Chapter 14 Principles of Evolution 14.1 How did evolutionary thought evolve? 14.2 How does natural selection work? 14.3 How do we know that evolution has occurred? 14.4 What is the evidence that populations evolve by natural selection? 14.5 A postscript by Charles Darwin

Two Meanings of Evolution Evolution as a process – change in the features of individuals in a population over generations Examples: Head lice resistant to pesticide Cancer cells resistance to chemotherapy Plants resistant to Round Up

Figure 9.1 The process of evolution. The evolution of pesticide resistance in lice occurs as a result of natural selection, one of the mechanisms by which traits in a population can change over time.

The Process of Evolution The process of evolution has been widely seen and accepted: Pesticide resistance in insects Antibiotic resistance in bacteria However, acceptance that traits in populations can evolve is not the same as acceptance of the theory of evolution…

The Theory of Evolution The theory of common descent—the idea that all living things on the planet can be traced back to a common ancestor—is what most people (especially opponents) think of when they hear “evolution”

Figure 9.2 The theory of common descent. This theory states that all modern organisms descended from a single common ancestor. Each branching point on the tree represents the origin of a new species from an ancestral form.

Evolutionary Thought Evolution by natural selection is a unifying theme for all of biology The foundation of evolutionary thought developed gradually over centuries Main ideas of evolution were not widely accepted until after Charles Darwin published On the Origin of Species in 1859

FIGURE 14-1 A timeline of the roots of evolutionary thought Each bar represents the life span of a key figure in the development of modern evolutionary biology.

14.1 How Did Evolutionary Thought Evolve? Early biological thought did not include the concept of evolution Pre-Darwinian science was heavily influenced by theology All organisms were created simultaneously Each life-form is distinct and unchanging from the moment of creation Each life-form was a divinely established “ideal form” (Greek philosophers Plato & Aristotle 427-322 B.C.) This view remained unchallenged for ~2,000 years

Aristotle’s Ladder of Nature FIGURE 14-2 Aristotle's Ladder of Nature In Aristotle's view, fixed, unchanging species could be arranged in order of increasing closeness to perfection, with inferior types at the bottom and superior types above. Aristotle’s Ladder of Nature

14.1 How Did Evolutionary Thought Evolve? Exploration of new lands revealed a staggering diversity of life European naturalists explored new lands (Africa, Asia & the Americas) They found more species then suspected Some species closely resembled each other, and/or differed in some characteristics Maybe species did change, but how?

Speculation That Life Had Evolved Comte de Buffon (1707-1788) proposed that some modern species had evolved through natural processes Idea was not accepted Did not provide a mechanism for evolution Earth was not old enough to allow time for the process of evolution

14.1 How Did Evolutionary Thought Evolve? Fossil discoveries showed that life had changed over time As more and more fossils were discovered, it became clear that they were the impressions of plants and animals that had died long ago The way in which fossils are distributed in the rocks is consistent and show progression in development

Layer upon layer of sedimentary rock forms the walls of the Grand Canyon. The layers formed from the accumulation of sediments over more than a billion years.

eggs in nest fossilized feces (coprolites) bones footprints Any part or trace of an organism that is preserved in rock or sediments is a fossil. eggs in nest fossilized feces (coprolites) bones footprints skin impression

Fossils Certain fossils were always found in the same layers of rock Organization of fossils and rock layers was consistent The deeper (older) the layer, the more dissimilar the fossils from modern organisms Many fossils were of extinct organisms

FIGURE 14-4 Fossils of extinct organisms Fossils provide strong support for the idea that today's organisms were not created all at once, but arose over time by the process of evolution. If all species were created simultaneously, we would not expect (a) trilobites to be found in older rock layers than (b) seed ferns, which in turn would not be found deeper than (c) dinosaurs, such as Allosaurus. Trilobites became extinct about 230 million years ago, seed ferns about 150 million years ago, and dinosaurs 65 million years ago.

