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Darwin’s Theory of Evolution (Chapter 15)
Evolution ! change over time
• Theory ! a well supported, testable explanation of events that occurs in the natural world
Darwin’s Journey
• Traveled on the HMS Beagle starting in 1831
• His detailed drawings and observations helped him piece together his ideas on why life is so diverse
• Observations
o Plants and animals were well suited for the environment that they lived in
o Some animals are widely distributed while others are only found in certain areas
o Some living animals resembled fossils of animals from long ago
o Some fossils did not resemble any living organism
• Galapagos Islands
o Each island has a different climate
o Giant Tortoises found on each island were different
o Several types of small birds were found on each island but they all had different sized beaks
• On Darwin’s journey home he began to wonder if all the different animals on the islands were once the same
Ideas before Darwin
• James Hutton ! proposed that the geological forces that shape Earth’s surface occur very slowly
o Rocks are moved by forces under Earth’s surface
• Charles Lyell ! the same geological forces that occurred long ago are continuing today
• Jean-Baptiste Lamarck ! the use or disuse of certain features are passed on to offspring
o Giraffes have long necks because their parents stretched their necks
• Thomas Malthus ! if human population continues to grow unchecked, we will run out of room and food
On the Origin of Species by Means of Natural Selection
• The natural variation found in populations are important
o Artificial selection ! humans select the traits in animals or plants they want the next generation to
" Hairless Chihuahua
• Populations change as natural selection acts on its individuals
o Struggle for existence ! members of each species compete with each other for food, water, mates
and shelter
" Organisms have more offspring than can survive
" The ability of an organism to survive and reproduce in it’s environment is called fitness
• Adaptations are inherited characteristics that increase an organism’s fitness
o Natural selection ! organisms that are best suited for survival in an environment will reproduce
more and pass their advantageous traits on to their offspring
o Sexual Selection ! one sex chooses a mate based on behavior or appearance
• All living species have descended from other species over time! descent with modification
• All living things descended from a common ancestor
Evidence for evolution
• Fossil record ! shows that life on earth has changed over time
• Animals living in different areas with similar climate have similar features !biogeography
• Homologous body structures
o Structures that come from a common ancestor but are different in the adult form
o Vestigial structures ! the remains of structures that are no longer used
" Pelvic bone in whales
• Analogous body structures
o Structures that are similar in distantly related organisms due to similar environmental pressures
" Wings in butterflies and birds
• Similarities in embryological development