◦ Artificial Selection: Humans choose
individuals with certain traits for breeding
◦ After many generations of selection,
dramatic evolutionary changes can result
Dogs
English naturalist who proposed the theory of
Darwin sailed around the world on the HMS
On the Galapagos Islands Darwin found very
Different islands have different types of
Evolution is the gradual change in a population over time
Darwin was the first scientist to realize that
evolution can work by
natural
selection.◦ Natural Selection – Organisms with traits well suited to an environment are more likely to survive and
produce more offspring than organisms without these favorable traits
“Survival of the fittest”
Evolution by natural selection happens in
populations, not individuals. A single
organism cannot evolve. Populations evolve.
Populations evolve because there is
variation
Variation causes some organisms to be better
fit than others. These better fit organisms are more likely to survive and pass their
Adaptations
Fossil Record
Comparative Anatomy
Embryological Development
All organisms have adaptations which help
them survive in their particular environment
Adaptation: a structure or behavior that helps
Mimicry: a structural adaptation that
enables one species to resemble another species
◦ E.g. A harmless species might mimic a poisonous
Camouflage: a structural adaptation that
Many bacteria have evolved resistance to
antibiotics in the last 50 years
Fossil: Any trace of a dead organism
◦ Fossils show the evolution of species over the past millions of years
Homologous structures: Body structures on
different organisms that are
similar in
Analogous structures: Body structures on
different organisms that are
similar in
Analogous Wing Structures Moth (insect)
Pterodactyl (reptile)
Vestigial structure: body structure in an
organism that no longer serves its original purpose but was useful to an ancestor
Early in development, human embryos and
Nearly all organisms have DNA, ATP, and
many of the same proteins and enzymes
The DNA (genes) of closely related organisms
Mutations
Genetic Drift
Gene Flow
Gene pool: collectively, all of the alleles of the
population’s genes
Allelic frequency: the percentage of any
specific allele in the gene pool
Genes can enter and leave a population’s
gene pool for many reasons
Populations in which the gene pool is not
New genes can be added to the population by
errors in DNA copying called mutations
Very very rarely a mutation might come along
that improves an organism’s chance at survival or reproduction
These mutant genes will be passed along to
offspring and become more common in the gene pool over time
If the mutation offers a large advantage,
Genetic drift: when allelic frequencies are
changed by random events in a isolated population
Gene flow: the transport of genes by traveling
individuals
◦ When an individual leaves a population, its genes are lost from the gene pool
There are 3 basic types of natural selection
◦ Directional Selection
◦ Stabilizing Selection
Directional selection: favors one of the
extreme variations of a trait
◦ E.g. Male peacock tail feathers: Females favor larger tail feathers. Therefore males with larger feathers reproduced more often. Over many
Stabilizing selection: favors average
individuals in a population
Disruptive selection: favors individuals with
either extreme of a trait but intermediate individuals have a disadvantage
◦ E.g. Cuddlefish (a type of squid): Being large is an advantage because females prefer larger males. Being small is an advantage also. Small males
A certain population may become isolated
and evolve to fit new or different environmental conditions
The isolated population may change so much
that it can no longer mate with the original population
◦ Similar to the evolution of new languages
There are several reasons why similar
populations no longer breed, creating new species:
Geographic isolation: when a physical barrier
divides a population preventing them from mating
◦ E.g. Canyon, lava flow, continental drift
Ecological Isolation: populations occupy different
habitats and never encounter each other to mate
◦ E.g. Population of monkeys that lives on the ground
does not mate with tree dwelling monkeys
Temporal Isolation – Populations reproduce at
different times of the year
◦ E.g. Population of frogs that mate in March do not
North rim of Grand
Gradualism: idea that species originate through a
gradual change of adaptations (longer than 10,000 years)
◦ E.g. Fossil evidence shows that sea lilies evolved slowly
and steadily over time
Punctuated equilibrium: idea that species
originate in rapid bursts (10,000 years or less) with long periods of genetic equilibrium in
between
◦ Global ice age causes rapid adaptation of thick fur
Both gradualism and punctuated equilibrium are
Divergent evolution: species that once were
similar become increasingly different
Convergent evolution: distantly related
organisms evolve to become more similar
