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Chapter 15 Darwin’s Theory of Evolution

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1 Chapter 15 Darwin’s Theory of Evolution

2 Brain Warm Up What different ways do these animals use to move about?
What traits does each animal have that help it move about as it does?

3 15-1 The Puzzle of Life’s Diversity
Humans share the earth with millions of other kinds of organisms of every imaginable shape, size, and habitat. This variety of living things is called biological diversity. The evolutionary theory accounts for the diversity of life.

4 15.1 Evolution or change over time, is the process by which modern organisms have descended from ancient organisms. A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world.

5 Voyage of the Beagle Charles Darwin was born on February 12, 1809 – the same day as Abraham Lincoln In 1831, he set sail on the HMS Beagle. Figure 15-1, page 369 On a five year voyage, Darwin visited several continents and many remote islands.

6 Voyage of the Beagle During his travels, Darwin made numerous observations and collected evidence that led him to propose a revolutionary hypothesis about the way life changes over time. This hypothesis, now supported by a huge body of evidence, has become the theory of evolution.

7 Voyage of the Beagle Darwin was the naturalist on the ship, and he went ashore to collect plant and animal specimens that he added to his collection. Darwin proposed a scientific explanation for the diversity of life on this planet.

8 Darwin’s Observations
During a single day in the Brazilian forest, he collected 68 different beetle species – he wasn’t even searching for beetles. He began to realize that an enormous number of species inhabit the Earth.

9 Patterns of Diversity Darwin was intrigued by the fact that so many plants and animals seemed remarkably well suited to whatever environment they inhabited. He was also puzzled by where species lived and did not live. Why were there no rabbits in Australia? Why no kangaroos in England?

10 Living Organisms and Fossils
Living organisms represented just part of the puzzle posed by the natural world. Darwin collected fossils which are the preserved remains of ancient organisms. Some fossils looked like organisms that were still alive and others looked completely unlike any other creatures he had ever seen.


12 The Galapagos Islands He found that each island was a source of great diversity of environ-ments and animals.

13 The Journey Home When he returned, Darwin began to wonder if animals living on different islands had once been members of the same species. According to this hypothesis, these separate species would have evolved from an original South American ancestor species after becoming isolated from one another.

14 15-1 Section Assessment Answer questions 1 – 5 from page 372 on your own paper and in complete sentences. This will be taken up for a grade.

15 Brain Warm Up Read page 373 What was the way of thinking in Europe in Darwin’s day? What do you think people thought about what Darwin had to say?

16 15-2 Ideas That Shaped Darwin’s Thinking
During the 18th and 19th centuries, scientists examined the Earth in great detail. James Hutton and Charles Lyell helped scientists recognize that Earth is many millions of years old, and the processes that changed Earth in the past are the same processes that operate in the present.

17 Hutton and Geological Change
Hutton proposed the variety of natural forces, like rain, wind and temperatures, that shape the earth operate extremely slowly, often over millions of years. Hutton proposed the Earth had to be much more than a few thousands of years old.

18 Lyell’s Principles of Geology
Lyell’s work explained how awesome geological features could be built up or torn down over long periods of time. This helped Darwin, he thought if the Earth could change over time, might life change as well?

19 Lamarck’s Evolution Hypothesis
Jean-Baptiste Lamarck recognized that living things change over time and that all species were descended from other species. In 1809, Lamarck proposed that by selective use or disuse of organs, organisms acquired or lost certain traits during their lifetime. These traits could then be passed on to their offspring. Over time, this process led to change in a species.

20 Tendency Toward Perfection
Lamarck proposed that all organisms have an innate tendency toward complexity and perfection. As a result, they are constantly changing and acquiring features that help them live more successfully in their environment. Bird - flying

21 Use and Disuse Because of an organisms tendency toward perfection, Lamarck proposed that organisms could alter the size and shape of particular organs by using their bodies in new ways. Birds – wings

22 Inheritance of Acquired Traits
Lamarck thought that acquired characteristics could be inherited. Muscles

23 Evaluating Lamarck’s Hypothesis
Lamarck and Darwin did not know how traits are inherited and that an organism’s behavior has no effect on its heritable characteristics. He was right in realizing that organisms are adapted to their environments.

24 Population Growth In 1798, Thomas Malthus published a book in which he noted that babies were being born faster than people were dying. Malthus reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone. War, famine and disease worked against growth.

25 15-2 Section Assessment As a table, write a 2 – 3 sentence summary of each of the men we discussed today. Individually - Complete the vocabulary on page total words.

26 Brain Warm Up Why do you think organisms change and do not stay the same? Why do you think the topic of evolution is so controversial? You must answer in complete sentences.

27 15-3 Darwin Presents His Case
Darwin delayed publishing his work because of possible criticism. What current areas of scientific research are controversial, much as evolution was controversial in Darwin’s time?

