Download RACC BIO Natural Selection

Nature of Science…review of terms
 Science – a way of knowing about the natural
world
 Law – a description of how a natural
phenomenon will occur under certain
circumstances
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Ex. Kepler’s Law of planetary Motion
Fact – a natural phenomenon repeatedly
confirmed by observation. A fact is assumed to
be true.

It takes Venus 225 days to go around the sun
Nature of Science…terms
 Theory – a well substantiated explanation of some
aspect of the natural world that typically
incorporates many confirmed observations, laws,
and successfully verified hypothesis.
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Theory of evolution
Hypothesis – a possible and testable statement
about a natural phenomenon

If a plant isn’t watered then the plant will die.
Science Before Darwin
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Ideas that shaped Darwin’s Thinking
James Hutton - 1785
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Processes that changed the earth are the same
forces shaping the earth presently.
Most geological processes operate extremely
slowly
Charles Lyell
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Darwin read his book
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Principles of Geology

Lyell proposed that geological features could
be built up or torn down over long periods of
time
Scientists must explain past events in terms of
processes that they can observe

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Darwin became convinced the Earth was
much older than believed at that time
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If the earth could change over time, might
life change as well?
Jean Baptiste Lamarck
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(1744-1829)
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The first to recognize that living things have
changed over time, and proposed a hypothesis for
this process.

His hypothesis was incorrect.
Lamarck believed that the long neck of
giraffes evolved as generations reached
for higher leaves. They used their necks
more.
Thomas Malthus
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Darwin read his essay written in 1798
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Wrote that human populations are able to
increase faster than the food supply.
Controlled by famine, disease, or war
Darwin observed this applies to animals and plants as well
If all offspring of a species would survive, they would
overrun the world
What factors determine which offspring survive and
reproduce, and which do not?
Darwin’s Journey
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Darwin’s Theory of Evolution
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Who is Charles Darwin…the voyage of the
Beagle
Wrote
“On the Origin of Species By Means of Natural
Selection”
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Published 1859
23 years after his return home
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PBS Evolution Who was Charles Darwin
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Darwin’s Return Home
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Darwin didn’t publish his findings until 23
years later!
He was given an incentive when he
received a manuscript from Alfred
Wallace.

Wallace wrote about the exact same ideas that
Darwin had.
Evolution at a Glance

The changes, over time, in organisms
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Deals with a very specific type of change
Changes in the frequencies of different genes
(made up of alleles), within a species.
What causes changes to genes?
What sorts of things happen when gene
frequencies change?
What is gene frequency?
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We know genes determine traits
We know genes are inherited
Alternative versions of a trait are called alleles
Some alleles are dominant and some are
recessive.
Within a population scientists can actually
measure the frequency, or how often a
particular gene appears in a population.
Changes in Gene Frequency – Evolution on the smallest scale

Example: A population
of Beetles
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half have the gene for
brown color, the gene
frequency is 50%
half have the gene for
green color, its gene
frequency is 50%
Campbell bio: ch 23 bioflix mechanisms of evolution
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Several years later the
gene frequency changes
the brown color gene is
now at 75%
the green color gene is at
25% the frequencies are
changing, and evolution
has happened.
The Origin of Species - 1859

To explain how and why evolution occurred,
Darwin needed a mechanism.

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A scientific explanation
Darwin realized that most organisms do not survive
and reproduce
He wanted to know which individuals do survive and
reproduce
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Today this mechanism explains how gene frequencies
could change over generations
Natural Selection
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The mechanism to explain “descent with
modification”
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Changes to an organism through generations
Not all individuals have an equal chance of
contributing to the next generation
Some are selected for and some are selected
against.
Natural Selection is the driving force.
Darwin Gains insight into Natural
Selection through Artificial Selection
Artificial Selection

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Plant and animal breeders use artificial
selection or selective breeding to choose
the best traits
Humans select the natural variations they
find useful

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Cows that produce more milk, the fastest
horses, etc.
This has produced many diverse organisms
that look different from their ancestors.
Artificial Selection
All domesticated
animals, livestock
and crops have
been produced this
way!

