Historical Geology

 

EVOLUTION—THE THEORY AND

ITS SUPPORTING EVIDENCE

 

OUTLINE

INTRODUCTION

EVOLUTION: WHAT DOES IT MEAN?

            Jean-Baptiste de Lamarck and His Ideas on Evolution

The Contributions of Charles Darwin and Alfred Wallace

            Natural Selection—What is Its Significance?

 ¨Perspective The Tragic Lysenko Affair

MENDEL AND THE BIRTH OF GENETICS

            Mendel’s Experiments

            Genes and Chromosomes

THE MODERN VIEW OF EVOLUTION

            What Brings About Variation?

            Speciation and the Rate of Evolution

            Divergent, Convergent, and Parallel Evolution

            Microevolution and Macroevolution

Cladistics and Cladograms

            Mosaic Evolution and Evolutionary Trends

            Extinctions

WHAT KINDS OF EVIDENCE SUPPORT EVOLUTIONARY THEORY?

            Classification—A Nested Pattern of Similarities

            How Does Biological Evidence Support Evolution?

            Fossils: What Do We Learn from Them?

            Missing Links—Are They Really Missing?

The Evidence—A Summary

SUMMARY

 

 

CHAPTER OBJECTIVES

The following content objectives are presented in Chapter 7:

¨     The central claim of the theory of evolution is that today’s organisms descended, with modification, from ancestors that lived in the past.

¨     Jean-Baptiste de Lamarck in 1809 proposed the first widely accepted mechanism—inheritance of acquired characteristics—to account for evolution.

¨     In 1859, Charles Darwin and Alfred Wallace simultaneously published their views on evolution and proposed natural selection as a mechanism to bring about change.

¨     Experiments carried out by Gregor Mendel during the 1860s demonstrated that variations in populations are maintained rather than blended during inheritance, as previously thought.

¨     In the modern view of evolution, variation is accounted for mostly by sexual reproduction and by mutations in sex cells.

¨     The fossil record provides many examples of macroevolution—that is, changes that result in the origin of new species, genera, and so on—but these changes are simply the cumulative effect of microevolution, which involves changes within a species.

¨     Fossils showing the transition from ancestor to descendant groups, as in fish to amphibians and reptiles to mammals, are well known.

¨     A number of evolutionary trends, such as size increase or changing configuration of shells, teeth, or limbs, are well known for organisms for which sufficient fossil material is available.

¨     The theory of evolution is truly scientific, because we can think of observations or experiments that would support it or render it incorrect.

¨     Fossils are important as evidence for evolution, but additional evidence comes from classification, biochemistry, molecular biology, genetics, and geographic distribution.

 

 

LEARNING OBJECTIVES

To exhibit mastery of this chapter, students should be able to demonstrate comprehension of the following:

¨     the central claim and historical development of the theory of evolution

¨     Darwin's and Wallace's theory of natural selection as a mechanism for evolution

¨     Mendel’s concept of inheritance

¨     variation sources within populations as well as natural selection’s effects on variation

¨     the models for speciation

¨     the modern view of evolution, including rates of evolutionary change

¨     the types of evolutionary trends

¨     the use of cladograms, and the insight into evolutionary relationships between groups of organisms that is provided by cladistics

¨     the evidence for evolution provided by classification, modern biological studies, and the fossil record

 

 

CHAPTER SUMMARY

   1.    Darwin’s observations on the Galapagos Islands provided him with the raw data that eventually led to the theory of evolution. The central claim of the theory of evolution is that all organisms have descended with modification from ancestors that lived during the past.

            Figure 7.1       The Galapagos Islands

            Figure 7.2       Charles Robert Darwin in 1840

            Figure 7.3       Darwin’s Finches of the Galapagos Islands

 

   2.    The idea of evolution is not new, but the first widely accepted mechanism to account for evolution—inheritance of acquired characteristics—was proposed in 1809 by Jean-Baptiste de Lamarck.

 

3.   Charles Darwin’s observations of variation in populations and artificial selection, as well as his reading of Thomas Malthus’ essay on population, helped him formulate his idea of natural selection as a mechanism for evolution.

         Figure 7.4       Artificial Selection

 

4.   In 1859 Charles Darwin and Alfred Wallace published their ideas of natural selection, which hold that in populations of organisms, some have favorable traits that make it more likely that they will survive and reproduce and pass on these variations. 

 

Enrichment Topic 1. Alfred Russel Wallace

Although students may have heard that Wallace independently developed a theory of evolution by natural selection, most do not know about the life of the “other” evolutionist. As a young naturalist, Wallace did fieldwork in the Malay Archipelago in the late 1850s and early 1860s.  He described two great faunal regions separated by a deepwater gap. Whereas marsupials dominated to the east, carnivores and primates dominated to the west. This line still bears his name. He was also a prolific collector, a “ruthless harvester of natural wonders.” Read more about Alfred Wallace in National Geographic, 214(6), 113-131.

 

   5.    Natural selection holds that (a) organisms in all populations possess heritable variations; (b) some variations are more favorable than others; (c) not all young survive; and (d) those with favorable variations are more likely to survive and pass on their favorable variations.

 

   6.    Gregor Mendel’s breeding experiments with garden peas provided some of the answers regarding variation and how it is maintained in populations. Mendel’s work is the basis for present-day genetics. 

Figure 7.5       Mendel's Experiments with Flower Color

 

   7.   Genes that are specific segments of chromosomes are the hereditary units in all organisms. Only the genes in sex cells are inheritable. Meiosis yields cells with only one half the chromosome number of the parent cell—the sex cells. After fertilization, the fertilized egg develops via a different type of cell division, mitosis.

Figure 7.6       The Double-Stranded, Helical DNA Molecule

Figure 7.7       Meiosis and Mitosis

 

   8.    Sexual reproduction and mutations, changes in chromosomes or genes, account for most variation in populations.

           

Enrichment Topic 2. How Genetic Engineering Can Further Evolution

Evolution via natural selection operates without consideration of an outcome. Some variations are favorable, and others are not. However, genetic engineering proceeds with an end goal in mind. Should technology be used to cure diseases, and alter the responsible genes so that harmful, disease-causing mutations cannot be passed to the next generation? Should parents be able to genetically engineer their future child with respect to physical appearance? There are numerous current sources of information, many on the Internet, about genetic engineering—including scientific, philosophical, religious, and political points of view.

 

   9.    Evolution by natural selection is a two-step process. First, variation must exist or arise and be maintained in interbreeding populations, and second, favorable variants must be selected for survival so that they reproduce.

 

10.    Many species evolve by allopatric speciation, which involves isolation of a small population from its parent population that is then subjected to different selection pressures.

Figure 7.8                   Allopatric Speciation

Figure 7.9                   Speciation in Songbirds

 

Enrichment Topic 3. Adaptive Radiation of Darwin’s Finches

Peter and Rosemary Grant have been studying Darwin’s finches in the Galapagos for more than 30 years, far longer than Darwin! They have identified 14 or 15 species that evolved from the same common ancestor, a seed eater from South America. While Darwin’s finches present a beautiful example of adaptive radiation, the model is not one of a tree that branches out into smaller and smaller branches and twigs. In this instance, the tree is lopsided, with the main trunk splitting into three main branches, only one of which breaks into several branches and many twigs. The other trunk produces only some thin twigs. For the adaptive radiation of Darwin’s finches, the Grants describe a model of allopatric speciation, in which a small population separates from the main population (in this case by colonizing a new island) and evolves to meet the demands of its new environment, eventually to become a new species. If the two species later come into contact, they may coexist if they have diverged sufficiently and are not in competition. American Scientist, March-April 2002 v.90 n.2 p.130.

 

11.    When diverse species arise from a common ancestor, it is called divergent evolution.  The development of similar adaptive features in different groups of organisms results from convergent evolution and parallel evolution.

 

Figure 7.10                 Divergent Evolution

Figure 7.11                 Convergent and Parallel Evolution

 

12.    Microevolution involves changes within a species, whereas macroevolution

encompasses all changes above the species level. Macroevolution is simply the outcome of microevolution over time.

 

13.    Scientists have traditionally used phylogenetic trees to depict evolutionary relationships, but now they more commonly use cladistic analyses and cladograms to show these relationships.  

