Bi 11
1
In this section you learned that evolutionary theory is a collection of carefully reasoned hypotheses about how evolutionary change occurs. The fact that plants and animals have changed over time has been obvious to scientists for many years. How and why this change occurs is not so obvious.
Jean Lamarck proposed one of the first explanations for evolutionary change. However, his theory was based on three assumptions that we now know to be incorrect: (1) Organisms have an inborn urge to better themselves , (2) organs can change in size and shape in response to the needs of the organisms, and (3) acquired traits can be passed from parents to offspring .
Charles Darwin’s explanation for evolutionary change was influenced by the ideas of many other people. After reading Charles
Lyell’s
book, Darwin became convinced that the Earth had existed for a long time – long enough for evolution to occur. The work of plant and animal breeders demonstrated that crops and livestock changed over time as a result of artificial selection . This indicated to Darwin that organisms could – and did- evolve as the result of naturally occurring selective forces. The ideas of Thomas Malthus also had a powerful influence on Darwin. In writing about human population and society, Malthus noted that the animal and plant populations are, like the human population, restricted(limited) to a certain size. Darwin recognized that the forces that restrict(limited) the growth of populations were also the forces behind evolutionary change.
Recall that the scientific usage of the term theory is different from the common usage. In common usage, a theory may be an idea or a hunch that is not backed up by strong evidence. In scientific usage, a theory is a verified, time-tested concept that logically explains past events and makes useful an dependable predictions about the natural world.
Read each of the following statements about evolutionary theory carefully. In the space provided, indicate whether each statement is true or false. t 1. Evolutionary change is indefinable.
F 2. Evolutionary theory is based on vague hunches.
F 3. Current evolutionary theory is exactly like Darwin’s theory.
T 4. Much research in many branches of biology is based on evolutionary theory.
F 5. Because some of Darwin’s original theory was not entirely correct, it is possible that evolution does not occur.
T 6. Evolutionary theory is a collection of carefully reasoned hypotheses about how the evolutionary changes occurs.
T 7. Evolutionary theory is the foundation on which the rest of biological science is built.
F 8. Darwin was the first person to come up with an explanation for evolution.
Influences on Darwin: Examining the Main Ideas
1. People who read Darwin’s book On the Origin of Species by Means of Natural Selection are often surprised that many pages at the beginning of the book discuss the breeding of pigeons. In these pages, Darwin also described the many varieties of domesticated pigeons. Why do you think Darwin chose to spend so much time discussing pigeons?
(Answers will vary) The many pigeon varieties were produced through artificial selection. Darwin wanted to sow that if humans can select desirable variants and thus produce new kinds of pigeons it is logical that

Bi 11
2
something in nature selects variants that are best suited to surive and thus eventually creates new kinds of organisms.
2. The following passage is from the first chapter of An Essay on the Principle of Population as It Affects the
Future Improvement of Society, by Thomas Malthus.
“Through the animal and vegetable kingdoms, nature has scattered the seeds of life abroad with the most profuse and liberal hand. She has been comparatively sparing in the room, and the nourishment necessary to rear them. The germs of existence contained in this spot of earth, with ample food, and ample room to expand it, would fill millions of worlds in the course of a few thousand years. Necessity, that imperious, all-pervading law of nature, restrains them within the prescribed bounds. The race of plants, and the race of animals shrink under this great restrictive law. And the race of man cannot, by any efforts of reason, escape from it. Among plants and animals its effects are waste of seed, sickness, and premature death…” a. What are the main ideas in this passage? (answers will vary) Space and food are limited; unchecked populations of organisms grow rapidly; populations are controlled; diseases and other factors kill off excess population. b. In your own words, define the “great restrictive law” mentioned in the passage.
The principle that in nature the size of populations is limited. c. According to this passage, how does nature keep the growth of a plant or an animal population under control.
Through “waste of seed, sickness, and premature death” d. How might the forces that control the size of populations relate to selection? forces might also act as the forces of selection.
(answers will vary) These
Consider the concepts presented in Section 14-1 and how you would organize them into a concept map. Now look at the concept map for Chapter 14 at the end of this package. Notice that the concept map has been started for you. Add the key facts and concepts you fell are important for Section 14-1. When you have finished the chapter, you will have a completed concept map.
In this section you were introduced to the concept of natural selection . Darwin proposed that natural selection operates in a fashion similar to the process of artificial selection used by farmers. Darwin observed that plants and animals showed variations , and he realized that many of them were inherited . He also observed that high birthrates and a shortage of life’s necessities forced organisms to constantly struggle in order to exist. Darwin concluded that those organisms that possessed characteristics that made them well-suited for their environment survived ; those less well equipped did not survive . Darwin called this principle survival of the fittest.
In this section you also read about an interesting example of natural selection in action. Recall that peppered moths come in two forms: a lighter colored form and a darker colored form. The form that blends in with the tree bark in a given area is more common than the noncamouflaged form. An experiment by H.B.D.
Kettlewell demonstrated that the camouflaged moth form has a higher survival rate.
In your words, define each of the following terms.

