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Vocabulary Chapter 15
• Artificial selection
• Natural selection
• Evolution
Artificial selection
 The process of directed breeding to
produce offspring with desired traits
also referred to as selective breeding
 Example: when humans develop
new breeds of dogs or new strains of
crop plants
Natural selection
 There is a competitive struggle for
existence in the natural world if some
competitors in this struggle are better
equipped for survival than others, then
those less equipped would die
 Occurs because there is variation,
heritability, overproduction, and
reproductive advantages
Evolution
 Cumulative changes in groups of
organisms (species) through
time
 Natural selection is a mechanism
of how this change occurs
Vocabulary Chapter 15
• Derived trait
• Ancestral trait
• Homologous structure
• Vestigial structure
• Analogous structure
Derived Traits
Newly evolved traits, that may
not appear in the fossils of
common ancestors
 When studying transitional fossils traits may be
classified in two major categories either derived traits
or ancestral traits
 Example: With Archaeopteryx fossils (possible ancestor
to modern birds with distinct dinosaur features) the
derived traits like feathers do not appear in the fossils
of common ancestors
Ancestral Traits
More primitive traits, that do
appear in the fossils of
common ancestors
 Example: In Archaeopteryx fossils the ancestral
traits may be the teeth and tails that do appear
in ancestral forms
Homologous Structures
 Anatomically similar structures
inherited from a common
ancestor
 May have different function
 Examples: The forelimbs of vertebrates show
homologous structures. The limbs are adapted for
different uses, but they all have similar bones.
Vestigial structures
 Structures that may no longer have a
function for that species and are reduced
in form
 May resemble functional structures in
other organisms
 Examples: Snake pelvis and human appendix
Analogous Structures
 Structures that can be used for the
same purpose and can be
superficially similar in construction
but are not inherited from a common
ancestor
 Example: Wings of an eagle and the wings of a beetle
have the same function (flight) but the wings are
constructed in different ways and from different material
Vocabulary Chapter 15
• Embryo
• Biogeography
• Fitness
• Camouflage
• Mimicry
Embryo
An early, pre-birth stage of an
organisms development
 Comparative embryology – vertebrate embryos
exhibit homologous structures during certain
phases of development but become totally different
structures in the adult forms
 Example: Vertebrate embryos have a tail and
pharyngeal pouches (in fish develop into gills, in
reptiles, birds, and mammals become part of the
ears, jaws and throats
Biogeography
 Study of the distribution of plants
and animals around the world
Fitness
 A measure of the relative contribution that
an individual trait makes to the next
generation
 Reproductive success
 Measured as the number of reproductively
viable offspring that an organism produces
in the next generation
Camouflage
 Morphological adaptation that allows
individuals of a species to blend in with
their environment
 Allows organisms to become almost
invisible to predators or prey, as a result
more of the camouflaged individuals
survive and reproduce
Mimicry
 Morphological adaptation where one
species evolves to resemble another
species
 Example: Mimicry can occur in a harmless
species that has evolved to resemble a harmful
species, such as the California kingsnake color
patterns mimicking those of the poisonous
western coral snake
Vocabulary Chapter 15
• Genetic drift
• Founder effect
• Bottleneck
Genetic Drift
 Change in allelic frequencies in a
population that results from chance
 A random circumstance causes a
certain genetic trait to become more
common or rarer over time
 Example: A man steps on a group of beetles, randomly
killing most of the green ones but leaving most of the
brown ones alive, resulting in fewer green beetles
being produced in the population
Founder Effect
 Occurs when a small sample of a population
settles in a location separated from the rest of
the population
 Alleles that were uncommon in the original
population might be common in the new
population and the offspring in the new
population will carry those alleles
 Example: Amish seldom marry outside of their immediate
community, in the Old Order Amish community there is a
high frequency of six-finger dwarfism, affected individuals
can trace their ancestry back to one of the founders of
the Order
Bottleneck
 Occurs when a population declines to a
very low number and then rebounds
 Results in decreased genetic variation
 Example: Northern elephant seals where hunted by
humans almost to extinction leaving only 20 individuals left
in the late 1890’s, since there population has rebounded to
over 30,000 but the reduced genetic variation in the
population is apparent