Download Review of evolution - Milton High School Science

Created by Kevin Bleier
Milton High School

On the Origin of Species published 1859
1)
Species change (they are not fixed)
2)
Selection as a mechanism for change
3)
“Descent with modification” implies all
species related, diverged over evolutionary
time (Earth is very old)
1)
Competitive force
2)
Genetic variety
3)
Selection
4)
Generations of continued selection
chapter 16.2
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Requirement 1: competitive force
something is making it hard for individuals
to survive
1) Competition within a species for
resources (too many organisms)
2) Competition between species
(predation / parasitism, etc)
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Requirement 2: genetic variety
(everyone has different traits)
Must be genetic (so traits potentially passed
on to offspring)
We have spent time here in fall – how do
organisms generate genetic variety?
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Result 1: selection
Individuals are selected for if they are able to
survive longer to reproduce more offspring
than other individuals (they have traits that
benefit them)
Individuals selected against if they do not
survive as well – meaning they do NOT
produce as many offspring
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Often summarized as “survival of the fittest”

Key idea there is not survival, but fittest
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Evolutionary fitness = how many offspring
individual can produce
(NOT strength, size, speed, etc)
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Result 2: selection over generations
Those with beneficial trait must continue to
out-reproduce the others
Eventually, overall population starts to
change (= evolution)
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Reduction in fish body size over 17 years off
coast of South Africa
Can human fishing (predation) drive evolution
of fish populations over time?
Big
fish
Small
fish
54%
42%
31%
70% 69%
46%
58%
30%
1) selection
competitive
force
4)
over
3) selection
many generations
2) genetic variety
1)
Competitive force
2)
Genetic variety
3)
Selection
4)
Generations of continued selection
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Darwin had many influences to help develop
his idea for evolution
Other scientists also believed that species
changed over time – alternative hypotheses
for evolution from Lamarck
Not supported
Supported by evidence

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Genetic variation
Individuals with
beneficial variations
reproduce more
Population evolves,
NOT individuals

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Individuals change
by use and disuse
Individuals pass
acquired changes in
life to offspring
Individuals evolve
because they “want”
change
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Darwin read other subjects for fun
Lyell and geology – studies proposing that
Earth is much older than previously thought
(now enough time for evolution)
Malthus and economics – growing human
population might lead to mass starvation and
competition for food
(leads to ideas about competitive force)
chapter 16.1
1)
2)
3)
Species change (they are not fixed)
Species changed from common ancestry
over evolutionary time (implying a much
older Earth)
Selection as a mechanism for change
chapter 16.2
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Darwin observes organisms with slight
differences
Ex: Galápagos
finches with
different beaks
Adapted to eat
different food sources

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Darwin also finds fossils of organisms unlike
any that live today
Ex: giant sloth in Argentina
(modern armadillos and
sloths related, but MUCH
smaller)

From “AIDS: Evolution of an Epidemic”
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http://www.hhmi.org/biointeractive/hl/
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Resistance to antibiotic medicines in some
species of pathogenic bacteria
We have only seen this recently (first wide use
of antibiotic penicillin in 1940s)
Open books to p. 484
1)
2)
3)
Species change (they are not fixed)
Species changed from common ancestry
over evolutionary time (implying a much
older Earth)
Selection as a mechanism for change
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Homo = _______
Same
evolutionary
history (same
bone structures)
Different
functions in
different
environments

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Genes and proteins with important cell
functions have been largely unchanged in
evolutionary history
Ex: Protein
involved in cell
division
(cytokinesis)

Embryo stage of development shows
similarities in many animals (then divergence)

Respiration / photosynthesis pathways

Mitosis pathways (eukaryotes)
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…and more!
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Proteins involved are very similar, unchanged
for billions of years of life’s history
“use it or lose it”
“use it or lose it”
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
A species does not always have to add
something new, it can evolve by LOSING traits
as well
Great example: tapeworm
1)
2)
3)
Species change (they are not fixed)
Species changed from common ancestry
over evolutionary time (implying a much
older Earth)
Selection as a mechanism for change

