Descent With Modification Chapter 22

Evolution change over time in the genetic composition of a population

Figure 22.2 The historical context of Darwin’s life and ideas 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.

Scala Naturae The Greek philosopher Aristotle viewed species as fixed and arranged them on a scala naturae

Carolus Linnaeus interpreted organismal adaptations as evidence that each was fixed and perfectly suited to an unchanging environment Linnaeus was the founder of taxonomy, the branch of biology concerned with classifying and naming organisms

Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier Cuvier advocated catastrophism, speculating that each boundary between strata represents a past sudden catastrophe

Geologists James Hutton and Charles Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today Hutton proposed the idea of gradualism – slow change over time in formation of geologic features Lyell’s principle of uniformitarianism states that the mechanisms of change are constant over time – processes we see today (like erosion) are the mechanisms of past change These ideas strongly influenced Darwin’s thinking (old Earth)

Younger stratum with more recent fossils Older stratum with older fossils

Lamarck (1744-1829) applied the concept of gradualism to biological evolution proposed 2 mechanisms for evolution (1809): use & disuse – parts of the body that are used become larger and stronger whereas parts that are not used deteriorate inheritance of acquired characteristics – modifications acquired during one’s lifetime can be passed to offspring

Darwin (1809-1882) descent with modification natural selection organisms are related through descent from a common ancestor as descendents of the ancestral organism encountered new habitats, they accumulated adaptations that fit them to specific ways of life natural selection differential success in reproduction among individuals that vary in their heritable traits

Figure 22.5 The voyage of HMS 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 Figure 22.5 The voyage of HMS Beagle For the Discovery Video Charles Darwin, go to Animation and Video Files. Isabela Santa Cruz Andes Cape of Good Hope Santa Fe San Cristobal Tasmania Florenza Española Cape Horn New Zealand Tierra del Fuego

In 1844, Darwin wrote an essay on the origin of species and natural selection but did not introduce his theory publicly, anticipating an uproar In June 1858, Darwin received a manuscript from Alfred Russell Wallace, who had developed a theory of natural selection similar to Darwin’s Darwin quickly finished The Origin of Species and published it the next year

On the Origin of Species (1859) 2 major points made by Darwin: many modern species are descendents of ancestral species the mechanism for this evolutionary process is natural selection: a population can change over generations if individuals with certain heritable traits leave more offspring than others result = evolutionary adaptation the accumulation of inherited characteristics that enhance an organism’s ability to survive & reproduce in a specific environment

Natural Selection OBSERVATION #1 – populations would grow exponentially if all individuals reproduced successfully OBSERVATION #2 – but populations tend to stay stable in size OBSERVATION #3 – resources are limited INFERENCE #1 – production of more individuals than the environment can support leads to a struggle for existence within a population so only a fraction of individuals survive each generation OBSERVATION #4 – variation exists among members of a population OBSERVATION #5 – much of this variation is heritable INFERENCE # 2 – individuals with inherited traits that increase their chances of survival are more likely to reproduce and leave more offspring INFERENCE #3 – the unequal ability of individuals to survive & reproduce will lead to a gradual change in the population, with favorable characteristics accumulating over generations

Fig. 22-7 Figure 22.7 “I think . . .”

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

Fig. 22-10

Figure 22.8 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

Keys to Natural Selection natural selection selects for adaptations already in existence (it doesn’t create new ones) natural selection depends on time & place (what is advantageous in one situation may be useless or harmful in another)

(a) A flower mantid in Malaysia (b) A stick mantid in Africa Fig. 22-12 (a) A flower mantid in Malaysia (b) A stick mantid in Africa

Darwin’s theory helps explain… homology – similarities between related species that are inherited from a common ancestor homologous structures (similar structures with different functions) anatomical similarities in vertebrate embryos vestigial organs (remnants of structures that served important functions in an organism’s ancestors) genetic code genes & proteins biogeography – geographic distribution of species closely related species tend to be found in the same geographic region (ex) most island species are similar to species on the nearest mainland rather than to species on distant islands with similar environments fossil record succession of life forms is consistent with “descent with modification”

Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters Fig. 22-9 Terminal bud Lateral buds Cabbage Brussels sprouts Flower clusters Leaves Kale Cauliflower Figure 22.9 Artificial selection Stem Wild mustard Flowers and stems Broccoli Kohlrabi

Homologous Structures

Comparative Embryology

Vestigial Structures

Molecular Similarities