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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.

Darwin and Natural Selection Evolution Videos

• 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

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

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.

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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

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.’

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.

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.

Early Contributions to

Evolutionary Thought

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.

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Early Contributions to Evolutionary Thought

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’.

Herbert Spenser

Charles Lyell

Explanations for change

Person Explanation they came up with for the data

Creative thought was needed to come up with the explanation? ( or )

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

Explanations for change 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.

Explanations for change 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.

Cuvier: …………………………………………………………………………………

…………………………………………………………………………………

Darwin: …………………………………………………………………………………

…………………………………………………………………………………

• Darwin gathered lots of evidence in support of his idea and it did 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. • 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

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.

What examples are there that disprove this theory?

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.

Julian Huxley 1887-1975

Ernst Mayr 1904-2005

T. Dobzhansky 1900-1975

Collaborated to formulate the modern

theory of evolution, incorporating

developments in genetics,

paleontology and other branches of

biology.

The New Synthesis

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

R.A. Fisher 1890-1962

J.B.S. Haldane 1898-1964

Sewall Wright 1889-1988

Founding of population genetics and

mathematical aspects of evolution and genetics.

Alfred Russel Wallace

1823 - 1913

‘Theory of Natural Selection’

Charles Darwin

1809 - 1882

‘Theory of Evolution

by Natural Selection’

Gregor Mendel

1822 - 1884

Developed the

fundamentals of the genetic

basis of inheritance. August Weismann

1834 - 1914

Proposed chromosomes as the

basis of heredity, demolishing the

theory that acquired

characteristics could be inherited.

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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

+

Mendel

+

Weismann

The Development

of Darwin’s Ideas 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’.

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.

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.

Fossil finds of extinct species.

Evidence from artificial selection.

Figure 13.4

Darwin in 1840

North America

Great Britain Europe Asia

Africa

South America

Cape of Good Hope

Cape Horn

Tierra del Fuego

Australia

Tasmania

New Zealand

HMS Beagle

ATLANTIC OCEAN

PACIFIC OCEAN

Equator Equator

PACIFIC OCEAN

Fernandina

Isabela

Pinta

Marchena

Santiago

Pinzón Daphne Islands

Genovesa

Florenza Española

Santa Cruz

Santa Fe San

Cristobal

40 km

40 miles

0

0

Galápagos Islands

Figure 13.12

(a) The large ground finch

(b) The warbler finch (c) The woodpecker finch

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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:

Overproduction

Variation

Competition

Survival of the fittest phenotype

Favorable combinations increase

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.

Natural Selection

Inheritance Variations are

inherited. The best

suited variants

leave more

offspring.

Natural Selection Natural selection favors

the best suited at the time

Variation Individuals show variation:

some variationsare more

favorable than others

Overproduction Populations produce too

many young: many must die

Natural selection

The evolution of superbugs?

Figure 13.15-1

Chromosome with gene conferring resistance to pesticide

Insecticide application

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Figure 13.15-2

Chromosome with gene conferring resistance to pesticide

Insecticide application Figure 13.15-3

Chromosome with gene conferring resistance to pesticide

Reproduction

Survivors

Insecticide application

• Warfarin kills most rats.

• But a few are resistant to the poison.

Natural selection in rats: warfarin

These statements describe how the number of warfarin resistant rats may increase in a population.

• People use warfarin to kill rats.

• 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.

• How do some rats

become resistant

to warfarin in the

first place?

But there is a big

unanswered question:

Click on the links to find out more.

• DNA controls the proteins that a cell makes.

Remind me about DNA.

• DNA is copied when a new cell is made.

Sometimes a mistake is made – this is called a mutation.

Tell me about mutations.

• Most mutations are harmless, some are harmful. Very rarely mutations may be helpful to an organism.

What sort of mutations can be helpful?

How do some rats become resistant to warfarin?

Next

Part of the DNA molecule

genes

chromosome DNA

• DNA molecules are very long.

• They have a double helix shape.

• Chromosomes are made of DNA.

• Genes are sections of chromosomes.

• A gene is the instruction for how to make one type of protein.

DNA

Back

• Each gene is the instruction for making one protein.

• Sometimes a mistake is made when the gene’s DNA is copied.

• The gene may code for a different protein.

• Mutations do happen naturally.

• They can also be caused by some chemicals, and ionizing radiation.

