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Darwin and Evolution
“There is grandeur in this view of life, with
its several powers, having been originally
breathed into a few forms or into one; and
that, whilst this planet has gone cycling
on according to the fixed law of gravity,
from so simple a beginning endless forms
most beautiful and most wonderful have
been, and are being, evolved.”
-Charles Darwin, On The Origin of Species,
1859
Do NOW!
What happens when specific traits are
passed down through many generations?
Charles Darwin
• Born February 12, 1809
• Died on April 19, 1882
Darwin's Importance
• Darwin’s father decided his son
should study for the clergy at
Cambridge - a very respectable
profession in the early 1800's.
• Beetle collecting during his time at
Cambridge taught Darwin many
vital scientific skills, which included:
how to identify species, the proper
manner of cataloguing specimens,
methods of comparative anatomy,
and how to work efficiently in the
field.
Darwin's Importance
• 1831-1836 sailed on H.M.S. Beagle
- Originally the ship's geologist,
eventually also naturalist (studied
living things & environments)
What to do with his collections?
• Between 1836-1837, Darwin observed,
catalouged, and wrote papers about the
specimens that he collected while on his
trip. This time period is what lead him to the
idea of a “transmutation of species”.
• Transmutation of species was a term
used by Jean Baptiste Lamarck in 1809 for
his theory that described the altering of one
species into another.
Transmutation of Species
• 1837 around July
Darwin began his "B" Notebook in which he put down his
thoughts on the subject of transmutation. In this notebook
Darwin examined four general questions -- what was the evidence for species transmutation?
- how did species adapt to a changing environment?
- how were new species formed?
- how one could account for the similarities between
different species?
One of the highlights of the B Notebook was his analogy of a
branching tree to represent common descent of all species.
The struggle for survival…
• 1838 October
Darwin read a book by the famous economist,
Revd. Thomas Malthus, titled "Essay on the
Principle of Population." In this book Malthus put
forward the economic theory that as human
populations grow and resources become scarce
the weak die off in a struggle for existence.
Darwin theorized that the same kind of
relationship may exist in the wild. In other words,
what Malthus saw in economics, Darwin saw in
nature.
To publish or not to publish?
• 1842
Darwin made an outline of reasons not to published his
transmutation ideas [1] Fellow naturalists would never accept his ideas.
[2] animal breeders would find a huge treatise too boring
to read.
[3] the trouble making atheists would use it for their evil
agendas.
[4] the church would scorn him.
[5] he did not want to be labeled an atheist.
[6] he would betray his friends and family to whom he
owed so much.
• 1854 December
At last Darwin figured out how populations split
off into separate species. Using the industrial
revolution as a metaphor, he saw that
populations of animals, like industry, expand
and specialize to fit into niches with competition
acting as the driving force. He saw nature as
the ultimate "factory." However, Darwin
preferred not to make much of this metaphor
because it seemed to depend more on
economic principles rather than pure science.
• 1858 June 18
Darwin received a paper from Alfred Russel
Wallace, who was still at the Malay Archipelago.
The paper was titled: "On the Tendency of
Varieties to Depart Indefinitely from the Original
Type." Darwin was shocked! Wallace had come
up with a theory of natural selection that was
very similar to his own. The paper contained
concepts like "the struggle for existence," and
"the transmutation of species."
• 1859 November 2
While at Ilkley Spa Darwin received an early copy of
his book, "On the Origin of Species by means of
Natural Selection."
The title for "Origins" went through a few changes
while it was being written:
-- An Abstract of an Essay on the Origin of Species
and Varieties through Natural Selection.
-- On the Origin of Species and Varieties by means of
Natural Selection.
-- On the Origin of Species by means of Natural
Selection.
1860 January
The repercussions of Origin of Species were mixed.
Thomas Huxley and Joseph Hooker thought very
highly of it and soon became stronger allies with
Darwin. Huxley soon became a ruthless defender of
evolution, even going so far as to suggest that
mankind was a transmuted ape!
