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Evolution

Change over time
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Theory that modern organisms
descended from ancient organisms
due to how they have changed over a
long period of time

Charles Darwin is credited for this
theory
Types of Evolution

Microevolution – changes that occur
over a relatively short amount of time
 Ex: Peppered moth

Macroevolution – changes that occur
over a relatively long amount of time
 Ex: Galapagos finches

Megaevolution – theory that every
living organism has one common
ancestor
Peppered Moths
Charles Darwin

Traveled to various places around the
world (Galapagos Islands, Argentina,
Australia) and made observations
about the organisms and
environments (ecosystems) he saw
Galapagos Islands

Had different species of finches and
tortoises

The different species of finch evolved
from same ancestor
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The different species of tortoise
evolved from same ancestor
Galapagos Finches
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Group of finches traveled from mainland
(Equador) to Galapagos Islands
Ate mainly one food source
One food source not enough for all finches
and their offspring
Different finches adapted to various food
sources (insects, nuts, fruit, berries, nectar
from flowers, etc.) and migrated to different
islands to look for those food sources
Different species of finch have different sized
beaks due to the food sources they eat
Galapagos Tortoises
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Evolved similar to finches
Group of tortoises traveled from
mainland to islands
Group eventually separated and went to
different islands
New species of tortoises resulted from
the subgroups mating within their own
groups
Evidence – different species have
different shaped shells
Darwin’s Observations

Darwin noticed that although some of the
places that he visited had similar
environments (similar ecosystems) but
had different organisms (plants and
animals)
 Ex: Argentina and Australia
○ Similar ecosystems (grasslands)
○ Australia had kangaroos but no rabbits
○ Argentina had rabbits but no kangaroos

Although Argentina and Australia have
similar ecosystems, why are some
organisms in one place but not the other?
Darwin’s Evidence for Evolution

Fossil record
 fossils of ancient organisms resemble present
day organisms

Geographic distribution of living
organisms
 similar but unrelated organisms in similar
environments

Homologous structures
 Structure of a body part is similar in another
organism, but its function may be different

Similarities in development
 embryos of many animals are similar
 organisms have same embryonic tissues but
different mature forms
Homologous Structures
Similarities in Development
Human Embryo
Whale Embryo
Dog Embryo
Cat Embryo
Chimpanzee Embryo
Natural Selection

Fitness – ability of an organism to survive
and reproduce

Survival of the fittest – organisms that are
best adapted to their environment and will
have the best chance to survive and
reproduce
 Ex: a fast fox will have a better chance of
survival than a slow fox (fast fox should be able
to catch more prey than the slow fox)

Adaptations – inherited traits that increase
an organisms chance of survival
Genes and Variation
In genetic terms, evolution is any
change in gene (alleles) frequencies in a
population over time
 Populations have a gene pool

 Gene pool – all the genes (and their alleles)
in a population

Relative frequency – how often a gene
occurs in a population
 Ex: how often the gene for brown fur
appears in a population of mice
Genes and Variation Cont’d…

Main sources of genetic variation
 Mutations – change in DNA sequencing
 Gene shuffling – different combinations of
genes are produced during gamete (sex cell)
formation

Phenotypes for a trait determined by
how many genes control the trait
 Single gene trait – trait controlled by one
gene
 Polygenic trait – trait controlled by multiple
genes
Evolution as Genetic Change

Hardy-Weinberg Principle – allele
frequencies in a population stay the
same unless one or more factors
change the frequencies
 For evolution to occur, at least one of these
factors MUST NOT happen:
○ Random mating
○ Large population size
○ No migrations
○ No mutations
○ No natural selection
Speciation
Speciation – formation of a new species
 Populations must become
reproductively isolated from one
another for a new species to evolve

 forms of reproductive isolation
○ behavioral isolation – populations have different
reproductive behaviors
○ geographic isolation – geographic barriers
○ temporal isolation – populations reproduce at
different times
Speciation of the Galapagos
Finches

Speciation of Galapagos Finches
occurred by:
 Founding a new population
 Geographic isolation
 Changes in new population’s gene pool
 Reproductive isolation
 Ecological competition
Big, hard
seeds
seeds
seeds
seeds
cactus
flowers
cactus
flowers
seeds