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6.2 Charles Darwin & His Theory of
Natural Selection
Image from: Biology by Miller and Levine; Prentice Hall Publishing©2006
Slide by Kim Foglia@ http://www.explorebiology.com/
Who Was Charles Darwin?
In 1831, 22-year old Charles Darwin left England as
naturalist aboard the HMS Beagle for 5 year voyage
around the world.
Mission: Chart the South American coastline
Darwin noticed plants
and animals were different
from those he knew in Europe
Wrote thousands of pages
of observations and
collected vast number of
specimens
http://www.solarnavigator.net/history/explorers_history/HMS_Beagle.jpg
Who Was Charles Darwin?
Darwin spent a month observing life on the Galapagos
Islands
Each island has different rainfall
and vegetation and its own unique
assortment of plant and animal
species.
Biology by Miller and Levine; Prentice Hall Publishing©2006
http://mikebaird.com/ecuador/images/galapagos_off_ecuador_ng_map.jpg
Who Was Charles Darwin?
Although animals on Galapagos
resemble species on the
South American mainland,
many species were found no
where else in the world = ENDEMIC
http://www.darwinadventure.com/pictures/galapagos_giantortoise.jpg
http://www.destination360.com/south-america/ecuador/galapagos-animals.php
http://www.photoseek.com/galapago.html
DARWIN’S
FINCHES
Darwin collected 14 species of finches and
hypothesized that the Galapagos had be
colonized by organisms from the mainland that
had then diversified on the various
Who Was Charles Darwin?
After Darwin returned to England in 1836, he spent
years examining specimens he brought back from
voyage and filling notebooks with his ideas.
He did not rush to publish his ideas because they
disagreed with the fundamental scientific views of his
day.
In 1844 he wrote an essay describing his ideas and
asked his wife to publish it if he died.
http://www.elsie.brandeis.edu/images/journals.gif
In 1858 Alfred Russel Wallace, another
Naturalist working in the West Indies,
wrote an essay describing his work that
summarized the same ideas Darwin had
been thinking about for 25 years!
http://www.thesecondevolution.com/wallace&darwin.jpg
Suddenly Darwin had incentive to publish
the results of his work!
In 1859
On the Origin of Species
by Means of Natural Selection
presented evidence
and proposed a
mechanism for evolution
that he called
NATURAL SELECTION
http://www.loc.gov/exhibits/world/images/s125.jpg
Darwin’s Theory of Evolution
Darwin Presents his Case
Image from: Biology by Miller and Levine; Prentice Hall Publishing©2006
Isn’t evolution “just a theory”?
In every day usage “theory” often refers to a
hunch or a speculation. When people say, “I
have a theory about what happened,” they are
often drawing a conclusion based on fragmentary
or inconclusive evidence.
The formal scientific definition of “theory” is
quite different from the every day meaning.
It refers to a comprehensive explanation of
some aspect of nature that is supported by a
vast body of evidence.
http://evolution.berkeley.edu/evosite/evohome.htm
Isn’t evolution just a theory?
In Science a theory is a well
supported, testable explanation of
phenomena that have occurred in the
natural world.
Example:
Cell theory
Atomic theory
Gravitational theory
http://www.avgoe.de/StarChild/DOCS/STARCH00/questions/apple_falling.gif
http://sixthsense.osfc.ac.uk/chemistry/atomic_structure2/atom.gif
VOCAB
ADAPTATION- Any inherited characteristic
that increases an organism’s chance of
survival
http://www.wildlife-traps.com/skunks.html
http://www.atomtigerzoo.com/photos/images/20060421233733_duckfeet.jpg
http://www.3kitty.org/travelrama/Photos/123-21-4x6.jpg
WHAT IS DARWIN’S THEORY?
OVERPRODUCTION of OFFSPRING
Capacity to over-reproduce seems
characteristic of all species.
http://www.biospheres.com/photogallery2ag/images/ladybugs_jpg.jpg
http://atthecreation.com/DEER/too.many.deer.jpg
WHAT IS DARWIN’S THEORY?
STRUGGLE FOR EXISTANCE means
that members of each species must
compete for food, space, and
other resources.
http://www.wasatchcomputers.net/gallery/elk_fight.jpg
WHAT IS DARWIN’S THEORY?
GENETIC VARIATION is found
naturally in all populations
Image from www.biologyzone.com
http://www3.nationalgeographic.com/animals/images/primary/zebra-herd.jpg
WHAT IS DARWIN’S THEORY?
Some organisms in a population are
less likely to survive.
http://www.cartoonstock.com/newscartoons/cartoonists/rrs/lowres/rrsn69l.jpg
VOCAB
Ability of an individual to survive and
reproduce in its specific environment
= FITNESS
http://www.cartoonstock.com/newscartoons/cartoonists/cga/lowres/cgan170l.jpg
WHAT IS DARWIN’S THEORY?
SURVIVAL OF THE FITTEST =
Organisms which are better adapted
to their environment tend to produce
more offspring than organisms without
those traits.
Competition for limited resources
results in differential survival.
WHAT IS DARWIN’S THEORY?
Over time,
NATURAL SELECTION
results in changes in the
inherited characteristics of a
population.
These changes increase a
species’ fitness in its environment.
How Does Evolution Really Work?
IMPORTANT TO REMEMBER !
•POPULATIONS evolve
NOT INDIVIDUALS.
•NATURAL SELECTION only
works on heritable traits.
•A trait that is favorable in one
environment may be useless or
detrimental in another.
WHAT IS DARWIN’S THEORY?
DESCENT WITH MODIFICATION
suggests that each species has
descended with changes
from other species over time.
This idea suggests that all living
species are related to each other
and that all species, living and extinct,
share a common ancestor.