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Photo by “davemee” flickr
creative commons
"nothing in biology makes sense
except in the light of evolution”
~Theodosius Dobzhansky (19001975)
• In science, theories are
statements or models that
have been tested and
confirmed many times.
In science, the term "Theory" does
not express doubt.
• They explain a wide variety of data
and observations
• They can be used to make
• They are not absolute, can be
changed as new evidence is found
• Why do so many different animals
have the same structures, the arm
bones in a human are the same
bones as a flipper in a whale?
• Why is the sequence of DNA very similar
in some groups of organisms but not in
• Why do the embryos of animals look very
similar at an early stage?
Photo courtesy of Swamibu, Flickr Creative Commons
• Charles Darwin
developed the
• which explained how
organisms changed
over time (ADAPTED)
• Lamarke's Theory of
• Some thought that you
would gain or lose
features if you
overused or didn't use
Photo courtesy of ucumari, creative
commons, flickr
• Darwin was a naturalist (what we today call
• He traveled the world and made observations and
sketches of many species
• His most famous travels were aboard the H.M.S.
Beagle where he traveled to the Galapagos Islands
Marine Iguana, photo courtesy of mtchm, flickr
creative commons
Blue-footed booby, photo courtesy of stirwise,
flickr creative commons
Finch, photo courtesy of stirwise, flickr,
creative commons
Giant tortoise, photo courtesy of Planetgordon,
flickr creative commons
• Darwin noted that there
existed many finches on
the islands, but while they
had similarities, each was
adapted to eating a
particular type of island
• He concluded that the
finches all came from one
ancestral species and
evolved into many new
Cactus finch, photo courtesy of zrim,
flickr creative commons
• Darwin published
this work to explain
the variety of
species that exist on
the planet
• He proposed the
“Theory of Evolution
by Natural
1. Variation exists among individuals in a
2. Individuals will compete for resources (food,
mates, and space)
3. Competition would lead to the death of some
individuals while others would survive
4. Individuals that had advantageous variations
are more likely to survive and reproduce.
This process came to be
known as Natural Selection
The favorable variations are
called Adaptations
Photo courtesy of
digitalART2, flickr
creative commons
• Say in a species of blob….there exists
blobs of all shapes and sizes (variation)
Blobs eat the little purple organisms that live
underground and on the surface.
During a particularly hot year, food became less
abundant (competition), blobs that had the ability to
dig into the soil to get food had a better chance of
Many blobs died that year…….
The ones that survived mated and passed their genes
to the next generation. (reproduction)
The next generation had move blobs with the pointed
Fossil Evidence
• Shows numbers extinct animals
• Shows similarities between extinct animals and animals that are
alive today
• The earth’s layers show a time scale of species and when they
appeared on earth (and when they died out)
Dinosaurs have always fascinated us, movies such as
Jurassic Park capitalize on that fascination.
How do we know what dinosaurs
looked like?
We create a picture based on the
bones we find (fossils) and use
modern reptiles to guess at their
texture and skin color.
• Homologous structures – these are parts of the
body that are similar, but have different functions
ex. The flippers of
whales, and the wings
of birds
All forelimbs of
vertebrates have the
same pattern of bones
• Common ancestry
• Vestigial Organs – these are organs or parts that
seem to have no function
Whales have pelvic bones that do not attach to legs
• Biochemistry and DNA
When comparing the DNA of one species to another, more
similarities are found in species that are more closely
Lion photo credit: ucumari Tiger photo credit: digitalART2
Embryological Development
Embryos of different species develop in almost identical
Human fetus at 8 weeks
Direct observation of species change
• Bacteria become resistant to antibiotics
• Wolves were bred over many generations to
become dogs (artificial selection) • and then bred
further to create a variety of breeds