Terminal
bud
Lateral
buds
Brussels sprouts
Cabbage
Flower
cluster
Leaves
Cauliflower
Broccoli
Kale
Flower
and
stems
Stem
Wild mustard
Figure 22.10
PBS dangerous idea #4
Kohlrabi
Artificial Selection…A Question?
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If variations could be selected for and
against by humans, then couldn’t this also
happen naturally in nature?
This selection would then affect how
organisms looked over time.
Evolution by Natural Selection

Under what conditions does natural
selection occur?
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The Struggle for Existence
Variation and Adaptation
Differential Reproductive Success
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Survival of the Fittest (lets discuss)
“Survival of the Fittest”
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Makes it sound like only the strong survive and
the weak die away.
Darwin didn’t coin this phrase. Herbert Spencer
did
Fitness is all about how an organism reproduces
and passes its genes on to the next generation.
In fancy terms its called differential reproductive
success
 Or how successful an individual is at
producing offspring
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Youtube cuttlefish mating trick
https://www.youtube.com/watch?v=OEqsgwyvtqc
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Observation #1:
For any species, population sizes would
increase exponentially if all individuals that
are born reproduced successfully
Figure 22.8
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Observation #2:
Nonetheless, populations tend to be stable in
size
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Except for seasonal fluctuations
Observation #3:
Resources are limited
Inference 1:
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Production of more individuals than the
environment can support, leads to a struggle
for existence among individuals of a
population, with only a fraction of their
offspring surviving
Natural Selection-Conditions
1. The Struggle for Existence
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Organisms produce more offspring than
can survive. Only a small fraction of
these offspring survive to reproduce.

Members compete for
Food
 Living space
 Other necessities of life
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Natural Selection
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Struggle for Existence
Which individuals come out on top?
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Observation #4:
Members of a population vary extensively in
their characteristics
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No two individuals are exactly alike
Figure 22.9
Observation #5:
Much of this variation is heritable
Inference #2
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Survival depends in part on inherited traits
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Individuals whose inherited traits give them a
high probability of surviving and reproducing
are likely to leave more offspring than other
individuals
Inference #3:
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This unequal ability of individuals to
survive and reproduce will lead to a
gradual change in a population, with
favorable characteristics accumulating over
generations
Natural Selection-Conditions
2. Variation and Adaptation

There is variation in nature
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Arises through sexual reproduction and mutation
Certain variations – called Adaptations –
increase an individual’s chance of surviving and
reproducing.
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Adaptation – any inherited characteristic that
increases an organism’s ability to survive and
reproduce.
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Sources of Variation
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http://learn.genetics.utah.edu/content/variation/sources/
Adaptations –What can be an Adaptation
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Structural Adaptations
Teeth and claws
 Rose thorns, porcupine quills
 Mimicry
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A harmless species has adaptations that result in a physical
resemblance to a harmful species
camouflage
Physiological adaptations – changes in metabolic
processes
Resistance to pesticides (insects and plants)
 Bacterial resistance to antibiotics
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Behaviors
Defensive behaviors-mothers protecting young
 Running from predators
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Natural Selection-Conditions
3. Differential Reproductive Success
 Fitness- how successful an organism is at
getting its genes into the next generation
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How successful are you at reproducing
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Nothing to do with how “buff” an organisms is
Fitness is key to the process of evolution
Individuals that are not well suited, die or leave fewer
offspring
Differences in adaptations affect an individuals fitness
If one individual produces twice as many offspring as the next, all
other things being equal, it’s twice as fit
Natural Selection