Bi 11
3
1. Natural Selection: The naturally occurring process in which only the organisms that are most fit survive and produce offspring.
2. Survival of the Fittest: The principle that those individuals with characteristics best suited for their environment produce the most offspring.
3. H.B.D. Kettlewell: British ecologist who performed a classic experiment showing that peppered moths that are camouflaged have a greater survival rate (greater fitness) than those that are not.
Consider the concepts presented in Section 14-2 and how you would organize them into a concept map. Now look at the concept map for Chapter 14 at the end of this package. Notice that the concept map has been started for you. Add the key facts and concepts you fell are important for Section 14-2. When you have finished the chapter, you will have a completed concept map.
Darwin worked under a serious handicap when he was developing his theory of evolution: He did not know how inheritable traits are passed from parents to offspring. And as you learned in this section, genetics and evolutionary theory are inseparable.
In this section you discovered how evolutionary theory is defined in genetic terms. You also became familiar with the terms that link genetics and evolution. For example, genes are the source of the variation upon which natural selection operates, and the group of genes possessed by a population is known as its gene pool. In addition, you learned new definitions for familiar terms. Evolution can be defined as any change in the relative frequency of alleles in the gene pool of a population . Species can be defined as a group of similarlooking organisms that breed with one another and produce fertile offspring in the natural environment.
In the space provided, write the term that best fits each of the following descriptions.
Phenotype 1. All the behavior and physical characteristics produced by the interaction of genotype and environment.
Evolution 2. Any change in the relative frequencies of alleles in a gene pool
Fitness 3. The success of an organism in passing on its genes
Population breed with one another.
4. A collection of individuals of the same species in a given area whose members can
Phenotypic variation 5. A graph of this often forms a bell-shaped curve.
Relative Frequency 6. The number of times an allele occurs in a gene pool compared with the number of times other alleles for the same gene occur.
Adaptation
Species
7. Any genetically controlled characteristic of an organism that increases its fitness
8. Once defined as a group of organisms that look alike.
Consider the concepts presented in Section 14-3 and how you would organize them into a concept map. Now look at the concept map for Chapter 14 at the end of this package. Notice that the concept map has been started for you. Add the key facts and concepts you fell are important for Section 14-3. When you have finished the chapter, you will have a completed concept map.

