Darwin and Natural Selection

Transcription

UNIT 3: Evolution and Diversity
Topic 16
How Populations Evolve
 CEB Textbook Chapter 13, pages 242-265
 Mastering Biology, Chapter 13
Learning Outcomes
After studying this topic you should be
able to:
• Define and describe the process of
natural selection, and explain how
this process can lead to evolutionary
adaptation.
•Compare the ideas of Lamarck,
Wallace, and Darwin on the ability of
species to change.
•Explain how each of the following
provides evidence that evolution
occurs: the fossil record,
biogeography, comparative
anatomy, comparative embryology,
and molecular biology.
Evolution Videos
Darwin and Natural Selection
Homework
• Watch Darwin Videos
• Draw a table with the
definitions of the following
terms: natural selection,
evolutionary adaptation and
evolution.
• Unit Assessment 3: Topic 16
• Mastering Biology Activities:
Reconstructing Forelimbs
• Evolution Assignment
Mastering Biology
• The Genius of Charles Darwin (Pt 1, 2 and 3) –
• (Note: Presenter Richard Dawkins is an Atheist.....
• BUT is it impossible for someone to agree with the theory of
evolution AND be religious? What’s your opinion?)
• http://www.youtube.com/watch?v=ptV9sNezEvk
• http://www.youtube.com/watch?v=shkWhBVfe3o
• http://www.youtube.com/watch?v=cARUZyBJtdY
• What Darwin Never Knew (NOVA)
• http://www.youtube.com/watch?v=AYBRbCLI4zU
2004: NEW EVIDENCE FOR
GLOBAL WARMING
Are rising CO2 levels threatening
global warming? Most scientists agree
that this happens because CO2 traps
radiation in the atmosphere. New data
gives more support to this explanation.
Ice samples have been taken from the
Antarctic up to 3 km deep. Air bubbles in
the ice have been tested for their CO2
levels. Levels now are the highest
recorded.
2003:
NEW
THEORY
FOR
START OF LIFE ON EARTH
Think life on Earth came from
Mars? So do some scientists. But
now two of them have come up
with a different explanation. They
say that evidence beneath the
seas can explain how life started
on Earth.
1
1859: DARWIN BOOK
CAUSES ANGRY DEBATE
Members of the clergy and
scientists are outraged by a new
book published today. In On the
Origin of Species Charles Darwin
explains how he thinks life has
developed on Earth. One of his most
outrageous claims is that men are
descended from apes!
These cartoons were
produced in the press
and show the strength
of feeling about Darwin’s
ideas of evolution
through natural
selection
Theories for change
Dates of theories:
• Lamarck (1809)
• Cuvier (1825)
• Darwin (1844, but not published until 1859)
In the early 19th century:
1. The Church taught that the Bible was true word for word.
The wife of the Bishop of
Worcester said of Darwin’s
ideas:
‘My dear, descended from
the apes! Let us hope it is
not true, but if it is, let us
pray that it will not become
generally known.’
2. Almost everyone believed that Earth and all living things had
been created in 4004 BC.
3. Scientists had collected lots of evidence of variation in
animals and plants.
4. Many people accepted that fossils were the remains of
organisms from the past.
5. Scientists saw that different layers of rocks contained
different sets of fossils.
6. A few people thought fossils showed that some living things
died out and were then replaced by others.
7. Small changes in living things had been observed.
Early Contributions to
Evolutionary Thought
Jean Léopold Nicolas Frédéric
Cuvier (1769 – 1832)
French naturalist and zoologist.
Cuvier
A major figure in natural sciences
research in the early 19th century,
and was instrumental in
establishing the fields of
comparative anatomy and
paleontology through his work in
comparing living animals with
fossils.
Contributors to the development of
Darwin’s ideas were:
Jean Baptiste de Lamarck
(1744-1829)
Believed that organisms could
pass on traits acquired during
their lifetime.
Discredited: when the
mechanisms of heredity became
known.
Important: because he was the
first to propose that change over
time was the result of natural
phenomena and not divine
intervention.
2
Thomas Malthus (1766-1834)
Believed that populations increased in
size until checked by the environment,
called the ‘struggle for existence’.
Charles Lyell (1797-1875)
Developed the geological theory of
uniformitarianism: the physical
features of the earth were the result of
slow geological processes that still
occur today.
Herbert Spenser (1820-1903)
Introduced the concept of ‘Survival of
the Fittest’.
Explanations for change
Person
Explanation they came up
with for the data
Lamarck
Evolution – organisms developed
new features as a result of an
‘inner urge’ for improvement and
they passed the improvements on
to their young

Cuvier
Catastrophism – organisms were
wiped out by a series of
catastrophies. Then God created
new, improved versions

Darwin
Evolution by natural selection.
All of these theories involved
creative thought

Charles Lyell
Herbert Spenser
2. All the explanations caused arguments.
a Round 1: Lamarck vs Cuvier
Cuvier won this round. Lamarck’s idea was unpopular.
Suggest some reasons why.
……………………………………………………………………………………………
• Cuvier criticized Lamarck’s theory.
……………………………………………………………………………………………
• Cuvier was a more influential scientist.
• The idea of an ‘inner urge’ was not enough to explain
……………………………………………………………………………………………
the appearance or disappearance of characteristics.
• Lamarck could not explain how features were passed on.
• Evolution went against what was written in the Bible, so
Catastrophism was more acceptable at the time.
• The accepted time-scale was too short for evolution.
Lamarck Vs Darwin
Lamarck proposed that organisms could gradually bring
about changes in themselves to suit the environment
and, that these changes could be passed on to their
offspring.
Creative thought was
needed to come up
with the explanation?
( or )
b Round 2: Cuvier vs Darwin
This time many, but not all, important scientists favoured
Darwin. Other scientists and some clergymen preferred
the explanations of the Bible. Suggest some challenges
that people made to each explanation.
• Darwin gathered lots of evidence in support of his idea and it did
Cuvier: …………………………………………………………………………………
not support Cuvier’s idea. Geologists challenged the idea that there
was no connection between the fossils in successive layers of rock
…………………………………………………………………………………
• Darwin had no explanation of how features were passed on.
Darwin: …………………………………………………………………………………
• Evolution went against what the Bible said.
• In drawing together the ideas, emphasize that:
…………………………………………………………………………………
• different theories can be suggested to explain the same data
• the theory that becomes generally accepted at any particular
time is the one that:
• best fits the data
• is not successfully challenged at the time
• explains new data
History of Evolutionary Thought
Hebert Spencer
1820 - 1903
Proposed concept of the
‘survival of the fittest’
Erasmus Darwin
1731 - 1802
Charles Darwin's grandfather
and probably an important
influence in developing his
thoughts on evolution.
John Baptiste de Lamarck
1744 - 1829
First to publish a reasoned theory
of evolution. Proposed idea of
use and disuse and inheritance of
acquired characteristics.
Rev. Thomas Malthus
1766 - 1834
Wrote: ‘An Essay on the
Principles of Population’,
attempting to justify the squalid
conditions of the poor.
Charles Lyell
1797 - 1875
Major influence on Darwin.
Lyell’s work ‘Principles of Geology’
proposed that the earth is very old.
What examples are there that disprove this theory?
Alfred Russel Wallace
1823 - 1913
‘Theory of Natural Selection’
Charles Darwin
1809 - 1882
‘Theory of Evolution
by Natural Selection’
August Weismann
1834 - 1914
Proposed chromosomes as the
basis of heredity, demolishing the
theory that acquired
characteristics could be inherited.
R.A. Fisher 1890-1962
J.B.S. Haldane
Sewall Wright 1889-1988
Julian Huxley 1887-1975
Ernst Mayr
1904-2005
T. Dobzhansky
The New Synthesis
1898-1964
Founding of population genetics and
mathematical aspects of evolution and genetics.
Gregor Mendel
1822 - 1884
Developed the
fundamentals of the genetic
basis of inheritance.
Neo-Darwinism: The version of Darwin’s
theory refined and developed in the light of
modern biological knowledge (especially
genetics) in the mid-20th century
1900-1975
Collaborated to formulate the modern
theory of evolution, incorporating
developments in genetics,
paleontology and other branches of
biology.
3
The Development
of Darwin’s Ideas
The Modern Theory of Evolution
The modern theory of evolution combines the
following ideas:
Darwin’s theory of the origin of species by
natural selection.
with an understanding of genetics (from Mendel).
and the chromosomal basis of heredity (from
Weismann).
+
Darwin
The first convincing case for evolution, The
Origin of Species, was published by Charles
Darwin in 1859.
In this book, Darwin argued that new species
developed from ancestral ones by natural
selection.
Darwin developed his theory of “survival of
the fittest” by building on earlier ideas and
supporting his views with a large body of
evidence he collected while voyaging
extensively on the ship the ‘HMS Beagle’.
+
Mendel
Alfred Russel Wallace, a young specimen
collector working in the East Indies,
developed a theory of natural selection
independently of Darwin.
However, Darwin supported the theory more
extensively and receives most of the credit for
it.
