13

Darwin’s Great Idea and Why It Matters

 

James T. Bradley

This essay is written mainly for four groups of people:

1. those who do not know very much about biological evolution but are interested in learning about it;
2. those who have some knowledge about evolution but do not believe it is a good explanation for the origin of the diverse life forms on Earth;
3. those who know about evolution and would like to be able to talk about it more easily with others who either know little about it or are adamantly opposed to it; and
4. those who are presently opposed to the theory of evolution.

In other words, this essay is written for all high school and university students, biology teachers, and naturally curious and communicative persons.

Evolution Literacy 150 Years After Origin of Species

Public knowledge about Darwin’s ideas and modern evolutionary biology is poor. A Gallup poll released in 2009 on the eve of Darwin’s 200th birthday reported that only 39 percent of Americans “believe in the theory of evolution.”[1] Reasons for rejection of Darwinian theory are multifaceted, but two major factors in the United States are: ineffective teaching in public grade schools of the basic principles of biological evolution, and effective teaching in the churches of several Christian denominations of misinformation about evolutionary theory and its implications. These two factors exist in a synergistic relationship fueled by fear.

On the one hand, public school teachers either omit or give cursory classroom attention to evolution for fear of offending or antagonizing students, parents, or school boards who oppose learning or teaching about evolution. On the other hand, clergy and other religious teachers, primarily in conservative Protestant denominations, often use fear of eternal damnation or misinformed statements to discourage their congregants from learning about evolution from those most qualified to teach about it: biologists.

Fear is also at the root of the anti-evolution positions of some churches—fear that accepting biological evolution as a science-based fact will undermine religious faith and the authority of scripture. R. Albert Mohler Jr., president of Southern Baptist Theological Seminary, claimed in a 2005 interview with Time magazine that evangelical Christianity and evolution are incompatible beliefs:

You cannot coherently affirm the Christian-truth claim and the dominant model of evolutionary theory at the same time . . . Personally, I am a young-Earth creationist. I believe the Bible is adequately clear about how God created the world, and that its most natural reading points to a six-day creation that included not just the animal and plant species but the Earth itself.[2]

So there is a vicious cycle. Fears of church leaders beget congregations which beget fears in public school systems which beget students who grow into adults unequipped to challenge the bases of church leaders’ fears. The result is that generations of Americans have a trained incapacity to draw upon principles of evolutionary theory in their professional, civic, and personal lives.

Public, private, and homeschool educators in all disciplines need to do a better job of learning and teaching about biological evolution. High school and university students also bear some responsibility to seek out information about biological evolution beyond what they may have been told in their homes and churches. Students and other citizens of the global village deserve to know what evolution is, what evolution is not, and why knowledge about evolution matters.

What Evolution Is

Evolution is, simply, change over time. We can speak of the evolution of art forms, car and hair styles, and musical instruments like the violin or piano. Biological evolution refers to changes in life forms over time, and these changes are manifestations of changing frequencies of genes in populations over time. That life forms have changed over time—evolved—is a fact. The fossil record is replete with extinct species of plants and animals.

Whether biological evolution occurred is not at issue. The question is: how did evolution occur? Darwin’s answer, natural selection, may not be the complete answer, but it is certainly a very important part of the answer, perhaps the major part. Evolution by natural selection occurs due to three facts of life:

(1) Living things produce more offspring than the environment can support. In other words, organisms’ reproductive potentials exceed the carrying capacity of the environment.

(2) Inherited variations exist among the individuals of breeding populations. For example, in a population of robins, some birds may be better at hearing worms in the soil, have a brighter orange color to their breasts, build nests faster and sturdier, or sing louder than others.

(3) On average, individuals with physical, physiological, or behavioral traits that give them a reproductive advantage over others leave more offspring in the next generation. This phenomenon is natural selection. Since offspring carry their parents’ genes, the frequency of genes for adaptive traits increases in a population. If an environmental change makes different traits more adaptive than those predominating before the environmental change, the genes for those different traits will be selected for, and their frequency will increase in the population. Darwin did not know about genes, but he did know that offspring somehow inherit traits from their parents.

