Chapter 18 (Sections 18.1-18.3) Introduction to Darwinian Evolution

1. Chapter 18(Sections 18.1-18.3)Introduction to Darwinian Evolution

2. Darwinian Evolution • Charles Darwin (1809–1882) proposed that all species currently living on our planet arose from earlier ones by a process of gradual divergence or evolution • Evidence supporting evolution: fossils, biogeography, comparative anatomy, molecular biology, developmental biology, and experimental studies of ongoing evolutionary change • Evolution is the cornerstone of biology because it links all life sciences into a unified body of knowledge

3. Evolution • Evolutionis the accumulation of genetic changes within populations over time • A populationis a group of individuals of one species that live in the same geographic area at the same time • Eventually, two populations may diverge to such a degree that they become different species (referred to as speciation) • A species is a group of similar organisms that are capable of interbreeding with one another

4. Two Perspectives on Evolution • Microevolution • The minor evolutionary changes of populations usually viewed over a few generations • Macroevolution • The major evolutionary events usually viewed over a long period, such as formation of different species from common ancestors

5. Applications of Evolution • Agriculture must deal with the evolution of pesticide resistance in insects and other pests • Medicine must respond to the rapid evolution of disease-causing organisms such as bacteria and viruses • Conservation management of rare and endangered species uses evolutionary principles of population genetics • Rapid evolution of microorganisms in polluted soils is used in the field of bioremediation(clean up of hazardous-wastes)

6. 18.2 PRE-DARWINIAN IDEASABOUT EVOLUTION LEARNING OBJECTIVE: • Discuss the historical development of evolutionary theory

7. Early History ofEvolutionary Theory • Aristotle (384–322 bce) • Visualized organisms as “moving toward a more perfect state” • Leonardo da Vinci (1452–1519) • Correctly interpreted fossils as the remains of animals that had existed in previous ages but had become extinct • Jean Baptiste de Lamarck (1744–1829) • Suggested that organisms pass traits they acquired during their lifetimes to their offspring

8. KEY CONCEPTS 18.2 • Ideas about evolution originated long before Darwin’s time

9. 18.3 DARWIN AND EVOLUTION LEARNING OBJECTIVES: • Explain the four premises of evolution by natural selection as proposed by Charles Darwin • Compare the modern synthesis with Darwin’s original evolutionary theory

10. Voyage of HMS Beagle • 1831: Darwin embarked on a 5-year exploratory cruise around the world aboard the HMS Beagle • He collected and cataloged thousands of plant and animal specimens and kept notes of his observations • He noticed similarities between animals and plants of the Galápagos and those of South America, and saw differences in reptiles and birds from one island to the next

11. Developing a Theory • Upon returning home, Darwin attempted to develop a explanation for the distribution of species among the islands • He studied Charles Lyell’s Principles of Geology, which described how Earth’s features developed slowly over long periods by geologic processes (plate tectonics) • He noted that many varieties of plants and animals could be developed in just a few generations by artificial selection

12. Artificial Selection in Brassica oleracea • Example: all members of the same species, Brassica oleracea Figure 18.3: Artificial selection inBrassica oleracea. • An enlarged terminal bud (the “head”) was selected in cabbage (lower left), flower clusters in broccoli (upper left) and cauliflower (middle right), axillary buds in brussels sprouts (bottom middle), leaves in collards (upper right) and kale (lower right), and stems in kohlrabi (middle). Fig. 18-3, p. 394

13. Developing a Theory (cont.) • Darwin studied an essay by Thomas Malthus (1766–1834) which suggested that inherited variations favorable to survival tend to be preserved, while unfavorable ones are eliminated because of a struggle for resources. • The result is adaptation,an evolutionary modification that improves the chances of survival and reproductive success in a given environment • Eventually, the accumulation of modifications might result in a new species

14. Darwin’s Theory of Natural Selection • Darwin called his explanation for evolution natural selection,in which better adapted organisms are more likely to survive and become the parents of the next generation • As a result of natural selection, the population changes over successive generations; the frequency of favorable traits increases, and less favorable traits become scarce

15. Darwin and Wallace • Alfred Russel Wallace (1823–1913), a British naturalist who studied plants and animals of the Malay Archipelago, arrived at the same conclusion at the same time as Darwin • Darwin’s book, On the Origin of Species by Natural Selection, was published in 1859 • Wallace’s book, Contributions to the Theory of Natural Selection, was published in 1870

16. Four Principles of Natural Selection • Darwin’s mechanism of evolution by natural selection consists of four observations on the natural world: • Variation: Individuals in a population exhibit variation in traits; some improve an individual’s chances of survival and reproductive success – others do not • Overproduction: In every generation each species has the capacity to produce more offspring than can survive • Limits on population growth: Organisms compete for limited resources; not all survive to reproduce • Differential reproductive success: Individuals with the most favorable combination of characteristics are more likely to survive and reproduce

17. Genetic variation in emerald tree boas

18. Island Populations • Over time, enough changes may accumulate in geographically separated populations (often with slightly different environments) to produce new species • Darwin noted that the 14 species of Galápagos finches may have evolved in this way • The different islands of the Galápagos kept the finches isolated from one another, allowing them to diverge into separate species in response to varying conditions

19. The Modern Synthesis • Darwin was unable to explain how individuals transmit traits to the next generation, or why individuals vary • About the same time, Gregor Mendel was working on the basic patterns of inheritance • It was not until the 1930s and 1940s that biologists combined the principles of Mendelian inheritance with Darwin’s theory of natural selection to produce the modern synthesis

20. The Modern Synthesis (cont.) • The modern synthesis explains Darwin’s observation of variation among offspring in terms of mutation,or changes in DNA, such as nucleotide substitutions • The modern synthesis incorporates our expanding knowledge in genetics, systematics, paleontology, developmental biology, behavior, and ecology

21. The Effect of Chance on Evolution • Natural selection appears to be a more important agent of evolutionary change than chance • Examples: • Fruit fly evolution proceeded the same way on two different continents (large and small wings)

22. Wing Size in Female Fruit Flies • The evolutionary pattern found in Europe also emerged in North America after accidental introduction of D. subobscura to the Americas Fig. 18-6, p. 397

23. KEY CONCEPTS 18.3 • Darwin’s scientific theory of evolution – natural selection –explained how environmental forces could cause evolution • Natural selection occurs because individuals with traits that make them better adapted to local conditions are more likely to survive and produce offspring than are individuals that are not as well adapted • Modern synthesis combines Darwin’s theory with genetics