Transcript Chs. 14-16: Evolution

Chapters 22-25
Evolution
Evolution
The definition of Evolution is:
change over time
Biological Evolution is:
genetic change in population over time
process by which modern organisms
have descended from ancient
organisms (slow change over long
time)
• Even relatively quick evolution takes
hundreds of thousands of years
History of Evolutionary Theories
Plato (427-347 B.C.) 2 worlds – 1 perfect, 1
imperfect. No change in organisms
Aristotle (384-322 B.C.) Organisms placed
on “ladder of complexity / perfection” (scala
naturae) No change
Judeo-Christian culture tried to explain the
Creator’s plan as observable, natural
phenomena – Natural Theology
History of Evolutionary Theories
Carolus Linnaeus (1707-1832) Designed
modern taxonomic system (binomial
nomenclature)
From this system, we can (he didn’t) now
infer evolutionary relationships between
different groups
Geologists:
Georges Cuvier
James Hutton
Charles Lyell
History of Evolutionary Theories
Georges Cuvier (1769-1832) helped
develop Paleontology – study of fossils
Discovery of fossils (extinct species,
similarities to modern species) put some
doubt into Earth’s age and the origin of
species
Cuvier explained differences in strata with
“catastrophism” – floods, droughts,
volcanoes, etc. changed local areas
drastically over short periods of time
• Organisms did not change, just migrate
History of Evolutionary Theories
James Hutton (1726-1797) proposed that
rocks, mountains, and valleys have been
changed by water, wind, temperature,
volcanoes, and other natural forces
He described the slow processes that shape
Earth as “gradualism”
History of Evolutionary Theories
Charles Lyell (1797-1875) – agreed with
Hutton and said that scientists must always
explain past events in terms of observable,
PRESENT events and processes
(“uniformitarianism” – what happens today
happened yesterday)
They theorized Earth was much
older than a few thousand
(6,000) years, which didn’t
set well in the traditional
timeframe of Creationism
Age of the Earth
We now know Earth is approximately 4.5
billion years old
Darwin used the work of Hutton and Lyell as
a basis for his theories of slow change over
time. Darwin’s work was a biological
duplicate of Hutton and Lyell’s works in
geology.
Geologists study Earth’s rocks
Fossils are preserved
remains of ancient
organisms
As fossils are found that
don’t resemble organisms today,
evidence increases that Earth has
changed and that organisms have
changed with it
Biologists and geologists date Earth’s
past with the help of rocks
Geological Time Scale
RELATIVE DATING
Technique used to determine age of
fossils relative to other fossils in
different strata
This technique is VERY approximate
Geological Time Scale
ABSOLUTE (RADIOMETRIC) DATING
Using radioactive elements in rock
that decay at a steady rate to
determine age
Decay measured in terms of HALFLIFE
• Half-life – time required for half the
radioactive atoms in a sample to
decay
Radioactive Decay
During radioactive decay, the atoms of
one element break down to form
something else
Lose a
proton
6 protons
4 neutrons
5 protons
4 neutrons
Rocks contain radioactive elements, each
having a different half-life
EXAMPLES:
Uranium-238  Lead-206
HL = 4.5 B yrs
Potassium-40  Argon-40 HL = 1.3 B yrs
Carbon-14  Nitrogen-14 HL = 5770 yrs
Scientists often date rocks using
Potassium-40, which decays to form the
stable element Argon-40
It has a half life of 1.3 billion years
This is used to date the oldest rocks on
earth
K-40
Formed
K-40 Ar-40
Ar-40
1.3 B yrs
2.6 B yrs
Uranium and Potassium are useful for
dating rocks
Carbon-14 is useful for dating things that
were once alive such as wood, natural
fiber, or cloth
C-14 is in the atmosphere; living things
take it in their cells. After the organism
dies, it doesn’t take in any more C-14.
We can then compare the amounts of
C-14 to N-14, knowing its half-life, to
determine the age of the sample
Fossil Evidence
Found in Sedimentary rock:
layers of sand, silt, and clay in streams,
lakes, rivers, and seas form rock that
may have trapped living organisms
Fossil records – Show change over time.
Some time frames are missing, but will
show change of climate and geography.
Ex: Shark teeth in Utah
How can this be?
Jean Baptiste de Lamarck
(1744-1829)
He also recognized that organisms were
adapted to their environments and that
they change
He relied on three ideas:
1. A desire to change (innate drive for
perfection)
2. Use and disuse (Giraffe’s necks and
vestigial organs)
3. Inheritance of acquired characteristics
Darwin’s Dilemma
Set sail around the world in 1831 on
HMS Beagle on a 5 year voyage
He had prior knowledge of geology
(Lyell was a good friend) and
agriculture that helped influence the
development of his theory
Anchored all along the way
and took samples from
each place
Darwin’s Dilemma
He collected and studied beetles from
Brazil, birds from Chile, and iguanas,
tortoises, and finches from the
Galápagos Islands
He noticed similarities between
mainland (Ecuador) and Galapagos
finches
Later, he noticed differences in beak
size among finches from different
islands in the Galapagos
Darwin’s Dilemma
Thomas Malthus – wrote paper on
population growth in Great Britain
Population grows exponentially
Limiting factors on growth (carrying
capacity)
• Food
• Area
• Resources
Darwin’s Dilemma
Darwin applied Malthus’, Hutton’s, and
Lyell’s work to species’ ability to change,
and called the mechanism Natural
Selection
Nat.Sel.: Process by which organisms
with favorable variations survive and
produce more offspring than less welladapted organisms
He was sure Nat.Sel. was true,
but he feared public ridicule. So,
he kept his ideas to himself
Darwin’s Dilemma
Alfred Russel Wallace (1823-1913),
working independently, came to the
same conclusions as Darwin
He sent a manuscript to Darwin, basically for
proofreading
“I never saw a more striking coincidence…
so all my originality, whatever it may amount
to, will be smashed.” – Charles Darwin
Letter to Charles Lyell, June 18, 1858
Darwin quickly abridged and published his
work “On the Origin of Species”
Darwin’s Natural Selection
Ernst Mayr, an evolutionary biologist, has
dissected the logic of Darwin’s theory into
three inferences based on five
observations (Pg. 435)
Observations:
Tremendous fecundity
Stable populations sizes
Limited environmental resources
Variation among individuals
Heritability of some of this variation.
Darwin’s Natural Selection
Observation #1: All species have such
great potential fertility that their population
size would increase exponentially if all
individuals that are born reproduced
successfully.
Darwin’s Natural Selection
Observation #2: Populations tend to remain
stable in size,except for seasonal
fluctuations.
Observation #3: Environmental resources
are limited.
Darwin’s Natural Selection
Inference #1: Production of more
individuals than the environment can
support leads to a struggle for existence
among the individuals of a population, with
only a fraction of the offspring surviving
each generation.
Darwin’s Natural Selection
Observation #4: Individuals of a
population vary extensively in their
characteristics; no two individuals are
exactly alike.
Observation #5: Much of this variation is
heritable.
Darwin’s Natural Selection
Inference #2: Survival in the struggle for
existence is not random, but depends in
part on the hereditary constitution of the
individuals.
Those individuals whose inherited
characteristics best fit them to their
environment are likely to leave more
offspring than less fit individuals.
Darwin’s Natural Selection
Inference #3: This unequal ability of
individuals to survive and reproduce will
lead to a gradual change in a population,
with favorable characteristics
accumulating over the generations.
Evidence in Living Organisms
Comparative embryology:
All vertebrate embryos look similar to
one another in early development, with
the development of a tail and gill
arches
• Ernst Haeckel made early drawings
– later exposed as frauds.
• Gave fuel to anti-evolutionists
Evidence in Living Organisms
Comparative embryology:
These anatomical similarities indicate
similar genetics are at work
Become more dissimilar as they grow
• Cell specialization and differentiation
Common ancestor?
Evidence in Living Organisms
Evidence in Living Organisms
Comparative anatomy:
Homologous Structures
Analogous Structures
Vestigial Organs
Evidence in Living Organisms
Homologous Structures –
structures that are similar in
anatomy, but may serve very
different functions
Ex: cat, whale, and human
forearm
Homologous Structures
Flying
Swimming Running Grasping
Evidence in Living Organisms
Analogous Structures – structures
that serve similar functions, but
have evolved independently of each
other
Not homologous;
analogous
Not homologous;
not analogous
Homologous;
not analogous
Homologous;
analogous
Evidence in Living Organisms.
