4.1.2-.4 Natural Selection Evolution of mammals

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Darwin and Evolution

Evolution are the changes in the gene pool of a population over time.

Natural selection process by which individuals that are better suited to their environment survive and reproduce most successfully.

Adaptation is an inherited characteristic that increases an organism’s chance of survival.

Isabela

Darwin

Wolf

Pinta

Marchena Genovesa

Fernandia

SantiagoBartolomé

RåbidaPin zon

SeymourBaltra

Santa Cruz

Santa Fe

Tortuga

Española

San Cristobal

Floreana

EQUATOR

GalåpagosIslands

Land Iguana

Marine Iguana

FOUNDER SPECIES

insect and nectar eatersfruit and seed eaters

KAUAI AKIALAOA

AMAKIHI

IIWI

APAPANE

KONA FINCH extinct

LAYSAN FINCH

AKIAPOLAAU

MAUI PARROTBILL

Based on his observations,

Darwin proposed that

EVOLUTION occurs by NATURAL

SELECTION.

Darwin’s Postulates

•Variation within populations.•Overproduction of offspring.•Struggle for existence.•Unequal survival and

reproduction rates.

http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html

Population of organisms

Limited resources leads to a struggle for survival

between offspring.

Overproduction of offspring

Survivors reproduce more successfully.

Mutations & Sexual reproduction

produces variations among offspring.

Population changes over time.

Evolution of Mammals

Fig. 27.19d, p. 471

DISPERSAL OF HIGHLY EVOLVED PLACENTAL MAMMALS

South America

Extinctions of many marsupials and early placental mammals

About 5 million years ago, during the Pliocene

Nonvertebrate chordates

Jawless fishes

Cartilaginous fishes

Bony fishes

Amphibians

Reptiles

Birds

Mammals

Fig. 27.19a, p. 471

North America

MONOTREMES, MARSUPIALS EVOLVE AND MIGRATE THROUGH PANGEA

South America

Antarctica

AustraliaIndia

Africa

Eurasia

About 150 million years ago, during the Jurassic

Spiny anteater

MONOTREMES

Platypus

Koala

MARSUPIALS

Tasmanian Devil

Fig. 27.19b, p. 471

PLACENTAL MAMMALS EVOLVE; ADAPTIVE RADIATIONS BEGIN

Isolation of the early

monotremes, marsupials on

this land mass

Between 100 and 85 million years ago, during the Cretaceous

PLACENTAL MAMMALS

Walruses

Bat

Manatee

Arctic Fox

Beaver

NORTH AMERICA

Muskrat

Capybara SOUTH AMERICA

Coypu

Beaver

Muskrat

Beaver andMuskrat

Coypu

Capybara

Coypu andCapybara

Fig. 27.19c, p. 471

North America

ADAPTIVE RADIATIONS OF MORE EVOLVED PLACENTAL MAMMALS

South America

Antarctica

Africa

Eurasia

Continued isolation of early monotremes

and marsupials

Extinctions of mammals

About 20 million years ago, during the Miocene

Fig. 20.10, p. 319

RACCOON RED PANDA GIANT PANDA

DIVERGENCE approximately 40 million years ago

DIVERGENCE 15-20 million years ago

SPECTACLED BEAR

SLOTH BEAR

SUN BEAR

BLACK BEAR

POLAR BEAR

BROWN BEAR

What is a Species?A group of potentially or actually

interbreeding populations, with a common gene pool, which are reproductively

isolated from other groups

The problem with the species definition

The species concept is a human construct used to make sense of the natural world.

While extraordinarily helpful in understanding life, it fails to capture the

full complex reality of continually evolving populations of organisms.

Sibling SpeciesSpecies that can’t interbreed, but have

no significant differences in appearance.

Very different appearance that can interbreed?!

Two tigons (male to the left, female to the right)

•

A Liger-Lion/Tiger

A "boblynx" -- a hybrid of bobcat and lynx;

A "zonkey" -- a hybrid of zebra and donkey;

• The "Toast of Botswana",  -- a hybrid of a female goat to a male sheep;

A "cama" -- a hybrid of camel and llama;A "yakalo" - a hybrid of buffalo or bison and yak;A "cattalo" (or "beefalo") -- a cross of a bison with a domestic cattle;A "coywolf" -- a hybrid of coyote and wolf; A "wholphin" -- a hybrid of a bottlenose dolphin mother and a false killer whale father. Same situation like with the "pumapard" (parents belong to different genera).

Some intraspecies hybrids (both genders fertile):

A "wig" -- a cross of a wild and a domestic pig;An unnamed cross of a Siberian and a Manchurian tiger.

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