Ideas for selection started with interviewing
pigeon breeders

= artificial
selection

(domesticating
plants)
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(domesticating
silver foxes)
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Sure
Antibiotic resistance only occurs in era of
antibiotics
Also example of bedbug resistance to
insecticide chemicals
1)
2)
3)
Species change (they are not fixed)
Species changed from common ancestry
over evolutionary time (implying a much
older Earth)
Selection as a mechanism for change

Evolution does not “finish” at “perfection”

Ex: Eye setup and blind spots
incoming light


Populations are not isolated, and often evolve
in response to each other
Coevolution – two species are competing to
“one up” each other with adaptations
◦ Ex: predators and prey,
plants and herbivores
chapter 16.3
Fake homology
new species
some similarities begin to
develop in same environment
common
ancestor
True homology
different
ancestries
Special case
of divergent
evolution when many
niches
available
European mole
(mammal)
Australian mole
(marsupial)
similar adaptations to live
underground but very different
ancestries

Gradualism
Slow, even change
throughout history
vs. punctuated equilibrium
Long periods of no change
with bursts of rapid change
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Radiometric dating – half-life of radioactive
atoms is very reliable, like a clock ticking
Half-life: how long it takes for half of any size
sample to become stable (some take millions
of years, some thousands of years)
Relative dating – using commonly found
fossils to estimate age of new fossil
chapter 19.2

1) Competitive force makes it hard to survive

2) Variety of heritable traits

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How is this variety generated?
How does inheritance work?
3) Selection of organisms to out-reproduce
others
4) Generations of out-reproduction to foster
population change
chapter 17.2
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Variety of traits caused by genes (with
different alleles)
New evolution definition: When allele
frequencies change in a population’s gene
pool over generations
R = black fur
r = sandy fur
rr
RR
rr
rr
rr
rr
rr
rr
Rr
Rr
Rr
rr
Rr
rr
rr
14 / 20 = rr = 70%
Gene pool
rr
rr
1 / 20 = RR = 5%
5 / 20 = Rr = 25%
rr
rr
20 total organisms
7 / 40 R = 17.5%
Rr 33 / 40 r = 82.5%
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Evolution = change in gene pool allele %s
Ex: Lava flow creates black rock environment
R = black fur
r = sandy fur
black fur
phenotype
sandy fur
phenotype
Genotypes
# organisms
initially
# organisms
25 years later
RR
1
12
Rr
5
8
rr
14
0
initially:
R = 17.5%
r = 82.5%
25 yrs: R = 80.0%
r = 20.0%
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Natural selection chose organisms with
phenotypes to survive longer and reproduce
more offspring
Over generations, this causes allele
frequencies to shift
Modern evolutionary theory identifies five
total evolutionary forces (four others besides
natural selection)
1.
2.
3.
4.
5.
Natural selection
Sexual selection
Mutation
Genetic drift
Gene flow
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Mate choice for particular characteristics
makes certain traits more prominent
Mates “selecting” other mates because their
phenotypes are “sexy”
Increased reproduction
makes trait more
prominent in future
generations
G = boring coloration g = sexy, bright coloration
Genotypes
# peacocks
(initially)
# peacocks
(25 generations
later)
GG
25
4
Gg
17
8
gg
3
28
Initially:
R = 74.4%
r = 25.6%
25 generations: R = 20.0% r = 80.0%
later
1.
2.
3.
4.
5.
Natural selection
Sexual selection
Mutation
Genetic drift
Gene flow
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Raw material for any change, but causes very
little change by itself
Example: new recessive mutation at another
gene causes albino coloration in just one
mouse
1.
2.
3.
4.
5.
Natural selection
Sexual selection
Mutation
Genetic drift
Gene flow
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Any random change that shifts allele %s
Evolution does NOT have to be caused by
selection
Especially affects small populations – may
even eliminate alleles from gene pool