Mutations

Back

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This bacterium is resistant to most antibiotics.

A person who is a carrier of the sickle cell allele is protected from malaria.

• 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.

• 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.

How can mutations be helpful?

Back

List the factors which can combine to produce a new species

• mutation

• environmental change

• natural selection

Who Wants to Live a Million Years?

http://science.discovery.com/games-and-interactives/charles-darwin-game.htm

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

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

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.

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Evolutionary theory is now supported by a wealth of observations and experiments

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.

Comparative anatomy:

The study of the morphology

of different species.

Comparative anatomy

Paleontology

Evidence for Evolution

Paleontology

Evidence for Evolution

Biogeography: The study of geographic distributions can indicate where species may have originally arisen.

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.

Molecular genetics: Sequencing of

DNA and proteins indicates the degree of relatedness between organisms.

From gray wolf to

Yorkshire terrier:

selective breeding

can result in

phenotypic change

The Fossil Record The fossil record is a substantial, but incomplete, record of evolutionary history:

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.

Numerous extinct species are found as fossils.

Fossils can be dated to establish their approximate absolute age.

New fossil types mark changes in the past environmental conditions on the Earth.

Rates of evolution can vary, with bursts of species formation followed by stable periods.

These fossil teeth, from Mastodon,

an extinct elephant, are similar to the

deciduous teeth of modern

elephants.

Fossil fish Types of Fossils

Bird bones

preserved in a tar

pit

A layer of shell

still covers the

stone interior

of this

ammonite

Trilobites

preserved in

sedimentary rock

The term fossil refers to any parts or impressions of an

organism that may survive after its death.

Fossils form best when organisms are buried quickly in conditions that slow the

process of decay.

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.

On rare occasions, fossils retain organic material, as when plant material is compressed between layers of shale or sandstone.

The Archaeopteryx Fossil Eight well-preserved fossil specimens have been discovered in fine-grained limestone in Germany (dated late Jurassic, about 150 million years ago).

Avian Features

Vertebrae are

almost flat-

faced.

Impressions of

feathers attached

to the forelimb.

Belly ribs.

Incomplete fusion

of the lower leg

bones.

Impressions of

feathers attached

to the tail.

Forelimb has three

functional fingers

with grasping

claws.

Reptilian Features

Lacks the reductions

and fusions present

in other birds.

Breastbone is small

and lacks a keel.

True teeth set in

sockets in the jaws.

The hind-limb girdle

is typical of

dinosaurs, although

modified.

Long, bony tail. LEFT: Archaeopteryx lithographica

Found in 1877 near Blumenberg, Germany

Fossils in a Rock Profile

Layers of sedimentary rock are arranged in the order in which they were deposited, with the most recent layers nearer the surface.

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.

Only primitive

fossils are found in

older sediments

New fossil types

mark changes in

environment

Fossil types

differ in each

sedimentary

rock layer

Numerous

extinct species

Recent fossils are

found in recent

sediments Most recent

sediments

Oldest

sediments

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Dating Fossils The relative age of fossils is useful, but fossils provide reliable historical data only if we can determine their absolute age.

A number of methods are used to date fossils.

A fossil trilobite, a primitive arthropod

that dwelled in the seas of the

Devonian period 370 million years ago

Dating Method Age Range (years) Material Dated

Electron Spin Resonance 500 000 – 1000

Bone, tooth

enamel, cave

deposits

Fission Track 1 million – 100 000 Volcanic rock

Obsidian Hydration 800 000 – present Obsidian

(volcanic glass)

Amino acid racemization 1 million – 2000 Bone

Thermoluminescence less than 200 000 Pottery, fired clay,

bricks, burned rock

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

Figure 14.15

Carbon-14 in shell

Time (thousands of years)

Radioactive decay

of carbon-14

How carbon-14 dating is used to determine the vintage of a fossilized clam shell

Ca

rbo

n-1

4 r

ad

ioa

cti

vit

y

(as

% o

f liv

ing

org

an

ism

’s

C-1

4 t

o C

-12

ra

tio

)

100

75

0

50

25

0 5.6 50.4 11.2 16.8 22.4 28.0 33.6 39.2 44.8

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 half- life 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

found in 3500 million year

old chert in Western

Australia

Oxygen produced by

plants accumulates in

the atmosphere

Precambrian Eon

Millions of years ago

Qu

ate

rna

ry

Millions of years ago

Eras

© 2013 Pearson Education, Inc.

