Download Darwin and Evolution - Appoquinimink High School

“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
Darwin and Evolution
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)
The struggle for survival…
• 1838 October
Darwin read a book by the famous economist,
Revd.
• Thomas Malthus, titled "Essay on the Principle
of Population."
– the economic theory that as human populations grow
and resources become scarce the weak die off in a
struggle for existence.
– 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
• 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.“
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. 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.
Warm UP: 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.
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
Darwin was not the first
naturalist to think of
evolution…
Jean-Baptiste Lamarck
• Change through use and disuse
– When environments changed, organisms had
to change their behavior to survive. If they
began to use an organ more than they had in
the past, it would increase in its lifetime.
Meanwhile organs that organisms stopped
using would shrink.
• If a giraffe stretched its neck for leaves, for
example, a "nervous fluid" would flow into
its neck and make it longer. Its offspring
would inherit the longer neck, and
continued stretching would make it longer
still over several generations.
Natural Selection
• overproduction- producing
many more offspring than will
survive
Natural Selection
• competition- "fighting" for
available resources (food, shelter,
mates). Those that are not
successful will die, those that are
will reproduce.
Natural Selection
• variation- differences among
individuals in the same
species or group.
Natural Selection
• Differential survival and reproduction -
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.
• The central ideas of evolution
– that life has a history—it has changed over
time
– that different species share common
ancestors.
– are represented in “family trees,” and affects
biological classification.
The central ideas of evolution
• Fitness
– describes the ability to both survive and reproduce,
– is equal to the average contribution to the gene pool
of the next generation that is made by an average
individual of the specified genotype or phenotype.
Coevolution
• The term coevolution is used to describe
cases where two (or more) species
reciprocally affect each other’s evolution.
• Coevolution is likely to happen when different
species have close ecological interactions
with one another. These ecological
relationships include:
– Predator/prey and parasite/host Example:
– Competitive species
– Mutualistic species
Convergent evolution
• A kind of evolution wherein organisms
evolve structures that have similar
(analogous) structures or functions in spite
of their evolutionary ancestors being very
dissimilar or unrelated.
Example:
Divergent evolution
• The process of tracing back two or more
species to their common ancestor that
indicate how they have diversified and
diverged.
Example:
Adaptive radiation
• The diversification of several new species
from a recent ancestral source, each
adapted to utilize or occupy a vacant niche
Example:
WHAT TO DO:
• Complete the packet using your notes from today’s
information.
• Using the data table from Friday. Calculate the total
number of each color of “worm” collected. (I placed 23 of
each color outside). Create a bar graph of how many of
each were “captured”.
• Figure the percent of color “captured”.
• Which color had the highest percent of capture? Which
one the least? Why?
• How does this activity relate to natural selection and
evolution? Which color would begin to increase it’s
population size? Why?
WARM UP:
• What are the four types of evolution?
• What are the central ideas of evolution?
Evidence of Evolution: Fossils
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:)
Evidence for Evolution: Anatomy
Analogous Structures
• have the same
function, but not the
same structure.
• The bird wing and
insect wing are
analogous
structures.
Evidence for Evolution: Anatomy
Examples:
Homologous structuresstructures that share similar bone
arrangements and/or function in
organisms that share ancestors
Evidence for Evolution:
Anatomy
• Vestigial structure: a body structure in a
present-day organism that no longer serves
it’s original purpose, but was probably
useful to an ancestor
Evidence of Evolution:
Biochemistry
• Every organism has a
specific DNA sequence
• The more closely related
organisms are the more
similar their sequence is.
• For example a human’s
DNA sequence is more
similar to a chimp’s than
to a frog’s so we are
more closely related to
chimps than frogs.
Evidence for
Evolution:
Embryology
Phylogeny vs. Ontogeny
• Phylogeny: the connections between all
groups of organisms as understood by
ancestor/descendant relationships
• Ontogeny: a purely biological unfolding of
events involved in an organism changing
gradually from a simple to a more complex
level
Two major hypothesis on how
evolution takes place
• Gradualism: the slow
and constant change
of an organism
Two major hypothesis on how
evolution takes place
• Punctuated equilibrium:
species evolved rapidly,
then stayed the same
for longer periods of
time
Activity: Examining the Fossil
Record
• Follow the directions in the packet.