Weismann
Figure 13.4
The Development of
Darwin’s Ideas
Darwin’s theory was
supported by data collected
from:
The flora and fauna of South America.
These showed different adaptations for
diverse environments but were distinct from
the European forms.
Observations of the fauna of the Galapagos
Islands confirming his already formulated
ideas from earlier in the trip. He found that
most of the Galapagos species are
endemic, but resembled species on the
South American mainland.
HMS Beagle
Darwin
in 1840
North
America
Great
Britain
Europe
Asia
ATLANTIC
OCEAN
Africa
Galápagos
Islands
PACIFIC
OCEAN
Pinta
Marchena
South
America
Genovesa
Equator
Santiago
Isabela
0
0
Equator
Daphne Islands
Pinzón
Fernandina
40 km
Santa
Cruz Santa
Fe
Florenza
San
Cristobal
Australia
PACIFIC
OCEAN
Cape of
Good Hope
Cape Horn
Española
Tasmania
40 miles
Tierra del Fuego
New Zealand
Fossil finds of extinct species.
Evidence from artificial selection.
Figure 13.12
(a) The large ground finch
(b) The warbler finch
(c) The woodpecker finch
4
The Concepts of Darwinism
Darwin’s view of life was of ‘descent with
modification’: descendants of ancestral
forms adapted to different
environments over a long period of
time.
The mechanism for adaptation is called
‘natural selection’, and is based on a
number of principles:
The Concepts of Darwinism
Overproduction: Species produce more young than will
survive to reproductive age (they die before they have
offspring).
Variation: Individuals vary from one another in many
characteristics (even siblings differ). Some variations are
better suited then others to the conditions of the time.
Competition: There is competition among the offspring for
resources (food, habitat etc.).
Survival of the fittest phenotype: The individuals with
the most favorable combinations of characteristics will be
most likely to survive and pass their genes on to the next
generation.
Favorable combinations increase: Each new generation
will contain more offspring from individuals with favorable
characters than those with unfavorable ones.
Overproduction
Variation
Competition
Survival of the fittest phenotype
Favorable combinations increase
Natural Selection
Natural selection
Overproduction
Variation
Populations produce too
many young: many must die
Individuals show variation:
some variationsare more
favorable than others
Natural Selection
Natural selection favors
the best suited at the time
Inheritance
Variations are
inherited. The best
suited variants
leave more
offspring.
Figure 13.15-1
The evolution of superbugs?
Insecticide application
Chromosome with gene
conferring resistance
to pesticide
5
Figure 13.15-2
Figure 13.15-3
to pesticide
to pesticide
Survivors
Reproduction
Natural selection in rats: warfarin
How do some rats become resistant to warfarin?
These statements describe how the number of
warfarin resistant rats may increase in a
population.
• Warfarin kills most rats.
Click on the links to find out more.
• But a few are resistant to the poison.
• DNA controls the proteins that a cell makes.
Remind me about DNA.
• People use warfarin to kill rats.
• DNA is copied when a new cell is made.
• The resistant rats survive the poison.
• The resistant rats breed.
• They pass on their features to the next
generation.
• The number of resistant rats increases with
each generation.
But there is a big
unanswered question:
Sometimes a mistake is made – this is called a
mutation.
• How do some rats
become resistant
to warfarin in the
first place?
• Most mutations are harmless, some are harmful.
Very rarely mutations may be helpful to an
organism.
Tell me about mutations.
What sort of mutations can be helpful?
Next
DNA
Mutations
• Each gene is the
instruction for making
one protein.
• DNA molecules are
very long.
• They have a double
helix shape.
• Sometimes a mistake
is made when the
gene’s DNA is copied.
genes
• The gene may code
for a different
protein.
• Chromosomes are
made of DNA.
• Genes are sections of
chromosomes.
• A gene is the
instruction for how to
make one type of
protein.
• Mutations do happen
naturally.
chromosome
DNA
• They can also be
caused by some
chemicals, and ionizing
radiation.
Part of the DNA
molecule
Back
Back
6
How can mutations be helpful?
List the factors which can combine to produce a new
species
• Most mutations do not help the organism.
• The different protein that is made cannot do its
job well.
• But mutations are random – a very small number
may help the organism survive in some
environments.
• mutation
This bacterium is resistant
to most antibiotics.
• environmental change
• natural selection
• For example, some bacteria have mutations that
make them resistant to certain antibiotics.
• Sickle-cell anaemia is a serious blood disease.
People with two copies of the disease allele can
be very ill. But people who carry just one copy of
the allele have protection from malaria. This
helps them to survive in countries where malaria
is common.
A person who is a carrier of
the sickle cell allele is
protected from malaria.
Back
Who Wants to Live a Million Years?
http://science.discovery.com/games-and-interactives/charlesdarwin-game.htm
Homework
• Watch Darwin Videos
• Draw a table with the
definitions of the following
terms: natural selection,
evolutionary adaptation and
evolution.
• Unit Assessment 3: Topic 16
• Mastering Biology Activities:
Reconstructing Forelimbs
Evolution Videos
• The Genius of Charles Darwin (Pt 1, 2 and 3) – VERY
GOOD!
• http://www.youtube.com/watch?v=ptV9sNezEvk
• http://www.youtube.com/watch?v=shkWhBVfe3o
• http://www.youtube.com/watch?v=cARUZyBJtdY
• What Darwin Never Knew (NOVA)
• http://www.youtube.com/watch?v=AYBRbCLI4zU
What is Evolution?
Evolution refers to the
permanent genetic change
(change in gene
frequencies) in population
of individuals.
It does not refer to changes
occurring to individuals within
their own lifetimes.
Populations evolve, not
individuals.
Microevolution describes the
small-scale changes within
gene pools over generations.
Macroevolution is the term
used to describe large scale
changes in form, as viewed in
the fossil record, involving
whole groups of species and
genera.
7
Evidence for Evolution
Evidence for Evolution
Evolutionary theory is now supported by a
wealth of observations and experiments
Biogeography: The study of
geographic distributions can indicate
where species may have originally
arisen.
Paleontology: The identification,
interpretation and dating of fossils
gives us some of the most direct
evidence of evolution.
Embryology and evolutionary developmental
biology: The study of embryonic development
in different organisms and its genetic control.
Paleontology
Paleontology
Artificial selection: Selective breeding
of plants and animals has shown that
the phenotypic characteristics of
species can change over generations
as particular traits are selected in
offspring.
Biochemistry: Similarities and
differences in the biochemical make-up
of organisms can closely parallel
similarities and differences in
appearance.
Comparative anatomy:
The study of the morphology
of different species.
From gray wolf to
Yorkshire terrier:
selective breeding
can result in
phenotypic change
Molecular genetics: Sequencing of
DNA and proteins indicates the degree
of relatedness between organisms.
Comparative anatomy
The Fossil Record
Types of Fossils
The fossil record is a
substantial, but incomplete,
record of evolutionary history:
Fossils form best when
organisms are buried quickly
in conditions that slow the
process of decay.
Modern species can be traced through fossil
relatives to distant origins.
Fossil species are often similar to, but usually
differ from, today's species.
Fossil types often differ between
sedimentary rock layers.
These fossil teeth, from Mastodon,
an extinct elephant, are similar to the
deciduous teeth of modern
elephants.
Numerous extinct species are found as
fossils.
Fossils can be dated to establish their
approximate absolute age.
Fossils are most commonly
found in sedimentary rock.
Mineral-rich hard parts (bones,
teeth, shells) may remain as fossils,
or minerals dissolved in water, may
seep into tissues and replace
the organic matter of the organism.
The Archaeopteryx Fossil
Fossils in a Rock Profile
Eight well-preserved fossil specimens have been discovered in finegrained limestone in Germany (dated late Jurassic, about 150 million years
ago).
Avian Features
Forelimb has three
functional fingers
with grasping
claws.
Vertebrae are
almost flatfaced.
Lacks the reductions
and fusions present
in other birds.
Impressions of
feathers attached
to the forelimb.
Breastbone is small
and lacks a keel.
Belly ribs.
The hind-limb girdle
is typical of
dinosaurs, although
modified.
Long, bony tail.
A layer of shell
still covers the
stone interior
of this
ammonite
Bird bones
preserved in a tar
pit
Rates of evolution can vary, with bursts of
species formation followed by stable periods.
True teeth set in
sockets in the jaws.
Trilobites
preserved in
sedimentary rock
On rare occasions, fossils retain organic
material, as when plant material is compressed
between layers of shale or sandstone.
New fossil types mark changes in the past
environmental conditions on the Earth.
Reptilian Features
Fossil fish
The term fossil refers to any parts or impressions of an
organism that may survive after its death.
Incomplete fusion
of the lower leg
bones.
Impressions of
feathers attached
to the tail.
LEFT: Archaeopteryx lithographica
Found in 1877 near Blumenberg, Germany
Layers of sedimentary
rock are arranged in
the order in which they
were deposited, with
the most recent layers
nearer the surface.
Most recent
sediments
Numerous
extinct species
Fossil types
differ in each
sedimentary
rock layer
Sedimentary layers can be
disturbed by subsequent
tectonic activity.
