Evolution
Evolution Theories
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Jean Lamark- Proposed the first method for
explaining the change of organisms over time.
Lamark thought that organisms had a tendency
to move toward perfection
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Proposed the idea of in heritance of acquired
characteristics
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Ex. If a rat had its tail cut off that rat would produce
offspring without tails
Lamark
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Lamark also put forth was the theory of use and
disuse
-Under this idea Lamark Hypothesized
that organisms that used a certain body the
most it would grow.
Ex. Giraffes
Hutton and Lyell
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These scientists proposed that the earths geologic
structures were formed slowly over long periods of
time.
They proposed that the earth was several million years
old
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Lyell proposed that past geologic events such as the
formation of mountains must be able to be explained using
current observable processes
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Mountains formed by earthquakes, rivers, and glaciers
Geologists Currently estimate the earth to be 4.5- 5
billion years old
Malthus
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First to bring forth the idea of carrying capacity
Recognized that if any population continued to
grow unchecked that the community would run
out of resources required to survive
Scientific theories of evolution
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Darwin
HMS Beagle
 Collected data in the form of fossils and living
organisms
 Main place of collection were the Galapagos islands
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The different island had different environmental
conditions
Darwin and Wallace
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Charles Darwin and Alfred Wallace
independently came up with the revolutionary
idea that organisms change over time through a
mechanism of natural selection
Darwin published The Origin of Species in
which he proposed the mechanism for
evolution, which he called natural selection.
Descent with Modification
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Darwin proposed that as a result of Natural
selection the characteristics of organisms change
The structures of organisms change, they establish
different niches, and occupy different habitats
 Each living species has descended from another
living species over time
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Common Descent
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Darwin’s idea of descent with modification was
revolutionary because it implied that there
existed the principle of common descent
This countered the idea that all living species have
always existed on earth unchanged in their present
form
 This principle implied that all living and extinct
species were derived from a common ancestor
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Divergent Evolution
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Divergent evolution is the process in which a
population of interbreeding species accumulate
differences and become anew species
Natural Selection
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Darwin felt that all organisms were constantly
struggling to stay in existence and that only the
fittest would survive
He felt that fitness was the result of adaptation
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Adaptations are any inherited characteristic that
would make an organism better suited to survive in
their environment
Natural Selection Vs. Artificial
Selection
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Darwin recognized that the selection that occurs
in the wild is different than that which occurs in
domesticated areas.
Artificial selection occurs when there is a variation
that occurs in nature and humans select for that
variation
 Selective breeding is an example of artificial selection
 Can any body tell any possible current practices in
farming that could be considered artificial selection?
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Mechanisms for Natural
Selection
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1. Overpopulation
2. Variation
3. Selection
4. Adaptation
Evidence of Evolution
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Scientists use many different forms of evidence
to establish that evolution has occurred
Fossils
 Comparative anatomy
 DNA
 Embryology
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Fossils
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Provide physical evidence that can be seen for
millions of years
Shows how organisms change over long periods
time
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Gradualism- Evolution occurs slowly over long
periods of time
Comparative Anatomy
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By comparing the structures of different
organisms scientists are able to determine
possible relationships between different species.
Homologous structures-Structures that have
different mature forms, but develop the same way in
the embryo
 Analagous Structutes
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Homologous Structures
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From looking at the structure below scientists
believe that there is strong evidence that these
organisms have descended from a common
ancestor
Vestigial Organs
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These are organs that serve no useful
functions
These are useful for scientists studying
evolution because they provide traces of
where the organisms descended from
Ex. In humans the appendix is classified as a
vestigial organ
 Ex. Skinks are lizards that live in the water, but
have legs that have no useful purpose.