• Answer the analysis questions.
Natural Selection
Evolution
Warm Up!
Explain the diagram
above… what does it
mean?
New Species
Vocab
• Gene pool: all the alleles of the
population’s together are referred to as a
gene pool
• Allelic frequency: The percentage of any
specific allele in a population’s gene pool
Natural Selection Acts on
Variations within the gene pool
• The allelic frequencies in a population’s
gene pool will change over generations
due to the natural selection of variations.
• Three different types of Natural selection
that act on variation:
– Stabilizing
– Directional
– Disruptive
Stabilizing selection
• Natural selection that
favors average
individuals in the
population
Directional selection
• Occurs when natural
selection favors one of
the extreme variations
of a trait
Disruptive selection
• Individuals with either
extreme of a trait’s
variation are selected
for.
What is a species anyway?
• A species is often defined as a group
of individuals that actually or
potentially interbreed in nature.
Defining Speciation
• Speciation is a
lineage-splitting
event that
produces two or
more separate
species.
Speciation Example
• The scene: a population of wild fruit flies
minding its own business on several
bunches of rotting bananas, cheerfully
laying their eggs in the mushy fruit...
Disaster strikes:
• A hurricane washes the bananas and the
immature fruit flies they contain out to sea.
The banana bunch eventually washes up
on an island off the coast of the mainland.
and produce healthy offspring with the
mainland flies. These flies begin to live a
happy life on the island.
The populations diverge:
• Ecological conditions are slightly different
on the island, and the island population
evolves under different selective pressures
and experiences different random events
than the mainland population does.
So we meet again:
• When another storm reintroduces the
island flies to the mainland, they will not
readily mate with the mainland flies since
they’ve evolved different courtship
behaviors. The few that do mate with the
mainland flies, produce inviable eggs
because of other genetic differences
between the two populations.
Modes of Speciation
• Geographical Isolation (allopatry)
• Reduction of Gene Flow
• Genetic Drift
– Bottlenecking
– Founder effect
• Reproductive Isolation
Geographic Isolation
• Scientists think that geographic isolation is a common
way for the process of speciation to begin: rivers change
course, mountains rise, continents drift, organisms
migrate, and what was once a continuous population is
divided into two or more smaller populations.
• It doesn’t even need to be a physical barrier -it might just
be unfavorable habitat between the two populations that
keeps them from mating with one another.
Reduction of Gene Flow
• speciation might also happen in a population
with no specific extrinsic barrier to gene flow.
• a population extends over a broad geographic
range, and mating throughout the population is
not random
• Individuals in the far west would have zero
chance of mating with individuals in the far
eastern end of the range.
Genetic Drift
• In each generation, some individuals may, just
by chance, leave behind a few more
descendents than other individuals. The genes
of the next generation will be the genes of the
“lucky” individuals, not necessarily the healthier
or “better” individuals.
• However, this reduces the genetic variation of a
species.
Bottlenecks
• Population bottlenecks occur when a population’s size is
reduced for at least one generation. Because genetic
drift acts more quickly to reduce genetic variation in
small populations, undergoing a bottleneck can reduce a
population’s genetic variation by a lot, even if the
bottleneck doesn’t last for very many generations.
Founder effect
• A founder effect occurs when a new
colony is started by a few members of the
original population. This small population
size means that the colony may have:
– reduced genetic variation from the original
population.
– a non-random sample of the genes in the
original population.
Reproductive Isolation
Genetic Material Differs
Mating times differ
• Population increase in
size to a point where
their genetic material
begins to differ and
they can no longer
reproduce.
• One group of frogs
mates during the fall,
and another similar
species mates in the
spring. Fall and spring
species shall never
mate… or will they?
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.