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Ch. 15
 The modern theory of evolution is a fundamental
concept in biology. This is the one, unifying concept of
biology that allows us to make sense of the natural,
biological world.
 Took a job as a naturalist on the English ship, HMS
Beagle, which sailed to S. America on a scientific trek.
 The biological specimens (animals) that he studied in
the Galapagos Islands were specifically interesting to
Darwin. These animals were distinctly their own
species but were similar to species found elsewhere,
which led Darwin to believe that organisms could
change over time.
 He spent the next 22 years studying how animals
could change over time.
 Darwin used an idea proposed by Thomas Malthus
about human population growth to explain that
through competition and limited resources, only some
are able to survive to reproduce.
 Darwin experimented with breeding pigeons and
discovered that different populations had
different traits and that these traits are passed
down to future generations.
 Breeding organisms with specific traits in order to produce
offspring with identical traits is known as artificial
 Darwin believed there was a force in nature that was
similar to this.
 Natural Selection is the mechanism by which
traits within a population change over time.
Natural Selection
 Though another naturalist, Alfred Russell Wallace,
was working on similar work and added to Darwin’s
work, Charles Darwin was the first to publish his book
on the subject, On the Origin of Species by Natural
Selection in 1859.
 Difficulties
 Because evolution is a slow and gradual process, it is difficult for
humans to directly observe.
 Due to the immensity of time in relation to the rather short span
of human life, it is hard to comprehend the time it involves.
 It can sometimes be considered contradictory to personal
religious beliefs.
 Adaptation
 Definition: any variation that aids an organism’s chance of
survival in its environment.
 Evolution explains how they develop in the 1st place.
 Develop over many generations.
 Mimicry
 Definition: structural adaptation that enables one species
to resemble another.
 ex: yellow jacket wasps and syrphid flies
 Camouflage
 Definition: adaptation that allows an organism to blend
into its surroundings
 ex: leaf frog
 Resistance
 Bacteria develop resistance to antibiotics.
 Insects and plants develop resistance to pesticides.
 Is direct evidence of evolution.
 The shorter the lifespan of an organism, the faster
adaptations can occur. (ex: bacteria)
 Fossils
 Provide a record of early life and evolutionary history.
 Like a puzzle, even with missing pieces we can envision the overall
 Anatomy
 Homologous Structures
 Structural features with a common evolutionary origin.
 the ex: forelimbs of whales and crocodiles
 Shows evidence of a common ancestor, which shared the same
 Always similar in arrangement and sometimes in function.
 Analogous Structures
 Structural features that have evolved independently of each other.
 ex: wings of a butterfly and wings of a bat
 Have similar function but not arrangement.
 Vestigial Structures
 Structural features that have no function in the present-day
organism but that was useful to its evolutionary ancestors.
 ex: eyes of moles / cave fish or pelvic girdles in pythons
 Embryology
 Similarities in early embryos suggest evolution from a
common ancestor
 Biochemistry
 The sequences of RNA or DNA can be compared between
 The closer in sequence a gene is, the more closely related
the organisms are to each other.
Homology vs. Analogy
Jellyfish Fossils
Vestigial Structures