Download 15-3 Darwin presents his case

15-3 DARWIN PRESENTS HIS CASE
PUBLICATION OF “ON THE ORIGIN OF THE
SPECIES”
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1859 ( 28 years after
the Beagle)
Darwin proposes a
mechanism to explain
the complexity of life.
Theory: evolution has
been going on for
millions of years, and
continues today.
INHERITED VARIATION
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Members of every
species vary from
one another.
This variation is
important .
With domesticated
plants & animals,
people have
artificially selected
desired traits.
NATURAL SELECTION
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In nature, there is
a struggle for
existence.
Those that are the
best suited to their
environment will
survive and
reproduce.
Darwin called this
ability fitness.
SURVIVAL OF THE FITTEST
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Polar bear and walking stick
Every generation, there
will be some individuals
that succeed better than
others.
They will live to
reproduce, their traits
going to their offspring.
The less fit will die, or
have fewer young.
EVOLUTION
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Over time, natural
selection results in
changes in the inherited
characteristics of a
population.
The changes increase a
species’ fitness in their
environment.
Evolution of the horse
DESCENT WITH
MODIFICATION
Each species alive
today descended, with
changes, from other
species.
• All species, living and
extinct, were derived
from common
ancestors.
• A single “tree of life”
links us all together.
•
EVIDENCE: FOSSIL RECORD
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Fossils show that life
has changed during
earth’s history.
Some species die
out, others change
and continue on.
Fossil dinosaur, bat, early human
HOMOLOGOUS BODY STRUCTURES
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Structures that develop from the same embryonic tissues, with different
mature forms.
All animals with backbones have similar body plans.
The forelegs of birds, reptiles & mammals all have similar bones.
The bones of birds closely resemble those of reptiles, where the bones of a
bat’s wing resemble a mammalian pattern
Vestigial organs
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Some organs in animals
are greatly reduced in
size- leaving only a trace,
of the former structure.
Examples: vestigial legs
on skinks, vestigial pelvis
in a humpback whale,
human appendix.
Embryos of species with a backbone are also very similar: cells develop in
the same order, making similar tissues and organs in a wide variety of
animals.
SUMMARY OF DARWIN’S THEORY
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Inherited variation: all species have individuals that
are slightly different from each other
Over reproduction: species produce excess offspring
Struggle for existence: there is competition to survive
Natural selection: the weak will die off
Survival of the fittest: the members best adapted to
their environment will live to reproduce, and their
traits will be passed on to their offspring.
Satirical drawing of Darwin printed after publication of
“On the Origin of Species”