The interpretation of
rock layers containing
fossils allows us to
arrange the fossils in
chronological order
(order of occurrence),
but does not give their
absolute date.
Recent fossils are
found in recent
sediments
New fossil types
mark changes in
environment
Oldest
sediments
Only primitive
fossils are found in
older sediments
8
Radioactive decay
of carbon-14
The relative age of
fossils is useful, but
fossils provide
reliable historical
data only if we can
determine their
absolute age.
Electron Spin Resonance
500 000 – 1000
Bone, tooth
enamel, cave
deposits
Fission Track
1 million – 100 000
Volcanic rock
Obsidian Hydration
800 000 – present
A number of
methods are used
to date fossils.
Obsidian
(volcanic glass)
Amino acid racemization
1 million – 2000
Bone
Thermoluminescence
less than 200 000
Pottery, fired clay,
bricks, burned rock
Dating Method
Age Range
(years)
Material Dated
Carbon-14 radioactivity
(as % of living organism’s
C-14 to C-12 ratio)
Figure 14.15
Dating Fossils
100
75
50
25
0
0
5.6 11.2 16.8 22.4 28.0 33.6 39.2 44.8 50.4
Time (thousands of years)
Uranium/Thorium
Less than 350 000 Bone, tooth dentine
Carbon 14
1000 – 50 000+
Bone, shell,
charcoal
Potassium/Argon
10 000 – 100 million
Volcanic rocks
A fossil trilobite, a primitive arthropod
that dwelled in the seas of the
Devonian period 370 million years ago
How
carbon-14
dating is
used to
determine
the vintage
of a
fossilized
clam shell
Carbon-14 in shell
Carbon-14 is taken up
by the clam in trace
quantities, along with
much larger quantities
of carbon-12.
After the clam dies,
carbon-14 amounts
decline due to
radioactive decay.
Measuring the ratio of
carbon-14 to carbon-12
reveals how many halflife reductions have
occurred since the
clam’s death.
The History of Life on Earth
The history of life is divided up into eons, eras,
periods, and epochs:
Formation of
the earth
4600 mya
Oldest known microfossils
Oxygen produced by
found in 3500 million year
plants accumulates in
old chert in Western
the atmosphere
Australia
Precambrian Eon
Millions of years ago
Quaternary
Animation: The Geologic Record
Eras
Right click slide / select “Play”
Evolutionary History
© 2013 Pearson Education, Inc.
Evolutionary History 2
Bacteria and algae
Bacteria, protists, and fungi
have an evolutionary history
extending back to the
Precambrian.
Some invertebrate groups
extend back to the Cambrian
Period, but land plants only
as far back as the Devonian
Period.
Land plants
Fungi
Sphenophytes (ferns etc)
Conifers
Cycads
Angiosperms
Cnidarians
Flatworms
Invertebrates
Based on fossil
evidence and radioisotope dating, the
evolutionary history
of plants, fungi,
bacteria, protists,
and non-chordate
animals can be
compiled.
Protists
Molluscks
Annelid worms
Insecta
Crustacea
Tunicates
Similarly, the
evolutionary
history of
chordates can be
traced back to the
Cambrian, but
most animal
groups are much
more recent than
this.
Agnatha (jawless fishes)
Sharks and rays
Ray finned fishes
Fish
Lungfish
Amphibians
Amphibians
Chelonia (turtles a& tortoises)
Reptiles
Crocodilia
Rhyncocephalia (tuatara)
Squamata (lizards & snakes)
Birds
Birds
Diplopoda
Monotremes
Arachnids
Echinoderms
Mammals
Marsupials
Placentals
9
Figure 14.26a
Figure 14.14
A researcher
excavating a
fossilized
dinosaur
skeleton from
sandstone
Ancestral
mammal
Monotremes
(5 species)
Extinction of
dinosaurs
Reptilian
ancestor
A sedimentary fossil formed
by minerals replacing the
organic matter of a tree
Marsupials
(324
species)
A 45-million-year-old
insect embedded
in amber
Eutherians
(5,010
species)
250
200
100
65 50
150
0
Trace fossils: footprints, burrows,
or other remnants of an ancient
organism’s behavior
Tusks of a 23,000-year-old mammoth
discovered in Siberian ice
Figure 13.10
Comparative Embryology
When we compare the
embryonic development
of different vertebrates, it
is evident that more
closely related forms
continue to appear
similar until a later stage,
compared to more
distantly related forms.
Note that although the
early developmental
sequences between all
vertebrates are similar,
phylogeny is not retraced
during development.
Developmental
Stage
Amphibian
Bird
Monkey
Human
Fertilized
egg
Pharyngeal
pouches
Late
cleavage
Body
segment
s
Gill
slits
Post-anal
tail
Limb
buds
Chicken embryo
Human embryo
Late fetal
Homologous Structures
Comparative Anatomy
The pentadactyl
(5 digit) limb
found in most
vertebrates has
the same general
bone structure.
This similarity of
structure is called
homology.
Homology –
Anatomical
similarity due to
common ancestry
Forelimb
Hind Limb
Humerus
(upper arm)
Ulna
Femur (thigh)
Fibula
Radius
Tibia
Carpals
(wrist)
Tarsals
(ankle)
Metacarpals
(palm)
Metatarsals
(sole)
Phalanges
(fingers)
Phalanges
(toes)
Note that forelimbs and hind limbs have
different names for equivalent bones.
In many vertebrates,
the basic pentadactyl
limb has been highly
modified to serve
specialized locomotory
functions.
The same pattern of
bones comprising the
pentadactyl limb can
be seen on each of
these examples.
Mole's
forelimb
Bird's wing
Such homologies also
indicate adaptive
radiation, as the basic
limb plan has been
adapted to meet the
needs of different
niches.
Dog's
front leg
Bat's wing
Seal's
flipper
Human arm
10
Figure 13.9
Figure 13.17
Common ancestor of
lineages to the right
Lungfishes
Tetrapods
Amniotes
Amphibians
1
Mammals
2
Tetrapod
limbs
Lizards
and snakes
3
Amnion
Crocodiles
4
Cat
Whale
Bat
Analogous Structures
Ostriches
6
Feathers
Hawks and
other birds
Analogy in Eye Structure
Not all similarities between
species are inherited from a
common ancestor.
Structures that have the same
function in different organisms
may come from quite different
origins. This phenomenon is
termed analogy.
Homologous trait
shared by all groups
to the right
Birds
5
Human
Fins
Eyes in cephalopods
(such as octopus) and Mammalian eye
mammals have the
same function and are
structurally similar, but
have evolved from
different origins.
Iris
Lens
Cornea
Flippers
Retina
Analogous structures do not
imply an evolutionary
relationship,
but may indicate
convergence. Examples:
Eye structure in octopus and
mammals.
Octopus eye
Retina
Iris
Wings
Lens
Cornea
Wings in birds and butterflies.
Fins in fish and flippers in mammals
Vestigial Organs
Organs
Vestigial
Many organisms have degenerate structures that no
longer perform the same function as in other
organisms.
These organs must have been important in some
ancestral form, but became redundant in later species.
The wings of kiwi are tiny vestiges and useless.
In snakes, one lobe of the lung is vestigial
and, in some species, there are also
vestiges of the pelvic girdle and hind limbs.
The vestigial eyes of burrowing animals are
no longer used for vision.
Vestigial Organs in Whales
Whales are the
descendants of large,
four-legged land
mammals that took up
an aquatic existence
some 60 million years
ago.
Femur
Pelvis
Over many millions of
years, the pelvis and
femur of whales have
become very small and
no longer fulfill a
locomotory function.
Hindlimb
Forelimb
11
Cladogram of
Whale Ancestors
Whale Ancestors
The fossil record exhibiting whale evolution
is extensive and well represented by
skeletons that show much of their anatomy.
The study of plant and animal
distribution is called
biogeography.
Black lines represent
cladistic relationship
(probable relatedness)
Pakicetus (Middle Eocene)
Biogeographical Evidence
Lemurs are endemic
to the island of
Madagascar
The basic principle of biogeography is that
each plant and animal species originated
only once. The place where this occurred is
the centre of origin.
The range of a species can be very
restricted or, as with humans, almost the
whole world (cosmopolitan).
Protocetus (Eocene)
Regions that have been separated from the
rest of the world for a long time (e.g.
Madagascar, Australia, and New Zealand),
often have distinctive biota comprising a
large number of endemic species (species
that are found nowhere else).
Basilosaurus (Late Eocene)
Red lines represents fossil
record for the genus
Map: University of Texas at
Austin (Public Domain image)
Biogeographical Distribution
The distribution of
species around the
world suggests that
modern forms
evolved from
ancestral
populations and
spread out (radiated)
out into new
environments.
Good examples are
found on islands
offshore from large
continental land
masses:
Galapagos Islands
The Galapagos Islands have
species very similar to, but distinct
from, the South American
mainland.
Ancestral forms probably migrated
to the islands from the mainland in
the past.
