Principles of Evolution

Principles of Evolution
14 Principles of Evolution 1

Chapter 14 At a Glance 14.1 How Did Evolutionary Thought Develop?
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?

14.1 How Did Evolutionary Thought Develop?
Evolution is the change over time in the characteristics of a population Population is all the individuals of one species in a particular area Modern biology is based on our understanding that life has evolved, a principle unrealized by early scientists

Early biological thought did not include the concept of evolution Pre-Darwinian science was heavily influenced by theological ideas, maintaining that all organisms were created simultaneously by God, and that each distinct life-form was permanently fixed and did not change over time Plato (427–347 B.C.) proposed that each object on Earth was merely a temporary reflection of its divinely inspired “ideal form”

Early biological thought did not include the concept of evolution (continued) Pre-Darwinian science was heavily influenced by theological ideas, maintaining that all organisms were created simultaneously by God, and that each distinct life-form was permanently fixed and did not change over time (continued) Aristotle (384–322 B.C.) arranged all organisms on a linear scale of increasing complexity (the “ladder of Nature”)

Figure 14-1 Aristotle’s Ladder of Nature
Humans Mammals Birds Reptiles and amphibians Whales and porpoises Fish Squids and octopuses Lobsters, crabs, etc. Snails, clams, etc. Insects, spiders, etc. Jellyfishes, sponges, etc. Higher plants Lower plants Inanimate matter 6

Exploration of new lands revealed a staggering diversity of life Europeans were often accompanied by naturalists who observed and collected plants and animals of previously unknown lands By the 1700s observations and collections accumulated by naturalists revealed the true scope of life’s variety The number of species was far greater than expected

Exploration of new lands revealed a staggering diversity of life (continued) Revelation of the discoveries led 18th-century naturalists to take note of fascinating patterns Geographic areas possessed their own sets of species Some species closely resembled one another yet differed in some characteristics To some naturalists, these patterns seemed inconsistent with the idea that species were fixed and unchanging

Figure 14-2 A timeline of the roots of evolutionary thought
Buffon (species created, than evolve) Hutton (gradual geologic change) Lamarck (mechanism of species change) Cuvier (successive catastrophes) Smith (sequence of fossils) Lyell (very old Earth) Darwin (evolution, natural selection) Wallace (evolution, natural selection) 1700 1750 1800 1850 1900 9

A few scientists speculated that life had evolved George Louis LeClerc (Comte de Buffon; 1707–1788) Suggested that the original creation provided a relatively small number of founding species Species changed over time through natural processes

Fossil discoveries showed that life has changed over time Fossils are the preserved remains or traces of organisms that had died long ago Fossils were the petrified remains of bones, wood, shells, or their impressions left in mud Other fossils included preserved traces such as tracks, burrows, pollen, eggs, and feces

Figure 14-3 Types of fossils
eggs in nest fossilized feces (coprolites) bones footprint skin impression 12

Fossil discoveries showed that life has changed over time (continued) Significance of fossil distribution The British surveyor William Smith (1769–1839), who studied rock layers and the fossils embedded in them, recognized that certain fossils were always found in the same layers of rock

Fossil discoveries showed that life has changed over time (continued) Significance of fossil distribution (continued) The organization of fossils and rock layers was consistent with fossils across different areas Fossil type A always found in a rock layer resting beneath a younger layer containing fossil type B, which is found rested beneath an even younger layer containing fossil type C, and so on

Fossil discoveries showed that life has changed over time (continued) Scientists of the period discovered that fossil remains showed remarkable progression Most fossils found in the oldest layers were very different from modern organisms The resemblance to modern organisms gradually increased in progressively younger rocks Many of the fossilized species were extinct, which means no members of the species still lived on Earth

Fossil discoveries showed that life has changed over time (continued) Scientists concluded that Different types of organisms had lived at different times in the past This countered the view that species were created at one time and did not change afterward

Figure 14-4 Different fossils are found in different rock layers
youngest rocks oldest rocks Trilobite Seed ferns Allosaurus 17

Some scientists devised non-evolutionary explanations for fossils To account for the existence of extinct species while preserving the notion of a single creation by God, Georges Cuvier (1769–1832) proposed the theory of catastrophism The Great Flood described in the Bible produced layers of rock and destroyed many species, fossilizing some of their remains in the process The organisms of the modern-day species are the survivors of these catastrophes

Geology provided evidence that the Earth is exceedingly old Charles Lyell (1797–1875) challenged Cuvier’s hypothesis of a world shaped by successive catastrophes Lyell, building on the earlier thinking of Hutton, considered the forces involved in catastrophes and concluded no need to invoke catastrophes to explain the finding of geology

Geology provided evidence that the Earth is exceedingly old (continued) Lyell presented the idea of uniformitarianism to explain that Earth’s landscape was produced by past action of the same geological processes observed today The acceptance of uniformitarianism by scientists implied that Earth is ancient

14.1 How Did Evolutionary Thought Evolve?
Some pre-Darwin biologists proposed mechanisms for evolution Jean Baptiste Lamarck (1744–1829) was one of the first scientists to propose a mechanism for evolution Observed that older fossils tend to be less like existing organisms than are more recent fossils

Some pre-Darwin biologists proposed mechanisms for evolution (continued) In 1809, Lamarck published a book in which he hypothesized that organisms evolved through the inheritance of acquired characteristics Acquired characteristics is a process in which the bodies of living organisms are modified during their lifetime through use or disuse of different parts inherited by the offspring

Some pre-Darwin biologists proposed mechanisms for evolution (continued) Understanding how inheritance works refutes Lamarck’s evolutionary mechanism Gregor Mendel, geneticist, began to understand how traits are passed on and that acquired characteristics are not heritable

Darwin and Wallace proposed a mechanism of evolution Charles Darwin (1809–1882) and Alfred Wallace (1823–1913) provided convincing evidence that evolution was driven by a simple yet powerful process

Darwin and Wallace proposed a mechanism of evolution (continued) Although Darwin and Wallace had different educational backgrounds, they possessed similar qualities They traveled extensively in the tropics and studied plants and animals Darwin and Wallace found that some species differ in only a few features

14.1 How Did Evolutionary Thought Evolve?
Darwin and Wallace proposed a mechanism of evolution (continued) Although Darwin and Wallace had different educational backgrounds, they possessed similar qualities (continued) Both were familiar with fossils previously discovered Both were aware of the studies of Hutton and Lyell, who proposed Earth was ancient Both men sought a mechanism that might cause evolutionary change

Darwin and Wallace proposed a mechanism of evolution (continued) Darwin was the first to propose a mechanism for evolution, sketched in 1842 and described more fully in his 1844 essay Wallace authored a paper outlining similar ideas 16 years after Darwin’s essay

Figure 14-5 Darwin’s finches, residents of the Galápagos Islands
Large ground finch, beak suited to large seeds Small ground finch, beak suited to small seeds Warbler finch, beak suited to insects Vegetarian tree finch, beak suited to leaves 28

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

14.2 How Does Natural Selection Work?
Darwin and Wallace proposed that life’s diverse forms arose through the 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

Darwin and Wallace’s theory rests on four postulates Postulate 1: Individual members of a population differ from one another in many respects 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

Darwin and Wallace’s theory rests on four postulates (continued) Postulate 3: In each generation, some individuals in a population survive and reproduce successfully but others do not Postulate 4: The face of individuals is not determined entirely by luck or chance; instead, an individual’s likelihood of survival and reproduction depends on its characteristics

Darwin and Wallace’s theory rests on four postulates (continued) Postulate 1: Individuals in a population vary People differ in size, eye color, skin color, and other physical features Variability is present in populations of other organisms

Figure 14-6 Variation in a population of snails
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Darwin and Wallace’s theory rests on four postulates (continued) Postulate 2: Traits are passed from parent to offspring The principles of genetics were unknown when Darwin published On the Origin of Species The later work by Mendel demonstrated conclusively that particular traits can be passed to offspring

Darwin and Wallace’s theory rests on four postulates (continued) Postulate 3: Some individuals fail to survive and reproduce Essay on the Principle of Population (Thomas Malthus) influenced Darwin’s formulation of Postulate 3 More organisms must be born than survive long enough to reproduce

Darwin and Wallace’s theory rests on four postulates (continued) Postulate 4: Survival and reproduction are not determined by chance Reproductive success depends on an individual’s characteristics In the competition to survive and reproduce, winners are determined not by chance but by the traits they possess

Animation: Natural Selection for Antibiotic Resistance

Natural selection modifies populations over time Natural selection acts on individuals within a population The population changes over time Over generations, the population changes, as the percentage of individuals inheriting favorable traits increases An individual cannot evolve, but a population can

14.3 How Do We Know That Evolution Has Occurred?
Evolution is an accepted scientific theory today A scientific theory is a general explanation of important natural phenomena, developed through extensive, reproducible observations

An overwhelming body of evidence supports the theory of evolution Fossils Comparative anatomy (the study of how body structures differ among species) Embryology (the study of developing organisms in the period from fertilization to birth) Biochemistry Genetics

Fossils provide evidence of evolutionary change over time If fossils are remains of species ancestral to modern species, fossils begin with the ancient organism, progress through intermediate stages, and culminate in a modern species

Fossils provide evidence of evolutionary change over time (continued) Several series of fossils have been found that exhibit the evolution of body structures over time These fossil series suggest that new species evolved from, and replaced, previous species One series reveals that modern whales evolved from land-dwelling ancestors

Figure 14-7 The evolution of the whale
Modern whales 40 Millions of years ago Basilosaurus 45 Dorudon Rhodocetus Ambulocetus 50 Pakicetus 44

Comparative anatomy gives evidence of descent with modification Comparing the bodies of organisms of different species can reveal similarities that can be explained only by shared ancestry Comparing the bodies of organisms of different species can reveal differences that could result only from evolutionary change during descent from a common ancestor

Comparative anatomy gives evidence of descent with modification (continued) Homologous structures provide evidence of common ancestry A body structure may be modified by evolution to serve different functions in different species Homologous structures are structures that have the same evolutionary origin despite their current appearance or function

Comparative anatomy gives evidence of descent with modification (continued) Homologous structures provide evidence of common ancestry (continued) Bird and mammalian forelimbs are homologous structures The forelimbs are used for flying, swimming, running, and grasping objects

Comparative anatomy gives evidence of descent with modification (continued) Homologous structures provide evidence of common ancestry (continued) Despite their different uses, they have strong anatomical similarities Such similarity is exactly what we would expect if bird and mammal forelimbs were derived from a common ancestor

Figure14-8 Homologous structures
humerus ulna radius carpals Pterodactyl meta- carpals Dolphin Dog phalanges Human Bird Seal Sheep Bat Shrew FLYING SWIMMING RUNNING GRASPING 49

Comparative anatomy gives evidence of descent with modification (continued) Functionless structures are inherited from ancestors Evolution by natural selection helps explain the curious circumstance of vestigial structures Vestigial structures have no apparent essential function Molar teeth in vampire bats (which live on a diet of blood and, therefore, don’t chew their food) are vestigial structures

Comparative anatomy gives evidence of descent with modification (continued) Pelvic bones in whales and in certain snakes also serve no function in modern species Both vestigial structures are homologous to structures found in and used by other vertebrates Evolutionary theory suggests that as the animals evolved into new habitats, some of their structures that made them less fit were reduced to the point of insignificance

Figure 14-9 Vestigial structures
The bones of a salamander’s hind limb function in support and locomotion Salamander These vestigial bones are similar in structure to those of the salamander but serve no function; all three animals inherited the bones from a common ancestor Baleen whale Boa constrictor 52

Comparative anatomy gives evidence of descent with modification (continued) Some anatomical similarities result from evolution in similar environments Some anatomical similarities do not stem from common ancestry

Comparative anatomy gives evidence of descent with modification (continued) Some anatomical similarities result from evolution in similar environments (continued) Convergent evolution is a process in which natural selection causes non-homologous structures that serve similar functions to resemble one another The similarity of the wings of insects and birds did not arise from evolutionary modification of a structure inherited from an ancestor The similarity arose from parallel modification of two different, non-homologous structures

Comparative anatomy gives evidence of descent with modification (continued) Some anatomical similarities result from evolution in similar environments (continued) Because natural selection favored flight in both birds and insects, they evolved wings of similar appearance

Comparative anatomy gives evidence of descent with modification (continued) Analogous structures are structures that are outwardly similar in appearance, but differ in their evolutionary origin Analogous structures are typically very different in internal anatomy because the parts are not derived from common ancestral structures

Figure 14-10 Analogous structures
Damselfly Swallow 57

Embryological similarity suggests common ancestry Karl von Baer, in the early 1800s, noted that all vertebrate embryos resemble one another in their early development Fish, turtles, chickens, mice, and humans develop a tail and gill slits (gill grooves) during their early embryonic stage Only adult fish retain gills and tail because the genes are active throughout their embryonic development

Figure 14-11 Embryological stages reveal evolutionary relationships
Lemur Pig Human 59

Modern biochemical and genetic analyses reveal relatedness among diverse organisms Modern technology revealed molecular similarities among organisms Biochemical similarities among organisms provide perhaps the most striking evidence of their evolutionary relatedness Relatedness is revealed by homologous molecules

Modern biochemical and genetic analyses reveal relatedness among diverse organisms (continued) DNA sequencing is a powerful tool for revealing molecular homologies The sequence of nucleotides in DNA molecules can be quickly determined

Modern biochemical and genetic analyses reveal relatedness among diverse organisms (continued) The sequences in DNA molecules of one organism can be compared a different organism The gene that encodes the protein cytochrome c is found in all plants and animals and performs the same function in both

Modern biochemical and genetic analyses reveal relatedness among diverse organisms (continued) The biochemical similarities are so fundamental that they extend to all living cells All cells use DNA as the carrier of genetic information All use RNA, ribosomes, and approximately the same genetic code to translate that genetic information into proteins

Modern biochemical and genetic analyses reveal relatedness among diverse organisms (continued) The biochemical similarities are so fundamental that they extend to all living cells (continued) All use roughly the same set of 20 amino acids to build proteins All use ATP as a cellular energy carrier

Figure 14-12 Molecular similarity shows evolutionary relationships
human mouse human mouse human mouse human mouse human mouse human mouse human mouse human mouse 65

14.4 What Is the Evidence That Populations Evolve by Natural Selection?
Controlled breeding modifies organisms Artificial selection is selective breeding of domestic plants and animals to produce specific desirable features Modern dogs are descended from wolves and readily crossbreed today In only a few thousand years, humans artificially selected for all breeds of modern dogs

Figure 14-13 Dog diversity illustrates artificial selection
Gray wolf Diverse dogs 67

Controlled breeding modifies organisms (continued) 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?

Evolution by natural selection occurs today Scientific observation and experimentation provide additional evidence of natural selection Brighter coloration Herbicide and pesticide resistance Experimental introductions of Anolis sagrei lizards

Evolution by natural selection occurs today (continued) Brighter coloration can evolve when fewer predators are present Trinidad guppy experiment Female guppies prefer to mate with brightly colored males; however, brightly colored males are more likely to be eaten by predators

Evolution by natural selection occurs today (continued) Brighter coloration can evolve when fewer predators are present (continued) Trinidad guppy experiment (continued) 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)

Evolution by natural selection occurs today (continued) Brighter coloration can evolve when fewer predators are present (continued) The conclusion was that when fewer predators are present, brighter coloration can evolve

Evolution by natural selection occurs today (continued) Brighter coloration can evolve when fewer predators are present (continued) An experiment confirmed the conclusion Predators were introduced to previously predator-free areas (where males were brightly colored) Within a few generations, male guppies in those areas evolved to become less colorful

Figure 14-14 Guppies evolve to become more colorful in predator-free environments
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Evolution by natural selection occurs today (continued) Natural selection can lead to herbicide and pesticide resistance Natural selection is evident in weed species that have evolved resistance to the herbicides with which we try to control them

Evolution by natural selection occurs today (continued) Natural selection can lead to herbicide and pesticide resistance (continued) Successful agriculture depends on farmers’ ability to kill weeds that compete with crop plants, but glyphosate, active ingredient found in Roundup, can no longer be used The glyphosate inactivates an enzyme essential to plants’ survival

Evolution by natural selection occurs today (continued) Natural selection can lead to herbicide and pesticide resistance (continued) Ragweed survivors of the glyphosate carry a mutation that causes them to produce a tremendous amount of enzyme that glyphosate attacks, more enzyme than glyphosate can destroy

Evolution by natural selection occurs today (continued) Natural selection can lead to herbicide and pesticide resistance (continued) The evolution of glyphosate-resistant superweeds was a direct result of changes in agriculture practice

Evolution by natural selection occurs today (continued) Natural selection can lead to herbicide and pesticide resistance (continued) Just as weeds have evolved to resist herbicides, many of the insects that attack crops have also evolved resistance to the pesticides that farmers use to control them More than 500 species of crop-damaging insects have been documented

Evolution by natural selection occurs today (continued) Natural selection can lead to herbicide and pesticide resistance (continued) Just as weeds have evolved to resist herbicides, many of the insects that attack crops have also evolved resistance to the pesticides that farmers use to control them (continued) Virtually every pesticide has fostered the evolution of resistance in at least one important species

Evolution by natural selection occurs today (continued) Experiments can demonstrate natural selection 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 on the thick branches of these trees

Evolution by natural selection occurs today (continued) Experiments can demonstrate natural selection (continued) After 14 years, comparisons were made between lizards on the Bahamian islands and those of Staniel Cay The original small groups of lizards had given rise to thriving populations of hundreds of individuals Lizards on all 14 Bahamian islands had shorter, thinner legs The lizard populations changed in response to new environments

Evolution by natural selection occurs today (continued) Experiments can demonstrate natural selection (continued) Natural selection appeared to favor individuals with shorter, thinner legs because they were able to move more agilely along the thinner vegetation of their new islands Because they could move more agilely, they were able to escape predators better than their longer-legged ancestors in the new environment

Evolution by natural selection occurs today (continued) Experiments can demonstrate natural selection (continued) Natural selection appeared to favor individuals with shorter, thinner legs because they were able to move more agilely along the thinner vegetation of their new islands (continued) More of the shorter-legged lizards survived to pass their genes for shorter legs on

Figure 14-15 Anole leg size evolves in response to a changed environment
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Evolution by natural selection occurs today (continued) Experiments can demonstrate natural selection (continued) The variations on which natural selection works are produced by chance mutations that arose spontaneously Trinidadian guppies Extra enzyme in giant ragweed plants Shorter legs in Bahamian lizards

Evolution by natural selection occurs today (continued) Experiments can demonstrate natural selection (continued) Natural selection selects for organisms that are best adapted to a particular environment Natural selection does not select for the “best” in any absolute sense, but only for what is best in the context of a particular environment

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