Decent with Modification: A Darwinian View of Life

Darwin made 2 major points in his book – Organisms presently inhabiting the Earth are descendants of ancestral species – Proposed a mechanism for the evolutionary process, natural selection

Fossils Study of fossils helped lay the groundwork for Darwin’s ideas Remains or traces of organisms from the past – Usually found in sedimentary rock, which appears in layers or strata Figure 22.3

Gradualism – Profound change can take place through the cumulative effect of slow but continuous processes

Figure 22.5 England EUROPE NORTH AMERICA Galápagos Islands Darwin in 1840, after his return SOUTH AMERICA Cape of Good Hope Cape Horn Tierra del Fuego AFRICA HMS Beagle in port AUSTRALIA Tasmania New Zealand PACIFIC OCEAN Andes ATLANTIC OCEAN

Observed and collected many specimens of South American plants and animals Observed adaptations of plants and animals to diverse environments

 Adaptation to the environment and the origin of new species as closely related processes

Darwin’s finches Large ground finch Small ground finch Geospiza magnirostris Seed eater Sharp-beaked ground finch Camarhynchus psitacula Green warbler finch Large tree finch Large cactus ground finch Ground finches Tree finches Insect eaters Bud eater Warbler finches Common ancestor from South American mainland Gray warbler finch Certhidea olivacea Certhidea fusca Geospiza difficilis Cactus flower eater Geospiza scandens Seed eater Geospiza conirostris Geospiza fortis Medium ground finch Geospiza fuliginosa Mangrove finch Cactospiza heliobates Cactospiza pallida Woodpecker finch Medium tree finch Camarhynchus pauper Small tree finch Vegetarian finch Camarhynchus parvulus Platyspiza crassirostris Cactus ground finch Figure 1.23

Darwin’s 2 main ideas – Evolution explains life’s unity and diversity – Natural selection is a cause of evolution

Darwinian view: the history of life is like a tree Figure 22.7 Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Years ago Millions of years ago Deinotherium Mammut Stegodon Mammuthus Platybelodon Barytherium Moeritherium Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa)