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15-1 The Puzzle of Life’s Diversity Evolution, or change over time, is the process by which modern organisms have descended from ancient organisms. = Change over time
= Change in the frequency of
an allele in a population
Evolution is not
something that only happened in the past;
it is still going on. It does not happen to individuals, it happens
to populations.
The Galapagos Islands greatly
influenced Darwin’s ideas.
Observed: • Marine fossils atop mountains • Organisms have variations based upon
environment • Similarities between extinct fossils &
modern life • Organisms seem remarkably well suited
for their environment
Charles Darwin
Darwin found 13 species of finches on Galapagos Island. Each group of finches had its own niche (an organism’s habitat and its role in that habitat).
The shape of a tortoise’s shell corresponded to its habitat. • Tortoises on hot, dry islands had long necks and shells that curved
open around the neck and legs.
• On islands with rich vegetation, tortoise’s had a shorter neck and dome-shaped shell.
15-2 Ideas That Shaped Darwin’s Thinking Most people in Darwin’s day believed that Earth was only a few thousand years old, and that all of today’s species had existed unchanged since their creation.
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•Acquired Inheritance: Early theory where organisms could acquire and pass traits after birth
•Cause: environmental changes forced individuals to change
- organisms strive to improve themselves - unused body structures wasted away and most used structures develop
•Early Belief: Giraffes & Long Necks
–Long necks are result of stretching to reach leaves
–Extra length was passed on to offspring
•Problem: Traits acquired after fertilization cannot be passed to offspring
15.3 Darwin Presents His Case
• Darwin mulled over his ideas for 25 years before publishing
• Alfred Wallace sent Darwin an essay containing similar ideas; they presented their ideas together
• Darwin published his book 18 months later (1859)
The Theory of Natural Selection
Natural Variation • Defined: Inherited traits that make an individual different
from others
• Natural variation is found in all types of organisms.
• Much of this variation can be inherited
Artificial Selection
• Defined: Humans select (not naturally) traits thought to be advantageous
• Humans created diversity choosing specific traits to breed
–Dogs, Crops, Livestock
• Only inheritable traits can be passed down
• Importance: Shows life can change over a period of time
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Dog traits have been
selected by breeders for
centuries to produce
various breeds.
Plants have been
bred to produce
certain traits for
human use also!
•Four factors: 1) Overpopulation: more offspring are born than can survive
2) Variation: individuals of a population have differences 3) Adaptation: Some variations allow a better chance of survival
4) Descent w/ modification: Over time, those with advantages makeup more of the population
Not all these
wildebeest will
survive These kittens have
variations
The Myth
The Truth
- Natural selection
can act only on traits
that currently exist.
What is the beaver comic showing?
• Individuals don’t grow something
because they need it.
• Individuals don’t evolve.
Populations evolve!!!
Struggle for Survival
•High birth rates and limited resources cause competition
•Fitness: measure of the ability to survive & produce more offspring; fitness is a result of adaptation
•Adaptations can be physical, behavioral, or temporal
Adaptation
Defined:
An inherited trait that increases a population’s chances of survival and reproduction in a particular environment
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Adaptations Mimicry
Structural Adaptations
Behavioral Adaptation
Blue-footed boobies have a courtship display that is unique to their species; they will not mate until that courtship display is completed.
Temporal Adaptation Some cicadas reproduce every 13 years while others reproduce every 17 years, so the two groups never cross paths and reproduce.
Which rabbit is best adapted?
Do the dark rabbits turn white? No! They get
eaten.
What happens when environments change? Year 1 Background Year 10 Background
Those best adapted survive and reproduce.
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Changing Environments •As environments change…
–Those with adaptation: more likely to survive & reproduce
–Those without adaptation: more likely to perish
•Populations do not grow unchecked
–Limiting Factors: food, water, shelter, disease, predators
Summary of Darwin’s Theory of Evolution by Natural Selection
Overproduction Populations produce too
many young; many must die
Variation Individuals show variation; some
variations are more favorable
than others
Natural Selection Natural selection favors
the best suited at the time
Limited
Resources
Inheritance Variations are
inherited. The best
suited variants leave
more offspring.
