Descent with Modification Darwinian View of Life Chapter 22

Why is Evolution So Controversial? Often evolution (and science in general) is pitted against religion in “winner take all” stance Modern debate mostly involves the teaching of evolution rather than the theory itself And that means mixing science, religion and politics, etc.- --Never an easy combination! Plenty of misconceptions and confusion surround evolution, adding to controversy

3 Key Observations About Life Organisms are suited for life in their environments. Organisms share many characteristics of life (unity). There is a rich diversity of life. These observations led Charles Darwin to develop a scientific explanation for these observations.

Endless Forms Most Beautiful Study of biology upended in 1859 when Darwin published The Origin of Species Darwin proposed: Descent with modification Species are descendants of ancestral species which were different from present day species Evolution: change in genetic composition of population from generation to generation

Summary of Other Ideas Many scientists before and during the time of Darwin theorized on what was the cause of the unity and diversity of living organisms Some ideas supported Darwin’s theories while some did not

Intellectual Context of Darwin’s Ideas 1809 Lamarck publishes his hypothesis of evolution. 1798 Malthus publishes “Essay on the Principle of Population.” 1812 1858 Cuvier publishes his extensive studies of vertebrate fossils. 1795 While studying species in the Malay Archipelago, Wallace (shown in 1848) sends Darwin his hypothesis of natural selection. Hutton proposes his principle of gradualism. 1830 Lyell publishes Principles of Geology. Figure 22.2 The intellectual context of Darwin’s ideas. 1790 1870 1809 183136 1859 Charles Darwin is born. Darwin travels around the world on HMS Beagle. On the Origin of Species is published. 1844 Darwin writes his essay on descent with modification. The Galápagos Islands

Not in Darwin’s “Camp” Aristotle viewed species as unchanging Arranged them on a scala naturae, ladder of permanent “rungs” Linneaus: Developed taxonomy and the binomial classification system Believed in a divine placement of organisms in this classification, not necessarily changing either Cuvier (geologist): Founded of modern paleontology (study of fossils) Saw that fossils are deposited in strata (layers) of rocks with older layers containing fossils of species that may be extinct now Believed in catastrophism, the sudden loss of local species due to disasters

Lamarck’s Hypothesis of Evolution Other scientists were thinking about life forms evolving over time Lamarck hypothesized: Use and disuse of body parts could change organisms over their lifespan These changes could be passed to offspring by Inheritance of Acquired Characteristics

Lamarck’s Hypothesis of Evolution Lamarckism unsupported by much of genetic evidence BUT emerging field of epigenetics may prove to support some of Larmarck’s ideas!

Scientists in Darwin’s “Camp” Hutton and Lyell believed: Earth’s surface changes from cumulative, SLOW continuous actions still operating today (uniformitarianism) Strongly influenced Darwin’s thinking He reasoned the Earth must be much older than previously believed Also reasoned biological organisms may also have slow, continuous change Malthus (economist): Limited resources shape population sizes

Voyage of the HMS Beagle Darwin in 1840, after his return from the voyage HMS Beagle in port Great Britain EUROPE NORTH AMERICA ATLANTIC OCEAN The Galápagos Islands Figure 22.5 The voyage of HMS Beagle. AFRICA PACIFIC OCEAN Pinta Genovesa Equator Marchena Malay Archipelago Equator SOUTH AMERICA PACIFIC OCEAN Santiago Daphne Islands Brazil Chile AUSTRALIA Pinzón Fernandina PACIFIC OCEAN Andes Mtns. Isabela Cape of Good Hope Santa Cruz Santa Fe San Cristobal Argentina Tasmania 20 40 Florenza Española Cape Horn New Zealand Kilometers

Darwin’s Focus on Adaptation During the voyage, Darwin observed many adaptations: Inherited characteristics of organisms which increase their survival and reproduction in different environments Darwin saw how adaptation to environment and the origin of species is closely related Theorized: Could new species arise from gradual accumulation of adaptations to different environments?

Darwin’s Focus on Adaptation How do adaptations arise? Largely dependent on: Natural selection: Process in which individuals with certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits

Example of Speciation in Galapagos Finches Figure 22.6 Three examples of beak variation in Galápagos finches. (a) Cactus-eater (b) Insect-eater (c) Seed-eater

Artificial Selection Humans have modified other species by selective breeding for 1000’s of years, a process called artificial selection

The Reason Why You Shouldn’t Procrastinate In 1844, Darwin wrote an essay on natural selection--but did not publicize it In June 1858, Wallace sent Darwin a paper to review with an almost identical theory of natural selection Darwin quickly finished The Origin of Species by Means of Natural Selection and published it Wallace graciously stepped away so now we call it “Darwinism” and not “Wallacism”!

Observations of Darwin Observation #1: Members of a population often vary in their inherited traits

Observations of Darwin Observation #2: All species can produce more offspring than the environment can support Many offspring fail to survive and reproduce

Important Points About Natural Selection Note that individuals do not evolve; but populations evolve over time Natural selection can only increase or decrease heritable traits that vary in a population If everyone is genetically identical, no basis for selection Adaptations vary with different environments Single adaptation not preferred for all environments

Direct Observations of Evolutionary Change The bacterium Staphylococcus aureus is commonly found on people One strain, methicillin-resistant S. aureus (MRSA) is a dangerous pathogen S. aureus became resistant to penicillin in 1945 and resistant to methicillin in 1961

Direct Observations of Evolutionary Change Methicillin works by inhibiting a protein used by bacteria in their cell walls But MRSA bacteria use a different protein in their cell walls When exposed to methicillin, MRSA strains are more likely to survive and reproduce than nonresistant S. aureus strains MRSA strains are now resistant to many antibiotics

Homology Homology is similarity resulting from common ancestry Homologous structures are anatomical resemblances that represent variations on a structural theme present in a common ancestor

Mammalian Forelimbs: Homologous Structures Humerus Figure 22.15 Mammalian forelimbs: homologous structures. Radius Ulna Carpals Metacarpals Phalanges Human Cat Whale Bat

Embryonic Homologies Pharyngeal pouches Figure 22.16 Anatomical similarities in vertebrate embryos. Post-anal tail Chick embryo (LM) Human embryo Comparative embryology reveals anatomical homologies not visible in adult organisms

Vestigial Structures Vestigial structures are remnants of features that served important functions in the organism’s ancestors Common human vestigial structures: Appendix Male nipples Wisdom teeth Body hair and goosebumps Ear muscles

Evolutionary Tree Branch point Lungfishes Amphibians 1 Tetrapods 2 Mammals Digit- bearing limbs Amniotes Figure 22.17 Tree thinking: information provided in an evolutionary tree. Lizards and snakes 3 Amnion 4 Crocodiles Homologous characteristic 5 Ostriches 6 Birds Feathers Hawks and other birds

Different Cause of Resemblance: Convergent Evolution Convergent evolution is the evolution of similar, or analogous, features in distantly related groups Analogous traits arise when groups independently adapt to similar environments in similar ways Convergent evolution does not provide information about ancestry

Examples of Convergent Evolution Figure 22.18 Convergent evolution.

Homology vs. Convergent Evolution Both are evidence of evolution Analogous features (convergent evolution) share similar function but not common ancestry Homologous features (homology) share common ancestry but not necessarily similar function