Download 15-3 - Kleins

15-3
Darwin Presents His Case
Darwin’s Return
Upon Darwin’s
return to England in
1836, he began to
take a close look at
the specimens he
brought back with
him
It was at this time he
noted that the the
species on the
Galapagos were like
none other
Darwin’s Return
Darwin did not
publish his findings
right away.
This was due mainly
because the ideas
he presented
radically changed
current scientific
thought
His work was not
published until 1859
Origin of Species
In his work, “Origin
of Species”, Darwin
proposed a
mechanism for
evolution that he
called natural
selection
He then presented
evidence that
suggests that the
process of evolution
has been taking
place for millions of
Natural Variation and Artificial
Selection
Darwin began his
explanation by
disregarding the idea
that a species is
perfect and
unchanging.
He argued that natural
variation, the
differences among
individuals of a
species, was found in
all organisms
Natural Variation and Artificial
Selection
Darwin stated that this
variation can be seen
in all forms of life.
He also stated that
variation can be
inherited
During Darwin’s time, it
was revolutionary to
suggest that variation
was a major feature of
life.
Natural Variation and Artificial
Selection
Darwin also noted how
human beings already
note that variation
exists and how we use
it to our advantage
He did this by looking
at English farmers
Farmers select only the
fastest horses, fattest
hogs, and high milk
producing cows
Natural Variation and Artificial
Selection
This idea of selectively
breeding an animal or
crop based on their
variation to improve the
outcome Darwin
termed, artificial
selection
In artificial selection,
nature provides the
variation and humans
select those variations
that they find useful
Evolution by Natural Selection
Darwin was convinced
that a process similar
to artificial selection
occurs in nature.
In order to explain this
he went back to
Malthus’ observations
on population growth
Evolution by Natural Selection
This lead Darwin to
realize that high birth
rates and a shortage of
life’s basic needs
would eventually force
organisms into a
competition for
resources
He called this the
struggle for existence
Survival of the Fittest
A key factor in the
struggle for existence
is how well suited an
organism is to its
environment
This ability of an
individual to survive
and reproduce in its
environment Darwin
called fitness
Survival of the Fittest
Darwin also proposed
that fitness is a direct
result of adaptations
Adaptations are any
inherited characteristic
that increases an
organisms chance of
survival
What are some
examples of
adaptations?
Survival of the Fittest
This concept of fitness
was central to the
process of evolution by
natural selection,
which is the key idea
behind Darwin’s work
This means that
organisms with the
best adaptations, will
have the highest level
of fitness, and
therefore survive more
Survival of the Fittest
Because of its
similarity to artificial
selection, Darwin
referred to survival of
the fittest as a type of
natural selection
The key difference
being that with natural
selection, the
environment forces the
selection of traits not
humans
Descent with Modification
Along with survival of
the fittest darwin also
proposed the idea of
descent with
modification.
Darwin proposed that
over long periods,
natural selection
produces organisms
that have different
structures and occupy
different places.
Descent with Modification
The idea that
organisms descend
with modification also
introduces another of
Darwin’s theories
The idea is that all
organisms must be
related to one another
in some way, shape, or
form
This is the idea of
Evidence of Evolution
With his unified and
dynamic theory of life,
Darwin was finally able
to explain his
observations during his
voyage aboard the
Beagle
He presented these
observations as
evidence for the theory
of evolution
Evidence of Evolution
Darwin argued that
living things have been
evolving on Earth for
millions of years
Evidence for this
process could be found
in the fossil record, the
geographical
distribution of living
species, homologous
structures, and
similarities in
The fossil Record
By the time that Darwin published his book, fossils
were known to be evidence of once living organisms
Darwin was the first to combine the idea that these
organisms were developing over a period of time and
used rock layers to help support his theory
Geographic Distribution of
living species
Because Darwin
suggested that
environments gave rise
to different adaptations
he needed to explain
this with evidence
He noted his
observations on the
Galapagos where he
saw organisms with
different features being
found in different
Homologous Body Structures
Darwin studied living
species as well to help
support his theory
By doing so, he noted
that living organisms
that had backbones all
had similar structures
that made up their
limbs
Homologous Body Structures
These structures are
similar in the
embryonic form yet
different in the adult
form
Darwin stated that this
is because they
develop from the same
time of embryonic cells
This is what Darwin
calls homologous body
Homologous Body Structures
Darwin also noted that
not all homologous
structures served
important functions
These structures that
are homologous but
have no purpose
anymore for the
organism are called
vestigial organs
They are usually too