Catalyst:

1. Which of the choices below is an appropriate representation of commensalism?

a. +/+ c. -/-

b. +/- d. +/0

2. How were the activities yesterday connected to evolution?

3. What is the difference between microevolution and macroevolution?

Evolution: A Darwinian View of Life

• Overview: Darwin Introduces a Revolutionary Theory

• A new era of biology began on November 24, 1859– The day Charles Darwin published: On the

Origin of Species by Means of Natural Selection

• The Origin of Species– Focused biologists’ attention on the great

diversity of organisms

Figure 22.1

• 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 Origin of Species

– Shook the deepest roots of Western culture

– Challenged a worldview that had been prevalent for centuries

Darwin: from childhood to publication

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

• Soon after Darwin received his B.A. degree– He was accepted on board the HMS Beagle,

which was about to embark on a voyage around the world

• Darwin’s interest in the geographic distribution of species was kindled by the Beagle’s stop at the Galápagos Islands near the equator west of South America

Figure 22.5

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

• As Darwin reassessed all that he had observed during the voyage of the Beagle

• He began to perceive adaptation to the environment and the origin of new species as closely related processes

Figure 22.6a–c

(a) Cactus eater. The long,sharp beak of the cactusground finch (Geospizascandens) helps it tearand eat cactus flowersand pulp.

(c) Seed eater. The large groundfinch (Geospiza magnirostris)has a large beak adapted forcracking seeds that fall fromplants to the ground.

(b) Insect eater. The green warbler finch (Certhidea olivacea) uses itsnarrow, pointed beak to grasp insects.

• Darwin developed two main ideas:

1. Evolution explains life’s unity and diversity

2. Natural selection is a cause of adaptive evolution

• The phrase descent with modification

– Summarized Darwin’s perception of the unity of life

– States that all organisms are related through descent from an ancestor that lived in the remote past

• In the Darwinian view, the history of life is like a tree

– With multiple branchings from a common trunk to the tips of the youngest twigs that represent the diversity of living organisms

Figure 22.7

Hyracoidea(Hyraxes)

Sirenia(Manatees

and relatives)

Yea

rs a

goM

illio

ns

of y

ea

rs a

go Dei

no

ther

ium

Ma

mm

ut

Ste

go

don

Ma

mm

uth

us

Pla

tyb

elo

don

Bar

yth

eriu

m

Mo

eri

ther

ium

Elephasmaximus

(Asia)

Loxodontaafricana(Africa)

Loxodontacyclotis(Africa)

• Observation #1: For any species, population sizes would increase exponentially if all individuals that are born reproduced successfully

Figure 22.8

• Observation #2: Nonetheless, populations tend to be stable in size– Except for seasonal fluctuations

• Observation #3: Resources are limited

• Inference #1: Production of more individuals than the environment can support leads to a struggle for existence among individuals of a population, with only a fraction of their offspring surviving

• Observation #4: Members of a population vary extensively in their characteristics– No two individuals are exactly alike

Figure 22.9

• Observation #5: Much of this variation is inheritable

• Inference #2: Survival depends in part on inherited traits– Individuals whose inherited traits give them a

high probability of surviving and reproducing are likely to leave more offspring than other individuals

• Inference #3: This unequal ability of individuals to survive and reproduce– Will lead to a gradual change in a population,

with favorable characteristics accumulating over generations

• Natural selection can produce an increase over time in the adaptation of organisms to their environment

Figure 22.11

(a) A flower mantidin Malaysia

(b) A stick mantidin Africa

• Humans have modified other species over many generations by selecting and breeding individuals that possess desired traits, this is called artificial selection

Figure 22.10

Terminalbud

Lateralbuds

Brussels sproutsCabbage

Flowercluster

Leaves

Cauliflower

Flowerandstems

Broccoli Wild mustard Kohlrabi

Stem

Kale