Animation: The Geologic Record

Right click slide / select “Play”

Evolutionary History

Based on fossil evidence and radio-isotope dating, the evolutionary history of plants, fungi, bacteria, protists, and non-chordate animals can be compiled.

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.

Millions of years ago

Echinoderms

Arachnids

Diplopoda

Crustacea

Insecta

Annelid worms

Molluscks

Flatworms

Cnidarians

Angiosperms

Cycads

Conifers

Sphenophytes (ferns etc)

Fungi

Protists

Bacteria and algae

Inve

rtebra

tes

Lan

d p

lan

ts

Evolutionary History 2

Similarly, the evolutionary history of chordates can be traced back to the Cambrian, but most animal groups are much more recent than this.

Placentals

Marsupials

Monotremes

Birds

Squamata (lizards & snakes)

Rhyncocephalia (tuatara)

Crocodilia

Chelonia (turtles a& tortoises)

Amphibians

Lungfish

Ray finned fishes

Sharks and rays

Tunicates

Agnatha (jawless fishes)

Millions of years ago

Mammals

Birds

Reptiles

Amphibians

Fish

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Figure 14.26a

Eutherians (5,010 species)

Millions of years ago

Monotremes (5 species)

Marsupials (324 species)

Ancestral mammal

Reptilian ancestor

Extinction of dinosaurs

250 200 150 100 50 65 0

Figure 14.14

A sedimentary fossil formed by minerals replacing the organic matter of a tree

Trace fossils: footprints, burrows, or other remnants of an ancient organism’s behavior

A 45-million-year-old insect embedded in amber

Tusks of a 23,000-year-old mammoth discovered in Siberian ice

A researcher excavating a fossilized dinosaur skeleton from sandstone

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

Late

cleavage

Body

segment

s

Limb

buds

Late fetal

Gill

slits

Figure 13.10

Post-anal

tail

Chicken embryo

Pharyngeal

pouches

Human embryo

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

Femur (thigh)

Fibula

Tibia

Tarsals

(ankle)

Metatarsals

(sole)

Phalanges

(toes)

Hind Limb Forelimb

Humerus

(upper arm)

Ulna

Radius

Carpals

(wrist)

Metacarpals

(palm)

Phalanges

(fingers)

Note that forelimbs and hind limbs have

different names for equivalent bones.

Homologous Structures In many vertebrates, the basic pentadactyl limb has been highly modified to serve specialized locomotory functions.

Such homologies also indicate adaptive radiation, as the basic limb plan has been adapted to meet the needs of different niches.

The same pattern of bones comprising the pentadactyl limb can be seen on each of these examples.

Bird's wing

Bat's wing

Human arm

Dog's

front leg

Mole's

forelimb

Seal's

flipper

11

Figure 13.9

Human Cat Whale Bat

Figure 13.17

Tetrapod limbs

Amnion

Feathers

Lungfishes

Mammals

Amphibians

Lizards and snakes

Crocodiles

Hawks and other birds

Ostriches

Am

nio

tes

Tetra

po

ds

Bird

s

Common ancestor of lineages to the right

Homologous trait shared by all groups to the right

2

1

3

4

6

5

Analogous Structures 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.

Analogous structures do not imply an evolutionary relationship, but may indicate convergence. Examples:

Eye structure in octopus and mammals.

Wings in birds and butterflies.

Fins in fish and flippers in mammals

Fins

Flippers

Wings

Analogy in Eye Structure Eyes in cephalopods (such as octopus) and mammals have the same function and are structurally similar, but have evolved from different origins.

Mammalian eye

Iris

Lens

Cornea

Retina

Retina

Iris

Lens

Cornea

Octopus eye

Vestigial Organs

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 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.

Over many millions of years, the pelvis and femur of whales have become very small and no longer fulfill a locomotory function.

Pelvis

Femur

Hindlimb

Forelimb

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Whale Ancestors

Basilosaurus (Late Eocene)

Protocetus (Eocene)

Pakicetus (Middle Eocene)

Cladogram of

Whale Ancestors

The fossil record exhibiting whale evolution is extensive and well represented by skeletons that show much of their anatomy.

Red lines represents fossil

record for the genus

Black lines represent

cladistic relationship

(probable relatedness)

Biogeographical Evidence

The study of plant and animal distribution is called biogeography.

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).

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).

Lemurs are endemic

to the island of

Madagascar

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

Cape Verde Islands

Tristan da Cunha

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.

The giant tortoises are

among the most well

known of the Galapagos

fauna

Island Colonizers

Active

flight

Oceanic island

Swimming Planktonic

larvae

Deep

ocean

Rafting on

drifting vegetation

Sea mammals have little

difficulty in reaching islands (e.g.

seals, sea lions). They do not

colonize the interior of islands.

Land mammals rarely colonize

islands. A high metabolic rate

requires much food and water.

Mammals cannot sustain

themselves on long sea

journeys.

Amphibians cannot live away

from fresh water. They seldom

reach offshore islands unless

that island is a continental

remnant.

Blown by

strong winds

Small birds, bats, and insects are

blown to islands by accident. They

must adapt to life there or perish.

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).

Reptiles probably reach distant

islands by floating in driftwood.

A low metabolic rate enables

them to survive long periods

without food and water.

Crustacean larvae drift to islands

(e.g. crabs). Some crabs have

adapted to an island niche.

Figure 13.8

Common ringtail possum

Red kangaroo

Common wombat

Australia

Koala

13

Molecular Biology

One way to reconstruct the evolutionary history of a species is using DNA hybridization.

In this technique, the DNA from different species is ‘unzipped’ and recombined to form hybrid DNA.

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).

EXAMPLE:

The relationships among the New World vultures and storks has been determined on the basis of DNA hybridization.

Stork

New World

vulture

DNA Hybridization Method

DNA is isolated from blood samples from each species:

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.

A crude measure of DNA relatedness can be achieved by measuring how hard it is to separate the hybrid DNA.

This is done by finding the temperature at which it unzips into single strands again (in this case it would be 83.6°C).

Extract human DNA Extract chimpanzee DNA

Some of the opposing

bases in the DNA

sequence do not match

Mix strands to

form a hybrid

Unzip the DNA using heat

(both human and

chimpanzee DNA unwinds at

86°C)

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.

Humans and chimpanzees have a 97.6% similarity in their DNA sequences and are very closely related.

An interesting finding was that the DNA of humans and chimpanzees is more closely matched than that of chimpanzees and gorillas.

Figure 13.11

Percent of selected DNA sequences that match a chimpanzee’s DNA

Chimpanzee

100% 96% 92%

Human

Gibbon

Orangutan

Gorilla

Primate

Old World

monkey

Primate No. of amino

acids different

from humans

Position of

changed amino acids

Chimpanzee Identical –

Gorilla 1 104

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

Amino Acid Sequencing Amino acid differences for beta-hemoglobin in primates compared to the human sequence:

The 'position of changed amino acids' is the point in the protein,

composed of 146 amino acids, at which a different amino acid

occurs.

Gibbon Squirrel

monkey

Gorilla

Chimpanzee

Rhesus

monkey

Artificial Selection in Dogs 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.

Example: The staffordshire bull terrier was produced by breeding bulldogs and terriers. From each litter, breeders selected pups with the characteristics they desired.

Staffordshire bull terriers

combine characteristics of both

bulldogs and terriers

Bulldog

Terrier

Staffordshire bull terrier

Gray wolf

14

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.

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.

Sheepdog

Originated in Europe

and bred for stock

protection.

Greyhound

One of the oldest

breeds, originating

the Middle East.

Wolf-type

Developed in snow-

covered habitats in

Alaska, northern

Europe, and Siberia.

Grey wolves are the

ancestors of all dogs.

Selective Breeding or Artificial Selection

• Salukis are thought to

be one of the oldest

domesticated dog

breeds.

• Pictures of them are

carved in Ancient

Egyptian tombs.

• Several breeds of dog

lived with the ancient

Greeks and Romans.

• 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.

15

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. the fossil record,

2. biogeography,

3. comparative anatomy,

4. comparative embryology, and

5. molecular biology.

© 2013 Pearson Education, Inc.

Activity – Process of Science

Complete

1) What are the Patterns of Antibiotic resistance

2) How Do Environmental Changes Affect a Population?

© 2013 Pearson Education, Inc.

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

UNIT 3: Evolution and Diversity

Topic 17

Microevolution

CEB Textbook Chapter 13, pages 256-262

Mastering Biology, Chapter 13

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.

16

What is Microevolution?

Microevolution describes the small-scale changes within gene pools over generations.

Who Evolves in Microevolution?

The smallest biological unit

that can evolve is the

POPULATION

Individuals do not evolve –

populations evolve.

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.

Example: human population,

Arctic tundra plant species

Continuous distribution

Example: Some frog species

Fragmented distribution

Gene Pool 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.

A gene pool made up

of 16 individuals

aa

AA

Aa

aa

aa

aa

Aa

Aa

Aa

Aa

AA

AA

AA

AA

AA

Gene Pool Geographic boundary

of the gene pool

A gene pool made up of 16 individual organisms

with gene A, and where gene A has two alleles

Individual is

homozygous

dominant (AA)

AA

AA

AA

AA

AA

AA

Aa

Individual is

heterozygous (Aa)

Aa

Aa

Aa

Aa

Aa

Individual is homozygous

recessive (aa)

aa

aa

aa

aa

aa

Changing Allele Frequencies

Boundary of

gene pool

Gene flow

Emigration

Mate selection (non-

random mating)

Immigration

Natural selection

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

Mutation

Geographical barrier

Genetic drift

AA A’A

17

The gene

pool

Activity – Process of Science

Complete

1) How Do Environmental Changes Affect a Population?

© 2013 Pearson Education, Inc.

Three Mechanisms of Microevolution

1) Mutations

2) Gene Flow

3) Genetic Drift

© 2013 Pearson Education, Inc.

aa Aa

AA

AA AA

AA

AA

AA

Aa

Aa

Aa

Aa

Aa

Aa Aa

Aa

aa

aa

aa

Mutations

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.

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

Environmental

conditions change

Generations

Mutation causes the

formation of a new

recessive allele

All

ele

fre

qu

en

cy

a’a

New recessive

allele

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

Aa

Aa

Gene Flow 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.

Barriers to gene flow

Migration into and out of

population B

Population C

Population B No gene flow

Population A

Population A

Population B

Population C

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

Aa

Aa

Aa

Aa

Aa

Gene flow

AA AA

AA

Genetic DriftDrift

Genetic Drift = Random changes in the allele frequencies in a population

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).

18

Allele Frequencies and Population Size

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.

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.

Small population

Large 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

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

Cheetahs have a small

population with very

restricted genetic diversity

Genetic Drift: Generation 1

A = 16 (53%) a = 14 (47%)

Fail to locate a

mate

aa AA Aa

AA

AA

Aa

Aa

Aa

Aa Aa

Aa

aa

aa AA Aa

In the following hypothetical example, the allele frequencies in the gene pool of a small population are recorded over three generations.

Generation 1: As a result of the sparse distribution of the population, two beetles fail to locate a mate.

This factor alone prevented them from contributing their genes to the next generation.

An example may be the sparsely distributed individuals of the Siberian tiger population.

Genetic Drift: Generation 2

A = 15 (50%) a = 15 (50%)

Fail to locate a mate due

to low population density

Killed in a

rock fall

aa AA Aa Aa

Aa

Aa

Aa Aa aa

aa Aa

AA

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.

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.

The effect this had on the gene

pool was to reduce the frequency of the dominant allele from 53% to 50%.

The change in allele frequencies is directionless; there is no selection pressure operating on the alleles.

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

Genetic Drift: Generation 3

Killed in a

cyclone

A = 13 (43%) a = 17 (57%)

aa AA Aa

AA

Aa

Aa Aa

Aa Aa

aa

aa Aa

aa

aa

AA

Genetic Drift in Populations

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.

Very small gene pool

Breeding population = 20

Fluctuations are so extreme that

the allele may become fixed

(100%) or lost altogether (0%)

Small gene pool

Breeding population = 200

Fluctuations are more

severe because random

changes in a few alleles

cause a greater percentage

change in allele frequencies.

Large gene pool

Breeding population = 2000

Fluctuations are minimal

because large numbers of

individuals buffer the

population against large

changes in allele

frequencies.

Allele lost from

the gene pool

The Bottleneck Effect Populations may be reduced to low numbers through periods of:

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.