Galapagos Islands
The giant tortoises are
among the most well
known of the Galapagos
fauna
Cape Verde Islands
Tristan da Cunha
Island Colonizers
Land mammals rarely colonize
islands. A high metabolic rate
requires much food and water.
Mammals cannot sustain
themselves on long sea
journeys.
Small birds, bats, and insects are
blown to islands by accident. They
must adapt to life there or perish.
Blown by
strong winds
Reptiles probably reach distant
islands by floating in driftwood.
A low metabolic rate enables
them to survive long periods
without food and water.
Figure 13.8
Active
flight
Seabirds fly to and from islands
with relative ease. Some adapt to
life on land, (e.g. the flightless
cormorant in the Galapagos
Islands). Others, may treat the
island as a stopping place (e.g. the
frigate bird).
Australia
Common
ringtail
possum
Koala
Oceanic island
Rafting on
drifting vegetation
Amphibians cannot live away
from fresh water. They seldom
reach offshore islands unless
that island is a continental
remnant.
Planktonic
larvae
Swimming
Sea mammals have little
difficulty in reaching islands (e.g.
seals, sea lions). They do not
colonize the interior of islands.
Common wombat
Deep
ocean
Crustacean larvae drift to islands
(e.g. crabs). Some crabs have
adapted to an island niche.
Red kangaroo
12
Molecular Biology
DNA Hybridization Method
One way to reconstruct the
evolutionary history of a
species is using DNA
hybridization.
DNA is isolated from
blood samples from
each species:
Stork
In this technique, the DNA from different
species is ‘unzipped’ and recombined to
form hybrid DNA.
The greater the similarity in the
DNA base sequences, the
stronger the attraction between
the two strands and the harder it
is to separate them again.
Heat can be used to separate the
hybridized strands. The amount of heat
required to do this is a measure of how
similar the two DNA strands are (%
bonding).
Extract human DNA
Unzip the DNA using heat
(both human and
chimpanzee DNA unwinds at
86°C)
A crude measure of DNA
relatedness can be achieved by
measuring how hard it is to
separate the hybrid DNA.
EXAMPLE:
The relationships among the New World
vultures and storks has been
determined on the basis of DNA
hybridization.
Extract chimpanzee DNA
Mix strands to
form a hybrid
This is done by finding the
temperature at which it unzips
into single strands again (in this
case it would be 83.6°C).
New World
vulture
Some of the opposing
bases in the DNA
sequence do not match
Figure 13.11
DNA Sequencing
Recent advanced
techniques have enabled the
sequence of DNA in different
species to be determined.
Species thought to be
closely related on the basis
of other evidence, were
found to have a greater
percentage of DNA
sequences in common.
92%
100%
Human
Gorilla
Orangutan
Gibbon
An interesting finding was that the DNA of
humans and chimpanzees is more closely
matched than that of chimpanzees and
gorillas.
Old World
monkey
Amino Acid Sequencing
Artificial Selection in Dogs
Squirrel
monkey
Gibbon
Dogs were probably first domesticated at least 14 000
years ago from a gray wolf ancestor.
Some 400 breeds have been bred from this single
wild species as a result of selective breeding by
humans.
Rhesus
monkey
Primate
No. of amino
acids different
from humans
Chimpanzee
Identical
Gorilla
1
104
Position of
changed amino acids
–
Gibbon
3
80 87 125
Rhesus monkey
8
9 13 33 50 76 87 104 125
Squirrel monkey
9
5 6 9 21 22 56 76 87 125
Gorilla
Chimpanzee
96%
Chimpanzee
Humans and chimpanzees have a 97.6%
similarity in their DNA sequences and are
very closely related.
Amino acid
differences for
beta-hemoglobin in
primates
compared to the
human sequence:
Percent of selected DNA
sequences that match a
chimpanzee’s DNA
Primate
The 'position of changed amino acids' is the point in the protein,
composed of 146 amino acids, at which a different amino acid
occurs.
Example: The staffordshire bull terrier was
produced by breeding bulldogs and terriers.
From each litter, breeders selected pups with
the characteristics they desired.
Bulldog
Gray wolf
Terrier
Staffordshire bull terrier
Staffordshire bull terriers
combine characteristics of both
bulldogs and terriers
13
Artificial Selection in Dogs
The gray wolf is distributed throughout Europe, North America and
Asia. Amongst this species, there is a lot of phenotypic variation.
Selective Breeding or Artificial Selection
Selection is based on both physical and behavioral characteristics. In
this way, different breeds have been suited to different tasks.
Five ancient dog breeds are recognized, from which all other breeds
are thought to have descended by artificial selection.
Mastiff-type
Originally from Tibet,
this breed dates back
to the Stone Age
Pointer-type
Bred for the
purpose of hunting
small game.
Greyhound
One of the oldest
breeds, originating
the Middle East.
Sheepdog
Originated in Europe
and bred for stock
protection.
Wolf-type
Developed in snowcovered habitats in
Alaska, northern
Europe, and Siberia.
Grey wolves are the
ancestors of all dogs.
• Salukis are thought to
be one of the oldest
domesticated dog
breeds.
• Several breeds of dog
lived with the ancient
Greeks and Romans.
• Pictures of them are
carved in Ancient
Egyptian tombs.
• These included the
greyhound, mastiff,
and bloodhound.
• In the 1800s
dalmations were
trained to run next to
horse carriages.
• They guarded the
horses from other
dogs.
There are over 400 different breeds of domestic
dog.
14
Artificial selection vs Natural
selection
SUMMARY EVIDENCE OF EVOLUTION
Evolution leaves observable signs.
Five of the many lines of evidence in support of
evolution:
1.
2.
3.
4.
5.
the fossil record,
biogeography,
comparative anatomy,
comparative embryology, and
molecular biology.
Activity – Process of Science
Complete
1) What are the Patterns of Antibiotic resistance
2) How Do Environmental Changes Affect a Population?
More Evolution Videos (Useful)
• Crash Course in Biology – Natural Selection
• http://www.youtube.com/watch?v=aTftyFboC_M&list=PL5C9
56FAA7ADD146E
• Crash Course in Biology – Comparative Anatomy
• http://www.youtube.com/watch?v=7ABSjKS0hic
Topic 17
Microevolution
Learning
Outcomes
After studying this topic you
should be able to:
•Define a population,
describe its properties, and
explain why a population is
the smallest unit of evolution.
•Define microevolution.
•Explain the three
mechanisms of
microevolution: Genetic
drift, gene flow and
mutations.
15
Who Evolves in Microevolution?
What is Microevolution?
Microevolution describes the
small-scale changes within
gene pools over generations.
The smallest biological unit
that can evolve is the
POPULATION
Individuals do not evolve –
populations evolve.
Gene Pool
Populations
From a population genetics
viewpoint:
A population comprises
the total number of one
species in a particular
area.
All members of a
population have the
potential to interact with
each other. This includes
breeding.
he same species.
Continuous distribution
Example: human population,
Arctic tundra plant species
AA
A gene pool is
defined as the sum
total of all the
genes/allelles
present in a
population at any
one time.
Evolution is a
change over time in
the gene pool of a
species as more fit
individuals are
selected for leading
to those alleles
building up in the
gene pool
complement of the
population.
AA
Aa
aa
Aa
AA
AA
aa
Aa
AA
Aa
A gene pool made up
of 16 individuals
Example: Some frog species
Gene Pool
Changing Allele Frequencies
Geographic boundary
of the gene pool
Emigration
AA
aa
AA
Immigration
AA
aa
Aa
AA
AA
AA
Aa
Aa
Aa
Aa
AA
Aa
Aa
Aa
Aa
AA
Aa
Aa
AA
Aa
AA
aa
aa
Aa
Fragmented distribution
Individual is homozygous
recessive (aa)
aa
AA
aa
A’A
AA
Boundary of
gene pool
Natural selection
Aa
Mutation
Individual is
homozygous
dominant (AA)
aa
aa
AA
Aa
aa
Aa
Aa
Mate selection (nonrandom mating)
AA
AA
Gene flow
Geographical barrier
Aa
aa
Aa
Aa
Aa
Aa
Individual is
heterozygous (Aa)
Aa
AA
A gene pool made up of 16 individual organisms
with gene A, and where gene A has two alleles
aa
Aa
aa
aa
Aa
aa
Genetic drift
16
Complete
1) How Do Environmental Changes Affect a Population?
The gene
pool 
Three Mechanisms of Microevolution
Mutations
1) Mutations
2) Gene Flow
3) Genetic Drift
AA
New recessive
allele
Aa
AA
AA
a’a
In the graph below, a mutation
creates a new recessive allele: a'
The frequency of this new allele
increases when environmental
conditions change, giving it a
competitive advantage over the
other recessive allele: a
Aa
aa
Aa
Aa
Aa
Aa
Aa
aa
Aa
AA
aa
AA
AA
Aa
aa
Environmental
conditions change
Allele frequency
Mutations are the
source of all new
alleles.
Mutations can
therefore change
the frequency of
existing alleles by
competing with
them.
Recurrent
spontaneous
mutations may
become common
in a population if
they are not
harmful and are
not eliminated.
Mutation causes the
formation of a new
recessive allele
Generations
Gene flow is
the movement
of genes into
or out of a
population
(immigration
and emigration).
A population
may gain or lose
alleles through
gene flow.
Gene flow tends
to reduce the
differences
between
populations
because the
gene pools
become more
similar.
Gene Flow
Genetic DriftDrift
Barriers to gene flow
AA
AA
AA
AA
Aa
Aa
Aa
Aa
Aa
aa
Aa
Aa
AA
AA
Aa
AA
Aa
aa
AA
Aa Aa
AA
AA
AA
AA
aa
aa
aa Aa
aa
Aa
AA
Aa
Aa
AA
Population A
Aa
Aa
AA
Aa
aa
aa
Aa
Aa
AA
aa
No gene flow
Aa
aa
Population B
Population C
AA
AA
Aa
Aa
Aa
Aa
Aa
aa
AA
AA
Aa
AA
AA
Migration into and out of
population B
AA
Aa
AA
Aa
aa
AA
AA
Aa
Aa
Aa
AA
Population A
aa
Aa
aa
AA
aa
Aa
aa
Gene flow
aa
Aa
Aa
aa
aa
Aa
AA
AA Aa
AA
aa
aa Aa
aa
AA
Aa
AA
Aa Aa
Genetic Drift = Random
changes in the allele
frequencies in a population
aa
Aa
AA
AA Aa
aa
aa
Aa
AA
aa
Population B
Aa
For various reasons, not all
individuals will be able to
contribute their genes to the
next generation. As a result,
random changes occur in
allele frequencies in all
populations.
Genetic drift is often a
feature of small populations
that become isolated from
the larger population gene
pool, as with island
colonizers (right).
Population C
17
Allele Frequencies and
Population Size
Genetic Drift: Generation 1
In the following hypothetical
example, the allele frequencies in
the gene pool of a small
population are recorded over three
generations.
Aa
The allele frequencies of large
populations are more stable
because there is a greater
reservoir of variability and they
are less affected by changes
involving only a few individuals.
Aa
aa
Aa Aa
Small population
Cheetahs have a small
population with very
restricted genetic diversity
Small populations have fewer
alleles to begin with and so the
severity and speed of changes
in allele frequencies are
greater.
Endangered species with very
low population numbers or
restricted distributions may be
subjected to severe and rapid
allele changes.
AA
AA
aa
AA
AA
AA
Aa
Aa
aa
aa
Aa
aa
Aa
Aa
Aa
Aa
Aa
aa
AA
AA
Aa
aa
aa
AA
Aa
Aa
Aa
Aa
Aa
AA
AA Aa
AA
aa
AA
Aa
Aa
Aa
AA
Aa
aa
aa
Aa
AA
AA
aa
Aa
Aa
AA
The effect this had on the gene
pool was to reduce the frequency
of the dominant allele from 53%
to 50%.
Aa
Aa
aa
AA
Aa
Aa
Aa
aa
Aa
Aa
aa
An example may be the
sparsely distributed individuals
of the Siberian tiger population.
AA
AA
Fail to locate a
mate
A = 15 (50%) a = 15 (50%)
Aa
AA
Aa
Aa
The change in allele frequencies is directionless;
there is no selection pressure operating on the
alleles.
A = 13 (43%) a = 17 (57%)
aa
AA
Aa
Aa
Aa
aa
AA
Aa
Aa
Aa
aa
Killed in a
rock fall
Generation 3:
In another chance event, a
dark beetle was blown out to
sea by the strong winds during
a cyclone.
The effect on the gene pool
was to further reduce the
frequency of the dominant
Fail to locate a mate due
to low population density
Genetic Drift in Populations
Large gene pool
The changes in
allele
frequencies as
a result of
random genetic
drift can be
modelled in a
computer
simulation.
The breeding
populations
vary from 2000
(top) to 20
(bottom). Each
simulation runs
for 140
generations.
Aa
Large population
Two dark beetles were
accidentally killed in a rock fall.
This could equally have killed
any beetle; it was not a test of
the ‘fitness’ of the phenotype.
AA
This factor alone prevented
them from contributing their
genes to the next generation.
AA Aa Aa
With the random loss of alleles carried by these
individuals, the allele frequency changes from one
generation to the next.
Generation 2:
Another two beetles fail to breed
because they could not find a
mate in the dispersed population.
A = 16 (53%) a = 14 (47%)
Generation 1:
As a result of the sparse
distribution of the population,
two beetles fail to locate a mate.
Breeding population = 2000
Fluctuations are minimal
because large numbers of
individuals buffer the
population against large
changes in allele
frequencies.
AA
Aa
Aa
aa
aa
AA
Aa
Aa
aa
aa
AA
Aa
Aa
Aa
aa
Killed in a
cyclone
The Bottleneck Effect
Populations may be reduced to low numbers through
periods of:
Small gene pool
Fluctuations are more
severe because random
changes in a few alleles
cause a greater percentage
change in allele frequencies.
Very small gene pool
Allele lost from
the gene pool
Fluctuations are so extreme that
the allele may become fixed
(100%) or lost altogether (0%)
Seasonal climatic change
Heavy predation or disease
Catastrophic events (e.g. flood,
volcanic eruptions, landslide)
As a result, only a small number of individuals remain in
the gene pool to contribute their genes to the next
generation.
The small sample that survives will often not be
representative of the original, larger gene pool, and the
resulting allele frequencies may be severely altered.
In addition to this ‘bottleneck’ effect, the small surviving
population is often affected by inbreeding and genetic
drift.
18
Population Bottlenecks
Population Bottlenecks
Large, genetically
diverse population
The original gene pool is made up of the offspring of
many lineages (family groups and sub-populations)
aa
aa
AA
Genetic
Extinction event such
bottleneck as a volcanic eruption
All present day descendants of the original gene pool trace
their ancestry back to lineage B and therefore retain only a
small sample of genes present in the original gene pool
AA
AA
AA
AA
AA
Aa
Aa
Aa
Aa
AA
Aa
AA
AA
Aa
Aa
Population grows to a large
size again, but has lost
much of its genetic
diversity
AA
AA
AA
AA
Aa
AA
AA
AA
Aa
AA
AA
AA
AA
AA
Aa
Population bottleneck:
the population nearly
becomes extinct as
numbers plummet
Population numbers
Only two descendants of
lineage B survive the
extinction event
AA
Population reduced to a
very low number with
consequent loss of alleles
Time
Genetic Bottlenecks & the
Cheetah Population
The world population of
cheetahs has declined in
recent years to fewer than
20 000.
Recent genetic analyses has found that the
total cheetah population has very little
genetic diversity.
Cheetahs appear to have narrowly escaped
extinction at the end of the last ice age: 1020 000 years ago.
All modern cheetahs may have arisen from
a single surviving litter, accounting for the
lack of diversity.
Genetic Diversity in Cheetahs
The lack of genetic
variation has led to:
sperm abnormalities
decreased fecundity
high cub mortality
sensitivity to disease
Since the genetic
bottleneck, there
has been
insufficient time for
random mutations
to produce new
genetic variation.
At this time, 75% of all large mammals
perished (including mammoths, cave bears,
and saber-toothed cats).
Figure 13.24-1
Original
population
Figure 13.24-2
Original
population
Bottleneck
event
19
Figure 13.24-3
The Founder Effect
Occasionally, a small
number of individuals may
migrate away or become
isolated from their
original larger population.
This colonizing or
founder population will
have a small and probably
non-representative
sample of alleles from the
parent population’s gene
pool.
Original
population
Bottleneck
event
The Founder Effect
Small founder
populations are subject
to the effects of
random genetic drift.
The founder effect is
typically seen in the
populations of islands
which are colonized by
individuals from
mainland populations.
Often these species
have low or limited
mobility; their dispersal
is often dependent on
prevailing winds (e.g.
butterflies and other
insects, reptiles, and
small birds).
Natural selection
acts on phenotype
Offshore islands can provide an environment in
which founder populations can evolve in
isolation from the parental population.
As a consequence of this
founder effect, the
colonizing population may
evolve in a different
direction than the parent
population.
Surviving
population
Island
population
The Founder Effect
The marine iguana of the Galapagos has
evolved in an isolated island habitat
Colonizing
island
population
Aa
AA
AA
AA
AA
Aa
Aa
Aa
Colonization
Mainland
population
In this hypothetical
population of
beetles, a small,
randomly selected
group is blown
offshore to a
neighboring island
where they establish
a breeding
population.
This population may not
have the same allele
frequencies as the
mainland population
Some individuals
from the mainland
population are
carried at random to
the offshore island
by natural forces
such as strong
winds
Mainland
population
Aa
AA
Aa
AA
AA
Aa
aa
AA
AA
Aa
aa
Aa
Aa
aa
Aa
AA
aa
Aa
aa
AA
AA
AA
Aa
aa
AA
AA
Aa
Aa
aa
AA
Aa
aa
EXAMPLE OF NATURAL SELECTION:
Gene pool of grey and white alleles
• Natural selection
therefore changes
the composition of a
gene pool and
increases the
probability that
favourable alleles will
come together in the
same individual.
20
Environment is the Selective
Pressure
The environment is never constant in different parts of
the world, so natural selection acts on different
characteristics, depending on where the selection is
taking place
• Disruptive Selection
Environment selects
against intermediate
phenotype, allowing
both extremes to
become more
prevalent.
Types of natural selection
• Directional Selection
Environment selects
against one
phenotypic extreme,
allowing the other to
become more
prevalent. English
peppered moth. Gene
pool changed
dramatically in 50
generations.
• Stabilizing Selection
Environment selects
against two extreme
phenotypes, allowing
the intermediates to
become more
prevalent.
Sickle cell anaemia
As an example of natural
selection:
Sickle cell anemia is an
inheritable disease that causes
red blood cells to form a sickle
shape that is inefficient at
carrying oxygen
Sickle cell allele is recessive
Homozygous recessive
condition is detrimental to
health
Heterozygous condition has
minor affect on health
21
Heterozygous Advantage
If individuals who are heterozygous for a particular gene have
greater fitness than homozygotes, natural selection will tend to
maintain the two alleles.
Malaria
• Heterozygotes have a protection against malaria
•In America –
Homozygous recessive: selected against
Heterozyogous: Slightly less fit than Homozygous Dominant
• In areas where malaria is a major killer,
heterozygotes are selected for.
•In Africa –
Homozygous recessive: selected
against
• This leads to the recessive allele being
maintained in those populations
Heterozygous: More fit than
Homozygous Dominant
Artificial selection – A Form of
Microevolution
Artificial selection (selective
breeding)
The ability of people to control the breeding of
domesticated animals and crop plants has
resulted in a astounding range of phenotypic
variation over relatively short time periods
It is people that is the selective force rather than
the environment!
Domestication of animals
What characteristics impacted what animals were
domesticated?
•
•
•
•
•
•
Artificial selection
• Artificial selection involves breeding from individuals with the most
desirable phenotypes. The aim of this is to alter the average
phenotype within the species.
• In this way the gene pool gradually changes
• Artificial selection is a form of directional selection and depends on
the presence of genetic variability
Use of animal – food, milk, wool, leather, work
Breeding – need to be able to breed in captivity
Disposition – ability to be domesticated
Social structure – dominance hierarchies, herds
Growth rate – fast growth rate more beneficial
Tendency to panic – slower less nervous = easier to
catch
22
Hunting large game dog
Example of the domestic dog
• 400 different breeds
• One species – Canis familaris
- different species can interbreed = Xs
• Descended from the grey wolf over 15,000years
ago
• Good sense of smell
(tracking)
• Fearless
• Aggressive
• Strong bite
• Strong neck muscles
Game fowl hunting
• Excellent sense of smell
(detection)
• Good eyesight
• Understanding of need to
hold, point, retrieve
• Obedience/ self-control (not
eating or mauling prey)
Stock control
• Must not regard stock as prey
– low aggression
• Obedience
• Ability to anticipate behaviour
of stock
• Ability to control stock with
bark and body language
• Ability to protect stock from
predators
Family pet
•
•
•
•
Low level aggression
Playful attributes
Friendly disposition
Obedience?
23
Guard dog
• Aggressive to strangers
• Excellent hearing and
smell
• Alert to the arrival of
intruders
• Bark response
• Size?
Jack Russels
• The Jack Russell Terrier was breed to hunt the
red fox, who live in small underground dens.
Traits selected for in the breeding of JRTs are
size - must be small enough to get to its quarry.
Vocal – the hunt requires a dog that will bark at
prey so it can be located underground and be
dug out if necessary. High intelligence, highenergy dogs – requirements of a working dog
which must problem-solve in the field and work
tirelessly against often formidable quarry.
• However the selected traits for the breed mean
they can also be problematic pets. They may
exhibit unmanageable behaviour, including
excessive barking, escaping from the yard, or
digging.
• Breed to chase small furry animals, so can tend
to be cat aggressive
• Some JRT's exhibit a Napoleon complex
regarding larger canines that can get them into
dangerous situations. Their fearlessness can
scare off a larger animal, but their apparent
unawareness of their small size can lead to a
lopsided fight with larger dogs if not kept in
check.
Artificial selection vs Natural
selction
Domesticating foxes? - http://www.youtube.com/watch?v=-L58NPPQ5eI
Artificial selection in dog breeding
Artificial Selection in Brassica
Different parts of
the wild brassica
have been
developed by
human selection to
produce at least six
distinctly different
vegetables.
Cauliflowe
r
(flower)
Cabbage
(terminal
buds)
All these
vegetables form a
single species and
will interbreed if
allowed to flower.
Example: The new
“broccoflower” is a
cross between broccoli
and cauliflower.
Pedigree Dogs Exposed - http://www.youtube.com/watch?v=yZMegQH1SPg
Secret Life of Dogs - http://www.youtube.com/watch?v=5h8lWBd1hmE
Broccoli
(inflorescence)
Brussels sprout
(lateral buds)
Kale
(leaf)
Wild Form
Brassica oleracea
Kohlrabi
(stem)
24
Homework
• Unit Assessment 3 Topic
17
• Mastering Biology
Activities: Genetic Variation From
Sexual Recombination, Causes of
Evolutionary Change, Mechanisms of
Evolution
• Complete Bioflix study
sheet: Mechanisms of
Evolution
• Complete Evolution
Assignment on Mastering
Biology – Due first lesson
back after break.
Evolution Videos
• Crash Course in Biology – Evolution
• http://www.youtube.com/watch?v=P3GagfbA2vo
Key Words
•
•
•
•
•
•
•
•
•
•
•
Natural Selection
Gene Pool
Allelle Frequencies
Population
Gene Flow
Bottleneck Effect
Mutations
Founder Effect
Artificial Selection
Microevolution
Directional, Stabilizing or Disruptive Selection
Topic 18
Macroevolution
Learning
Outcomes
After studying this topic you
should be able to:
•Define macroevolution and
explain what differentiates it
from microevolution.
•Define and explain the
biological species concept.
Describe and explain the two
types of reproductive
isolating mechanisms: prezygotic and post-zygotic.
•Define and describe the
differences between:
allopatric and sympatric
speciation.
What is Macroevolution?
Macroevolution is the term
used to describe large scale
changes in form, as viewed in
the fossil record, involving
whole groups of species and
genera.
25
Macroevolution
Macroevolution refers to evolutionary changes above the level
of the species: changes in genera or orders.
Macroevolution is concerned with changes in the kinds of
species over evolutionary time and includes:
The origin of unusual features (evolutionary novelties).
The origin of evolutionary trends (e.g. increased brain size in primates).
Adaptive radiation (a form of divergent evolution).
Extinction.
Example of an evolutionary trend: brain size in hominids
Increasing Brain Size
Animation: Macroevolution
H. erectus
1100 ml
H. sapiens
1450 ml
Micro- vs Macroevolution
The mechanisms of gene pool
change and natural selection
represent the modern synthesis
of evolution.
The gradualist view is that, over long periods of
time (millions of years), microevolutionary
processes are sufficient to account for the origin
of new genera, families, orders and phyla.
The punctuated equilibrium view is that most
morphological change occurs during abrupt
speciation events and, once in existence,
species then change very little.
The debate is not about the fact
of evolution; only about the
relative importance of different
evolutionary mechanisms.
The
Biological Species Concept
Species
Species are often
composed of different
populations (often in
different habitats) that are
quite distinct.
These are often called
subspecies, races, and
varieties depending on
the degree of
reproductive isolation.
There are up to 20 000
species of butterfly;
they are often very
different in appearance
and do not interbreed.
The Biological Species Concept
– Species is a Latin word meaning
• “kind” or
• “appearance.”
Species are recognized on the basis of their
morphology (size, shape, and appearance)
and, more recently, by genetic analysis.
A biological species is:
a group of interbreeding (or potentially
interbreeding) individuals, reproductively
isolated from other such groups.
These are often called subspecies, races,
and varieties depending on the degree of
reproductive isolation.
Species
The boundaries of a species gene pool can be
sometimes unclear, such as the genus to which all
dogs, wolves, and related species belong:
Coyote–red wolf hybrids
Coyote
Canis latrans
Red wolf
Canis rufus
Interbreedin
g
Interbreeding
Domestic dog
Canis familiaris
Dingo
Canis familiaris dingo
Side-striped jackal
Canis adjustus
Interbreedin
g
Black-backed jackal
Canis mesomelas
Gray wolf
Canis lupus
No interbreeding
H. habilis
575 ml
No interbreeding
A. afarensis
440 ml
Golden jackal
Canis aureus
26
Figure 14.2a
Figure 14.2b
Similarity between different species
Reproductive Isolating
Mechanisms
Reproductive isolating mechanisms (RIMs)
prevent successful breeding between different
species. They are barriers to gene flow.
A single barrier may not completely isolate a
gene pool, but most species have more than one
isolating mechanism operating to maintain a
distinct gene pool.