28 Publication of On the Origin of Species
Darwin filled notebooks with his ideas about species diversity and the evolution process. He shelved his manuscript for years and told his wife to publish it in case he died. In 1858, Darwin received a short essay from naturalist Alfred Wallace. In 1859, Darwin published his book, On the Origin of Species.

29 Publication of On the Origin of Species
In his book, Darwin: proposed a mechanism for evolution called natural selection. presented evidence that evolution has been taking place for millions of years—and continues in all living things.

30 Inherited Variation and Artificial Selection
Members of each species vary from one another in important ways. In Darwin’s day, variations were thought to be unimportant, minor defects. Darwin noted that plant and animal breeders would breed only the largest hogs, the fastest horses, or the cows that produced the most milk. Darwin termed this process artificial selection.

31 Inherited Variation and Artificial Selection
Artificial selection is the selection by humans for breeding of useful traits from the natural variation among different organisms.

32 Evolution by Natural Selection
Darwin compared processes in nature to artificial selection. By doing so, he developed a scientific hypothesis to explain how evolution occurs.

33 The Struggle for Existence
Darwin realized that high birth rates and a shortage of life's basic needs would force organisms to compete for resources. The struggle for existence means that members of each species compete regularly to obtain food, living space, and other necessities of life. The struggle for existence was central to Darwin's theory of evolution.

34 Survival of the Fittest
The ability of an individual to survive and reproduce in its specific environment is fitness. Darwin proposed that fitness is the result of adaptations. An adaptation is any inherited characteristic that increases an organism's chance of survival. Successful adaptations enable organisms to become better suited to their environment and better able to survive and reproduce.

35 Survival of the Fittest
Individuals with characteristics that are not well suited to their environment either die or leave few offspring. Individuals that are better suited to their environment survive and reproduce most successfully. Darwin called this process survival of the fittest.

36 Survival of the Fittest
Because of its similarities to artificial selection, Darwin referred to the survival of the fittest as natural selection. In natural selection, the traits being selected contribute to an organism's fitness in its environment. Over time, natural selection results in changes in the inherited characteristics of a population. These changes increase a species' fitness in its environment.

37 Descent With Modification
Natural selection produces organisms that have different structures, establish different niches, or occupy different habitats. Each living species has descended, with changes, from other species over time. Darwin referred to this principle as descent with modification. Descent with modification implies that all living organisms are related to one another. This is the principle known as common descent.

38 Evidence of Evolution Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found in the fossil record, the geographical distribution of living species, homologous structures of living organisms, and similarities in early development, or embryology.

39 What do you believe? Do you personally, believe in the theory of evolution, do you not believe in the theory of evolution, or don’t you have an opinion either way? Darwin Poll

40 The Fossil Record  Darwin saw fossils as a record of the history of life on Earth. By comparing fossils from older rock layers with fossils from younger layers, scientists could document that life on Earth has changed over time.

41 Geographic Distribution of Living Species

42 Geographic Distribution of Living Species
Darwin decided that all Galápagos finches could have descended with modification from a common mainland ancestor. Darwin’s theory was that species now living on different continents had each descended from different ancestors. However, because some animals on each continent were living under similar ecological conditions, they were exposed to similar pressures of natural selection and ended up evolving features in common.

43 Geographic Distribution of Living Species

44 Homologous Body Structures
Structures that have different mature forms but develop from the same embryonic tissues are called homologous structures. Similarities and differences in homologous structures help biologists group animals according to how recently they last shared a common ancestor.

45 Homologous Body Structures

46 Homologous Body Structures
Not all homologous structures serve important functions. The organs of many animals are so reduced in size that they are just vestiges, or traces, of homologous organs in other species. These organs are called vestigial organs.

47 Homologous Body Structures
Examples: include the eyes of some cave dwelling fish and mole rats, the leg and hip bones found in whales, the teeth that quickly disappear in duck billed platypuses, pollen in dandelions, and the human appendix and wisdom teeth.

48 Similarities in Embryology
The early stages, or embryos, of many animals with backbones are very similar. The same groups of embryonic cells develop in the same order and in similar patterns to produce the tissues and organs of all vertebrates.


50 Summary of Darwin's Theory
Individual organisms differ, and some of this variation is heritable. Organisms produce more offspring than can survive, and many that do survive do not reproduce. Because more organisms are produced than can survive, they compete for limited resources.

51 Summary of Darwin's Theory
Individuals best suited to their environment survive and reproduce most successfully. These organisms pass their heritable traits to their offspring. Other individuals die or leave fewer offspring. This process of natural selection causes species to change over time. Species alive today are descended with modification from ancestral species that lived in the distant past.


53 Strengths and Weaknesses of Evolutionary Theory
Scientific advances in many fields of biology, geology, and physics have confirmed and expanded most of Darwin’s hypotheses. Evolutionary theory continues to change as new data are gathered and new ways of thinking arise.

54 15-3 Section Assessment On your own paper, please answer questions 1 – 4 on page 386. This will be for a grade.

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