Darwin’s great insight was that over immense stretches of time, natural selection can give rise to new species of plants and animals. Emergence of new species from preexisting species is called speciation. Several natural processes can lead to speciation. All involve the reproductive isolation of a subpopulation of breeding individuals from the main population. One way reproductive isolation can occur is by geographical isolation of a subpopulation from its parent population. As depicted in Figure 13.1, this may happen when geological forces create a mountain range, splitting an existing population into two subpopulations, one on each side of the mountain range. Different climates and biological communities exist on opposite sides of a mountain range. For example, the Cascade Mountains in the Pacific Northwest create a rain shadow that results in a desert on the eastern side and lush woodlands on the western side. Exposed to different environments on either side of the mountain range, subpopulations of plants and animals experience different pressures from natural selection and accumulate different adaptive traits. Now imagine glaciations that wear a pass through the mountains, allowing individuals in the previously isolated subpopulations to intermingle. If one or more of their differing adaptive traits makes it impossible for individuals from the two subpopulations to interbreed, speciation will have occurred.

 

 

Figure 13.1 - Depiction of speciation due to geographical isolation. Individual variants in populations are represented by circles, triangles, and asterisks. (A) A population of individuals belonging to the same species lives in a forest where circles are better adapted than triangles and asterisks, so they contribute more offspring to succeeding generations. (B) A mountain range rises and separates the original population into two geographically isolated populations. On the west side of the range, a forest environment remains and circles still predominate; on the east side of the range, a rain shadow causes a desert environment where asterisks are better adapted and come to predominate. (C) Much later, glaciers erode a pass through the mountain range, allowing organisms on each side of the range to mingle; but by now natural selection has produced enough other changes (physiological, behavioral, physical) that the two populations can no longer interbreed. Speciation has occurred.

 

Sometimes subpopulations of individuals from one species become isolated on different islands and give rise to different species. This is what Darwin correctly surmised to have happened with the finches and tortoises on the Galapagos Islands. Modern-day biologists have also documented rapid speciation among fruit flies on the Hawaiian islands and fish in large freshwater lakes such as Lake Victoria in east Africa and Lake Apoyo in Nicaragua.[3]

Darwin recognized that traits distinguishing individuals from each other are inherited, but he had no idea how inheritance happened. Modern genetics and molecular biology have solved that mystery. We now understand the sources of genetic variation upon which natural selection acts. These sources include mutations in the bases of DNA and a shuffling of gene segments that creates new genes with new functions overnight. However, the greatest source of genetic variation is the random recombination and mixing of genes that happens during sexual reproduction. Although gene variants arise largely by chance in a population, we will see below that the paths taken by evolution are not random.

Evolution Is Not “Just” a Theory

Saying that evolution is “just” a theory suggests that evolution is a guess or a hypothesis about how Earth’s diverse array of living things came to be. This is a misuse of what scientists mean by the word theory.

Scientific theories are about the closest that science can come to factual explanations for natural phenomena. Science progresses by examining the validity of hypotheses via empirical tests and/or observation of nature. The more predictions from a hypothesis that are borne out by experimentation or observation, the surer one can be that the hypothesis is correct. When many different predictions based on a particular hypothesis are tested and retested over a long period of time and shown to be accurate, a hypothesis may be elevated to the level of scientific theory. This process of testing and retesting has given rise to several well-known theories:

• the heliocentric theory for the solar system—the Earth and other planets orbit the sun;
• the germ theory for disease—infectious diseases are caused by small vectors like bacteria and viruses; and
• the atomic theory for matter—matter is composed of atoms, e.g. H2O being comprised of hydrogen and oxygen atoms.

The theory of evolution (that all life forms on Earth arose from ancestral life forms) is just as certain as the heliocentric, germ, and atomic theories. This is not to say that scientists know completely and exactly how evolution occurs. For example, biologists continuously argue over which sources of genetic variation are most important for evolution and over the relative importance of natural selection, sexual selection (see Chapter 5), and genetic drift in evolution. But the reality of evolution itself having occurred is not controversial among biologists.