Vestigial organs – organs that have little
or no purpose in the organism; may
become smaller or even disappear
Ex: Tailbone or appendix in humans
Ex: Tiny leg bones in
snakes (boas and pythons)
thought to come from 4
legged ancestor
Evidence in Living Organisms
Comparative biochemistry and
molecular biology:
All cells have DNA, RNA, ribosomes,
the same 20 amino acids and use
ATP to do work
Similarities in biochemistry indicate
relationship
Evidence in Living Organisms
Cytochrome c
is a highly
conserved
respiratory
protein
containing 104
amino acids in
humans
Evidence in Living Organisms
Amino acid
differences of
hemoglobin
between
species
What Homologies tell us…
Similarities in structure and chemistry
provide powerful evidence that all
living things evolved from a common
ancestor
Darwin Concluded:
Living organisms evolved through
gradual modifications of earlier forms
 descent with modification
What Similarities tell us…
Two types of evolution can account for
homologous AND analogous structures
Convergent evolution
Divergent evolution
What Similarities tell us…
Divergent evolution – two species
evolve from a common ancestor
(speciation)
They share similarities in anatomy,
biochemistry, and embryology due to
common ancestry
Explains homologous structures
What Similarities tell us…
Convergent – two species apparently
becoming more similar
Two species have adapted in similar
ways to similar environmental
conditions
NOT due to common ancestry
Explains analogous structures
Convergent Evolution
Ocotillo from California and allauidi
from Madagascar have evolved similar
mechanisms for protecting themselves
Convergent Evolution
Adaptive radiation of anoles has
occurred on the islands of the Greater
Antilles in a convergent fashion. On
each island, different species of the
lizards have adapted to living in
different parts of trees, in strikingly
similar ways.
Convergent Evolution
Convergent Evolution
Diversity of Life
Fitness:
Physical traits and behaviors that
enable organisms to survive and
reproduce in their environment arises
from adaptation.
Adaptation allows species to be better
suited to their environment and therefore
can survive and reproduce.
Evolution on Different Scales
Microevolution – generation-togeneration change in a population’s
allele frequencies
Macroevolution – origin of new
taxonomic groups; speciation
4 Driving Forces behind Evol.
1. Mutation
Any change in the original DNA
ONLY ultimate source of variation in
a population
2. Gene Flow
Movement of genes either into or
out of a population
Migration – Immigration (add alleles)
and Emigration (subtract alleles)
4 Driving Forces behind Evol.
3. Genetic Drift
Change in the allele frequency in a
small population by chance alone
• Bottleneck Effect
• Founder Effect
4 Driving Forces behind Evol.
3. Genetic Drift
Bottleneck Effect:
population
undergoes a high
mortality rate;
genetic variation
decreases
dramatically
Ex: Cheetahs
Genetic Drift: Bottleneck Effect
4 Driving Forces behind Evol.
3. Genetic Drift
Founder Effect:
few individuals
leave a large
population to start
their own; gene
pool is very
limited
Ex: polydactyly in
PA Amish
Genetic Drift: Founder Effect
Genetic Drift: Founder Effect
4 Driving Forces behind Evol.
4. Selection
Natural – differential success in the
reproduction of different phenotypes
resulting from the interaction of
organisms with their environment
• Nature does the selecting
4 Driving Forces behind Evol.
4. Selection
(Natural)
Resistance –
overuse of
insecticides
and antibiotics
have bred
resistant
species of
bugs and
germs
4 Driving Forces behind Evol.
4. Selection
Artificial – breeding of domesticated
plants and animals
• Humans intentionally
do the selecting
• Cabbage, cauliflower,
Brussels sprouts, kale,
kohlrabi and broccoli have
a common ancestor in one
species of wild mustard
4 Driving Forces behind Evol.
Problems with artificial selection – not
enough genetic variation
4 Driving Forces behind Evol.
4. Selection (Sexual)
Intrasexual selection – selection
within the same sex (competition,
usually between males
 Competition, usually between
males
 Exaggerated
anatomy
Bighorn Sheep
Rocky
Mountain
Elk
Five-horned
Rhinoceros Beetles
Stagbeetles
4 Driving Forces behind Evol.
4. Selection (Sexual)
Intersexual selection – one sex
selects mate based on phenotypes
Exaggerated anatomy
Selection can influence populations in
three major ways:
Directional Sel.
Stabilizing Sel.
Disruptive (diversifying) Sel.
Directional Selection
Environment selects
against one phenotypic
extreme, allowing the
other to become more
prevalent
Disruptive Selection
Environment selects
against intermediate
phenotype, allowing
both extremes to
become more prevalent
Stabilizing Selection
Environment selects
against two extreme
phenotypes, allowing
the intermediates to
become more prevalent
Key Points
1. Natural selection does not cause genetic
changes in individuals.
2. Natural selection acts on individuals;
evolution occurs in populations.
3. Evolution is a change in the allele
frequencies of a population, owing to
unequal success at reproduction among
organisms bearing different alleles.
4. Evolutionary changes are not “good” nor
“progressive” in any absolute sense.