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Comparative Embryology
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Scientists compare the embryos of different
species to show that many different organisms
develop in similar ways
DNA
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The most recent way scientists have been
researching the descent of organisms is through
DNA
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Scientists often use mitochondrial DNA because it
has little impact on the survival of an organism
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Maternal lineage can be traced
Progression of Evolution
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Scientist have two theories on how evolution
progresses
Gradualism- Evolution occurs slowly and gradually
over long periods of time
 Punctuated equilibrium- Scientists use this term to
describe long stable periods interrupted by brief
periods of more rapid change.
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Variation in Gene Pools
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Gene pool- consists of all the genes including
the different alleles
Relative frequency- the number of times an
allele occurs in a gene pool
Selection
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These types of selection only occur in polygenic
traits
Directional
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Stabilizing
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Occurs on end or the other
Occurs at both ends
Disruptive
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Selects against the middle traits
Genetic Drift
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Genetic drift is the random change in allele
frequencies that occur in small population
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The expression of a few recessive traits could
dramatically affect the overall gene frequency
Founder effect
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This is the change in allele frequencies as a result of
the migration of a small group of organisms from a
population
Speciation
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Speciation is the formation of new species
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Caused by different isolation factors
Reproductive Isolation
 Behavioral Isolation
 Geographic
 Temporal
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Reproductive Isolation
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This is when two organisms of different
populations cannot interbreed and produce
fertile offspring
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At this point the organisms have separate gene pools
Behavioral Isolation
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This occurs when two populations of organisms
do not interbreed because they have different
courting rituals
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This is seen in birds through their different songs
Geographic Isolation
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Geographic isolation occurs when two populations are
separated by some type of geographic barrier such as a
lake, mountain, or a river.
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Geographic isolation does not guarantee the formation of a
new species. As long as the two populations can still
interbreed the still belong to the same species
Geographic barriers do not cause isolation for all organisms
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Birds can fly over rivers where rabbits cannot cross rivers
Temporal Isolation
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This occurs when two or more species
reproduce at different times
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Ex. Three different species of orchids release their
pollen a single day at different times during the year,
as a result they never have the opportunity to
fertilize each other.
Darwin’s finches
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Darwin observed at least
six species of finches
during his trip to the
Galapagos
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Each of these different
species had different
niches, which made their
individual characteristics
best fit for their different
environments
Adaptive Radiation
Speciation that
originates with a
single ancestor and
diverge into several
different species
Coevolution
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The change of one
species sparks the
evolution of another
species
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Flowers and bees
Grass and horses
Darwin’s Evolution Principles
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1) Overpopulation: Within a population more offspring
are produced than can possibly survive
2) Competition: Because there are more organisms
produced than can survive there is competition
between them for food, water, space and mates
3) Survival of the fittest: Variations among the
population make some individuals fitter than others!
Darwin’s Principles Continued
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4) Natural Selection: Those individuals best able to
survive due to certain traits pass those traits on to
their offspring
5) Reproduction: Those that survive and thrive live
long enough to reproduce
6) Speciation: The development of new species
occurs as variations or adaptations accumulate over
many generations
The modern theory of evolution uses Darwin’s
work and adds a few new ideas
Major Things to Remember
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Evolution Rates are dependent on
environmental change and reproductive rates.
Evolution does not happen on purposes in a
specified direct, but happens purely by chance.
The higher variation in a species the higher the
survival rate will be
Taxonomy
Taxonomy
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Scientists have a highly organized way of naming and
grouping similar organisms together
This is called taxonomy.
The system of classification created by Carolus
Linnaeus has seven different levels. From the largest to
smallest there is kingdom, phylum, class, order, family
genus, species.
- An easy way to remember the order is Kids Pick
Candy Over Fancy Green Salads
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Binomial nomenclature- This is a two word
naming system that utilizes the genus and
species of an organism. Ex. Humans are called
Homo sapiens because humans are classified under
the genus Homo and the species sapiens
Dichotomous key
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A dichotomous key is used to identify unfamiliar
organisms based on physical characteristics
These keys are step by step guides that lead you