Macroevolution Does Not Contradict Darwin

Overwhelming evidence, now bolstered by DNA sequencing data, supports evolutionary biology’s claim that all living things share a common ancestry. Yet the outward appearance of organisms, especially to persons not trained in biology, can make this claim difficult to fathom. For example, evolution’s evidence shows that fish gave rise to amphibians, which gave rise to reptiles, which gave rise to birds and mammals. Our feathered, flying friends using the birdbath look so different from the turtle leisurely crossing the road or the squirrel perched on the bird feeder that it is hard to imagine all three sharing a common ancestor. Yet they do. On the one hand, the changes that occurred above the species level for an ancestral group of organisms like reptiles to give rise to a very different-appearing group such as mammals is sometimes called macroevolution. Microevolution, on the other hand, refers to very small-scale genetic changes that can produce different gene frequencies within subgroups of a population (e.g., for human stature or hair color) or, over time, groups of closely related species (e.g., the several species of fruit flies on the Hawaiian Islands).

Biologist colleagues that I know personally do not use the term macroevolution, although most evolution textbooks have a section on it.[4] There is no doubt among evolutionary biologists that Darwin’s theory of evolution by natural selection accounts for macroevolution. But some controversy does exist over the rate of macroevolutionary changes and the details of the process. Most biologists view macroevolution as microevolution spread out over immense time spans. When relatively rapid and dramatic evolutionary changes are seen in the fossil record, they may be explained by changes in the patterns of activity of genes that control embryonic growth and development. For example, changes in the onset and duration of cell divisions in certain regions of an embryo can result in gross alterations in the morphology of the adult form. Also, changes in just one or a very few genes can alter the placement, size, and/or identity of body appendages. Not all biologists agree on the relative importance of small, stepwise microevolutionary events and more rapid evolutionary changes due to genetic variations that act upon early, embryonic development. But biologists overwhelmingly agree that evolution via natural selection and a few other natural processes sufficiently explain the wondrous diversity of plant and animal life in Earth’s biosphere.

Some people who do not accept biological evolution as the source of life’s many forms believe that the dramatic, visible differences between different groups of plants and animals (e.g., moss versus redwood trees, fish versus mammals, etc.) cannot be explained by the theory of evolution. They may accept microevolution as the process whereby the various and sundry breeds of dogs arose from a wolf-like ancestor, but they deny that macroevolution could have occurred.

If macroevolution is real, they ask, why have no new phyla or classes of animals recently appeared on Earth? It is true: no new phyla or classes of plants or animals have appeared on Earth since long before humans were around. But evolutionary theory does not predict that this should happen. In fact, it predicts just the opposite.

The tree of life has many large boughs (phyla), many sizeable branches (classes), and millions of tiny twigs (species). As one evolutionary biologist points out, asking why no new phyla have recently appeared on Earth is like asking why no new boughs have recently sprouted from the twigs in the upper reaches of an oak tree in your backyard.[5] Various phyla of plants and animals diverged from ancestral life forms hundreds of millions of years ago. Since then, branches with countless twigs grew from those ancient phylogenetic boughs. Many twigs and branches, and even a few boughs, stopped growing and became extinct. But the descendants of some boughs persist into the present as members of today’s rich and diverse microbial, botanical, and zoological worlds.

So evolutionary theory cannot predict macroevolution, in the sense of major new groups of plants or animals suddenly appearing. Instead, it predicts that the fossil record should document the sequential appearance of major groups of living things, generally from simplest to more complex. And this is exactly what is seen: first, single-celled life, then multi-celled invertebrates, and, finally, vertebrates; likewise, within the vertebrates, first came fish, then amphibians, dinosaurs, mammals, and birds.

Transitional Fossil Forms Are Not Lacking

Evolution by gradual changes over time predicts that transitional forms of life should appear in the fossil record. For example, if birds emerged from dinosaurs, there should once have been dinosaur-like animals with wings, and if fish gave rise to four-legged land animals, there should have been fish-like creatures with leg-like appendages. Remarkably, many detractors of evolutionary theory claim that transitional forms are absent from the fossil record, but this is simply not true. The fossil record contains many transitional forms, and modern DNA analyses are revealing more and more about the evolutionary relationships between groups of living organisms.

