Transcript Chapter 15 - Midway ISD

Chapter 15-16 Darwin and the
Theory of Evolution
15-1 Charles Darwin
Born 2/12/1809
• Sailed on the Beagle in 1831
• Travels- particularly to the Galapagos
Islands
Sailed around the world
Darwin’s Observations
• The plants and animals were well-suited to their
environment
• Certain species live in one environment, and not
another
• On Galapagos Islands –
– Finches had differentshaped beaks from
finches on the mainland
– Tortoises had differentshaped shells from
mainland tortoises
15.2
Ideas that shaped Darwin’s thinking
• James Hutton and Charles Lyell
– Recognized that the Earth is millions of years
old and still changing
• Thomas Malthus
– If the human population continues to grow
unchecked, then eventually there would not
be enough resources
• There was already a rich fossil record that
was challenging the traditional thinking
that all organisms exist as created.
Charles Lyell’s Principles of Geology showed
evidence of Earth’s extreme age.
This book led Darwin to wonder if life could
have changed very slowly over a long period
of time.
Jean-Baptiste Lamarck
• One of the first scientists to
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notice living things have
changed over time
Proposed that by selective use
or disuse of organs, organisms
acquired or lost certain traits
during their lifetimes
These traits could then be
passed on to their offspring
Do you agree with this theory?
Checkpoint!
• Where is Darwin most known for his research?
– A. Caribbean Islands
– B. Hawaiian Islands
C. Galapagos Islands
D. English Islands
• What did Darwin consider as a reason for the
different beaks on the island and mainland
finches?
– A. they had a common ancestor
– B. they were the same species with mutations
– C. they were not the same species
– D. they had no common relatives
15-3 Darwin Presents His Case
• observations on species led to his concept
of evolution
• In 1858 another scientist named Alfred
Wallace sent an essay summarizing his
thought on evolutionary change. This
spurred Darwin to go ahead and publish
his ideas.
• In 1859, Darwin published On the Origin
of Species
– In it, he proposed a mechanism for evolution
he called natural selection – (process of
change in species over time)
Natural Selection
• “Survival of the Fittest”
• Members of the same population compete for
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food, living space, and other necessities of life
The predators that are successful in getting food
and the prey that are successfully camouflaged
or better protected will survive and pass on their
DNA
Fitness – the ability of an individual to survive
and reproduce in its specific environment
Checkpoint!
• Whose idea stated that organisms changed
through generations by passing on acquired
characteristics?
– A. Malthus
– C. Lamarck
B. Lyell
D. Hutton
• What was the reason Darwin decided to publish?
– A. he died
– B. Wallace’s essay
– C. Malthus theory was right
– D. Hutton encouraged him
Adaptation
• Over time, natural selection results in
changes in the inherited characteristics of
a population
• These changes increase a species’ fitness
in its environment
• Adaptation – inherited characteristic that
can be physical or behavioral
• Artificial Selection
– Nature provides the variation, and humans
selected those variations that they found
useful
• This process has been used in choosing the best
domesticated animals and plants to increase food
production
Checkpoint!
• What is the term for the ability to survive and
reproduce?
– A. exercise
– C. cardio
B. fitness
D. fertility
• If a white moth and a black moth live in a
forest of black-barked trees, and the white
moths get hunted more regularly by birds, what
is that called?
– A. competition
– C. adaptation
B. artificial selection
D. survival of the fittest
Evidence of Evolution
• Fossils
– People in Darwin’s time understood that fossils were
preserved remains of ancient organisms.
• Geographic Distribution of Living Things called
biogeography
– Species varied by location
• Homologous Body Structures
– Structures that have different mature forms but
develop from the same embryonic tissues
– Vestigial Organs – traces of homologous organs that
serve no obvious purpose
– Examples: limbs of reptiles, birds, and mammals
• Similarities in Embryology
– Early stages of embryos, many animals with backbones
are similar
WARM UP
• How might vestigial organs provide clues
to an animal’s evolutionary history?
Chapter 16 – Evolution of Populations
• 16-1 Genes and Variations
• Genetic variation is studied in populations
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(group of same species that interbreed)
Gene pool – all genes that are present in a
population
Relative frequency – number of times an allele
occurs in a gene pool, compared with the
number of times other alleles for the same gene
occur
Evolution is change in the relative frequency of
alleles in a population
Genetic Variation
• Two main sources of genetic variation
– Mutations
• Change in a sequence of DNA
– Gene shuffling
• Independent movement of chromosomes during
meiosis and Crossing-Over
Checkpoint!
• Write down 2 different things that Darwin
thought of as evidence for evolution.
• What is the term for all the genes present in a
population?
– A. gene pool
B. relative frequency
– C. possible inheritance D. gene shuffling
• Write down two sources of genetic variations?