Richard Owen was outraged by the Origin. He saw the
ideas expressed in the book as being dangerous to
society. He also thought the book left too many
unanswered questions, and worst of all it leaned
natural science away from its respectable position as
an investigator of god's creation. Most readers,
however, simply did not understand how natural
selection worked. They could not see who or what
was doing the selecting. Many assumed god was the
selector.
Darwin wondered: Why were these
animals different? Why would they have
these obviously different characteristics if
they were similar organisms?
Differences in Similar Organisms
 Darwin observed similar organisms on
mainland South America and the
Galapagos Islands
Examples:
Cormorants: on the
mainland, these could fly,
but the species that lived
on the islands was flightless
Tortoises: each island had a species of giant tortoise,
but the shape of their shells varied on each island;
Darwin could identify which island the tortoises came
from just by looking at their shells.
Iguanas: on mainland they had small claws to
climb trees and ate cactus & flowers while
island iguanas could swim, had long claws to
grip rocks and ate seaweed
Adaptations
• These differences are called adaptations
• In order to survive in different places, the
original organism had to change
• This change was not a choice, but
through genetic diversity
Cormorants: no predators, everything they
needed was close to the ground,
therefore, they lost the ability to fly
Loss of flight is an
adaptation.
Darwin's Finches
Finches on different islands have different
beaks. Why????
Beak type depends on the
food available. Finches that
are adapted to eat the
available food on their island
will survive long enough to
reproduce. This will pass the
trait for the beak that is best
suited for survival in that
area.
Different Beaks
Natural Selection
the idea that animals
that are better
adapted for a
particular
environment will
survive, reproduce
and pass on these
desirable attributes
to the next
generation
Natural Selection
• overproduction- producing many
more offspring than will survive; crabs
& fish lay thousands of eggs, but only
a few will become adults. What
happens to the rest???
• competition- "fighting" for available
resources (food, shelter, mates).
Those that are not successful will die,
those that are will reproduce. Do you
see a pattern here? Why do
organisms want to survive???
Natural Selection
variation- differences among individuals in the
same species or group. Good variations help an
organism survive better and are kept through
reproduction. Bad variations that are not helpful
are lost, because those organisms do not
survive to reproduce and pass on the traits.
• Differential survival and reproduction Individuals with the most successful adaptations
to their environment are most likely to survive
and reproduce. Over generations the character
of a population changes as the frequency (how
often it is available) of a trait increases or
decreases.
Can you Spot the moths?
Adaptations work by mutations. If a mutation in an individual
helps it to survive, it will survive and reproduce, passing the
gene for the mutation on to its offspring.
Species have three “choices”:
Go extinct in that area.
Move to another area (emigrate).
Adapt to survive the stress.
Darwin wondered: So what is evolution
anyway? What evidence suggests this
process?
Evolution
• Many generations of
natural selection lead to
permanent changes in a
species. This is called
evolution and occurs
gradually over time.
• Different organisms
have different rates of
evolution, depending on
their life spans.
Evolution
All organisms evolve- insects, mammals,
bacteria, plants and fungi.
• The central ideas of evolution are that life has a
history—it has changed over time—and that
different species share common ancestors.
• evolutionary change and evolutionary
relationships are represented in “family trees,”
and affects biological classification.
Evolution is a theory- which is
an idea supported by a large
amount of evidence.
