12Galapagos Islands Figure 21.00 The Galápagos islands are located in the Pacific Ocean, off the coast of Ecuador. Different islands in the group are ome to distinct species of marine tortoises, finches, mockingbirds, and other organisms. Darwin formulated the theory of evolution by natural selection in part to explain why closely related species are found on nearby islands.
14Diversification of finches on the Galápagos Islands
15The Origin of Species Descent with Modification (evolution) unity of lifeall organisms related through a distant ancestorNatural Selection and Adaptationthe mechanism of evolutioncapacity for “overproduction” of offspringa struggle for survivalvariability in population favors some individuals over others
22A Darwinian View of Life (Darwin’s main ideas) Natural selection is differential success in reproductionNatural selection occurs through an interaction between the environment and the inherent variability among the individuals making up a populationThe product of natural selection is the adaptation of populations to their environment
23Evidence for Evolution Evidence that Species are RelatedGeographic proximity of similar but distinct species.Homologies: structural, developmental, and genetic.
24Structural homology Humerus Radius and ulna Carpals Metacarpals Figure: 21.2aCaption:(a) Even though their function varies, all vertebrate limbs are modifications of the same basic configuration, or basic plan. Darwin interpreted structural homologies like these as a product of descent with modification. Note that the limbs are not drawn to scale.PhalangesTurtleHumanHorseBirdBatSeal
25Developmental homology Both the chick andthe human have gillpouches and tailsGill pouchFigure: 21.2bCaption:(b) These photos show the strong resemblance of the early embryonic stages of a chick and a human.TailChickHuman
26Figure 21.2c( c) Each letter in the sequences given here represents an amino acid. The sequences are from a portion of the protein products of the Aniridia gene found in humans and the eyeless gene found in Drosophilia.
27Evidence for Evolution – Darwin’s Predictions Evidence that Species Change over Time:Law of successionIn a given geographic region, species are succeeded by similar speciesEvidence of extinctions in the fossil recordVestigial traits
28The Law of Succession Present-day sloth Fossil sloth Figure: 21.3 Caption:Present-day sloth and representation of fossil sloth. The Law of Succession: Living and fossil sloths are found only in Central America and South America. Darwin interpreted similarities among fossil and living species in the same geographic area as evidence for evolution.
29ExtinctionsFossils of trilobites, animals that lived in the seas hundreds of millions of years ago
30Vestigial Traits Capuchin monkey tail Human coccyx (used for balance, locomotion)Human coccyxFigure: 21.4, leftCaption:The tailbone is a human trait that is functionless. But is homologous to functioning structures in related species.
31Vestigial Traits Erect hair on chimp (insulation, emotional display) Human goosebumpsFigure: 21.4, rightCaption:Goose bumps are human traits that are functionless. But they are homologous to functioning structures in related species.
36Major Features of Human Evolution Enlarged Brain Size450 cm3 (Homonoids 6 my) 1300 cm3 (Modern Humans)Jaw ShapePrognathic jaw (flattened face)Bipedal PostureAdaptation to non-arboreal lifestyleReduced Sexual Dimorphismmales ~ 1.2 times female body sizeChanges in Social Structurepair bonding, increased parental care
37Upright posture predates an enlarged brain in human evolution Lucy mya
39Two hypotheses for the origin of anatomically modern humans
40Clock analogy for some key events in evolutionary history Challenges to the understanding of evolution:ChanceContingencyDeep timeExtinctionsContinuity of process
41Conclusion of “On the Origin of Species” “There is grandeur in this view of life, with its several powers, having been originally breathed (by the Creator) into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.” - Charles Darwin, 1859
42Questions?1) How does the idea that evolution is a continuous process, happening all around us all the time, rather than some remote process that happened long ago, influence the way you think about life on Earth? 2) Of the various challenges to a conceptual understanding of evolutionary theory (i.e. the role of random chance, contingency, vast stretches of time, Earth’s long history of extinctions, the process of natural selection, etc.) what gives you the most difficulty intellectually. 3) Over the years, a variety of Creationistic “alternatives” to evolution have surfaced in the popular media. This has included “scientific creationism” in the 1980s and most recently “intelligent design.” Why is the general public often quick to embrace these ideas and why have they been quickly rejected by the scientific community?