Figure 7.12                 Phylogenetic Tree and Cladogram

Figure 7.13                 Cladograms for Dogs, Birds, and Bats

 

14.    Mosaic evolution means that organisms have recently evolved characteristics as well as some features of their ancestral group. Size increase is a common evolutionary trend, but trends are usually complex and subject to reversal.  Evolutionary trends are a series of adaptations to a changing environment or adaptations that occur in response to exploitation of new habitats. Some organisms, however, show little evidence of any evolutionary trends for long periods.

            Figure 7.14                 Evolutionary Trends in Titanotheres

            Figure 7.15                 Two Examples of So-Called Living Fossils

 

 15.    Background extinction occurs continually, but several mass extinctions have also taken place, during which Earth’s biotic diversity has been decreased markedly. 

 

16.    The theory of evolution is truly scientific because we can think ob observations that would falsify it, that is prove it wrong.

            Table 7.1                     Some Predictions from the Theory of Evolution

 

17.    Much of the evidence supporting evolutionary theory comes from classification, comparative anatomy, embryology, genetics, biochemistry, molecular biology, and present-day examples of microevolution.

  Table 7.2                     Expanded Linnaen Classification Scheme

Figure 7.16                 Classification of Organisms Based on Shared

Characteristics

 

18.    Studies in biochemistry provide evidence for evolutionary relationships.

         Homologous structures are variations in organs derived from a common ancestor. Conversely, analogous structures serve a common function, but are dissimilar in structure and development. Vestigial structures are remnants of structures that were fully functional in ancestors but serve no function or a reduced function in modern organisms.

            Figure 7.17                 Homologous Structures

Figure 7.18                 Analogous Structures

Figure 7.19                 Vestigial Structures

 

Enrichment Topic 4. Vestigial Structures in Humans?

Are there vestigial structures in humans? Scientists consider the small muscles around the ear, as well as the coccyx (tail bone), vestigial structures that are no longer necessary in modern humans. Students can investigate other proposed vestigial structures (including the appendix, wisdom teeth), and determine whether features are actual vestigial structures. Although more than 100 vestigial structures were once proposed for Homo sapiens, scientists have discerned uses for these once-proposed “useless” features.

 

19.    The fossil record also provides evidence for evolution in that it shows a sequence of different groups appearing through time, and some fossils show features we would expect in the ancestors of birds, mammals, horses, whales, and so on.

Figure 7.20     The Fossil Record and Evolution

Figure 7.21     Cladogram Showing the Relationships among Horses,

Rhinoceroses, and Tapirs (Order Perissodactyla)

 

 

LECTURE SUGGESTIONS

Evolution as a Theory via the Mechanism of Natural Selection

 

   1.    Briefly review “What Kinds of Evidence Support Evolutionary Theory?" (p. 145-150) and place it in the context of the scientific method. Emphasize that a theory in science is a hypothesis that has withstood repeated testing and, as such, is a powerful tool that offers a good explanation, and is predictive. It has a very different connotation that our common, everyday use of the word “theory” or “theoretical.”

 

   2.    It is important to provide beginning students (particularly non-majors) with adequate information concerning the vast amount of accumulated evidence in favor of modern evolutionary theory. However, most students acknowledge evolution, at least on some basic level.

 

                  A. Ask students if any are involved in breeding animals. Ask these

                        students and the class in general what procedure you should follow if

          you have a champion German Shepherd and wish to make money breeding your dog and selling the puppies.

When students acknowledge that a championship dog results from favorable characteristics from both parents (and not from a champion dog and a mutt on the street!), question why favorable genes from both parents are required.  If organisms do not change, would it be important to search for a favorable mate for your dog?

     

                 B.   Ask students to think of special features of animals (a giraffe’s long neck,

                        a shark’s streamlined form, camouflage in some moths), and how these

                        features imparted an evolutionary advantage to the species.

 

                 C.  Note that the DNA testing techniques that are used to establish

              evolutionary relationships among different organisms are also used to

              determine whether an individual’s DNA is at a crime scene. Are DNA techniques effective in the criminal court system? Is it possible that DNA techniques would not be effective when establishing relationships among organisms?

 

                   D.  It may be necessary to emphasize that natural selection and evolutionary

                        theory make no mention of a higher power or a spiritual realm. (The

          theory does not rely on—nor does it deny—the existence of a higher power.) Emphasize that evolutionary theory is science where religious beliefs are not scientific because they rely on faith and cannot be tested. 

