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CHAPTER 15 NOTES
EVOLUTION
EVOLUTION –
change over time
CHARLES DARWIN
Contributed more
to our
understanding of
evolution than
anyone
Journeyed around the world on the
HMS Beagle and made
observations and collected
evidence
Collected fossils (preserved
remains of ancient organisms)
The islands that influenced Darwin
the most were the Galapagos
Islands (a group of islands with
very different climates)
Darwin on HMS Beagle – A 5 year trip
Darwin’s Observations
Darwin was intrigued by the fact that so
many plants and animals seemed
remarkably well suited to whatever
environment they inhabited.
He was also puzzled by where different
species lived – and did not live.
He soon realized that living animals
represented just part of the puzzle posed
by the natural world.
The Galapagos Archipelago
Land Iguana
Marine Iguana
Darwin learned that the giant tortoises
varied in predictable ways from one
island to another.
The shape of a tortoise's shell could be
used to identify which island a particular
tortoise inhabited.
Darwin later admitted in his notes that he
“did not for some time pay sufficient
attention to this statement.”
One tortoise from an island with sparse
vegetation has a long neck and shell
that is curved to reach.
Another tortoise has a dome-shaped
shell and a shorter neck because
vegetation on this island is more
abundant and easier to reach.
Another tortoise has a shell that is
intermediate between these two forms.
Darwin Gathers More
Evidence
English animal breeders were
selectively breeding birds to get large,
colorful feathers for ladies hats.
This was a type of “artificial selection”
because the breeders were controlling
which traits were crossed.
Darwin wondered if some force in
nature also selected which
organisms would survive.
Results of Artificial Selection
Other Scientists that
influenced Darwin:
1. Hutton & Lyell
studied geological
change to show
that the Earth
changes over
long periods of
time
2. Malthus reasoned
that if the human
population continued
to grow unchecked,
sooner or later there
would be insufficient
living space and food
for everyone (war,
famine and disease
help keep this growth
in check)
3. Lamarck was
the first scientist
to recognize that
living things
change over time
Lamarck’s ideas:
1. Organisms constantly strive to improve
themselves (tendency toward perfection)
2. Most-used body structures develop, but
unused ones waste away (use and disuse)
3. Once a structure is modified by
use or disuse, the modification is
inherited by the organism’s offspring
(inheritance of acquired
characteristics)
A giraffe’s neck gets long because he
reaches. His offspring inherit the
long necks.
ALL OF THESE WERE PROVEN WRONG,
but Lamarck paved the way for the work
of later biologists.
Darwin’s Grand Idea
Darwin spent over 20 years gathering
facts that might have some bearing on
how species originated.
Putting all of his amassed data together,
Darwin developed his grand idea.
Darwin didn’t go public with his ideas
because the dominant philosophy of his
day placed the most value on gathering
facts, not on hypothesizing.
Darwin’s Dilemma
On June 18, 1858, Darwin received
a letter from a fellow scientist,
Alfred Russell Wallace.
In the letter was an abstract of a
theory of evolution that Wallace
was about to publish.
He was asking Darwin for a peer
review of his theory before
submitting it for publication.
Alfred Russell Wallace (18231913)
Darwin & Wallace
Wallace’s theory was exactly the
same as Darwin’s!
Darwin was ready to concede, but
mutual friends encouraged Darwin &
Wallace to allow their theory to be
jointly presented.
Thus, on July 1, 1858, their theory
was jointly presented to the
Linnaean Society of London.
Charles Robert Darwin in
1859
Darwin Gets Credit
Darwin is given primary credit for
the theory of evolution by natural
selection because: (1) he had
collected more evidence than
Wallace and (2) he had written, but
not published, a general outline and
an essay on evolution at an earlier
date (1844).
Although controversial, many
prominent scientists supported
Darwin & Wallace.
Darwin’s Book
The following year, 1859, Darwin
published his full theory with
evidence.
The title was: On The Origin of
Species by Means of Natural
Selection. All 1,250 copies of the
first printing were sold on the first
day!
“Survival of the Fittest”
In 1866, the English philosopher
Herbert Spencer, in an attempt to
explain what Darwin meant by the
struggle of organisms in nature,
coined the phrase “survival of the
fittest”.
The phrase is often attributed to
Darwin but it does not appear in any
of his writings.
Definitions:
 Variation – differences between
individual members of a population
(ex. Color of fur, shape of teeth)
 Adaptation – an inherited
characteristic that increases an
organism’s chance of survival
Darwin’s Theory of Natural
Selection:
1. There is
variation within a
population.
2. Some variations are favorable.
3. Not all young produced in each
generation can survive. (struggle for
existence)
4. Individuals that survive and
reproduce are those with favorable
variations (survival of the fittest)
5. All species have common ancestors.
(Descent with modification)
EVIDENCE OF EVOLUTION
According to evolutionary theory, all
life originated from a common
ancestor.
Common descent – the theory that all
species were derived from common
ancestors
WAYS TO DETERMINE HOW
RELATED ORGANISMS ARE:
1. Fossils
The fossil record reveals changes in
populations over time and supports the
theory of evolution.
Scientists can calculate a fossil’s age by
using radioactive dating or relative dating
(we will discuss this later)
The fossil record
is incomplete, but
it still shows us
relationships
between species
and how their
structures have
changed over
time.
Fossils are mostly
found in
sedimentary rock.
2. Homologous Structures
Homologous structures
– structures that have
different mature
forms, but develop
from the same tissues
Ex. Arms, wings,
and flippers are all
constructed from the
same basic bones
Homologous Structures
Flying
Swimming Running Grasping
3. Vestigial
structures –
structures
reduced in size
and often unused
Ex. Leg/hip bones
in pythons and
whales or
appendix in
humans
4.Embryology & Biochemistry
Embryology – compare how embryos
of different species look during
certain stages of development
Biochemistry – compares the
biochemicals that make up our body
(amino acid)
Comparison of Organisms
Two orders of mammals
Birds vs. mammals
Percent Substitutions
of Amino Acids in
Cytochrome c Residues
5 and 10
8-12
Amphibians vs. birds
14-18
Fish vs. land vertebrates
18-22
Insects vs. vertebrates
27-34
Algae vs. animals
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The Fact of Evolution
Darwinism is not “just a theory” as
many believe.
Darwin’s conclusion that species
change over time is a scientific,
proven fact.
The mechanism suggested by
Darwin for that change, natural
selection, is a theory.