Seasonal climatic change Heavy predation or disease Catastrophic events (e.g. flood,

volcanic eruptions, landslide)

19

Population Bottlenecks

The original gene pool is made up of the offspring of

many lineages (family groups and sub-populations)

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

Genetic

bottleneck

Only two descendants of

lineage B survive the

extinction event

Extinction event such

as a volcanic eruption

Population Bottlenecks Population grows to a large

size again, but has lost

much of its genetic

diversity

Population reduced to a

very low number with

consequent loss of alleles

Large, genetically

diverse population

Popu

lation

nu

mbers

Population bottleneck:

the population nearly

becomes extinct as

numbers plummet

Time

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

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: 10-20 000 years ago.

All modern cheetahs may have arisen from a single surviving litter, accounting for the lack of diversity.

At this time, 75% of all large mammals perished (including mammoths, cave bears, and saber-toothed cats).

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.

Figure 13.24-1

Original

population

Figure 13.24-2

Original

population

Bottleneck event

20

Figure 13.24-3

Original

population

Bottleneck event

Surviving population

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.

As a consequence of this founder effect, the colonizing population may evolve in a different direction than the parent population.

The marine iguana of the Galapagos has

evolved in an isolated island habitat

Offshore islands can provide an environment in

which founder populations can evolve in

isolation from the parental population.

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).

Mainland

population

Colonization

Island

population

The Founder Effect

In this hypothetical population of beetles, a small, randomly selected group is blown offshore to a neighboring island where they establish a breeding population.

Mainland

population

Colonizing

island

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

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

Natural selection

acts on phenotype

• Natural selection

therefore changes

the composition of a

gene pool and

increases the

probability that

favourable alleles will

come together in the

same individual.

EXAMPLE OF NATURAL SELECTION:

Gene pool of grey and white alleles

21

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

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.

• 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.

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

22

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.

•In America –

Homozygous recessive: selected against

Heterozyogous: Slightly less fit than Homozygous Dominant

•In Africa –

Homozygous recessive: selected

against

Heterozygous: More fit than

Homozygous Dominant

Malaria

• Heterozygotes have a protection against malaria

• In areas where malaria is a major killer,

heterozygotes are selected for.

• This leads to the recessive allele being

maintained in those populations

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?

• 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

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

23

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

Hunting large game dog

• 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?

24

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, high-energy 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

Pedigree Dogs Exposed - http://www.youtube.com/watch?v=yZMegQH1SPg

Secret Life of Dogs - http://www.youtube.com/watch?v=5h8lWBd1hmE

Artificial Selection in Brassica Different parts of the wild brassica have been developed by human selection to produce at least six distinctly different vegetables.

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.

Cauliflowe

r

(flower)

Broccoli

(inflorescence)

Cabbage

(terminal

buds) Brussels sprout

(lateral buds)

Kohlrabi

(stem)

Wild Form

Brassica oleracea

Kale

(leaf)

25

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.

Key Words • Natural Selection

• Gene Pool

• Allelle Frequencies

• Population

• Gene Flow

• Bottleneck Effect

• Mutations

• Founder Effect

• Artificial Selection

• Microevolution

• Directional, Stabilizing or Disruptive Selection

Evolution Videos

• Crash Course in Biology – Evolution

• http://www.youtube.com/watch?v=P3GagfbA2vo

UNIT 3: Evolution and Diversity

Topic 18

Macroevolution

CEB Textbook Chapter 13, pages 256-262

Mastering Biology, Chapter 13

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: pre-

zygotic 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.

26

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

A. afarensis

440 ml

H. habilis

575 ml

H. erectus

1100 ml

H. sapiens

1450 ml © 2013 Pearson Education, Inc.

Animation: Macroevolution

Right click slide / select “Play”

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 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

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

No

in

terb

ree

din

g

Dingo

Canis familiaris dingo

Coyote

Canis latrans

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

Inter-

breeding

Inter-

breedin

g

Domestic dog

Canis familiaris

No

in

terb

ree

din

g

Inter-

breedin

g

Gray wolf

Canis lupus

Red wolf

Canis rufus

Black-backed jackal

Canis mesomelas

Golden jackal

Canis aureus

Side-striped jackal

Canis adjustus

27

Figure 14.2a

Similarity between different species

Figure 14.2b

Diversity within one 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.

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.

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.

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

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.

28

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.

Breeding season

for species A

Breeding season

for species B

Prezygotic

Isolating

Mechanisms

Prezygotic Isolating Mechanisms Behavioral:

Species may have specific calls, rituals, postures etc. that enable them to recognize potential mates (many bird species have elaborate behaviors).