Evolutionary Theory
Foundation on which the rest of the
biological science is built. Collection of
carefully reasoned and tested
hypotheses about how evolutionary
change occurs.
Speciation
What is a species?
Biological definition: a group of
closely related organisms
(population) that can interbreed to
produce fertile, viable offspring
Speciation
Why can’t/don’t populations
interbreed?
Prezygotic barriers
Postzygotic barriers
Prezygotic Barriers
Ecological (habitat) isolation – pops live
in different habitats and do not meet
Parasites generally don’t transfer
hosts
Temporal isolation – active or fertile at
different times
Flowering plants pollinate on different
days or different times of the day
Prezygotic Barriers
Behavioral isolation – differences in
activities
Mating calls or actions are different
Prezygotic Barriers
Mechanical isolation – mating organs
do not fit or match
Enough said
Gametic isolation – gametes cannot
combine
Sperm destroyed in “different” vaginal
cavity
Sperm and egg don’t fuse due to
different membrane proteins
Postzygotic Barriers
Hybrid inviability – hybrid zygotes fail to
develop or reach sexual maturity
Hybrid infertility – hybrids fail to
produce functional gametes
Summary
2 or more mechanisms may
occur at once
Ex: Bufo americanus and
Bufo fowleri are ecologically,
temporally, and behaviorally
isolated
Bufo americanus breeds in
early spring in small, shallow
puddles or nearby dry creeks
Bufo fowleri breeds in late
spring in large pools and
streams
Their mating calls also differ
Limitations of Biological
Species Concept
How do you classify organisms that:
have the potential to interbreed, but
do not do so in nature?
do not reproduce sexually?
exist only as fossils?
Alternative species concepts
(ecological, pluralistic, morphological,
genealogical) help address limitations
Modes of Speciation
Allopatric (Greek, allos = other;
Latin, patria = homeland)
Speciation due to geographic
separation
Barrier stops gene flow
between populations
Evolutionary change acts
independently on each pop to
establish reproductive barriers
Mitochondrial DNA
analysis has shown that
certain tamarin monkey
pops (those separated
by wide rivers) are
diverging toward
speciation
Where the Amazon is very wide, tamarins on
one side are brown, but on the other side
are white. Where the Amazon is narrow,
tamarins of both colors are found on either
side
Allopatric Speciation
Birds can move freely across the gorge
of the Grand Canyon; squirrels cannot
A. leucurus
A. harrisi
Two species arose when their original
pop was disrupted by the carving of the
canyon
A. harrisi
A. leucurus
Allopatric Speciation
If not given enough time, speciation will
not occur
Also, even
if they do
come
back
together,
they need
to interbreed to be the same species
Allopatric Speciation
Figure 24.11
Adaptive
Radiation:
evolution of many
diversely-adapted
species from a
common ancestor
Ex: Hawaiian
archipelago
Sympatric Speciation
Sympatric (Greek, sym = together;
Latin, patria = homeland)
Speciation occurs in populations that
share a habitat
Results from:
Ecological isolation
Polyploidy (number of sets of
chromosomes increases)
Sympatric Speciation
Polyploidy (number of sets of
chromosomes increases)
A result of accidents in meiosis
Will Speciation Occur?
p+q=1
p2 + 2pq + q2 = 1
Will speciation occur? You tell me!
Hardy-Weinberg PPT 1
Hardy-Weinberg PPT 2
Evolutionary Time Scales
Evolution can take a long time or can
occur relatively quickly
Gradualism
Punctuated Equilibrium
Evolutionary Time Scales
Gradualism – big
evolutionary
changes are the
result of many
small ones over a
long period of
time
Evolutionary Time Scales
Punctuated
Equilibrium –
speciation occurs
fairly rapidly then
remain constant
Evolutionary Novelties
Unique and highly specialized organs
seem to complicated to have been
naturally selected
Ex: eyes are really just photoreceptors;
some are more developed, but all do
the basic function: receive light
Evolutionary Novelties
Evo-devo
Evolutionary development
A field of interdisciplinary research that
examines how slight genetic
divergences can become magnified into
major morphological differences
between species
Evo-devo
By blocking expression of one gene,
researchers forced a chicken’s foot to
develop to resemble a duck’s foot
Two embryos from the same animal
Evo-devo
Left, a normal
chicken leg will
develop
Right, a normal duck leg will develop…
from a chicken embryo
Chicken leg: scaled with 4 digits
Duck leg: smooth and webbed
Duck legs, due to one genetic
evolutionary difference, help ducks do
many things chickens cannot, like swim