Whale evolution is a fine example of how fossils and DNA analyses tell us about the transitional forms that led to a modern-day group of animals. Whales are mammals whose ancestors lived on land. Many fossils from the first 10 million years of whale evolution are from aquatic creatures that still had limbs like those of terrestrial mammals. DNA analyses show that whales are closely related to even-toed ungulates (cows, sheep, pigs, and hippos), and a raccoon-sized, terrestrial, fossil ungulate with several whale-like characteristics was described in 2007.[6] A second example of transitional forms is in the evolution of birds from feathered dinosaurs living about 160 million years ago. The famous winged dinosaur-like bird, Archaeopteryx, was discovered in Bavaria in 1861. In 2009, scientists unearthed a chicken-sized fossil of a four-winged, feathered dinosaur in northern China which apparently used its four feathered appendages for gliding.[7] As a third example, consider the movement of fish-like creatures onto land. Paleontologists have discovered many transitional forms between fish and four-legged land creatures. One dramatic 2004 find was in northern Canada. Tiktaalik, a fossil predatory “fish” with leg-like fins, a flexible neck, and a skull resembling that of a salamander, lived 375 million years ago. It was three feet long and had weight-supporting forelimbs that could bend at the elbow.[8]

Biological Evolution Is Not a Random Process

Genetic variants arise randomly in populations, but natural selection is not random. Pressures exerted by natural selection are directional. If hard-shelled nuts become the main food source for a population of finches, natural selection will produce a preponderance of birds with strong, sturdy beaks good at cracking the nut shells, not dainty, slender beaks better at sipping nectar from flowers. Natural selection is simply the preferential reproduction of individuals with traits best suited for keeping them healthy and alive long enough to successfully reproduce. The name of the game is reproduction, and reproductive fitness is not necessarily the same as physical strength. A big, strong, male duck with aberrant courtship behavior will probably not pass its genes into the next generation of ducks, and the same goes for humans. Evolution moves in the direction of increased reproductive fitness.

No Contradiction of the 2nd Law of Thermodynamics

Some anti-evolutionists invoke the 2nd law of thermodynamics to bolster their belief that Earth’s diverse species do not share a common ancestry. They say that evolutionary theory contradicts the 2nd law of thermodynamics and therefore cannot be true. Their claim is based on misunderstanding or misrepresentation of both thermodynamics and evolution. Their mistaken notion about thermodynamics is that highly ordered entities cannot arise from less-ordered systems. And their mistaken notion about evolution is that random genetic variation cannot give rise to increasingly ordered and complex organisms over time without violating laws of nature.

Let’s examine both notions.

Thermodynamics is the study of heat and other forms of energy. Specifically, it deals with transformations between different kinds of energy, as when chemical energy in gasoline is transformed into the kinetic energy of a moving car. Two laws about energy and the universe discovered in the 19th century are relevant to this discussion. The 1st law of thermodynamics states that energy can neither be created nor destroyed; in other words, the total energy content of the universe remains constant. The 2nd law of thermodynamics states that every energy transformation occurs so as to result in an increased randomness or disarray in the universe (or in a closed system). I’ve italicized in the universe because this is what is usually forgotten about in arguments that claim contradiction between evolution and the 2nd law.

Energy comes in many different forms including kinetic, electrical, nuclear, chemical, matter itself, potential, and heat. The first law means that when one form of energy, such as the kinetic energy in falling water, is transformed into other kinds of energy, such as electrical energy and heat via a turbine at the base of a waterfall, there is no energy lost in the process. However, since heat energy is unusable for performing work, there is a loss of energy useful for driving processes that create order ranging from cell growth to the building of a cathedral. In this example, the amount of electrical energy produced by the turbine will always be less than the kinetic energy of the falling water since some of the water’s kinetic energy is transformed into heat energy. This loss of usable energy is happening all over the universe all of the time—as stars burn, as galaxies rotate, and as plants and animals reproduce, grow, and die. The constant loss of usable energy translates into an increased disarray of the universe as a whole. Another word for disarray is entropy. So another way of stating the second law is to say that the entropy of the universe is constantly increasing. The only way this could be avoided is if new energy were constantly being added to the universe. But due to the 1st law, this does not happen.

Now, what is crucial to note is that just because the universe is constantly becoming more disorganized, it does not mean that increasing organization cannot occur at various sites throughout the universe. In fact, we see this happening all around us. Water molecules in snowflakes are more organized than in the vapor from which snowflakes crystallize. Michelangelo carved his exquisite David from a crude block of marble, single fertilized egg cells develop into organisms with complex tissues and organ systems, Mustangs and Ferraris are constructed from tiny particles of iron from inside rocks of iron ore, and beautiful buildings are assembled from bricks made from clay in the soil. You get the idea. And evolution is no exception. In Darwin’s words, “. . . from so simple a beginning endless forms most wonderful and beautiful have been, and are being evolved.”

