Chapter 22 Descent with Modification: A Darwinian View of Life

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AP Biology 2006-2007

Chapter 22 Descent with Modification:

A Darwinian View of Life

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AP Biology

In historical context

 Darwin did not originate the idea of evolution

 Geologic theories of Earth’s age & history cleared the path for evolutionary biologists

…immeasurable time…

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•

Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier

•

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

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•

Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still

operating today

•

Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time

•

This view strongly influenced Darwin’s thinking

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End Show

15–2 Ideas That Shaped Darwin's Thinking

Slide 5 of 27

Copyright Pearson Prentice Hall

Population Growth

Malthus Theory of Population Growth

In 1798, Thomas Malthus published a book in

which he noted that babies were being born faster than people were dying.

The only forces he observed that worked against this growth were war, famine, and disease.

Malthus reasoned that if the human population

continued to grow unchecked, sooner or later there would be insufficient living space and food for

everyone.

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Lamarck's Evolution Hypotheses

Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime.

These traits could then be passed on to

their offspring. Over time, this process

led to change in a species.

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Slide 7 of 27

Lamarck's Hypothesis A male fiddler

crab uses its front

claw to ward off

predators and to

attract mates.

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Lamarck's Hypothesis Because the front

claw is used repeatedly, it

becomes larger.

This characteristic (large claw) is

passed onto its

offspring.

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Lamarck vs Darwin

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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

•

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

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Figure 22.5

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

Andes Mtns.

Cape of Good Hope

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Figure 22.6

(a) Cactus-eater (b) Insect-eater

(c) Seed-eater

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Darwin’s finches

Leaf-browser? Wren?



Darwin was amazed to find out there were 14 species of finches on

Galapagos island

 but only one species on South American mainland

 500 miles away

 all the birds had to originally come from mainland

species _{Why were}

the finches so different now?

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Warbler finch Woodpecker finch

Small insectivorous tree finch

Large insectivorous tree finch

Vegetarian tree finch

Cactus finch

Sharp-beaked finch

Small ground finch

Medium

ground finch

Large ground finch Insect eaters

Bud eater

Seed eaters Cactus

eater

Darwin’s finches

 Differences in beaks



associated with eating different foods



adaptations to foods available on islands

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Darwin’s finches

 Darwin’s conclusions



small populations of original South American finches reached islands

 variation in beaks enabled some to obtain food successfully in the different environments



over many generations, the populations of finches changed anatomically & behaviorally

 accumulation of advantageous traits

 emergence of different species

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 Finches with beak differences that

allowed them to…



successfully compete



successfully feed



successfully reproduce

 pass successful traits onto their offspring

Adaptive radiation

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

•

Natural selection is a process in which individuals with favorable inherited traits are more likely to

survive and reproduce

•

In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a

theory of natural selection similar to Darwin’s

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Darwin quickly finished The Origin of Species and published it the next year

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Slide 18 of 27

Evolution by Natural Selection

Descent With Modification

• Natural selection produces organisms that have different structures, establish different niches, or occupy different habitats.

• Each living species has descended, with changes, from other species over time.

• Darwin referred to this principle as descent with

modification.

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Slide 19 of 27

Evolution by Natural Selection

Survival of the Fittest

• The ability of an individual to survive and

reproduce in its specific environment is fitness.

• Darwin proposed that fitness is the result of adaptations.

• An adaptation is any inherited characteristic that

increases an organism's chance of survival.

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(5) Over long periods of time, and given a steady input of new variation into a population, these processes lead to the emergence of new species

Essence of Darwin’s ideas

(1) Variation exists in natural populations

(2) Many more offspring are born each season than can possibly survive to maturity

(3) As a result, there is a struggle for existence - competition

(4) Characteristics beneficial in the struggle for existence will tend to become more common in the population, changing the average characteristics of the population - adaptations

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Summary of Darwin's Theory

Individuals best suited to their environment survive and reproduce most successfully.

These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer

offspring.

This process of natural selection causes species to change over time.

Natural Selection

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•

In general, natural selection operates not to create variation, but to edit existing variation.

–

For example, resistant insects are favored and non-resistant insects are not when

insecticides are applied.

•

Natural selection favors those characteristics in a variable population that fit the current, local environment.

- For example, dark peppered moth had survival advantage over light colored moth

during times of heavy industrial air pollution.

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Artificial Selection, Natural Selection, and Adaptation

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

•

Darwin drew two inferences from two observations

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•

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

•

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

reproduce

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Natural Selection: A Summary

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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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Figure 22.12

(a) A flower mantid in Malaysia (b) A leaf mantid in Borneo

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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

•

Adaptations vary with different environments

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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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•

In all cases, beak size has evolved in

populations that feed on introduced plants with fruits that are smaller or larger than the native fruits

•

These cases are examples of evolution by natural selection

•

In Florida this evolution in beak size occurred in less than 35 years

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Figure 22.13a

Soapberry bug with beak inserted in balloon vine fruit FIELD STUDY

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Figure 22.13b

On native species, southern Florida

Museum-specimen average

On introduced species, central Florida

Number of individuals

10 8 6 4 2 0

Beak

Beak length (mm)

6 7 8 10 11

RESULTS

9

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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

• 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

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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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Concept Map

Section 15-3

includes

Evidence of Evolution

Physical remains of organisms

Common ancestral species

Similar genes Similar genes which is composed of which indicates which implies which implies

The fossil record

Geographic distribution of living species

Homologous body structures

Similarities in embryology

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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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Evidence supporting evolution

 Fossil record

 transition species



Anatomical record

 homologous & vestigial structures

 embryology & development



Molecular record

 protein & DNA sequence



Artificial selection

 human-caused evolution

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?

Land Mammal

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2006 Fossil Discovery of Early Tetrapod

 Missing link from sea to land animals

 Fossil of sea animal that had four limbs

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Reconstruction of Archaeopteryx : transitional fossil from reptile to bird

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Anatomical record

 Homologous structures



similarities in characteristics resulting

from common ancestry

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Homologous structures

 Forelimbs of human, cats, whales, & bats share same skeletal structures



similar structure



similar embryological development



different functions



evidence of recent common ancestor

 branched off from common 4-limbed ancestor

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Analogous structures

 Separate evolution of structures



similar functions



similar external form



different internal structure &

development



different origin

 no evolutionary relationship

Solving a similar problem with a similar solution

Don’t be fooled by their looks!

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Convergent evolution

 Flight evolved in 3 separate animal groups

 evolved similar “solution” to similar “problems”

 analogous structures

Does this mean they have a recent common

ancestor?

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Convergent evolution

 Fish: aquatic vertebrates

 Dolphins: aquatic mammals



similar adaptations to life in the sea



not closely related

Those fins & tails

& sleek bodies are analogous structures!

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Parallel Evolution



Parallel, but separate, evolutionary paths

 Parallel evolution occurs when two species that share a common ancestor evolve a similar trait independently of each other.

 filling similar ecological roles in similar environments, so similar adaptations were selected

marsupial mammals

placental mammals

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Parallel Evolution

Niche Placental Mammals Australian Marsupials

Burrower

Mole

Anteater Mouse

Lemur

Flying squirrel

Ocelot

Wolf Tasmanian “wolf”

Tasmanian cat Sugar glider Spotted cuscus

Numbat Marsupial mole

Marsupial mouse Anteater

Nocturnal insectivore

Climber

Glider

Stalking predator

Chasing predator

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Vestigial organs

 Modern animals may have structures that serve little or no function



remnants of structures that were functional in ancestral species



evidence of change over time

 some snakes & whales show remains of the pelvis & leg bones of walking ancestors

 eyes on blind cave fish

 human tail bone

This is not LaMarck’s loss

from “disuse”!

