Intellectuals / Ideas in Darwin’s Era Linnaeus (classification) Hutton (gradual geologic change) Lamarck (species can change) Malthus (population limits) Cuvier (fossils, extinction) Lyell (modern geology) Darwin (evolution, natural selection) Wallace (evolution, natural selection) American Revolution French Revolution U.S. Civil War 1750 1800 1850 1900 1795 Hutton proposes his theory of gradualism. 1798 Malthus publishes “Essay on the Principle of Population.” 1809 Lamarck publishes his hypothesis of evolution. 1830 Lyell publishes Principles of Geology. Figure 22.2 The historical context of Darwin’s life and ideas 1831–1836 Darwin travels around the world on HMS Beagle. 1837 1837 Darwin begins his notebooks. 1844 Darwin writes essay on descent with modification. 1858 Wallace sends his hypothesis to Darwin. 1859 The Origin of Species is published.

Layers of deposited sediment Younger stratum with more recent fossils Figure 22.3 Formation of sedimentary strata with fossils Older stratum with older fossils

Darwin’s Voyage on the Beagle GREAT BRITAIN EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands AFRICA Pinta Genovesa Marchena Equator SOUTH AMERICA Santiago Daphne Islands Pinzón AUSTRALIA Fernandina PACIFIC OCEAN Isabela Figure 22.5 The voyage of HMS Beagle For the Discovery Video Charles Darwin, go to Animation and Video Files. Santa Cruz Andes Cape of Good Hope Santa Fe San Cristobal Tasmania Florenza Española Cape Horn New Zealand Tierra del Fuego

Speciation of Galapagos Finches (a) Cactus-eater (c) Seed-eater Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater

(a) Cactus-eater Fig. 22-6a Figure 22.6 Beak variation in Galápagos finches (a) Cactus-eater

(b) Insect-eater Fig. 22-6b Figure 22.6 Beak variation in Galápagos finches (b) Insect-eater

Fig. 22-6c Figure 22.6 Beak variation in Galápagos finches (c) Seed-eater

Descent With Modification Hyracoidea (Hyraxes) Sirenia (Manatees and relatives) Moeritherium Barytherium Deinotherium Mammut Platybelodon Stegodon Mammuthus Figure 22.8 Descent with modification Elephas maximus (Asia) Loxodonta africana (Africa) Loxodonta cyclotis (Africa) 34 24 5.5 2 104 Millions of years ago Years ago

Observation #1: Members of a population often vary greatly in their traits. Figure 22.10 Variation in a population

Natural Selection EXPERIMENT RESULTS 12 12 10 10 8 8 Area of colored Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Guppies: Adult males have brighter colors than those in “pike-cichlid pools” Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools” RESULTS 12 12 Figure 22.13 Can predation result in natural selection for color patterns in guppies? 10 10 8 8 Area of colored spots (mm2) colored spots Number of 6 6 4 4 2 2 Source population Transplanted population Source population Transplanted population

Fossil Evidence of Change Over Time 2 4 4 6 4 Bristolia insolens 8 3 Bristolia bristolensis 10 12 3 Depth (meters) 2 Bristolia harringtoni 14 16 18 1 Bristolia mohavensis 3 Figure 22.15 Fossil evidence of evolution in a group of trilobites 2 1 Latham Shale dig site, San Bernardino County, California

Paleontologists study fossils of possible transitional forms: Whale Ancestors (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic) Figure 22.16 The transition to life in the sea Pelvis and hind limb (c) Dorudon (fully aquatic) Pelvis and hind limb (d) Balaena (recent whale ancestor)

Homologous Structures Humerus Radius Ulna Carpals Metacarpals Figure 22.17 Mammalian forelimbs: homologous structures Phalanges Human Cat Whale Bat

Comparative embryology reveals anatomical homologies not visible in adult organisms: Pharyngeal pouches Post-anal tail Figure 22.18 Anatomical similarities in vertebrate embryos Chick embryo (LM) Human embryo

Homologies and “Evolutionary Tree” Branch point (common ancestor) Lungfishes 1 Amphibians Tetrapods 2 Mammals Tetrapod limbs Amniotes 3 Lizards and snakes Amnion 4 Crocodiles Figure 22.19 Tree thinking: information provided in an evolutionary tree Homologous characteristic 5 Ostriches Birds 6 Feathers Hawks and other birds

NORTH AMERICA Sugar glider AUSTRALIA Flying squirrel Fig. 22-20 Figure 22.20 Convergent evolution Flying squirrel

Darwin : Natural Selection Observations Individuals in a population vary in their heritable characteristics. Organisms produce more offspring than the environment can support. Inferences Individuals that are well suited to their environment tend to leave more offspring than other individuals and Over time, favorable traits accumulate in the population.

Mutation = Resistance to DDT Mutation = Resistance to DDT. Natural Selection Favors this Resistance --> Number of Resistant Individuals Increases Over Time.

You should now be able to: Describe the contributions to evolutionary theory made by Linnaeus, Cuvier, Lyell, Lamarck, Malthus, and Wallace. Describe Lamarck’s theories, and explain why they have been rejected. Explain what Darwin meant by “descent with modification.” Explain Darwin’s observations and inferences. Explain why an individual organism cannot evolve. Describe evidence for evolution by natural selection.