Over time, natural selection results in changes in inherited characteristics of a population.
• Darwin’s principle states that over time, living species have descended, with changes, from other species.
• This implies that all living organisms are related to one another.
•Defined: Collection of every known fossil
•Most fossils found in sedimentary rock
•Age determined by depth
–new rock forms on top of older rock
•Evidence Conclusions:
1) Newer fossils are
more complex
2) Common ancestors:
relationships between
ancient & modern life
•AKA: Transition Fossils
–Archaeopteryx: shares both bird & reptile features
–Basilosaurus: shares whale & land mammal features
–Tiktaalik: shares fish & amphibian features
•Evidence Conclusion : Indicates common ancestry
Reptile Evidence
Teeth
Bony tail
Bird Evidence
Wishbone
Feathers
Whale Evidence
Long spine
Found in dried up
oceans
Land Evidence
Wolf-like teeth
Hind legs
Fish evidence
Scales
Fins
Found in dried-
up oceans
Amphibian evidence
Eyes on top of head
Wrist bones
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•Different
species show
similar
development
patterns
•Different body
plans become
noticeable
later in
development
•Evidence
Conclusion :
Indicates
common
ancestry
• Defined: similar body structures with very different functions
• Different environments lead to adaptations
– Ex: The forelimbs of animals
• Evidence Conclusion : Indicates common ancestry
• Defined: similar function with very different structures
• Analogous structures are not evidence of a common ancestor.
•Defined: Organs which have lost
most or all their original function
•Vestigial Human Parts:
–Gill slits = once used to breath
oxygen in water
–Yolk sac = once used to nourish
developing embryo
–Tailbone = once used for balance
–Appendix = once used to digest
plants
–Wisdom teeth = once used to
grind plant tissue
•Evidence Conclusion : Indicates
common ancestry
Human Embryo w/ Vestigial Structures Pythons have tiny femurs (leg bone)
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• DNA, RNA,
proteins
compared
• Genetic code
same for most
life
•More related species
have more similar
biochemistry
•Evidence
Conclusion:
Indicates common
ancestry
Ch. 16 Evolution of Populations
How Twitter is upgrading our gene pool…
16.1 Genes & Variation
•Gene Pool: All alleles within a population
•Relative Frequency: number of times that an allele occurs in a gene pool; usually expressed as a percent
Allele Frequencies: Sum = 100% Frequency of black allele =
Frequency of white allele =
Does gene frequency
equal phenotype frequency?
Why or why not?
No, because some black
mice carry the recessive allele.
12/20 = 60%
8/20 = 40%
White allele is recessive to black allele.
Sources of Genetic Variation
•Genetic variation can increase chances some survive changing environments
•Two main causes of genetic variation:
1. Mutations: Random changes to DNA sequence affect phenotypes; may affect fitness (ability to survive and reproduce)
2. Gene Shuffling: During meiosis, genes recombine in varying patterns; does NOT change the relative frequencies of alleles!
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16.2 Evolution as Genetic Change
Individuals that are better suited to their environment
(have high levels of fitness) survive & reproduce most successfully.
Natural Selection acts on phenotypes, not genotypes
• Happens over generations
• Can lead to changes in allele frequency (Evolution!)
Freq. of green allele:
Freq. of brown allele:
Directional Selection—Individuals at one end of the curve have a higher fitness than the rest.
Types of Selection
Disruptive Selection—Individuals at the upper and lower ends of the curve have a higher fitness; Selection creates two distinct phenotypes.
Types of Selection
Stabilizing Selection—Individuals near the center of the curve have higher fitness.
Types of Selection Genetic Drift
• Defined: Changes in allele frequencies due to chance –NOT natural selection
• Bottleneck effect
–Results in a loss of genetic variation (alleles)
–More likely in smaller populations
–Example: Natural disaster
•Pre-forest fire: Green is best adapted (blend better)
•Post-forest fire: Brown more likely to reproduce
–Survival UNRELATED to adaptations
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Genetic Drift: Founder Effect • Situation in which allele frequencies change as a
result of the migration of a small subgroup of a population.
