Week 8: Evolu,on: The cornerstone of all biology Outline 1)  Darwinian revolu,on 2)  The history of the idea 3)  Contras,ng views of Evolu,on 4)  Descent with modifica,on: phylogene,c (evolu,onary) trees 

and how to interpret these 5)  Links with ar,ficial selec,on 6)  Evidence for evolu,on (drug resistance, adapta,on) 7)  Homology versus analogy 8)  Convergence 9)  Micro‐versus macro‐evolu,on 10)  The fossil record 

Darwin (and Wallace) challenged the tradi,onal view of life on earth and ushered in a new era of biology 

• On the Origin of Species focused biologists’ aSen,on on the great diversity of organisms • Darwin noted that current species must be descendants of ancestral species • Evolu&on as defined by Darwin can be understood as descent with modifica5on 

  

Scala Naturae and Classification of Species •  The Greek philosopher Aristotle viewed

species as fixed and arranged them on a scala naturae (from lowest to highest)

The intellectual context of Darwin’s work: the history of the notion of ‘species’

The Old Testament holds that species were individually designed by God and therefore perfect

Aristotle (384-322 BC)

Also called the Great Chain of Being

Noah’s Ark

Waved Albatross, Galapagos Island

•  Carolus Linnaeus (1707-1778) interpreted organismal adaptations as evidence that the Creator had designed each species (=distinct form) for a specific purpose (“for the greater glory of God”)

•  Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying organisms

•  He developed the binomial format for naming species (for example, Homo sapiens)

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Species Genus Family Order Class Phylum Kingdom

Keep Pond Clean Or Froggy Gets Sick

Ursus americanus (American black bear

Ursidae

Carnivora

Mammalia

Chordata

Animalia Eukarya

Ursus

Ideas About Change in Organisms over Time •  The study of fossils helped to lay the

groundwork for Darwin’s ideas •  Fossils are remains or traces of organisms

from the past, usually found in sedimentary rock, which appears in layers or strata

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Video: Grand Canyon

Figure 22.3

Sedimentary rock layers (strata)

Younger stratum with more recent fossils

Older stratum with older fossils

•  Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier (1769-1832)

•  Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe

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•  Geologists James Hutton (first, late 1700’s) and Charles Lyell (later, contemporary of Darwin) perceived that changes in Earth’s surface can result from slow continuous actions still operating today (e.g., earthquakes, tsunamis, volcanoes, erosion, rivers, glaciers)

•  Lyell proposed the principle of uniformitarianism which stated that the mechanisms of change are constant over time

•  This view strongly influenced Darwin’s thinking •  These views suggested that the earth must be

much older than widely accepted age of 6000 years.

Charles Lyell (1797-1875)

Jean-Baptiste Lamarck (1744-1829): One of the first and most prominent Evolutionists

•  Lamarck hypothesized that species evolve through use and disuse of body parts and the inheritance of acquired characteristics

•  The mechanisms he proposed are unsupported by evidence (although there are modern ‘Lamarckians’ and there is some evidence that exposure of the DNA to environmental influences can lead to changes in the offspring).

Figure 1.5a

Thomas Robert Malthus (1766-1834)

Darwin’s Early Life

•  As a boy and into adulthood, Charles Darwin had a consuming interest in nature

•  Darwin first studied medicine (unsuccessfully), and then theology at Cambridge University

•  After graduating, he took an unpaid position as naturalist and companion to Captain Robert FitzRoy for a 5-year around the world voyage on the Beagle

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The Voyage of the Beagle

•  During his travels on the Beagle, Darwin collected specimens of South American plants and animals

•  He observed that fossils resembled living species from the same region, and living species resembled other species from nearby regions (e.g., islands and mainlands)

•  He experienced an earthquake in Chile and observed the uplift of rocks

•  He also read Malthus’ essay

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Darwin in 1840, after his return from the voyage

The Galápagos Islands

NORTH AMERICA

ATLANTIC OCEAN

PACIFIC OCEAN

PACIFIC OCEAN

Pinta

Marchena Genovesa

Equator

Chile Santiago

Daphne Islands

Fernandina

Isabela Santa Cruz Santa

Fe San Cristobal

Española Kilometers

0 20 40 Florenza

Pinzón

SOUTH AMERICA

AFRICA

EUROPE Great Britain

HMS Beagle in port

Equator PACIFIC OCEAN

Malay Archipelago

AUSTRALIA

Tasmania New Zealand

Brazil

Argentina

Cape Horn

And

es M

tns.

Cape of Good Hope

The formative experiences of Darwin

•  In 1844, Darwin wrote an essay on natural selection as the mechanism of descent with modification, but did not introduce his theory publicly

Source: Darwin-online.org.uk

Alfred Russell Wallace: A British Naturalist working in the Malay Archipelago sent Darwin a manuscript (1858)

The Origin of Species (1859)

Figure 22.2 1809

1798

1812

1795

1830

1790 1809 1831-36

1844

1859 1870

Lamarck publishes his hypothesis of evolution.