Nonevolutionary Explanations Georges Cuvier (1769-1832) proposed theory of catastrophism which hypothesized that High numbers of species were created originally A series of catastrophes produced rock layers and destroyed many species, preserving some as fossils Modern day species are the survivors of these catastrophes

Catastrophism If true, the oldest rock layers should contain fossils of present-day species, but the vast majority of fossils are of extinct species So, French geologist Louis Agassiz (1807-1873) proposed new creations after each catastrophe Even with just the fossils known at that time, Agassiz had to include 50 separate catastrophes and creations

14.1 How Did Evolutionary Thought Evolve? A few scientists speculated that life had evolved In the early 1700s, most people thought the earth was only 4,000-10,000 old – and evolution cannot happen that quickly

Earth Is Exceedingly Old James Hutton (1726-1797) and Charles Lyell (1797-1875) studied geologic processes (wind, water, earthquakes, volcanism) Developed theory of uniformitarianism: geologic change resulting from slow, continuous actions similar to those at work today Now the earth could be very old. In fact, Lyell thought the earth was eternal

Earth Is Exceedingly Old Rock formations reflect repeated cycles of geologic change occurring over vast periods of time Conclusions: Earth was older than the 6,000 years proposed by theologians There was enough time for evolution to occur Most scientists now think the earth is about 4.5 billion years old

Pre-Darwin Proposal Jean Baptiste Lamarck (1744-1829) proposed that organisms evolved through inheritance of acquired characteristics Organisms are modified during their lifetime through use or disuse of different parts These modifications are passed to offspring

Pre-Darwin Proposal Inheritance of acquired characteristics mechanism was rejected when it was determined that acquired characteristics are not heritable

Darwin and Wallace By mid-1880s the concept of evolution was increasingly accepted 1858 Charles Darwin and Alfred Russel Wallace independently Provided evidence for its occurrence Proposed the mechanism through which it occurs

Darwin and Wallace Darwin and Wallace shared experiences that shaped their thinking Aware that fossils showed a trend of increasing complexity Aware of Hutton and Lyell’s proposal that Earth is extremely old

Darwin and Wallace Darwin and Wallace shared experiences, continued Traveled extensively studying tropical plants and animals Observed that similar species differed only in a few ecologically important features Darwin had collected 30 years of data but was afraid to tell people. Why?

Large ground finch, beak suited to large seeds Small ground finch, beak suited to small seeds Darwin studied a group of closely related species of finches on the Galapagos Islands. Each species specializes in eating a different type of food and has a beak of characteristic size and shape, because natural selection has favored the individuals best suited to exploit each food source efficiently. Aside from the differences in their beaks, the finches are quite similar. Warbler finch, beak suited to insects Vegetarian tree finch, beak suited to leaves

Darwin and Wallace Darwin and Wallace independently proposed that organisms evolved by natural selection Both presented papers to the Linnaean Society in London (1858) Darwin published On the Origin of Species by Means of Natural Selection in 1859

Thomas Malthus English economist and clergyman (1766-1834) His writings were extremely influential In his essay on population, he wrote “It may safely be pronounced, therefore that [human] population, when unchecked, goes on doubling itself every 25 years, or increases in a geometric ratio.”

Section 14.2 Outline 14.2 How Do We Know That Evolution Has Occurred? Fossils Provide Evidence of Evolutionary Change Over Time Comparative Anatomy Gives Evidence of Descent with Modification Embryological Similarity Suggests Common Ancestry Modern Biochemical and Genetic Analyses Reveal Relatedness Among Diverse Organisms

Evidence from Fossils Fossils of ancient species tend to be simpler in form than modern species Several series of fossils have been found that exhibit the evolution of body structures over time One series reveals that modern whales evolved from land-dwelling ancestors

FIGURE 14-6 The evolution of the whale Over the past 50 million years, whales have evolved from four-legged land dwellers, to semiaquatic paddlers, to fully aquatic swimmers with shrunken hind legs, to today's sleek ocean dwellers.

Comparative Anatomy Homologous structures provide evidence of common ancestry Homologous structures are structures that have the same evolutionary origin despite their current appearance or function Bird and mammalian forelimbs are homologous structures

FIGURE 14-7 Homologous structures Despite wide differences in function, the forelimbs of all these animals contain the same set of bones, inherited through evolution from a common ancestor. The different colors of the bones highlight the correspondences among the various species.

Comparative Anatomy Vestigial structures are remnants of structures that are inherited from ancestors Had important functions in ancestors Serve no obvious purpose in present day organism Vestigial structures include: Molar teeth in vampire bats Pelvic bones in whales and certain snakes

Figure 14-8 Vestigial structures Many organisms have vestigial structures that serve no apparent function. The (a) salamander, (b) whale, and (c) snake all inherited hindlimb bones from a common ancestor; the bones remain functional in the salamander but are vestigial in the whale and snake.