Structural:

For successful mating, species must have compatible copulatory apparatuses, appearance, and chemical make-up (odor, chemical attractants).

Gamete mortality:

If sperm and egg fail to unite, fertilization will be unsuccessful.

Peacock

Sperm

Attempted

fertilization

Egg

Insects have very

specific copulatory

organs which act like a

lock and key

Figure 14.4

Temporal Isolation Habitat Isolation

PREZYGOTIC BARRIERS

Mechanical Isolation Gametic Isolation Behavioral Isolation

Postzygotic IsolatingMechanisms

Postzygotic isolating mechanisms act after fertilization to prevent successful reproduction.

Hybrid inviability:

The fertilized egg may fail to develop properly

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 non-viable.

Species A X Species B

F1

F2

Hybrid AB Hybrid AB

Reduced viability Reduced viability

Non-viable or sterile

X

Hybrid AB

This mule is a hybrid

between a horse and a

donkey

Hybrids in the Horse Family

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.

Donkey mare

(2n = 62)

Zebra stallion

(2n = 44)

‘Zebronkey’

offspring (2n = 53)

X

Chromosomes

contributed by donkey

mother

Chromosomes contributed

by zebra father

X Y

Figure 14.5

Hybrid Breakdown Reduced Hybrid Fertility Reduced Hybrid Viability

POSTZYGOTIC BARRIERS

Donkey

Mule

Horse

29

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

Types of Speciation

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 Sympatric speciation

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.

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).

Parent population

Allopatric 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).

Isolated

Population B

River barrier

prevents gene flow

Some natural

variation exists in

each population

Isolated

Population C

Isolated

Population A

Mountain

barrier

prevents gene

flow

Allopatric Speciation

STAGE 3:

Formation of a subspecies

The isolated populations may be subjected to quite different selection pressures.

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).

Cooler climate

Sub-species A

Drier climate

Sub-species C

Sub-species A

Wetter climate

30

Allopatric Speciation

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

River barrier

removed

Species B Species A

Mountain barrier remains

Species A

Allopatric

species

Sympatric species: Closely related species with overlapping

distribution

Allopatric species: Closely related species still geographically

separated

Figure 14.7

Ammospermophilus

harrisii

Ammospermophilus

leucurus

Figure 14.8

Geographic barrier

Populations interbreed

Time

Populations become allopatric

Populations become sympatric

Populations cannot interbreed

Reproductive isolation: Speciation has occurred

Gene pools merge: No speciation

Figure 14.10

Punctuated

pattern

Gradual

pattern

Time

© 2013 Pearson Education, Inc.

Animation: Allometric Growth

Right click slide / select “Play”

Sympatric Speciation Sympatric speciation: A new species within the same area as the parent species.

There is no geographical separation between the

speciating populations.

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.

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

Wild Einkorn

31

Sympatric Speciation

A change in habitat preference:

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.

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

New host

plant species

Original host

plant species

Sympatric Speciation Establishing reproductive isolation:

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.

Ultimately, the two groups will diverge to be recognized as separate species.

Each host plant will attract flies that

were reared on that plant where they

will mate with other flies with a similar

preference

New host plant species Original host plant species

No

gene

flow

Gene

flow

Sympatric Speciation 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.

Stages in Species Formation

Different types of isolating mechanisms operate and different amounts of gene flow take place as two populations diverge to form new species.

Homogeneous

Ancestral Population

Population splits

Population A Population B

Geographic

isolation

Gene flow

common

Gene flow

uncommon

Geographic

isolation

Prezygotic

isolation

Prezygotic

isolation

Postzygotic

isolation

Gene flow

very rare

No gene

flow

Race A

Subspecies A

Species A

Race B

Subspecies B

Species B

Evolu

tion

ary

De

ve

lop

me

nt

Postzygotic

isolation

Allopatric speciation Sympatric speciation

32

Speciation summary

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

UV Light Summary: Forces

Operating in

Evolution

At the chromosomal level:

Crossing over

Block mutations

Polyploidy

Aneuploidy

Independent assortment

Recombination

Sperm

Egg

Forces Operating

in Evolution

Forces Operating in

Evolution

At the organism level:

Environmental modification of phenotype

Reproductive success

Selection pressures

'Fitness' of the phenotype

At the population level:

Genetic drift and population size

Natural selection altering gene frequencies

Mate selection

Intraspecific competition

Founder effect

Immigration/emigration (gene flow)

Population bottlenecks

Forces Operating in

Evolution

AA

AA

AA

AA

AA

AA

Aa

Aa

Aa

Aa

Aa

Aa

aa

aa

aa

aa

At the species level:

Geographical barriers

Reproductive isolation (prezygotic and postzygotic)

Selection pressures

Interspecific competition

Forces Operating

in Evolution

33

Activity – Process of Science

Complete

1) How Do New Species Arise by Genetic Isolation?

© 2013 Pearson Education, Inc.

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

• Allopatric Speciation

• Sympatric Speciation

• Prezygotic Barrier

• Postzygotic Barrier

What do we know about human evolution?

(For your own interest: Will not be assessed)

Starter 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

34

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?

• Chimps and gorillas are apes.

• Human beings share many features with them.

• Humans are NOT descended from modern apes.

• But we do share a common ancestor.

From all this evidence, do you think human beings are closest to

chimps or gorillas?

Feature Gorillas Human beings Chimpanzees

Chromosomes

Head hair

Calf muscle

Buttocks

Arms vs legs

Canine teeth

Thumbs

short

small

thin

shorter legs

large

long

48

shorter arms

46 48

small

long

fat

large

long short

small

thin

shorter legs

large

short

• It’s not a trick question!

• So far we haven’t found enough evidence to

decide.

• But there is enough evidence to say that humans

and apes share the same ancestor.

human beings

chimps or gorillas?

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.

• 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.

35

Scientists use the evidence to work out how living

apes are related to fossil apes.

fossils

gibbons

orang-utans

chimpanzees and gorillas

human beings

Do human beings have any closer relatives in the

fossils?

chimpanzees and gorillas

?

human beings

• Australopithecines

lived in Africa 1.5 to 4

million years ago.

• Lucy – the most

complete

Australopithecine

skeleton found.

• So is Lucy more

closely related to us

or to living apes?

• Australopithecines share some features with

human beings:

- eye sockets are wide and set apart

- broad nose

- sinus inside front of skull

jaw more like human than chimpanzee

sinus (spaces inside skull)

eye socket

broad nose

modern human A. africanus chimpanzee

• 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?

jaw more like human than chimpanzee

sinus (spaces inside skull)

eye socket

broad nose

modern human A. africanus 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.

36

So Australopithecines were more like human beings

than chimps and gorillas.

chimpanzees and gorillas

Australopithecines

human beings

• But scientists think that

we have even closer fossil

relatives.

• Habilines lived in Africa

1.6 to 2 million years ago.

• Fossils showed that their

spines were joined to the

middle of their skull, so

Habilines walked upright.

• 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.

Species Brain size (ml)

Human beings

Australopithecines

Habilines

1400

500

650

• 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.

Australopithecines

habilines

human beings

• Fossils of other early humans have also been

found.

• Homo erectus lived in Africa 1.5 million years

ago.

Species Brain size (ml)

Human beings

Australopithecines

Habilines

1400

500

650

Homo erectus 900

• 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.

Habilines (Homo habilis)

Homo erectus

modern humans

37

• Homo erectus were also the first early humans

to leave Africa.

• Their skeletons have been found in Asia and

Europe.

• But Homo erectus are not quite the same as

modern humans. For example, their skulls have a

thick, straight brow ridge.

• So scientists think that we must have at least

one more recent ancestor.

• 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.

• Modern humans are called Homo sapiens.

• They left Africa about 120 000 years ago.

• Homo sapiens fossils this old have been found in

Israel.

Habilines

Homo erectus

modern humans (Homo sapiens)

• 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.

• These modern humans were hunters and

farmers.

• The symbols in their paintings tell us that they

had language.

• They also had ceremonies like burials.

38

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.

modern humans

early humans

Australopithecines

living apes, like chimps and gorillas

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?

• Explore these • Science Museum, London, Evolution of language:

www.sciencemuseum.org.uk/exhibitions/brain/256.asp

• Hunterian Museum, University of Glasgow, illustrates the human evolution story with images of its exhibits and brief text passages:

www.hunterian.gla.ac.uk/museum/hominid/hominid.html

• 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/

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