Geographical barriers prevent species
interbreeding but are not considered to be
RIMs because they are not operating through
the organisms themselves.
Diversity within one species
Geographical
Barriers
Geographical barriers
isolate species and prevent
interbreeding.
Geographical barriers include
mountains, rivers, and
oceans. Geographical
features that may be barriers
to some species may not be
barriers to others.
In the USA, two species of antelope
squirrels occupy different ranges
either side of the Grand Canyon.
Their separation is both geographical
and ecological. They are separated
by the canyon and by the different
habitat preferences in the regions
they occupy.
Reproductive Isolating
Mechanisms
Reproductive isolating mechanisms
can be categorized according to when
and how they operate:
Prezygotic (pre-fertilization) mechanisms include:
habitat preference
behavioral incompatibility
structural incompatibility
physiological incompatibility
Postzygotic (post-fertilization) mechanisms include:
zygote mortality
poor hybrid fitness
hybrid sterility
Although they are in the same region, the white
tailed antelope squirrel inhabits desert to the
north of the canyon, while Harris’s antelope
squirrel (above) has a more limited range to the
south.
Prezygotic Isolating Mechanisms
Prezygotic isolating
mechanisms act before
fertilization to prevent
successful reproduction or
mating.
1) Ecological or habitat:
Different species may
occupy different habitats
within the same
geographical area, e.g.
desert and coastal species,
ground or tree dwelling.
In New Zealand,
Hochstetter’s and Archey’s
frogs occur in the same
relatively restricted region
but occupy different
habitats within that range.
Archey’s frog (top) has no webbing between the
toes and is found in forested areas away from
water. Hochstetter's frog (bottom) has partial toe
webbing and can be found in stream margins.
27
Prezygotic
Isolating
Mechanisms
Prezygotic Isolating Mechanisms
Behavioral:
Peacock
Species may have specific
calls, rituals, postures etc. that
enable them to recognize
potential mates (many bird
species have elaborate
behaviors).
Breeding season
for species A
Temporal (time-based):
Species may have
different activity patterns;
they may be nocturnal or
diurnal, or breed at
different seasons.
In this hypothetical
example, the two species
of butterfly will never mate
because they are sexually
active at different times of
the year.
Structural:
Breeding season
for species B
Insects have very
specific copulatory
organs which act like a
lock and key
For successful mating,
species must have compatible
copulatory apparatuses,
appearance, and chemical
make-up (odor, chemical
attractants).
Gamete mortality:
Egg
If sperm and egg fail to unite,
fertilization will be
unsuccessful.
Attempted
fertilization
Sperm
Figure 14.4
Postzygotic IsolatingMechanisms
PREZYGOTIC BARRIERS
Temporal Isolation
Behavioral Isolation
Postzygotic isolating
mechanisms act
after fertilization to prevent
successful reproduction.
Hybrid inviability:
Habitat Isolation
Mechanical Isolation
The fertilized egg may fail to develop properly
Gametic Isolation
Species A
F1
X
Hybrid AB
Reduced viability
F2
Species B
X Hybrid AB
Reduced viability
Hybrid AB
Non-viable or sterile
Fewer young may be produced and they may
have a low viability (survivability).
Hybrid sterility:
The hybrid of two species may be viable
but sterile, unable to breed (e.g. the mule).
Hybrid breakdown:
The first generation may be fertile but
subsequent generations are infertile or nonviable.
This mule is a hybrid
between a horse and a
donkey
Figure 14.5
Hybrids in the Horse Family
Zebra stallion
(2n = 44)
Sterile hybrids are
common among
the horse family.
The chromosomes
of the zebra and
donkey parents
differ in number
and structure,
producing a sterile
zebronkey.
POSTZYGOTIC BARRIERS
Donkey mare
(2n = 62)
Reduced Hybrid Viability
Reduced Hybrid Fertility
Hybrid Breakdown
Horse
X
‘Zebronkey’
Donkey
offspring (2n = 53)
Chromosomes contributed
by zebra father
Y
Chromosomes
contributed by donkey
mother
Mule
X
28
Speciation
Types of Speciation
Speciation refers to
the process by which
new species are
formed.
Speciation occurs
when
gene flow has
ceased between
populations where
it previously existed.
Speciation is brought
about by the
development of
reproductive
isolating
mechanisms which
maintain the integrity
of the new gene pool.
Different species of
swallowtail butterflies in
the genus Papilio
Several models have been
proposed to account for new
species among sexually
reproducing organisms:
Allopatric speciation:
Populations become
geographically separated,
each being subjected to
different natural selection
pressures, and finally
establishing reproductive
isolating mechanisms.
Sympatric speciation: A
population forms a new species
within the same area as the
parent species.
Figure 14.6
Allopatric Speciation
STAGE 1:
Moving into new
environments
The parent population expands its
range and occupies new parts of the
environment.
Expansion of the range may
be due to competition.
Allopatric speciation
The population has a
common gene pool with
regular gene flow (any
individual has potential
access to all members
of the opposite sex for the
purpose of mating).
Sympatric speciation
STAGE 2:
Geographical isolation
Gradual formation of physical
barriers may isolate parts of the
population at the extremes of the
species range
As a consequence, gene flow
between these isolated
populations is prevented
or becomes rare.
Agents causing
geographical
isolation include:
continental drift,
climatic change, and
changes in sea level
(due to ice ages).
Mountain
barrier
prevents gene
flow
STAGE 3:
Formation of a
subspecies
River barrier
prevents gene flow
Isolated
Population A
The isolated populations may be
subjected to quite different
selection pressures.
Isolated
Population B
Some natural
variation exists in
each population
Isolated
Population C
Parent population
These selection pressures
will favor those individuals
with traits suited to each
environment.
Allele frequencies for
certain genes change and
the populations take on the
status of a subspecies
(reproductive isolation is
not yet established).
Wetter climate
Sub-species A
Cooler climate
Sub-species A
Drier climate
Sub-species C
29
Figure 14.7
STAGE 4:
Reproductive isolation
Each separated subspecies
undergoes changes in its genetic
makeup and behavior. This will
prevent mating with individuals from
other populations.
Each subspecies’ gene pool
becomes reproductively
isolated from the others
and they attain species status.
Even if geographical barriers
are removed to allow mixing
of the populations, genetic
isolation is complete.
Sympatric species
Species A
Ammospermophilus
harrisii
Ammospermophilus
leucurus
Species B
Mountain barrier remains
River barrier
removed
Allopatric
species
Species A
Sympatric species: Closely related species with overlapping
distribution
Allopatric species: Closely related species still geographically
separated
Figure 14.8
Figure 14.10
Populations
become
allopatric
Populations
become
sympatric
Populations
interbreed
Gene pools merge:
No speciation
Punctuated
pattern
Time
Geographic
barrier
Populations
cannot
interbreed
Reproductive
isolation:
Speciation has
occurred
Gradual
pattern
Time
Sympatric Speciation
Sympatric speciation: A new
species within the same area as
the parent species.
There is no geographical separation between the
speciating populations.
Wild Einkorn
All individuals are, in theory, able to meet each other
during the speciation process.
Sympatric speciation is rarer than
allopatric speciation among animals, but
it is probably a major cause of
speciation among plants!
Sympatric speciation may ocur
through:
A change in host preference, food preference or
habitat preference.
Animation: Allometric Growth
The partitioning of an essential but limiting resource.
Instant speciation as a result of polyploidy (particularly
among plants, as in the evolution of wheat).
Common Wheat
30
A change in habitat
preference:
An insect forced to lays its eggs on
an unfamiliar plant species may
give rise to a new population of
flies isolated from the original
population
It is not uncommon for some
insect species to be
conditioned to lay eggs on
the plant species on which
they themselves were reared.
If the normally preferred
plant species is
unavailable, then the
insect may be forced to
choose another species to
lay eggs on.
A few eggs surviving on
this new plant will give rise
to a new population with a
new plant species
preference.
Original host
plant species
Polyploidy involves the
multiplication of whole sets of
chromosomes (each set being the
haploid number N).
Polyploids occur frequently in
plants and in some animal groups
such as rotifers and earthworms.
When such individuals
spontaneously arise, they are
instantly reproductively isolated
from their parent population.
As many as 80% of flowering
plant species may have
originated as polyploids.
Different species of Chrysanthemum (right)
have arisen as a result of polyploidy.
They have chromosome numbers (2n)
that are multiples of 18: 2n = 18, 36, 54, 72, and 90.
Allopatric speciation
New host
plant species
Establishing
reproductive
isolation:
Each host plant will attract flies that
were reared on that plant where they
will mate with other flies with a similar
preference
If mating and rearing of
offspring takes place
entirely within the habitat,
then the population will
become reproductively
isolated.
Further differentiation of the
two populations is likely as
each
becomes increasingly
adapted to their respective
habitats.
No
gene
flow
Gene
flow
Original host plant species
Ultimately, the two groups
will diverge to be
recognized as separate
species.
