Mechanisms of Evolution

AP Biology Chapter 22

Endless Forms Most Beautiful

• A new era of biology began in 1859 when Charles Darwin published The Origin of Species

• The Origin of Species focused biologists’ attention on the great diversity of organisms

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

• Darwin noted that current species are descendants of ancestral species

• Evolution can be defined by Darwin’s phrase descent with modification

• Evolution can be viewed as both a pattern and a process

pattern - data accumulated

process - mechanisms in place to

cause change

Fig. 22-2

American Revolution French Revolution U.S. Civil War1900185018001750

1795

1809

1798

18301831–1836

1837

1859

18371844

1858The Origin of Species is published.Wallace sends his hypothesis to Darwin.

Darwin begins his notebooks.Darwin writes essay on descent with modification.

Darwin travels around the world on HMS Beagle.

Malthus publishes “Essay on the Principle of Population.”

Lyell publishes Principles of Geology.

Lamarck publishes his hypothesis of evolution.

Hutton proposes his theory of gradualism.

Linnaeus (classification)

Cuvier (fossils, extinction)Malthus (population limits)

Lamarck (species can change)

Hutton (gradual geologic change)

Lyell (modern geology)

Darwin (evolution, natural selection)

Wallace (evolution, natural selection)

• The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae

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

• Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose

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

• 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

Fig. 22-3

Younger stratumwith more recentfossils

Layers of depositedsediment

Older stratumwith older fossils

• 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

• Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today. He called his ideas gradualism.

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

• This view strongly influenced Darwin’s thinking

• 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

• However, he did come up with a mechanism for evolution.

About Darwin

• 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

• His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America

Fig. 22-5

NORTHAMERICA

EUROPE

AFRICA

AUSTRALIA

GREATBRITAIN

SOUTHAMERICA

ATLANTICOCEAN

PACIFICOCEAN Cape of

Good Hope

Tierra del Fuego

Cape HornTasmania

NewZealand

An

des

Equator

TheGalápagosIslands

Pinta

MarchenaGenovesa

SantiagoDaphneIslands

PinzónFernandina

IsabelaSan

Cristobal

SantaFe

SantaCruz

Florenza Española

Fig. 22-6

(a) Cactus-eater (c) Seed-eater

(b) Insect-eater

• In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar

• 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

Let’s get together on this so we can both be famous!

The Origin of Species

• Darwin developed two main ideas:– Descent with modification explains life’s unity and

diversity– Natural selection is a cause of adaptive evolution

• 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

Fig. 22-7

Fig. 22-8

Hyracoidea(Hyraxes)

Sirenia(Manateesand relatives)

Moeritherium

Barytherium

Deinotherium

Mammut

Elephas maximus(Asia)

Stegodon

Mammuthus

Loxodontaafricana(Africa)

Loxodonta cyclotis(Africa)

010425.52434

Millions of years ago Years ago

Platybelodon

Adaptations

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

• Darwin then described four observations of nature and from these drew two inferences

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

• Observation #2: Traits are inherited from parents to offspring

• Observation #3: All species are capable of producing more offspring than the environment can support

• Observation #4: Owing to lack of food or other resources, many of these offspring do not survive

My idea Precisely!

• 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

• Favorable – NOT BEST NECESSARILY

• Darwin was influenced by Thomas Malthus who noted the potential for human population to increase faster than food supplies and other resources

• 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

Fig. 22-12

(b) A stick mantid in Africa

(a) A flower mantid in Malaysia

Evidences for Evolution

• Direct observations

• The Fossil Record

• Homology

• Biogeography

1. Direct Evidences Today

• Ex- Evidence of Drug-resistant HIV

• Ex – Evidence of Drug-resistant bacteria such as MRSA

• Ex – Evidence of Pesticide-resistant insects

• Coloration patterns in guppies due to predation

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

2. Fossil Evidence

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

Fig. 22-15

Bristolia insolens

Bristolia bristolensis

Bristolia harringtoni

Bristolia mohavensis

Latham Shale dig site, SanBernardino County, California

Dep

th (

met

ers

)

0

2

4

6

8

10

12

14

16

18

1

2

3

3

3

1

2

44

Fig. 22-16

(a) Pakicetus (terrestrial)

(b) Rhodocetus (predominantly aquatic)

(c) Dorudon (fully aquatic)

Pelvis andhind limb

Pelvis andhind limb

(d) Balaena (recent whale ancestor)

3. Homology

• Homology is similarity resulting from common ancestry

• Can be both anatomical and molecular

• Anatomical similarities seen in comparative embryology suggest common ancestry

Fig. 22-17

Humerus

Radius

Ulna

Carpals

Metacarpals

Phalanges

Human WhaleCat Bat

Homologous structures are anatomical resemblances that represent variations on a

structural theme present in a common ancestor

Fig. 22-18

Human embryoChick embryo (LM)

Pharyngealpouches

Post-analtail

• Vestigial structures are remnants of features that served important functions in the organism’s ancestors

• Examples of homologies at the molecular level are genes shared among organisms inherited from a common ancestor

Examples of homologies at the molecular level are genes shared among organisms inherited

from a common ancestor

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

• Analogous - having the same function but not necessarily evolutionarily related.

Fig. 22-20

Sugarglider

Flyingsquirrel

AUSTRALIA

NORTHAMERICA

4. Biogeography

• Darwin’s observations of biogeography, the geographic distribution of species, formed an important part of his theory of evolution

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

Bird Biogeography

Is natural selection the ONLY mechanism responsible for

evolution?