Comparative Anatomy Analogous structures are structures that are outwardly similar in appearance, but differ in their evolutionary origin Analogous structures include Wings of insects and birds

Figure 14-9a Analogous structures Convergent evolution can produce outwardly similar structures that differ anatomically. The wings of (a) insects and (b) birds and the sleek, streamlined shapes of (c) seals and (d) penguins are examples of such analogous structures.

Figure 14-9b Analogous structures Convergent evolution can produce outwardly similar structures that differ anatomically. The wings of (a) insects and (b) birds and the sleek, streamlined shapes of (c) seals and (d) penguins are examples of such analogous structures.

Comparative Anatomy Analogous structures include Streamlined shapes of seals and penguins

Figure 14-9c Analogous structures Convergent evolution can produce outwardly similar structures that differ anatomically. The wings of (a) insects and (b) birds and the sleek, streamlined shapes of (c) seals and (d) penguins are examples of such analogous structures.

Figure 14-9d Analogous structures Convergent evolution can produce outwardly similar structures that differ anatomically. The wings of (a) insects and (b) birds and the sleek, streamlined shapes of (c) seals and (d) penguins are examples of such analogous structures.

Comparative Anatomy Analogous structures result from convergent evolution rather than descent from a common ancestor Convergent evolution occurs when similar environmental pressures and natural selection give rise to similar (analogous) structures in distantly related organisms

Figure 9.6 Divergence from a common ancestor. (a) Prickly pear cactuses, like this Opuntia on continental South America, are shrub-like and low to the ground.

Figure 9.6 Divergence from a common ancestor. (b) On the Galápagos Islands, some prickly pears are tree-sized, such as this variety of Opuntia echios. The overall similarity of these two species despite their difference in form supports the hypothesis that they descended from a common ancestral prickly pear.

Embryology All vertebrate embryos, resemble one another in their early development

Embryology All vertebrate embryos possess genes that direct development of gill slits and a tail These genes were inherited from a common ancestor

Embryology Adult fish retain gills and tail because the genes are active throughout their embryonic development Humans are born without gills and a tail because the genes are active only during early embryonic development

Biochemistry and Genetics All organisms share related biochemical processes: All cells use DNA as genetic blueprint All use RNA, ribosomes, and approximately the same genetic code for translation All use roughly the same set of 20 amino acids to build proteins All use ATP to transfer energy

Biochemistry and Genetics Striking genetic similarities between organisms imply evolutionary relatedness For example, the DNA nucleotide sequence of the human and mouse cytochrome c gene is very similar, suggesting shared ancestry

Figure 14-11 Molecular similarity shows evolutionary relationships The DNA sequences of the genes that code for cytochrome c in a human and a mouse. Of the 315 nucleotides in the gene, 30 (shaded in blue) differ between the two species.

Biochemical Evidence Similar organisms have similar DNA sequences DNA sequences reflect evolutionary relationships

08-11 Title: DNA sequences reflect evolutionary relationships. Caption: DNA sequences evolve over time. Species that share more recent common ancestors have undergone less evolution separately than species that share more distant common ancestors, and thus have DNA that is more similar.

Figure 9.17 Similar organisms have similar DNA sequences. (a) The order of DNA bases contains information about the traits of an organism. We can compare the DNA of various organisms by looking at similarities and differences in the DNA sequences for various genes. The number of nucleotide differences between species is exaggerated in this example for illustration purposes. Mathematical models can be used to determine the distance between organisms

Figure 9.18 Using DNA evidence to test an evolutionary hypothesis. Scientists comparing several physical features hypothesized a tree of relationships among swallowtail butterflies; a small portion of the tree is illustrated here. When another group of scientists measured similarity in DNA sequences for several genes in these species, the results supported the original hypothesis.

Section 14.3 Outline 14.3 How Does Natural Selection Work? Darwin and Wallace’s Theory Rests on Four Postulates Natural Selection Modifies Populations Over Time

Evolution by Natural Selection Darwin and Wallace proposed that life’s diverse forms arose through process of descent with modification Individuals in each generation differ slightly from the members of the preceding generation Over long time periods, small differences accumulate to produce major transformations

Evolution by Natural Selection Postulate 1: Individual members of a population differ from one another in many respects Variations arise purely by chance resulting from random mutations in DNA Differences are obvious in many physical characteristics and extend to molecular level

Figure 14-12 Variation in a population of snails Although these snails are all members of the same population, no two are exactly alike.

Evolution by Natural Selection Postulate 2: At least some of the differences among members of a population are due to characteristics that may be passed from parent to offspring However, the mechanism of inheritance was not understood at this point in time

Evolution by Natural Selection Postulate 3: In each generation, some individuals in a population survive and reproduce successfully but others do not Darwin observed that many more individuals are born than survive Some individuals have more offspring than others

Evolution by Natural Selection Postulate 4: Individuals with advantageous traits survive longest and leave the most offspring, a process known as natural selection

Evolution by Natural Selection Gregor Mendel’s theories of inheritance (1865) confirmed Darwin’s assumption that certain traits are heritable New variations arise by chance as a result of random mutations in DNA New variations may be good, bad, or neutral

Section 14.4 Outline 14.4 What Is the Evidence That Populations Evolve by Natural Selection? Controlled Breeding Modifies Organisms Evolution by Natural Selection Occurs Today

Controlled Breeding Artificial selection is selective breeding to produce plants and animals that possess desirable traits Modern dogs descended from wolves In only a few thousand years, humans artificially selected for all breeds of modern dogs

Figure 14-13a Dog diversity illustrates artificial selection A comparison of (a) the ancestral dog (the gray wolf, Canis lupus) and (b) various breeds of modern dogs. Artificial selection by humans has caused a great divergence in size and shape of dogs in only a few thousand years.

Figure 14-13b Dog diversity illustrates artificial selection A comparison of (a) the ancestral dog (the gray wolf, Canis lupus) and (b) various breeds of modern dogs. Artificial selection by humans has caused a great divergence in size and shape of dogs in only a few thousand years.

Controlled Breeding Humans have created tremendous variation in several species over relatively short periods of time through artificial selection Isn’t it plausible that much larger changes could result from hundreds of millions of years of natural selection?

Natural Selection Today Examples include: Coloration in Trinidadian guppies Pesticide resistance Experimental introductions of Anolis sagrei lizards

Coloration Female guppies prefer to mate with brightly colored males; however, brightly colored males are more likely to be eaten by predators Males found in areas lacking predators were brightly colored Males found in areas with predators were duller by comparison (predators eliminated brightly colored males before they could reproduce) Copyright © 2005 Pearson Prentice Hall, Inc.

Coloration Conclusion: When fewer predators are present, brighter coloration can evolve Conclusion was confirmed Predators were introduced to previously predator-free areas (males were brightly colored) Within a few generations male guppies in those areas evolved to become less colorful Copyright © 2005 Pearson Prentice Hall, Inc.

Copyright © 2005 Pearson Prentice Hall, Inc. Figure 14-14 Guppies evolve to become more colorful in predator-free environments Male guppies (top) are more brightly colored than females (bottom). Some male guppies are more colorful than others. In some environments, brighter males are naturally selected; in other environments, duller males are selected. Copyright © 2005 Pearson Prentice Hall, Inc.

Pesticide Resistance Numerous insect pests have evolved resistance to pesticides Roaches developed resistance to Combat®, an insecticide bait that acted as an agent of natural selection Resistant roaches possessed a rare mutation that caused them to dislike glucose, the main attractant in Combat® At least one insect species is resistant to every pesticide in existence

Experiments Small groups of Anolis sagrei lizards were introduced onto 14 small Bahamian islands with thinly-branched bushes and no trees Lizards were originally from Staniel Cay, an island with thickly-branched trees Their long legs were adaptive for maneuvering in these trees The introduced lizards thrived and reproduced

Experiments After 14 years, comparisons were made between lizards on the Bahamian islands and those of Staniel Cay Lizards on all 14 Bahamian islands had shorter, thinner legs

FIGURE 14-15 Anole leg size evolves in response to a changed environment

Experiments Conclusion: Individuals with shorter, thinner legs evolved because they were able to escape predators better than their longer-legged ancestors in the new environment

Natural Selection of Phenotypes The variations on which natural selection works are produced by mutations that arise spontaneously

Natural Selection of Phenotypes Natural selection selects for organisms that are best adapted to a particular environment If the environment changes, a previously advantageous trait may become disadvantageous

14.4 What Is the Evidence That Populations Evolve by Natural Selection? Evolution by natural selection occurs today Experiments can demonstrate natural selection

Natural Selection Today? Selection acts on random variation to favor the traits that work best in particular environments Environments are constantly changing Organisms are not perfect, and natural selection can only work on traits already present Evolution by natural selection occurs today Experiments can demonstrate natural selection