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Vestigial organs

 Hind leg bones on whale fossils

Why would whales have pelvis & leg bones

if they were always sea creatures?

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Comparative embryology

 Similar embryological development in closely related species



all vertebrate embryos have similar structures at different stages of

development

 gill pouch in fish, frog, snake, birds, human, etc.

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Molecular record

0 25 50 75 100 125

0 25 50 75 100

Millions of years ago Horse/

donkey Sheep/

goat

Goat/cow Llama/

cow

Pig/

cow Rabbit/

rodent

Horse/cow

Human/rodent Dog/

cow

Human/

cow

Human/kangaroo

Nucleotide substitutions

 Comparing DNA & protein structure



universal genetic code!

 DNA & RNA



compare common genes

 cytochrome C (respiration)

 hemoglobin (gas exchange) Closely related species have

sequences that are more similar than distantly related species

 DNA & proteins are a molecular

record of evolutionary relationships

Why compare these genes?

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Similarity in Primate Chromosomes

6 longest chromosomes of humans (Hu), matched with 7 chromosomes from chimpanzees ONLY (Ch)

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Similarity in Primate Chromosomes

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Primate Cladogram Based on Chromosome changes

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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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Each branch point represents the common ancestor of the lineages beginning there and to the right of it.

Branch point

Lungfishes

Amphibians

Mammals

Lizards

and snakes Crocodiles

Ostriches

Hawks and other birds Feathers

Amnion Digit-

bearing limbs

A hatch mark represents a homologous

characteristic shared by all the groups to the right of the mark.

Tetrapods

Amniotes

Birds

1

2

3

4

5

6

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Evolutionary trees depict clades. A clade is a group of organisms that includes an ancestor and ALL descendants of that ancestor. You can think of a clade as a branch on the tree of life.

Some examples of clades are shown on the

tree below.

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Cladogram (family tree) of a "large" biological group, showing the last common ancestor at the bottom of the composite tree.

The blue and red subgroups (at left and right) represent clades, or monophyletic (that is, complete) taxonomic groups; each

shows the last common ancestor and all descendant branches.

The green subgroup is not a clade; it represents paraphyletic group, which is incomplete because the blue clade, although descended from it, is excluded.

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Paraphyletic groups do not include all of the descendants of a single common ancestor.

Polyphyletic groups are those which have multiple origins and thus do not share a common ancestor

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More Parsimonious (and preferable) Less Parsimonious Parsimony refers to a rule used to choose among possible cladograms, which states that the cladogram implying the least number of changes in character states is the best.

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PARSIMONY – Fewer Evolutionary Changes

Hypothesis 1 requires six evolutionary changes and Hypothesis 2 requires seven evolutionary changes, with a bony skeleton evolving

independently, twice. Although both fit the available data, the parsimony principle says that Hypothesis 1 is better — since it does not

hypothesize unnecessarily complicated changes.

6 evolutionary changes 7 evolutionary changes

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Taxonomists who use cladistic methods have created an extraordinary vocabulary to help them. Ancestral traits are called plesiomorphic(shown here as black

numbers).

Derived traits are called apomorphic(shown here as

colored numbers). All the members of a clade must share one or more apomorphic traits not found in any other

species.

Derived traits shared by two or more species are

called synapomorphic. Here species A and B share the synapomorphic trait designated with a blue 3 .

Ancestral traits shared by two or more species are called symplesiomorphic. Here, the trait shown as black 1 is a symplesiomorphic trait retained by all 4 species.

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Shared Characters on a Cladogram Shared derived

character from recent common ancestor

Apomorphy-character

shared by recent common ancestor and descendants

Homoplasy-

character present in descendants but not in recent

common ancestor

Plesiomorphy-

character inherited from ancestors older than recent common

ancestor

•.

Autapomorphy-character shared by recent common ancestor and a single

descendant

Synapomorphy-character shared by recent common ancestor and 2 or more descendants

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