Single-Gene and Polygenic Traits
• The number of phenotypes produced for a
trait depends on how many genes control
the trait
– Single-gene trait
• Single gene with two alleles
• Fewer phenotypes than polygenic traits
• Ex: widow’s peak
– Polygenic trait
• Controlled by two or more genes (each with more
than 2 alleles)
• Many different genotypes and phenotypes
• Ex: height
Distribution of Phenotypes
Polygenic Traits
• Directional Selection
– Individuals at one end of the curve have higher
fitness than those in the middle or the other end
Directional Selection
Food becomes scarce.
Low mortality,
high fitness
High mortality,
low fitness
• Stabilizing Selection
– Individuals near the center have higher
fitness than those at either end of the curve.
Stabilizing Selection
Key
Low mortality,
high fitness
High mortality,
low fitness
Birth Weight
Selection
against both
extremes keep
curve narrow
and in same
place.
• Stabilizing selection favors the norm, the common,
average traits in a population. Look at the Siberian
Husky, a dog bred for working in the snow. The Siberian
Husky is a medium dog, males weighing 16-27kg (3560lbs). These dogs have strong pectoral and leg
muscles, allowing it to move through dense snow. The
Siberian Husky is well designed for working in the snow.
If the Siberian Husky had heavier muscles, it would sink
deeper into the snow, so they would move slower or
would sink and get stuck in the snow. Yet if the Siberian
Husky had lighter muscles, it would not be strong
enough to pull sleds and equipment, so the dog would
have little value as a working dog. So stabilizing
selection has chosen a norm for the the size of the
Siberian Husky.
• Disruptive Selection
– Individuals at the upper and lower ends of the
curve have higher fitness than those in the
middle.
Disruptive Selection
High mortality,
low fitness
Population splits
into two subgroups
specializing in
different seeds.
Beak Size
Number of Birds
in Population
Low mortality,
high fitness
Number of Birds
in Population
Largest and smallest seeds become more common.
Beak Size
• Suppose there is a population of rabbits. The color of the rabbits is
governed by two incompletely dominant traits: black fur represented
by “B” and white fur represented by “b”. A rabbit with the genotype
of “BB” would have a phenotype of black fur, a genotype of “Bb”
would have gray fur (a display of both black and white) and a
genotype of “bb” would have a phenotype of white fur.
• If this population of rabbits were put into an area that had very dark
black rocks as well as very white colored stone, the rabbits with
black fur would be able to hide from predators amongst the black
rocks and the white furred rabbits would be able to hide in the
white rocks, but the gray furred rabbits would stand out in both of
the habitats and would suffer greater predation.
• As a consequence of the selective pressures of their environment,
our hypothetical rabbit population would be disruptively selected for
extreme values of the fur color trait: white or black, but not gray.
Genetic Equilibrium
Hardy-Weinberg principle
• If a population did not evolve, or change, the
population would reach equilibrium – when
allele frequencies stay the same
• Conditions required to reach equilibrium:
– Random mating
– Large population
– No movement in or out of population
– No mutations
– No natural selection
Speciation
• Isolation prevents interbreeding between
populations
– Behavioral isolation
• Different courtship rituals or reproductive
strategies
• Example: remember the Drosophila fly songs?
– Geographic isolation
• Two populations are separated by geographic
barriers (rivers, mountains, oceans, etc..)
– Temporal isolation
• Species reproduce at different times (winter –vsspring)
• Genetic Drift
– Random changes in allele frequencies that
occur in a small population because of
possible reproductive abilities of some and not
others
– Could result from a bottleneck or founder
effect
– Example:
Northern elephant seals have reduced genetic variation probably
because of a population bottleneck humans inflicted on them in the
1890s. Hunting reduced their population size to as few as 20 individuals
at the end of the 19th century. Their population has since rebounded to
over 30,000 — but their genes still carry the marks of this bottleneck:
they have much less genetic variation than a population of southern
elephant seals that was not so intensely hunted.
Bottleneck: an intense pressure or calamity
reduces the numbers in a population
Founder Effect:
– Changes in allele frequencies as a result of
migration of a small subgroup
– Example: the Afrikaner population of Dutch settlers in South
Africa is descended mainly from a few colonists. Today, the
Afrikaner population has an unusually high frequency of the gene
that causes Huntington's disease, because those original Dutch
colonists just happened to carry that gene with unusually high
frequency. This effect is easy to recognize in genetic diseases,
but of course, the frequencies of all sorts of genes are affected
by founder events
Checkpoint!
• Which of these is not a characteristic of a
population in equilibrium?
– A. no mutations
B. no movement
– C. no natural selection D. non random mating
• When a daffodil blooms in the spring and a
sunflower blooms in the summer, what kind of
isolation keeps them from interbreeding?
– A. behavioral
– C. geographic
B. temporal
D. physical