• Example: Hawaiian fruit flies descended from 1 main type—very different from mainland fruit flies
Species •Defined: group of organisms that can interbreed and produce fertile offspring
–Different species rarely breed
–Interspecies breeding often
results in sterile offspring
•Ex: Horse x Donkey = Mule
•Ex: Lion x Tiger = Liger
–New species = when unable to successfully reproduce
16-3 The Process of Speciation
Defined: evolution of new species from an existing
species
• 5 factors that lead to evolution Natural Selection
Gene flow
Mutations
Sexual selection
Genetic drift
Speciation Gene Flow (Migration) •Defined: Movement of alleles from one population to another
- Increases variations in a
population
- Keeps differing populations similar
•If gene flow is prevented
- No variations (alleles) exchanged
- Populations are isolated
- Organisms adapt to their own
environment
- Can lead to speciation!
Reproductive Isolation •When populations are isolated for
a long time…gene flow stops
•When populations can no longer mate or no longer reproduce fertile offspring
•Final step in the development of a new species
1) Geographic Isolation:
o Organisms isolated by geographic barrier
Random DNA
mutations
Random DNA
mutations
Different
predators
Different
predators
Different
resources
Different
resources
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Reproductive Isolation •When populations are isolated for a
long time…gene flow stops
•When populations can no longer mate or no longer reproduce fertile offspring
•Final step in the development of a new species
1) Geographic Isolation:
o Organisms isolated by geographic barrier
2) Behavioral Isolation
o Organisms isolated by differing mating rituals
If the mating calls do not attract
each other, will they reproduce?
Is gene flow stopped?
Reproductive Isolation •When populations are isolated for a
long time…gene flow stops
•When populations can no longer mate or no longer reproduce fertile offspring
•Final step in the development of a new species
1) Geographic Isolation:
o Organisms isolated by geographic barrier
2) Behavioral Isolation
o Organisms isolated by differing mating rituals
3) Temporal Isolation
o Organisms isolated by differing times of reproduction
If one group mates during the spring…
And the other mates during the fall…
Is gene flow stopped?
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
Alexander
Fleming
discovered the
first
antibiotic…
penicillin
Current Evolution: •Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
Bacteria A
antibiotic
antibiotic
antibiotic
antibiotic
Bacteria B
antibiotic
antibiotic
antibiotic
antibiotic
Bacteria A has genes to create
enzymes that destroy the antibiotic Bacteria B does not have the genes to
make the enzymes to destroy the antibiotic
Bacteria A
Bacteria A is more likely to survive and _________________. REPRODUCE
When infected with a bacteria, we take
antibiotics.
The antibiotics are absorbed into the
bacteria.
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
–Ex: Pesticides
eliminating unfit pests
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•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
–Ex: Pesticides
eliminating unfit pests
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics
eliminating unfit bacteria
–Ex: Pesticides
eliminating unfit pests
Pesticides pesticides pesticides pesticides pesticides pesticides
Some “pests” are able to resist the
pesticides and survive. They will
reproduce with others who are
resistant. Over time, the entire
population is resistant.
•Constant creation of
chemicals for human use
is eliminating the “unfit”
organisms
–Ex: Antibiotics eliminating
unfit bacteria
–Ex: Pesticides eliminating
unfit pests
–Ex: Antivirals…
–Ex: Fungicides…
•This is natural selection!
–Allows resistant to
survive and reproduce
Read before the video, answer after…..
1. Why is the Russian prison system considered to be "ground zero" in the fight against TB?
2. What is responsible for the evolution of TB strains that are resistant to multiple drugs?
3. How does the misuse of antibiotics affect the evolution of disease-causing bacteria? Use the theory of natural selection to explain the growing resistance to antibiotics.
4. Why should we care about a resistant strain of TB in Russia?
Why Does Evolution Matter Now?
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