New host plant species
Stages in Species Formation
Homogeneous
Ancestral Population
Different types
of isolating
mechanisms
operate and
different
amounts of
gene flow take
place as two
populations
diverge to form
new species.
Population splits
Population A
Geographic
isolation
Population B
Gene flow
common
Race A
Prezygotic
isolation
Gene flow
uncommon
Species A
Prezygotic
isolation
Subspecies B
Subspecies A
Postzygotic
isolation
Geographic
isolation
Race B
Evolutionary Development
Gene flow
very rare
No gene
flow
Postzygotic
isolation
Species B
Sympatric speciation
31
Summary: Forces
Operating in
Evolution
Speciation summary
UV Light
Various “forces” or
phenomenon have a
part to play in the
evolutionary process:
At the molecular level:
Point mutations
Control of gene expression
Rate of protein synthesis
Forces Operating
in Evolution
Forces Operating in
Evolution
At the organism
level:
At the
chromosomal
level:
Environmental
modification of phenotype
Crossing over
Reproductive success
Block mutations
Selection pressures
Polyploidy
'Fitness' of the phenotype
Aneuploidy
Egg
Independent assortment
Recombination
Sperm
Forces Operating in
Evolution
At the population
level:
Forces Operating
in Evolution
AA
Aa
AA
Genetic drift and
population size
AA
At the species
level:
Geographical barriers
Aa
Aa
Natural selection altering
gene frequencies
aa
Aa
Mate selection
Intraspecific
competition
Reproductive isolation
(prezygotic and postzygotic)
aa
Selection pressures
aa
Aa
Aa
AA
Interspecific competition
AA
Founder effect
Immigration/emigration
(gene flow)
aa
AA
Population bottlenecks
32
Complete
1) How Do New Species Arise by Genetic Isolation?
Homework
• Unit Assessment 3 Topic
18
• Mastering Biology
Activities: Polyploid Plants, A
Scrolling Geologic Record
• Complete Evolution
Assignment on Mastering
Biology – Due first lesson
back after break.
• Watch Crash Course
Biology: Speciation
Evolution Videos
• Crash Course in Biology – Speciation
• http://www.youtube.com/watch?v=2oKlKmrbLoU
Key Words
•
•
•
•
•
Speciation
Prezygotic Barrier
Postzygotic Barrier
Starter
What do we know about
human evolution?
(For your own interest: Will
not be assessed)
Watch the introductory ‘Prologue’ clip from
www.becominghuman.org
Note:
•
new observations may or may not support
the current explanation
•
if they do not support it, the explanation
may need to be reconsidered
•
our understanding of human evolution is
still developing
33
What to do…
Review Presentation Evidence for human evolution
and answer the following questions:
a. Is there any evidence that humans evolved in a similar way
to other animals?
b. What sort of evidence should we look for?
There are still problems with our interpretation of the human
evolution story…
a. We can never know whether what we call different species
were different. Why?
b. We can see variation between the bones – but there is lots
of variation within our species, Homo sapiens, today. Give
some examples of such variation.
c. The number of specimens found is too small to provide
conclusive evidence. Why is this an issue?
Feature
Gorillas
Human beings
• Human beings share many features with them.
• Humans are NOT descended from modern apes.
• But we do share a common ancestor.
human beings
Chimpanzees
Head hair
short
long
short
Calf muscle
small
large
small
thin
fat
thin
Arms vs legs
shorter legs
shorter arms
shorter legs
Canine teeth
large
small
large
Thumbs
long
long
short
Chromosomes
48
46
48
Buttocks
• Chimps and gorillas are apes.
chimps or
gorillas?
chimps or
gorillas?
• It’s not a trick question!
• So far we haven’t found enough evidence to
decide.
From all this evidence, do you think human beings are closest to
chimps or gorillas?
• We know that ape-like animals were living in
Africa over 20 million years ago.
• The evidence:
- scientists have found skulls with ape-like
features
- they can date the fossil apes.
• But there is enough evidence to say that humans
and apes share the same ancestor.
• These early apes share some features with living
apes:
- no tail
- shoulder blades at the back of the body
• But they do also have some differences.
34
human beings
human beings
chimpanzees and gorillas
?
orang-utans
gibbons
fossils
Scientists use the evidence to work out how living
apes are related to fossil apes.
Do human beings have any closer relatives in the
fossils?
sinus (spaces
inside skull)
eye socket
broad
nose
• Australopithecines
lived in Africa 1.5 to 4
million years ago.
modern human
• Lucy – the most
complete
Australopithecine
skeleton found.
jaw more like
human than
chimpanzee
A. africanus
chimpanzee
• Australopithecines share some features with
human beings:
- eye sockets are wide and set apart
• So is Lucy more
closely related to us
or to living apes?
- broad nose
- sinus inside front of skull
sinus (spaces
inside skull)
eye socket
broad
nose
modern human
jaw more like
human than
chimpanzee
A. africanus
•
Chimps and gorillas also have these features. But
other apes don’t.
•
So are Australopithecines more closely related to:
(a) human beings?
or
(b) chimps and gorillas?
chimpanzee
• In 1978 scientists
found the evidence to
answer this question.
• Evidence suggests that
these footprints were
made in Africa by
Australopithecines.
• They walked on two
legs.
35
human beings
Australopithecines
• But scientists think that
we have even closer fossil
relatives.
• Habilines lived in Africa
1.6 to 2 million years ago.
So Australopithecines were more like human beings
than chimps and gorillas.
Species
Human beings
• Fossils showed that their
spines were joined to the
middle of their skull, so
Habilines walked upright.
Brain size (ml)
human beings
1400
Australopithecines
500
Habilines
650
• We have more evidence about Habilines. They
had much bigger brains than Australopithecines
like Lucy.
• We also know that they made tools.
• So the evidence tells us that Habilines are more
closely related to modern humans than
Austalopithecines.
habilines
Australopithecines
• Habilines were probably the first animals on
Earth to make tools.
• Tool making is a very important feature of human
beings.
• So scientists think Habilines were the first early
humans.
• They are called Homo habilis.
modern humans
Species
Brain size (ml)
Human beings
1400
Australopithecines
500
Habilines
650
Homo erectus
900
• Fossils of other early humans have also been
found.
• Homo erectus lived in Africa 1.5 million years
ago.
Homo erectus
Habilines
(Homo habilis)
• Their large brains mean that Homo erectus are
more closely related to modern humans.
• Scientists have also found evidence that they
were able to make fire.
36
• Homo erectus were also the first early humans
to leave Africa.
• But Homo erectus are not quite the same as
modern humans. For example, their skulls have a
thick, straight brow ridge.
• Their skeletons have been found in Asia and
Europe.
• So scientists think that we must have at least
one more recent ancestor.
modern humans
(Homo sapiens)
Homo erectus
Habilines
• The search goes back to Africa. We know that
not all Homo erectus left when they first moved
out of Africa.
• Those that stayed carried on evolving into
modern humans.
• We know this because skulls shaped more like a
modern human have been found in Africa. This
one from Ethiopia is only 160 000 years old.
• By 40 000 years ago
modern humans had
spread across the
world.
• Evidence like cave
paintings and tools
tells us where and
how they lived.
• Modern humans are called Homo sapiens.
• They left Africa about 120 000 years ago.
• Homo sapiens fossils this old have been found in
Israel.
• These modern humans were hunters and
farmers.
• The symbols in their paintings tell us that they
had language.
• They also had ceremonies like burials.
37
modern humans
What to do…
Review Presentation Evidence for human evolution
and answer the following questions:
early humans
a. Is there any evidence that humans evolved in a similar way
to other animals?
Australopithecines
living apes, like
chimps and
gorillas
Summary:
• Different groups of humans evolved from a
common ancestor.
• All but one of these groups died out.
• Only Homo sapiens (modern humans) survived.
• Modern humans evolved in Africa.
•
Explore these
•
Science Museum, London, Evolution of language:
•
Hunterian Museum, University of Glasgow, illustrates the human evolution
story with images of its exhibits and brief text passages:
•
Institute of Human Origins, Arizona State University, Becoming Human,
broadband documentary: www.becominghuman.org/
•
US Public Broadcast Service hosts a large, attractive site with masses of
information on aspects of evolution: www.pbs.org/wgbh/evolution/
b. What sort of evidence should we look for?
There are still problems with our interpretation of the human
evolution story…
a. We can never know whether what we call different species
were different. Why?
b. We can see variation between the bones – but there is lots
of variation within our species, Homo sapiens, today. Give
some examples of such variation.
c. The number of specimens found is too small to provide
conclusive evidence. Why is this an issue?
www.sciencemuseum.org.uk/exhibitions/brain/256.asp
www.hunterian.gla.ac.uk/museum/hominid/hominid.html
including: Is love in our DNA? Has evolution shaped human beings’ choice
of mates? Higher level, useful case study option:
www.pbs.org/wgbh/evolution/sex/love/index.html
•
Smithsonian Institute Human Origins exhibit is more appropriate for
teachers’ information: www.mnh.si.edu/anthro/humanorigins/index.htm
38

Darwin and Natural Selection

Transcription

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