Darwin's observations are the
beginning of this evidence
Many others have added to
his work
Natural Selection
Evolution
New Species
Modes of Speciation
•
•
•
•
•
•
•
•
Ecological opportunity
Geographical Isolation (allopatry)
Founder Effect
Genetic Drift
Speciation by Hybridization
Intense Competition
Adaptive Radiation
Cospeciation
geographic isolation
when a group
of organisms is
separated from
the rest of its
species long
enough, it
gains new
adaptations for
survival
*** some characteristics will be similar, but
usually new adaptations will will make it
different enough to be considered a new
species
continental driftwhen an entire area is isolated, preventing
migration or movement of animals; specific &
unique features develop as a result
*** After Pangea,
organisms that started
out similar and
adapted to survive on
these "new
continents", forming
very specific species
on each
Example: Australia has
kangaroos, echidnas & goannas
Genetic Drift
• DNA sequence, genotype, & phenotype
• In the example to the right, these driftworms have a
single gene, the Color gene. The DNA sequence for
this gene is 9 base pairs long.
• There are five phenotypes for this gene -- pink, blue,
navy, green and yellow. Each phenotype has a
different genotype. The genotypes are different from
one another because their DNA sequences are
different. These different genotypes are referred to as
alleles.
The role of chance
• In real life, some individuals have more offspring than
others--purely by chance. The survival and
reproductions of organisms is subject to unpredictable
accidents. It doesn't matter how good your driftworm
genes are if you get squished by a shoe before
producing offspring.
•
•
•
•
An ant gets stepped on.
A rabbit gets swept up by a tornado.
An elephant drinks up a protozoa living in a puddle.
A plane crashes killing a Nobel Laureate.
• None of the above events has anything to do with the
dead organism's genotype or phenotype--these events
occurred purely by chance.
Fixation of an allele
• In a population model with genetic drift, alleles
will eventually become "fixed". When an allele
is fixed, all members of the population have that
allele. In the graphic below, note that the dark
blue allele fixed after 4 generations.
Key points:
Speciation is integral to the evolutionary process:
• Natural selection shapes most evolutionary
adaptive change nearly simultaneously in
genetically independent lineages as speciation
is triggered by extinction in “turnover” events.
• When physical environmental events that go “too
far too fast” start triggering regional, specieslevel extinction, then evolutionary change —
predominantly via speciation — occurs.
• In times of environmental normalcy, speciation
and species-wide evolutionary change are
comparatively rare.
How do we know all of this???
Fossil records of past creatures &
plants...we can examine them and
compare them to organisms living
today to look for similarities
Sloths- Darwin found fossil sloths in
South America, but they were MUCH
larger than the living specimens he
saw in the jungles
Sharks- aside from being smaller,
sharks haven't changed much in
the last 100 million years...we
know this from fossil evidence:)
Homologous structuresstructures that serve a similar purpose in
organisms that share ancestors
Examples:
Natural Selection
Evolution Now?
Ernst Mayr
• A species consists of a group of populations which replace
each other geographically or ecologically and of which the
neighboring ones intergrade or hybridize wherever they are
in contact or which are potentially capable of doing so (with
one or more of the populations) in those cases where
contact is prevented by geographical or ecological barriers
(MAYR 1940, p. 256).
Theodosius Dobzhansky
• He is also known for his study
of the fruit fly Drosophilia,
which showed a large degree
of genetic variation within a
population.
• "The clear-cut mutants of
Drosophila, with which so
much of the classical research
in genetics were done, are
almost without exception
inferior to wild-type flies in
viability, fertility, longevity."—
*Theodosius Dobzhansky,
Heredity and the Nature of
Man (1964), p. 126.
George Gaylord Simpson
In 1953 published a small volume, Evolution and Geography,
that climaxed a series of writings published over more than
a decade, all of which addressed the principles for
explaining the past distributions of land animals, especially
mammals of the Cenozoic Era, representing the last 65
million years of Earth history.
Leigh M. Van Valen proposed the Red Queen
hypothesis (1973) as an explanatory tangent to
the Law of Extinction. The Red Queen
hypothesis captures the idea that there is a
constant 'arms race' between co-evolving
species. Its name is a reference to the Red
Queen's race in Lewis Carroll's Alice Through
the Looking Glass, in which the chess board
moves such that Alice must continue running just
to stay in the same place.