 

   3.    Prepared skeletons of various vertebrates (e.g., salamander, frog, cat, bird, and human) can be used to demonstrate homologies.

 

4.   Some well-studied fossils suites such as the horse or ammonoids can be used to illustrate how stratigraphic and paleontological studies support evolution.

 

5.   Have students identify and design a “mystery organism” based upon a given set of parameters. For example, students are told that there is an unseen pollinator of a giant flower in the rainforest. The flower is 50 cm long from the flower opening to the location of the pollen—in a very curved, very narrow flower.  Students can design an insect “mystery pollinator.”  Change the flower’s parameters, or ask students to redesign the pollinator as a bird, or a mammal.  What are the important features that the organism must possess in order to reach the pollen? Do any students’ designs mimic convergent evolution?

 

6.   Within the parameters of scientific theory, students can investigate why “creationism” and “intelligent design” are not acceptable topics within science classrooms.  It is not possible to design experiments to support or disprove a spiritual realm.

 

CONSIDER THIS

   1.    Discuss the difference between a scientific theory and a belief, with an emphasis on the origin and evolution of life. How are they different from each other?

 

   2.    What is some of the abundant evidence against the mechanism of acquired characteristics? For example, what if a baby is born to parents who originally had large noses before plastic surgery? Will the baby have a small nose?

 

   3.    Is there enough evidence for organic evolution on Earth to make it a respectable theory?

 

4.   How might Darwin's conclusions about evolution have been different if he had known about the cellular basis of heredity?

 

5.  How effective do you think mutations would be in a single-celled organism?

 

 

IMPORTANT TERMS

allele	homologous structure	mutation
allopatric speciation	inheritance of acquired	natural selection
analogous structure	characteristics	paleontology
artificial selection	living fossil	parallel evolution
chromosome	macroevolution	phyletic gradualism
cladistics	mass extinction	punctuated equilibrium
cladogram	meiosis	species
convergent evolution	microevolution	theory of evolution
deoxyribonucleic acid divergent evolution gene	mitosis modern synthesis mosaic evolution	vestigial structure

 

 

SUGGESTED MEDIA

Videos

1.     American Experience: The Monkey Trial, PBS Home Video

2.     Evolution (boxed set), WGBH Boston Video

3.     Evolution:  Darwin’s Dangerous Idea, WGBH Boston Video

4.     Evolution: Extinction, WGBH Boston Video

5.     Evolution: Evolutionary Arms Race, WGBH Boston Video

6.     Evolution: Why Sex?, WGBH Boston

7.     NOVA. Cracking the Code of Life, WGBH Boston Video

8.     Scientific American Frontiers Season X. Voyage to the Galapagos, PBS Home Video

9.     Evolution Through Time, Earth Revealed #11, Annenberg/CPB

10.  PaleoWorld: Mysteries of Evolution, The Learning Channel

11.  Biography: Charles Darwin: Evolution’s Voice, A & E Video

12.  Keys to Scientific Literacy: The Story of Evolution, Hawkhill Video

13.  The Shape of Life, National Geographic

14.  Earth Time: Evolution and Human Memory, BBC

15.  Evolution Video Library (17 video clips), Discovery Channel/FFH&S

16.  Why Humans Have Legs: The Missing Link, BBCW

17.  Galapagos: The Islands that Changed the World, BBC

18.  Judgment Day: Intelligent Design on Trial, NOVA, WGBH Boston

19.  Natural Selection, VEA

 

Software and Demonstration Aids

1.     Natural Selection, EME Corporation

2.     Mendelian Inheritance, slide set, Educational Images, Ltd.

3.     The Origins of Life, slide set, Educational Images, Ltd.

 

CHAPTER 7 – ANSWERS TO QUESTIONS IN TEXT

Multiple Choice Review Questions

1.    b	5.    a	9.    c
2.    c	6.    d	10.    b
3.    e	7.    e
4.    c	8.    a

 

Short Answer Essay Review Questions

11.    In natural selection, the better an organism is adapted to its environment, the longer it will survive and the more offspring it will produce relative to other members of its species. Fitness is measured, not in terms of how big or strong you are, but how well you elude danger and prosper. So if you’re a small mammal, it’s good to be well camouflaged and able to build a good burrow. If you’re a lion, a good roar and sharp claws will serve you well.