Malthus publishes “Essay on the Principle

of Population.”

Hutton proposes his principle of

gradualism.

Charles Darwin is born.

Darwin travels around the world on HMS

Beagle.

The Galápagos Islands

Darwin writes his essay on descent with modification.

On the Origin of Species is published.

While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection.

1858 Cuvier publishes his extensive studies of vertebrate fossils.

Lyell publishes Principles of Geology.

Descent with Modification

•  Darwin never used the word evolution in the first edition of On the Origin of Species

•  The phrase “descent with modification” summarized Darwin’s perception of the unity of life

•  The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past

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On the Origin of Species

•  Darwin explained three broad observations: –  The unity of life –  The diversity of life –  The match between organisms and their

environment

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The only figure from On the Origin of Species

A tree with branches represents life’s diversity Theory meshed well with the hierarchy of Linnaeus

Figure 22.8 Hyracoidea (Hyraxes)

Sirenia (Manatees and relatives)

†Deinotherium

†Mammut

†Platybelodon

†Stegodon

†Mammuthus

Elephas maximus (Asia)

Loxodonta africana (Africa)

Loxodonta cyclotis (Africa)

†Moeritherium

†Barytherium

60

Millions of years ago

34 24 5.5 2 104 0

Years ago

Artificial Selection, Natural Selection, and Adaptation

•  Darwin noted that humans have modified other species by selecting and breeding individuals with desired traits, a process called artificial selection

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Figure 22.9

Brussels sprouts

Kale

Selection for leaves

Selection for axillary (side) buds

Selection for apical (tip) bud

Cabbage

Broccoli

Kohlrabi Wild mustard

Selection for stems

Selection for flowers and stems

More frivolous pursuits also involved artificial selection!

The earliest pigeon fanciers. Blasco R1, Finlayson C1, Rosell J2, Marco AS3, Finlayson S1, Finlayson G1, Negro JJ4, Pacheco FG5, Vidal JR6. Sci. Rep. 2014 (Aug) “At Gorham's Cave, Gibraltar, the Neanderthals exploited Rock Doves for food for a period of over 40 thousand years, the earliest evidence dating to at least 67 thousand years ago. We show that the exploitation was not casual or sporadic, having found repeated evidence of the practice in different, widely spaced, temporal contexts within the cave. Our results point to hitherto unappreciated capacities of the Neanderthals to exploit birds as food resources on a regular basis. More so, they were practising it long before the arrival of modern humans and had therefore invented it independently.”

•  Observation #1: Members of a population often vary in their inherited traits

Asian Ladybird beetles (Harmonia axyridis, like the kind that has exploded in Montreal).

•  Observation #2: All species can produce more offspring than the environment can support, and many of these offspring fail to survive and reproduce

Remember Malthus!

Puffball fungus

Bald Eagle

•  Inference #1: Individuals whose inherited traits give them a higher probability of surviving and reproducing in a given environment tend to leave more offspring than other individuals

•  Inference #2: This unequal ability of individuals to survive and reproduce will lead to the accumulation of favorable traits in the population over generations

•  This process explains the match between organisms and their environment

Natural Selection: A Summary

•  Individuals with certain heritable characteristics survive and reproduce at a higher rate than other individuals

•  Natural selection increases the adaptation of organisms to their environment over time

•  If an environment changes over time, natural selection may result in adaptation to these new conditions and may give rise to new species

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•  Note that individuals do not evolve; populations evolve over time

•  Natural selection can only increase or decrease heritable traits that vary in a population (covered in a later lecture in more detail!)

•  Adaptations vary with different environments

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Short film showing Mammalian diversity

Evidence for Evolution

•  New discoveries continue to fill the gaps identified by Darwin in The Origin of Species

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Direct (and contemporary) Observations of Evolutionary Change

•  Micro-evolution is change in gene frequencies over time. (This week and next you will look at gene frequencies in the lab).

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Cliff Swallow wings evolve rapidly!

Brown and Bomberger Brown 2013

Natural Selection in Response to Introduced Plant Species

•  Soapberry bugs use their “beak” to feed on seeds within fruits •  In southern Florida soapberry bugs feed on balloon vine with larger

fruit; they have longer beaks •  In central Florida they feed on goldenrain tree with smaller fruit; they

have shorter beaks •  Correlation between fruit size and beak size has also been observed

in Louisiana, Oklahoma, and Australia

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Soapberry bug (Jadera haematoloma) with beak inserted in balloon vine fruit

Figure 22.13b

On native species Balloon vine, southern Florida

Museum-specimen average

On introduced species, goldenrain tree, in central Florida N

umbe

r of i

ndiv

idua

ls

10

8

6 4

2

0

10

8

6 4

2

0

Beak

Beak length (mm) 6 7 8 10 11

RESULTS

9 In Florida this evolution in beak size occurred in < 35 years

The Evolution of Drug-Resistant Bacteria

•  The bacterium Staphylococcus aureus is commonly found on people

•  One strain, methicillin-resistant S. aureus (MRSA) is a dangerous pathogen (killing 1000’s annually in Canada..mostly elderly)

•  S. aureus became resistant to penicillin in 1945, two years after it was first widely used

•  S. aureus became resistant to methicillin in 1961, two years after it was first widely used

•  Why so quickly??

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•  Methicillin works by inhibiting a protein used by bacteria in their cell walls

•  MRSA bacteria use a different protein in their cell walls

•  When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. aureus strains

•  MRSA strains are now resistant to many antibiotics

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1 2,750,000

2,500,000

2,250,000

2,000,000

1,750,000

1,500,000 1,250,000

1,000,000

750,000

500,000

250,000 base pairs

Chromosome map of S. aureus clone USA300

Key to adaptations

Methicillin resistance Ability to colonize hosts Increased disease severity Increased gene exchange (within species) and toxin production

Figure 22.14

•  Natural selection does not create new traits, but edits or selects for traits already present in the population

•  The local environment (e.g., a body with a soup of antibiotics) determines which traits will be selected for or selected against in any specific population

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Anatomical and Molecular Homologies

•  Homology is similarity resulting from common ancestry

•  Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

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Figure 22.15

Humerus

Radius Ulna

Carpals Metacarpals Phalanges

Human Cat Whale Bat

Figure 22.16

Pharyngeal pouches

Post-anal tail

Chick embryo (LM) Human embryo

Comparative embryology reveals anatomical homologies not visible in adult organisms

•  Vestigial structures are remnants of features that served important functions in the organism’s ancestors (e.g., human appendix, leg bones in snakes, eye remnants in blind fishes from

caves)

.

Astyanax mexicanus

Homologies at the molecular level

Genes and genetic structures shared among organisms inherited from a common ancestor (e.g., rRNA)

Figure 17.17a

tRNA molecules

Growing polypeptide Exit tunnel

E P A

Large subunit

Small subunit

mRNA 5′ 3′

(a) Computer model of functioning ribosome

Pseudogenes Some homologous genes acquire new functions, others

have retained the original function. Some have lost function so are called pseudogenes (in effect, ‘vestigial genes’)

Homologies and “Tree Thinking”

•  Evolutionary trees are hypotheses about the relationships among different groups

•  Homologies form nested patterns in evolutionary trees

•  Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data

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Figure 22.17

Branch point Lungfishes

Amphibians

Mammals

Lizards and snakes

Crocodiles

Ostriches

Hawks and other birds

Feathers

Amnion

Digit- bearing limbs

Homologous characteristic

Tetrapods A

mniotes

Birds

1

2

3

4

5

6

Each branch point (1-6) represents common ancestor of lineage beginning to the right

A Different Cause of Resemblance: Convergent Evolution

•  Convergent evolution is the evolution of similar, or analogous, features in distantly related groups

•  Analogous traits arise when groups independently adapt to similar environments in similar ways

•  Convergent evolution does not provide information about ancestry

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Appendix (!) has evolved between 18-32 times independently!

Proposed function is to provide safe house for beneficial bacteria to reinoculate the gut after a serious gastro-intestinal illness

Figure 22.18

Sugar glider

Flying squirrel

NORTH AMERICA

AUSTRALIA

Australia

The Fossil Record

•  The fossil record provides evidence of the extinction of species, the origin of new groups, and changes within groups over time

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Figure 22.19

Most mammals Cetaceans and even-toed ungulates

(a) Canis (dog) (b) Pakicetus (c) Sus (pig) (d) Odocoileus (deer)

Figure 22.UN01

•  Fossils can document important transitions –  For example, the transition from land to sea

in the ancestors of cetaceans

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Figure 22.20

Other even-toed ungulates

Hippopotamuses

†Pakicetus

†Rodhocetus

†Dorudon

Living cetaceans

Common ancestor of cetaceans

Millions of years ago 70 Key 60 50 40 30 20 10 0 Pelvis Tibia

Femur Foot

Biogeography

•  Biogeography, the geographic distribution of species, provides evidence of evolution

•  Earth’s continents were formerly united in a single large continent called Pangaea, but have since separated by continental drift

•  An understanding of continent movement and modern distribution of species allows us to predict when and where different groups evolved

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•  Endemic species are species that are not found anywhere else in the world

•  Islands have many endemic species that are often closely related to species on the nearest mainland or island

•  Darwin explained that species on islands gave rise to new species as they adapted to new environments

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What Is Theoretical About Darwin’s View of Life?

•  In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena

•  Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions

•  Ongoing research adds to our understanding of evolution

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Figure 22.UN02

Observations

Individuals in a population vary in their heritable

characteristics.

Organisms produce more offspring than the

environment can support.

Individuals that are well suited to their environment tend to leave

more offspring than other individuals.

Inferences

and

Over time, favorable traits accumulate in the population.

Figure 22.UN03

Figure 22.UN04