How can this happen? How can order arise from disorder and not violate the 2nd law of thermodynamics? The answer is that these examples—snowflakes, works of art, developing embryos, cars, buildings under construction, and evolution—are not closed systems. They are open systems, systems that receive an input of energy from outside them that more than compensates for the usable energy lost as heat.

Consider Michelangelo and his block of marble. For months he hammered and chiseled away at the marble, gradually revealing the David within. This hammering and chiseling required lots of energy. Chemical energy in Michelangelo’s arm muscles was converted into kinetic energy in a swinging hammer. The chemical energy in his muscle cells came from the breakdown of highly organized food molecules like starch in bread and pasta and animal proteins in sausage and fish. Energy stored in the molecular order of starch and proteins ultimately came from radiant energy of the sun used by green plants for photosynthesis. Recall that photosynthesis uses light energy to assemble simple water and carbon dioxide molecules into highly organized molecules of complex carbohydrates. At each step between photosynthesis and Michelangelo’s swinging hammer, some usable energy was lost as heat. But thanks to the sun and to the fact that Michelangelo continued eating, the David was completed. All of this happened at the expense of order in the universe.

If you add up all of the disorder created by Michelangelo digesting highly organized food molecules and compare that with the order created from the block of marble, the disorder would be greater. Not only the David, but life itself, exists at the expense of order in the universe. For the growth, building, and evolution of complex things here on Earth, the necessary input of energy ultimately comes from the sun.

Now what about evolution? Persons who believe that random genetic variation cannot lead to increased complexity fail to recognize the ratchet-like action of natural selection. Once a random genetic event gives an organism a reproductive advantage, natural selection preserves and amplifies that genetic variant. Succeeding variations add to preexisting ones, with natural selection ratcheting up the fitness and complexity of individuals in a population all the while.

Combining this view of natural selection with the 2nd law of thermodynamics, we see how evolution operates within the bounds of physical law. Natural selection constantly eliminates organisms less genetically adapted for successful reproduction. The eliminated die without reproducing, and their highly organized cells ultimately decompose back into water, carbon dioxide, nitrogen, and a few elemental minerals. Of course, the same fate awaits the winners of life’s competition, but not until their genes move into the next generation.

Without the sun to provide the energy needed for the growth and development of the many variants upon which natural selection acts, evolution would come to a screeching halt. But the sun does exist! And natural selection does its winnowing, without violating any laws of thermodynamics. All the while, the entropy in the universe continues to increase even as biological complexity on Earth, and perhaps at other sites in the universe, also increases. Evolution, like the sculpting of David, occurred without contradicting the 2nd law of thermodynamics.

Misunderstandings about Apes and Human Evolution

Some disbelievers in human evolution cite as evidence for their position the fact that no gorilla, gibbon, chimpanzee, or orangutan has ever birthed a human being. This is certainly true. But evolutionary theory does not claim that this ever happened or ever will happen. What evolutionary theory claims, and what the fossil record and DNA analyses show to be true, is that members of the great ape family (Hominidae) and other primates share common ancestors (see Figure 13.2). Hominids include Homo sapiens, the other four great ape groups named above, and numerous extinct species. So you and I and our parents are all apes. Our closest living, nonhuman relative is the chimpanzee. The common ancestor for humans and chimps lived about six million years ago and was neither a chimpanzee nor a human being. It was a species of the Hominidae; that is, it was an ape species which is now extinct.

 

 

Figure 13.2 - Higher primate phylogenetic tree showing that chimpanzees are more closely related to us than other living primates, and that the now extinct Neanderthals coexisted with us for a while and were closely related to us.

 

Another misunderstanding about apes and human evolution is the notion of a “missing link.” Persons doubting that Darwinian evolution applies to humans often ask, “Where is the missing link?” By missing link, evolution’s doubters usually mean an undiscovered, fossilized being with physical characteristics midway between apes and modern humans. Evolutionary biology has three responses to the missing link question:

(1) Modern humans are apes.

(2) Evolutionary theory does not claim that there ever was an animal that was half modern gorilla or chimpanzee and half modern human, only that humans and nonhuman apes had a common ancestor different from any modern forms of apes.