Bi 11
4
In the first part of this section you were introduced to the concept of the niche. A species niche is the combination of its role in the environment and the place in which it lives . If two species occupy two different niches, they can coexist . If their niches are the same or extremely similar, they will compete with each other for food and living space . If one species is much better at making a living than the other, it may cause its competitor to become extinct . No two species can occupy the same niche in the same location for a long period of time.
You then learned about speciation, the process in which new species evolve from old species, by reading about
Darwin’s finches
. Recall that the fourteen species of Darwin’s finches evolved from a single ancestral species.
In the past, populations of the ancestral finches became separated from other populations. The separated populations adapted to local conditions. In time, the gene pools of the finch populations had changed so much that the finch populations could not interbreed .
Finally, you learned about some basic patterns of evolution. Adaptive radiation, or divergent evolution, is the process in which an ancestral species gives rise to a diversity of new species. (like Darwin’s finches ).
Convergent evolution is the process in which species from different evolutionary lines grow to resemble one another because they adapt to similar conditions .
In your own word, define each of the following terms.
1. Divergent evolution: Process by which one species gives rise to many different species.
2. Analogous Structures: Structures that are similar in appearance and function by have different origins
3. Niche:
The combinations of an organism’s role in the environment and the pace in which it lives
4. Reproductive Isolation: The condition in which separated populations cannot interbreed to produce fertile offspring.
5. Adaptive Radiation: the process in which a number of different species diverge from a common ancestral form.
6. Speciation: The process in which new species arise from old ones
Convergent Evolution: The process in which species that are similar in appearance and behavior are produced b separate evolutionary lines.
Some of the animals shown in the accompanying diagrams lived long ago. Others are still alive today.
Examine diagrams A and B. then answer the following questions.

Bi 11
5
1.
What process is shown in diagram A? Explain. Divergent evolution, or adaptive aradiation; one ancestral species gives rise to many new species.
2.
Why do the animals in diagram A look different from one another? They have evolved to fit different niches.
3.
What process is shown in diagram B? Explain. Convergent evolution; the three organisms look similar but have been produced by separate evolutionary lines
4.
Why do the animals in diagram B look similar to one another? They have evolved to fit similar niches.
Consider the concepts presented in Section 14-4 and how you would organize them into a concept map. Now look at the concept map for Chapter 14 at the end of this package. Notice that the concept map has been started for you. Add the key facts and concepts you fell are important for Section 14-4. When you have finished the chapter, you will have a completed concept map.
Evolutionary theory has been modified over the years as scientists formulate theories about the details of evolutionary change. In this section you learned about some of the major modifications to Darwin’s original theory of evolution by natural selection.
Sometimes the relative frequency of an allele in a gene pool changes merely by chance . In other words, evolution may occur in the absence of natural selection. This is known as genetic drift .
Darwin envisioned evolution as being a slow, gradual and continuous process. However, this is not always the case. In a few cases, evolution may occur so slowly that gene pools remain the same for long periods of time.
Alternatively, evolution may occur relatively rapidly . This is theory is called punctuated equilibria.
In your own words, define each of the following terms.
1.
Punctuated Equilibria: Pattern of evolution in which long stable periods (equilibria) are punctuated by brief periods of rapid change.
2.
Genetic Drift: Changes in gene frequency that are random and not due to natural selection
3.
Gradualism: Theory that evolutionary change occurs slowly and gradually
4.
Mass extinction: Phenomenon in which many species vanish at about the same time.
5.
Equilibrium: State in which conditions are balanced.
1.
Under what circumstances might genetic drift occur? If, due to chance and not to natural selection, an individual produces more offspring than other members of its species; if a large part of a population is killed off by chance; if only a few individuals start a new population.
2.
What does genetic drift imply about an organism’s characteristics and its fitness? All characteristics of an organism do not have to contribute to its fitness.
3.
How might the theory of punctuated equilibria explain “missing links” in the fossil record?
(answers will vary) During a period of rapid evolution, changes occur so quickly that transitions are not recorded in the fossil record.

Bi 11
6
4.
Under what circumstances might rapid evolution occur? If a small population becomes isolated from the main part of the population; if a small population moves to a new environment that has many new niches; if a mass extinction creates many empty niches.
Consider the concepts presented in Section 14-5 and how you would organize them into a concept map. Now look at the concept map for Chapter 14 at the end of this package. Notice that the concept map has been started for you. Add the key facts and concepts you fell are important for Section 14-5. When you have finished the chapter, you will have a completed concept map.