The Process by which organisms with variations
most suited to their local environment survive and
leave more offspring.
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It only acts on inherited traits
Adaptations don’t have to be perfect-just good
enough
Doesn’t always move in a fixed direction
Evidence Supporting The Theory
of Evolution
Sources of evidence come from
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Fossils
anatomical
Embryology
DNA
The Fossil Record
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Fossils are the preserved remains of ancient organisms
How do fossils provide evidence of evolution?
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They provide a record of early life and evolutionary history
Show that the earth has changed over time and new species
arise from existing species
The evolutionary
path that led to
today’s camel
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Transitional Fossils
Provide evidence for how species
have changed over time.
These are intermediate forms
between older species and their
more modern descendants
Archaeopteryx (intermediate
between dinosaur and birds)
The transition to life in
the sea
Anatomical
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Structural similarities is evidence that organisms
evolved from a common ancestor
It would be unlikely for so many animals to have
similar structures if each species arose separately
All are mammals
Anatomical evidenceHomologous structures

Structures that may have different form and
functions but similar tissue

Share an evolutionary relationship
Anatomical evidenceAnalogous structures

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Structures that have similar functions but different components
in two unrelated organisms
Do not have a common evolutionary origin.
 Show that the organisms evolved separately.

Have adapted to similar environments
 Example: Wings
 Or fins of fish and dolphin

(swimming in water)
Vestigial structures

Organs, or body parts, that are so reduced
in size or function that they are merely
traces of homologous organs in other
species

These organs do not serve important
functions.
Examples of Vestigial structures
Hind limbs of whales
 Tiny bones in snakes that were once legs
 Miniature tailbones at the base of a human
spine (once supported a tail)
 The human appendix is a vestigial organ
Similarities in Embryology
Embryonic cells develop in the
same order and similar patterns.
It is the shared features in the
young embryos that suggest
evolution from a distant,
common ancestor
All embryos have a tail and pharyngeal pouches. In
fish, these pouches develop into the supports for the
gills, while in mammals, reptiles and birds they
develop into parts of ears, jaws and throat.
Ex. All limbs
develop from the
same clump of
cells
Zebra fish
What organism?
http://www.pbs.org/wgbh/nova/evolution/guess-embryo.html
Universal Genetic Code (DNA)
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Nearly all organisms share DNA, similar
proteins and genes
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ATP powers cellular respiration and
photosynthesis
Examples cytocrome c, an enzyme occurs in
almost all organisms
Utah.edu “all living things are related”
http://learn.genetics.utah.edu/content/variation/related
How can changes occur
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Mutations – can cause differences in
otherwise similar DNA sequences
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Occur at a certain rate
Indicate how long tow lineages have evolved
independently
The more common sequences, the more recent a
common ancestor
 The greater the differences, the more time has
passed between two species
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Evolutionary “trees”
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Comparing gene sequences
Hemoglobin Comparisons Between Humans and
Other Vertebrates
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Humans are more closely related to primates than other vertebrates.
Their difference is only one amino acid
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Anatomical resemblances among species
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Are generally reflected in their molecules, their
genes, and their gene products
Species
Closely related
species have a
larger
proportion of
DNA and
proteins in
common than
do more
distantly related
Figure 22.16
species
Percent of Amino Acids That Are
Identical to the Amino Acids in a
Human Hemoglobin Polypeptide
100%
Human
Rhesus monkey
95%
Mouse
87%
Chicken
69%
Frog
Lamprey
54%
14%
Biogeography
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The geographic distribution of species
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Influenced by continental drift
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The slow movement of Earth’s continents over time
Islands generally have many species of plants
and animals that are endemic
Meaning they are found nowhere else in the world
 Yet island species are closely related to species from
the nearest mainland or neighboring island
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Islands are colonized by species from the nearest mainland
In Summary
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Natural selection results in the evolution of
populations
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a population is a group of interbreeding individuals of the same species in a
common geographic area
Evolution is measured only as change in the relative
proportions of variations in a population over time
Natural selection affects only those traits that are
heritable
Natural selection depends on the specific
environmental factors present in a region at a given
time
If the environment changes, different adaptations
will be favored

Darwin’s theory of evolution by natural
selection

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Integrates diverse areas of biological study and
stimulates many new research questions
Evolution can sometimes occur more quickly
than Darwin originally hypothesized.

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New species can arise within a few thousand years
Evolutionary biologists now recognize that
natural selection is not the only mechanism
responsible for evolution.