(3) The human ancestral tree has a multitude of well-documented members, several of which Shawn Jacobsen describes in Chapter 6. Fossilized skeletons of hundreds of humankind’s extinct, bipedal cousins, many from Africa, span a period from Ardi (Ardipithecus ramidus) 4.4 million years ago[9] up to the cave artists of Spain and France who began painting just 32,000 years ago.

Atheism or Rejection of Scripture Not Required

Many persons who accept biological evolution as an established fact also believe in the existence of a supernatural being and use sacred scripture as a moral guide for living. Both scientists and clergypersons have written about the compatibility of evolution and religious belief. Evolutionary biologist, biology textbook author, and professed Christian Kenneth Miller writes elegantly and lucidly about reason and faith in his 1999 book, Finding Darwin’s God: A Scientist’s Search for Common Ground Between God and Evolution. National Institutes of Health director and former leader of the publicly funded Human Genome Project, Francis Collins, does similarly in his 2006 book, The Language of God: A Scientist Presents Evidence for Belief. And theoretical atomic physicist and Anglican priest John Polkinghorne writes about a compatible relationship between faith and science in his 1998 book, Belief in God in an Age of Science.

Most mainline denomonations have official statements about evolution. For example, a 1969 “Evolution Statement” by the Presbyterian Church (USA) reads in part:

. . . Nowhere is the process by which God made, created or formed man set out in scientific terms. A description of this process in its physical aspects is a matter of natural science. The Bible is not a book of science . . .”[10]

The governing body of the United Methodist Church passed three evolution-friendly petitions in 2008, and one of these specifically opposes the introduction of faith-based views such as creationism and intelligent design into the science curriculum of public schools.[11]

The position of the Roman Catholic Church on biological evolution is more difficult to pin down. The Vatican seems comfortable leaving the evolutionary development of physical entities, including human beings, to science so long as the human soul remains under the purview of God.[12] Finally, the Clergy Letter Project, an open letter signed by more than 12,000 Christian clergy in the Unites States, states: “Religious truth is of a different order from scientific truth. Its purpose is not to convey scientific information but to transform hearts.” On evolution, the Clergy Letter reads: “We believe that the theory of evolution is a foundational scientific truth, one that has stood up to rigorous scrutiny and upon which much of human knowledge and achievement rests. To reject this truth or to treat it as ‘one theory among others’ is to deliberately embrace scientific ignorance and transmit such ignorance to our children.”[13]

Testimonies from the above theistic scientists and many others and statements from clergy from diverse faiths provide strong evidence that reasonable minds find compatibility between the findings of science and religious faith. Acceptance of the theory of evolution requires neither atheism nor rejection of the wisdom found in sacred scripture.

Why Knowledge about Evolution Matters

Denying Darwin creates evolution illiteracy. The results of Darwin denial are the same whether the denial results from actively avoiding learning, or allowing others to learn, about biological evolution; grows from the deliberate misrepresentation of evolution; or stems passively from lack of knowledge. Regardless of its source, Darwin denial in the United States has reached the point where it threatens the country’s leadership in science, imperils the planet’s ecosystems, handicaps future biomedical research, undermines the positive roles of religion in society, and fetters the human spirit.

“Nothing in biology makes sense except in the light of evolution.” Biologist Theodosius Dobzhansky used this declaration as the title for his article written for biology teachers in 1973. The statement is as true today as it was then. Principles of biological evolution are foundational for every subdiscipline of biological science. Anatomy, biochemistry, plant and animal physiology, population biology, plant and animal ecology, cell biology, genomics, microbiology, neurobiology, nutrition, entomology, botany, ethnology, proteomics, genetics, molecular biology, parasitology, protozoology, marine biology, ornithology, mammalogy, and herpetology are all intimately integrated due to evolution. Discoveries in one subdiscipline guide research leading to new discoveries in other disciplines because plants, animals, and microbes have all coevolved. The DNA, biochemistry, physiology, behavior, and anatomy within individual organisms are also intimately integrated due to their coevolution.

