiometric dating
http://www.pbs.org/wgbh/evolution/library/03/3/l_033_01.html
Comparative anatomy: homologous
structures – structures that have similar
origins but may look different from the
outside. Analogous structures -- may
look similar but have different origins
 Vestigial structures – structures that are not
used any more but were used by our ancestors
 Biogeography of animals and plants and
continental drifts (geographic distribution of
species) – organisms with similar origin tend to
live in the same area
http://www.ucmp.berkeley.edu/geology/anim1.html
-- so similar fossils from different continents
could be found
 Developmental biology – the embryos of related
species look similar during their early embryonal
development.
Artificial selection – humans select traits
of organisms for human benefits
(domestication)
Molecular comparisons:
Universal genetic code
Proteins and DNA (the closer related two
species are the more similar their DNA and
proteins are)
Molecular clocks
Biogeography – geographic distribution of
species.
V. The Mechanisms of Evolution
Natural selection – you already know this
one.
Mutations (small changes in the
nucleotide sequence of DNA) result in new
traits and increasing variation in the
population. One mutation alone usually
does not change the population, however,
beneficial mutations can cause some
change
Genetic drift – change in the allele
frequency in a population based on
chance
Founder effect – small group of organisms
move away from the main population and give
rise to a new population
Bottleneck effect – after a natural disaster, a
small group of organisms with different
characteristics survive
Gene flow – movement of organisms from
one population to another
Nonrandom mating – sexual selection,
selecting mates because of their visual traits.

http://www.youtube.com/watch?v=cEh-zclVo44
VI. Examples of Evolution
Industrial Melanism
Human birth weight
Heterozygous advantage
Darwin’s finches
Antibiotic and pesticide resistance
VII. Modern Evolutionary Theory
Several scientists improved on Darwin’s
theory and this improvement is still going on.
We know that POPULATIONS EVOLVE
NOT INDIVIDUALS
Today we explain the causes of evolution
with mutations, changes in DNA and sexual
reproduction.
Evolution is closely related to genetics.
http://www.pbs.org/wgbh/evolution/library/03/4/l_034_04.html
Today’s definition of evolution: Genetic
change in a population or species over
generations; all the changes that transform
life on Earth; these heritable changes
produced Earth’s diversity of organisms
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Just for fun: http://www.youtube.com/watch?v=T1_vnsdgxII