• Chapter 22~ Evolutionary Thought

Evolution• Evolution:

change over time• Natural selection:

– populations of organisms can evolve if individuals having certain heritable traits leave more offspring than others (differential reproductive success)

• Evolutionary adaptations:– inherited characteristics that

enhance organisms’ survival and/or reproduction

November 24, 1859

The Origin of Species• Focused biologists’ attention on the

great diversity of organisms

Marine Iguanas of the Galàpagos Islands

• Darwin made two major points in his book– He presented evidence that the

many species of organisms presently inhabiting the Earth are descendants of ancestral species

– He proposed a mechanism for the evolutionary process, natural selection

• The Darwinian revolution challenged traditional views of a young Earth inhabited by unchanging species

• In order to understand why Darwin’s ideas were revolutionary– We need to examine his views in the

context of other Western ideas about Earth and its life

Evolutionary history• Linnaeus: biology, taxonomy• Hutton: geology, gradualism• Lamarck: biology, evolution• Malthus: economics, populations• Cuvier: paleontology, catastrophism• Lyell: geology, uniformity• Darwin: natural selection• Mendel: inheritance• Wallace: natural selection

Evolutionary history

Science Before Darwin

• The Great Chain of Being – Scala Naturae (Aristotle)

• People thought that each species was a divine creation (The Old Testament)

• Carolus Linnaeus (1700’s)– Interpreted organismal adaptations as

evidence that the Creator had designed each species for a specific purpose

– Was a founder of taxonomy, classifying life’s diversity “for the greater glory of God”

Questions Loom Large

• Fields of research investigating living things around the planet– Biogeography- Distribution of

organisms around the world– Comparative Morphology- Study of

similarities and differences in the body plans of major groups (phyla)

Fossils• 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 (strata)

9 million years of erosion caused by the Colorado River = Grand Canyon

Cuvier and Catastrophism

• Paleontology, the study of fossils– Was largely developed by French

scientist Georges Cuvier

• Cuvier opposed the idea of gradual evolutionary change– And instead advocated

catastrophism, speculating that each boundary between strata represents a catastrophe

• Gradualism– Is the idea that profound change can

take place through the cumulative effect of slow but continuous processes

• Geologists Hutton and Lyell (theory of uniformity)– Perceived that changes in Earth’s

surface can result from slow continuous actions still operating today

– Exerted a strong influence on Darwin’s thinking

Science Before Darwin

• Lamarck (1744 - 1829) proposed that evolution occurs through the use & disuse of physical features – “Inheritance of

Acquired Characteristics”

Darwin’s Voyage and Research

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

• Soon after Darwin received his bachelor’s degree in theology– He was accepted on board the HMS

Beagle as the ship’s “naturalist”

The Voyage of the Beagle

• During his travels on the Beagle– Darwin observed and collected

many specimens of South American plants and animals

• Darwin observed various adaptations of plants and animals– That inhabited many diverse

environments

• Darwin’s interest in the geographic distribution of species– Was heightened by the Beagle’s

stop at the Galápagos Islands near the equator west of South America

EnglandEUROPE

NORTHAMERICA

GalápagosIslands

Darwin in 1840,after his return

SOUTHAMERICA

Cape ofGood Hope

Cape Horn

Tierra del Fuego

AFRICA HMS Beagle in port

AUSTRALIA

TasmaniaNewZealand

PACIFICOCEAN

An

des

ATLANTICOCEAN

Darwin’s Voyage (1831-1836)

• Saw fossils of extinct armadillos that looked similar but not identical to living ones

• Finches on Galapagos islands resembled finches on the main land

Competition Keeps Populations in check• Malthus wrote that the human

population would cover the Earth if it went unchecked.

• Disease, war, and famine keep it from going out of control.