An orchid and a moth provide a fantastic example of a prediction based on coevolution. Noting a pool of nectar deep inside the blossom of an orchid nearly a foot from the flower’s opening, Darwin predicted the existence of a yet undiscovered moth with a proboscis long enough to reach the nectar and pollinate the plant. Sure enough, a half century later, a hawk moth with a proboscis long enough to do the job was discovered living in the same region of Madagascar as the orchid. The bottom line is that all of biology makes sense in the context of evolution, and anybody doing biological research without taking into account the evolutionary history of his or her objects of study is severely handicapped.

Modern Medicine Depends upon Evolution Theory

From the development of new drugs and surgical procedures to the annual development of flu vaccines, evolutionary principles guide biomedical research. Animals used in biomedical research have physiologies and biochemistries similar to that of humans. The reason mice and monkeys, rather than jellyfish and clams, are used by biomedical researchers is that they are closer to us on the evolutionary tree of life and therefore more likely to respond like humans to various drugs and procedures.

Evolution is why new flu vaccines must be grown each year. Flu-causing viruses do not stand still. As they reproduce inside host organisms, they rapidly evolve. After just one year our immune system cannot even recognize them as descendants of the bug that made us sick (or that we were immunized against) during the last flu season. The human immunodeficiency virus (HIV) that causes AIDS is another disease agent that evolves so rapidly that researchers have been stymied in their attempts to develop an effective vaccine against it. Bacteria that cause diseases like tuberculosis also evolve. They are especially good at evolving to become resistant to antibiotics we throw at them. The over-prescription and over-use of antibiotics is unwise because it gives bacteria the opportunity to evolve into resistant strains. The less prevalent antibiotics are in the environment and in our bodies, the more effective they will be in killing disease-causing bacteria when called upon to do so. Successful biomedical research for the cure and prevention of disease depends upon the understanding of the principles of biological evolution. The new field of evolutionary medicine is rapidly gaining momentum with journals, books, and medical school programs devoted to burgeoning medical applications of evolutionary biology.[14]

Environmental Protection Needs Evolution Theory

The lives of plants, animals, and microbes are interdependent within their communities and ecosystems. When human “progress” endangers or destroys just a single species of predator, prey, scavenger, decomposer (worms and microbes that recycle nutrients in dead plants and animals), pollinator, or photosynthetic producer, balance within the ecosystem is imperiled and the whole living pyramid may disintegrate. The interdependency living things have among each other and with particular physical environments, such as climate and nutrient availability, is a product of evolution. Understanding the principles of evolution helps us to determine when a population of plants or animals is so low that its continued existence and the health of the ecosystem are endangered. Principles of evolution also teach us about our own dependencies upon other living things and the physical environment. In fact, how well we understand and respect evolutionary principles may ultimately determine how long our species survives on the planet.

Biotechnology Needs Evolutionary Biology

Ten thousand years ago humans began changing the genetic make-up of plants and animals. Early agriculturalists unknowingly used principles of evolution by natural selection to domesticate wheat. Year after year they replanted the grain that they harvested the season before. In so doing, they selected seed stock for plants with grain heads able to hold on to their seeds rather than letting them fly away into the wind. Before long, humans were selectively breeding plant and animal variants to obtain offspring better able to meet human needs. We still use these slow and laborious methods to obtain new and better agricultural plants and animals. But since the 1980s humans also have been able to leapfrog over the slow steps of evolution by human selection and directly manipulate the DNA of virtually any organism on Earth.

Genetic engineering has produced corn plants with bacterial genes that make them insect-resistant, bean plants with a daffodil gene that makes them herbicide-resistant, and bacteria that produce human insulin and growth hormone. In 2009 researchers created designer bacteria that produce lycopene, an antioxidant in tomatoes that promotes heart health. Employing principles of biological evolution, the researchers selected and grew variants of the lycopene-producing bacteria that were most efficient at producing lycopene.[15] Genetic engineers, in collaboration with electrical and computer science engineers, have spawned a new discipline called synbio (synthetic biology). Synbio aims to create brand new forms of life, perhaps even multicelled organisms, to perform specific tasks. One can imagine many good results that could come from synbio technology, including cleaning toxic waste dumps, removing greenhouse gasses from the atmosphere, producing new food and energy sources, and fighting diseases in new and creative ways. But genetic engineering and synbio, done in the absence of knowledge about evolution and ecology, could also cause great harm to the planet.

