1809179818121795183017901809 1831−36184418591870Lamarck publishes hishypothesis of evolution.Malthus publishes“Essay on the Principleof Population.”Hutton proposeshis principle ofgradualism.Charles Darwinis born.Darwin travels aroundthe world on HMSBeagle.The Galápagos IslandsDarwin writes hisessay on descentwith modification.On the Origin ofSpecies is published.While studying speciesin the Malay Archipelago,Wallace sends Darwinhis hypothesis of naturalselection.1858Cuvier publishes his extensivestudies of vertebrate fossils.Lyell publishesPrinciples of Geology.Figure 22.2
Figure 22.6Cactus eater. The long,sharp beak of thecactus ground finch(Geospiza scandens)helps it tear and eatcactus flowers andpulp.Insect eater. The green warbler finch(Certhidea olivacea) uses its narrow,pointed beak to grasp insects.Seed eater. The largeground finch (Geospizamagnirostris) has a largebeak adapted for crackingseeds that fall from plantsto the ground.
Figure 22.8Hyracoidea(Hyraxes)Sirenia(Manateesand relatives)†Deinotherium†Mammut†Platybelodon†Stegodon†MammuthusElephas maximus(Asia)Loxodonta africana(Africa)Loxodonta cyclotis(Africa)†Moeritherium†Barytherium60Millions of years ago34 24 5.5 21040Years ago
Natural Selection and Adaptation• Evolutionary biologist Ernst Mayr has dissectedthe logic of Darwin’s theory into three inferencesbased on five observations
• Observation #1: For any species, population sizeswould increase exponentially if all individuals thatare born reproduced successfully• Observation #2: Populations tend to be stable insize, except for seasonal fluctuations• Observation #3: Resources are limited• Inference #1: Production of more individuals thanthe environment can support leads to a strugglefor existence among individuals of a population,with only a fraction of their offspring surviving
• Observation #4: Members of a population varyextensively in their characteristics; no twoindividuals are exactly alike
• Observation #5: Much of this variation is heritable• Inference #2: Survival depends in part on inheritedtraits; individuals whose inherited traits give thema high probability of surviving and reproducing arelikely to leave more offspring than other individuals• Inference #3: This unequal ability of individuals tosurvive and reproduce will lead to a gradualchange in a population, with favorablecharacteristics accumulating over generations
Figure 22.19Most mammals Cetaceans and even-toed ungulates(a) Canis (dog) (b) Pakicetus (c) Sus (pig) (d) Odocoileus (deer)Figure 22.19 Ankle bones: one piece of the puzzle. Comparing fossils and present- day examples of theastragalus (a type of ankle bone) provides one line of evidence that cetaceans are closely related to even-toed ungulates. (a) In most mammals, the astragalus is shaped like that of a dog, with a double hump onone end (indicated by the red arrows) but not at the opposite end (blue arrow). (b) Fossils show that theearly cetacean Pakicetus had an astragalus with double humps at both ends, a unique shape that isotherwise found only in even-toed ungulates, as shown here for (c) a pig and (d) a deer.