• Population: all the individuals of a species living in a specific location

• Adaptation: the changing of a species that makes them better suited to its environment

• In 1844, Darwin wrote a long essay on the origin of species and natural selection– But he was reluctant to introduce his

theory publicly, anticipating the uproar it would cause

• In June 1858 Darwin received a manuscript from Alfred Russell Wallace– Who had developed a theory of natural

selection similar to Darwin’s

• Darwin quickly finished The Origin of Species– And published it the next year

Theory of Evolution by Natural Selection• 1859 Darwin published his theory• Three major findings

– There is genetic variation in a population or species

– Some individuals are better suited to the environment and survive to have more offspring (fitness)

– Traits that are adaptive will spread in a population

Descent with Modification

• Darwin never used the word evolution in the first edition of 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

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

• In the Darwinian view, the history of life is like a tree with branches representing life’s diversity

• Darwin’s theory meshed well with the hierarchy of Linnaeus

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 22-7

Darwin’s Journey of Enlightenment

4 major observations: – Exponential

fertility – Limited resources – Individuals vary

– Variation is

heritable

Descent with Modification2 Inferences:• Non-random

survival• Natural

selection (differential success in reproduction)

Further Evidence used by Darwin

• In the process of artificial selection– Humans have modified other species

over many generations by selecting and breeding individuals that possess desired traits

Terminalbud

Lateralbuds

Brussels sproutsCabbage

Flowercluster

Leaves

Cauliflower

Flowerandstems

Broccoli Wild mustard Kohlrabi

Stem

Kale

• “Absence of evidence is not evidence of absence.”

22.3: Overwhelming Evidence

Macroevolutionary changes

Macroevolutionary change Is the cumulative change during thousands

of small speciation episodesThis section looks at the evidence

Direct evidence Observation Comparative Molecular Evidence:

Fossils: Morphology:

Then we will learn how to classify organisms based on the evidence

Fig. 22-13

Predator: Killifish; preysmainly on juvenileguppies (which do notexpress the color genes)

Guppies: Adult males havebrighter colors than thosein “pike-cichlid pools”

Experimentaltransplant ofguppies

Pools withkillifish,but noguppies priorto transplant

Predator: Pike-cichlid; preys mainly on adult guppies

Guppies: Adult males are more drab in colorthan those in “killifish pools”

Sourcepopulation

Transplantedpopulation

Sourcepopulation

Transplantedpopulation

Nu

mb

er o

fco

lore

d s

pot

s

Are

a of

col

ored

spot

s (m

m2 )

1212

1010

88

6 6

4 4

22

0 0

RESULTS

EXPERIMENT

The Evolution of Drug-Resistant HIV

• The use of drugs to combat HIV selects for viruses resistant to these drugs

• HIV uses the enzyme reverse transcriptase to make a DNA version of its own RNA genome

• The drug 3TC is designed to interfere and cause errors in the manufacture of DNA from the virus

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

• Some individual HIV viruses have a variation that allows them to produce DNA without errors

• These viruses have a greater reproductive success and increase in number relative to the susceptible viruses

• The population of HIV viruses has therefore developed resistance to 3TC

• The ability of bacteria and viruses to evolve rapidly poses a challenge to our society

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 22-14

Weeks

Patient No. 3

Patient No. 2

PatientNo. 1

Per

cen

t o

f H

IV r

esis

tan

t to

3T

C

00

25

50

75

100

2 4 6 8 10 12

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

• The local environment determines which traits will be selected for or selected against in any specific population

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Phylogeny: the evolutionary history of a species

Systematics: the study of biological diversity in an evolutionary context Lineages- lines of descent

that connect ancestral and derived organisms

The fossil record: the ordered array of fossils, within strata (layers) of rock

Evolution evidence: Comparative Anatomy

Homologous structures (homology)

Descent from a common ancestor

Vestigial organ whale/snake

hindlimbs; wings on flightless birds

Anatomy & Development

Vestigial structures: structures that either have no use or are reduced in size because they are not needed.

Homologous structures: structures that share a common ancestry.

Morphological Divergence: structural differences accumulate between lineages

Morphological Convergence: structural similarities accumulate between lineages (analogies form)

Sorting homology vs. analogy...Homology: likeness attributed to

common ancestryAnalogy: likeness attributed to

similar ecological roles and natural selection

Convergent evolution: species from different evolutionary branches that resemble one another due to similar ecological roles