Example: flood kills many of the mice in a
population randomly
R = black fur
black fur
phenotype
sandy fur
phenotype
r = sandy fur
Genotypes
# mice before
disaster
# mice after
disaster
RR
Rr
rr
8
14
6
0
2
4
Before disaster: R = 53.6% r = 46.4%
After disaster: R = 16.7% r = 83.3%
1.
2.
3.
4.
5.
Natural selection
Sexual selection
Mutation
Genetic drift
Gene flow

Entry of new individuals or exit of current
members (their genes are flowing in or out)
R = black fur
r = sandy fur
Genotypes
# mice in
desert
# mice + 10
new sandy fur
mice
RR
Rr
rr
25
17
3
25
17
13
black fur
phenotype
sandy fur
phenotype
Initially:
R = 74.4%
r = 25.6%
After migration: R = 60.9%
r = 39.1%
1.
2.
3.
4.
5.
Natural selection
Sexual selection
Mutation
Genetic drift
Gene flow
3 types:
a) Stabilizing
selection
b) Directional
selection
c) Disruptive
selection
a) Stabilizing selection
Original population
(green) shifts to
favor intermediate
phenotype, away
from both extremes
(blue)
Ex: Lizards have
become medium
size
b) Directional selection
Original population
(green) shifts toward
one direction of a
phenotype (blue)
Ex: anteater
populations have
evolved longer
tongues to reach ants
c) Disruptive selection
Original population
(green) shifts to
EITHER extreme,
away from
intermediate (blue)
Ex: white or black
limpet shells
camouflage, NOT tan
shells
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
Microevolution – “small” changes within a
population – chapter 17.2
Macroevolution – “large” scale change
involving new species, broader groups of
organisms – chapter 17.3
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When do populations become so different
that they are new species?
Biological species concept – when male and
female can make fertile offspring together
If they are so different that they do not mate
(or cannot mate), then they are different
species
chapter 17.3
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Populations separated by a landform (ocean,
mountain) (geographic isolation), begin to
become different in genetics
Eventually, they are so different that they do
not mate (reproductive isolation)
Diane Dodd’s fruit fly lab, 1989

1) Linnean system of groups

2) Cladistics
chapter 18.1 / 18.2
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Taxa – group names below to classify:
(least specific)
domain  kingdom  phylum  class 
order  family  genus  species
(most specific)

Early classifying based on structural analysis

Example: illustration p. 425
chapter 18.1

Organism’s scientific name: Genus epithet

Capitalize genus name, NOT species name

Italicize if typing, underline if handwriting

Humans: Homo sapiens
1) Misleading similarities result in mis-classifying
(often due to convergent evolution)

Ex: birds AND mammals have 4-chamber hearts
(but little else in common)
2) Transitional organisms strain the definitions of
groups

Ex: Platypus – the egg-laying mammal (or should
that be mammary-gland containing reptile?)


Creates a system based on traits, not on
group names
Organizes into clades – every organism and
their common ancestor who has a certain trait
chapter 18.2
the lungthe
/ lung
the
amniote
mammal
the
the
jaw
tetrapod
clade
clade
derivative clade
clade
clade
lamprey
no jaws
shark
no air
no swim
sac
bladder
Goal: to understand
the phylogeny =
evolutionary history
of species
tuna salamander turtle
no 4
legs
dog
common
evolution
of
amniote
mammary
glands
common
ancestor
evolution
ancestor
of
amniotic
with 4 egg
legs
evolution
of
common ancestor
tetrapody
legs)
with an air(4
sac
evolution
common of
ancestor
air sac
(swim
with abladder)
jaw
evolution
commonofancestor
jaws
to all these animals
connection to other
organisms on tree


“Humans evolved from chimpanzees”
Both are modern species … BOTH evolved to
their modern forms from a common ancestor
chimpanzees
humans
common
ancestor
other mammals, vertebrates,
animals, eukaryotes, life