 

12.    In allopatric speciation, new species arise when a small part of a population is isolated from the larger gene pool by some kind of barrier. Isolation may result from a marine transgression that effectively separates a once-interbreeding species. Another example would be if land animals are rafted from one area to another across open water.

 

13.    A vestigial structure is a remnant structure that was fully functional in an ancestor. The vestigial structure need not be totally functionless, but can have a reduced function. Examples include dogs’ dewclaws, whales and some snakes’ pelvis bones.

 

14.      In divergent evolution, an ancestral species gives rise to diverse descendants adapted to various aspects of the environment. An example would be an ancestral mammal of the Late Mesozoic that gave rise to platypuses, armadillos, rodents, bats, primates, whales, and rhinoceroses.  In convergent evolution, similar characteristics develop in distantly related evolution.  An example would be the similarities of the mammals of North and South America which developed independently.

 

15.    In punctuated equilibrium, species are stable for extended time periods, and then evolution occurs rapidly, giving rise to a new species. Proponents of punctuated equilibrium argue that there are few examples of gradual transition in the fossil record. In phyletic gradualism, gradual accumulation of minor changes eventually brings about the origin of a new species. Phyletic gradualism does appear in the fossil record as well (horse, ammonoids).

 

16.    See Table 7.1. If evolution has taken place, the oldest fossil-bearing rocks should have remains of organisms very different from those existing now, and more recent rocks should have fossils more similar to today’s organisms. If today’s organisms descended with modification from ones in the past, there should be fossils showing characteristics connecting orders, classes, and so on. If evolution is true, closely related species should be similar not only in details of their anatomy, but also in their biochemistry, genetics, and embryonic development, whereas distantly related species should show fewer similarities.

 

17.    Macroevolution involves changes such as the origin of a new species, or the origin of new genera, families, orders, and classes. Good examples would include the origin of birds from reptiles, the origin of mammals from mammal-like reptiles, and the evolution of whales from land-dwelling ancestors.

 

18.    Students will produce a variety of cladograms. The best-drawn cladograms will exhibit patterns based on derived characteristics (Sharks do not have a completely bony skeleton, so their skeleton is more “primitive” than the others. While whales can swim, they are examples of mammals who returned to the sea; their skeletons show vestigial structures—pelvis, hind limbs. Bears are mammals, and more closely related to whales—both have mammary glands, bony skeletons, etc.)

 

19.    Evolution just means change through time, so we would find changes from one organism to another and we would find terminal extinctions of organisms.

 

20.    Mendel’s experiments showed that the factors (genes) that control traits do not blend during inheritance, and even though these traits may not be expressed in each generation, they are not lost. Therefore, some variation in populations is accounted for by alternate expressions of genes. Mendelian genetics explains much about heredity and explains the origin of variations in populations, and how variations in populations are maintained.

 

 

Apply Your Knowledge

 

1.   The group in Congress is operating under the premise of Lamarckian evolution, which holds that new traits arise in organisms because of their needs. These new traits could supposedly be passed on to descendants. This mechanism is incorrect, and has been rejected by the scientific community. Natural selection is the mechanism for evolution accepted by the scientific community. Variation in populations is accounted for by genetics and sexual reproduction. Mutations may arise spontaneously, but only those in sex cells can be passed on to future generations.

 

2.   If present-day tapirs, horses, and rhinoceroses are more closely related to one another than they are to any other living hoofed mammal, then as we trace these animals back through the fossil record, it should become increasingly difficult to differentiate between them. Also, their anatomies should be similar, as well as their blood chemistries, and their embryological development.

 

3.  The first statement is irrelevant to theories in general, because the person is not using the word in the scientific sense. In science, a theory is supported by a multitude of data, it offers a good explanation for observable phenomena, and it is predictive. The second statement—that fossils are arranged in a sequence of density, shape, and habitat—can be refuted with several examples. The fossil record shows a sequence of the first appearances of various organisms through time, with one-celled organisms appearing before multicelled organisms, invertebrates appearing before vertebrates, etc. We can also see in the fossil record that organisms arising from a common ancestor are more and more similar and difficult to tell apart as we trace these animals back.