Natural Selection Evolution of mammals

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 Santiago Bartolomé Råbida Pin zon Seymour Baltra Santa Cruz Santa Fe Tortuga Española San Cristobal Floreana EQUATOR Galåpagos Islands

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.

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 d, 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 a, p. 471 North America MONOTREMES, MARSUPIALS EVOLVE AND MIGRATE THROUGH PANGEA South America Antarctica Australia India Africa Eurasia About 150 million years ago, during the Jurassic

Spiny anteater MONOTREMES Platypus

Koala MARSUPIALS Tasmanian Devil

Fig b, 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 and Muskrat Coypu Capybara Coypu and Capybara

Fig c, 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 , p. 319 RACCOONRED PANDAGIANT PANDA DIVERGENCE approximately 40 million years ago DIVERGENCE 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 Species Species 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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