Download Mechanisms of Evolution - Ms. Dawkins

The Voyage of the H.M.S. Beagle
•In 1831, Charles Darwin set
sail from England aboard the
H.M.S. Beagle on a voyage
around the world.
•Darwin collected numerous
plant and animal specimens for
his collection.
•He studied the specimens,
read the latest scientific
publications, and recorded his
observations/thoughts in
notebooks.
Darwin and the Galapagos Islands
•Darwin observed that the
Galápagos Islands were in
close proximity, but had very
different climates and
corresponding differences in
vegetation.
•Accordingly, he observed
that the characteristics of
many animals and plants
varied noticeably among the
different islands.
Darwin’s
Contribution to
Science
•Darwin’s evidence led him to
propose a revolutionary hypothesis
pertaining to the way life changes
over time.
•This hypothesis has become the
theory of evolution. It was
presented in his book, On the
Origin of Species, published in
1859.
Darwin’s Case: Key Idea #1
Variation Within Species
• Members within a
species vary from one
another in important
ways.
• At the time, variations
were thought to be
unimportant, minor
defects.
• Darwin argued that this
variation is significant.
Darwin’s Case: Key Idea #1
Variation Within Species
Darwin’s Case: Key Idea #2
The Struggle For Existence
•Darwin realized that high
birth rates and a shortage of
life's basic resources (food,
water, and shelter) inevitably
force organisms to compete
for resources.
•Competition, both within and
among species exists in almost
all natural environments.
•This struggle is ultimately
reflected by reproductive
success
Darwin’s Case: Key Idea #2
The Struggle For Existence
Darwin’s Case: Key Idea #3
The Inheritance of Traits
► Characteristics
exhibited by one
parent, whether beneficial or
harmful, are passed down from
one generation to the next
(assuming that organism is able
to reproduce).
Genetics presents a
mechanism for heredity.
► Modern
Darwin’s Case: Key Idea #3
The Inheritance of Traits
Darwin’s Influences: Thomas Mathus
Mathus’ An Essay on the Principle of
Population emphasized that population
growth will always overwhelm growth in food,
creating inevitable states of hunger, disease,
and competition. This perpetual struggle for
survival caught Darwin’s attention, and he
applied it to biology.
Darwin argued that some of the competitors
in Malthus' perpetual struggle scenario would
be better equipped to survive. Those that
were less able would die out, leaving only
those with the more desirable traits.
Darwin’s Influences: Charles Lyell
►
The world’s most renowned
geologist of the day and
author of author of
Principles of Geology,
prompted Darwin to think
of evolution as a slow
process in which small
changes gradually
accumulate over immense
spans of time…
Darwin’s Influences:
Jean-Babtiste Lamark
►
Lamarck's proposed the first truly cohesive
theory of evolution, in which all organisms
had an innate tendency toward perfection.
►
He correctly argued that species change
over time, and that environmental forces
adapted them to local environments.
►
Lamarck is widely remembered for his
inaccurate theory of inheritance of
acquired characteristics in which the use
and disuse of physiologic features
differentiated organisms over time.
What Darwin Couldn’t Know….
► Although
Darwin had no way of knowing, there is
a genetic mechanism for phenotypic change in
species over time.
Sweet!
►
Can you guess what this is?
Putting it all Together…
Survival of the Fittest
•The ability of an organism to
survive and reproduce in its
specific environment is fitness.
•Darwin proposed that fitness is
the result of adaptations.
•An adaptation is any inherited
characteristic that increases an
organism's chance of survival.
Survival of the Fittest
•Beneficial adaptations better
suit organisms to their
environment, and in turn,
they’re better able to survive
and reproduce.
•Individuals with characteristics
that are not well suited to their
environment either die or leave
few offspring.
(cont.)
Natural Selection:
Decent with Modification
•Natural selection yields
organisms that display different
structures, establish different
niches, and/or occupy different
habitats.
•Every living species has
descended, with changes, from
other species over time.
•Darwin referred to this
principle as descent with
modification.
Natural Selection in Action
•Darwin wondered if animals
living on different islands had
once been members of the same
species.
•These separate species would
have evolved from an original
South American ancestor species.
•His observations of finches,
tortoises, iguanas, and other
animals supported his
hypothesis.
Galapagos Tortoises
Natural Selection in Action:
Industrial Melanism and the Peppered Moth
► Coal
burning during the
industrial revolution
caused the trees in
nearby forests to turn
dark with soot.
► Within
a short time
period, the peppered
moth responded…
► Explain…
3 Key Misconceptions about
Darwin’s Theory
“Child
Please!”
“survival of the fittest means only
the strongest and fastest
survive”…
►
►
Why is this statement false?
How can you change it to make it
accurate?
3 Key Misconceptions about
Darwin’s Theory
“Say
What?”
“Natural selection is
random”…
►
►
Why is this statement false?
How can you change it to make it
accurate?
3 Key Misconceptions about
Darwin’s Theory
“Oh No
you
didn’t”
“Organisms can
evolve over their
lifetimes”…
►
►
Why is this statement false?
How can you change it to make it
accurate?