The wisdom of natural selection acting over four billion years has produced our present biosphere with its countless and exquisitely balanced interdependent components. What wisdom will guide the introduction of new life forms, completely foreign to anything the Earth has ever seen, into the biosphere? If it is the “wisdom” of the marketplace and the “wisdom” of human desire for comfort and entertainment, rather than a deep understanding of principles of ecology and biological evolution, the outcome for evolution’s splendid array of living things may be disastrous. Foreign, human-designed organisms could out-compete some of nature’s life forms and send entire ecosystems out of balance. Ethicists Joachim Boldt and Oliver Müller write that “seen from the perspective of synthetic biology, nature is a blank space to be filled with whatever we wish.”[16] Nature could easily become a blank space to be filled with our own clever constructions rather than a space already occupied with organisms to be appreciated, understood, and preserved. Effective environmental preservation depends upon knowledge about biological evolution.

“Equal Time” Undermines Both Science and Religion

Attempts to mandate Bible-based creationist views, or the more subtly veiled religion-based intelligent design views, of the origin of species to be taught alongside biological evolution in U.S. public school science classrooms have gone to court many times.[17] At issue is whether teaching creationism or intelligent design as credible alternatives to evolutionary theory violates the First Amendment of the U.S. Constitution, which prohibits laws respecting an establishment of religion. Two well-known federal court cases are McLean v. Arkansas Board of Education (1982) and Kitzmiller et al. v. Dover (2005). In the former, the court ruled that an Arkansas statute requiring public schools to give balanced treatment to “creation-science” and evolution-science violated the Establishment Clause of the First Amendment. In the latter case, U.S. District Court Judge John E. Jones III ruled similarly for the teaching of intelligent design in the Dover (Pennsylvania) Area School District.

When parents opt for private schooling or home schooling to shield children from the theory of evolution, or to teach religion-based accounts of creation as though they were science-based alternatives to evolutionary theory, they undermine children’s comprehension of what science is and fetter later careers in science. Confusion and conflation of two very different ways of knowing—knowing through revelation and symbolic language versus knowing through the self-correcting, hypothetico-deductive method of science—hampers students’ development in both realms of knowledge.

Denial Undermines Positive Influences of Religion

When a child’s religious training teaches that evolutionary theory lacks good scientific evidence and rigor, that evolution is an atheistic scheme to destroy belief in God, that believing in evolution precludes religious faith, that the Earth is only a few thousand years old, or that a literal reading of sacred scripture is a reliable account of how the physical universe actually came into being, the stage is set for a great disillusionment with religion down the road. For when that child begins reading and thinking for himself, gets out into the world and converses with honest and intelligent persons of different educational backgrounds, or takes a good biology course in high school or at the university, he will discover that what he was taught earlier about evolution and scripture is untrue. Any one of a multitude of discoveries about the world around him could jeopardize all of the religious teachings he received as a child. For example, learning the true meaning of the term scientific theory, how geologists date the Earth at 4.6 billion years, about Tiktaalik, feathered dinosaurs, or extinct species of the genus Homo, meeting a religious evolutionary biologist, or realizing that the two accounts of creation in the Bible’s Book of Genesis are mutually exclusive may create a crisis of faith. The result may be to discard religion as deceptive and unworthy of further attention. But religion can nurture courage and hope, kindness and compassion, cooperation and fellowship, and the ability to envision peace during times of war. To jeopardize these and other virtues of religion by railing dogmatically against evolution does violence against the future personal lives of children and society as a whole.

Galileo cited Cardinal Baronius (1598) when in 1615 he wrote to his friend, the Grand Duchess Christina of Tuscany, that scripture teaches “how to go to heaven, not how the heavens go.”[18] Galileo was writing about the conflict between his new telescopic discoveries and the Roman Catholic Church’s insistence that Aristotle’s Earth-centered universe was correct because it agreed with literal readings of scripture. In 1633 Galileo was arrested by the Holy Office of the Inquisition and convicted of teaching that the Earth orbits the sun. Nearly 350 years later, the Church officially forgave Galileo. Perhaps those who teach that evolution has not and does not occur can learn from this episode in the history of Christianity and consider the possibility that scripture teaches us how to live life, not how life came to be.

Pitfalls of Shielding Children from Knowledge

From anatomy and physiology to behavior, humans share many characteristics with other animals. But humans are unique in their abilities to devise language, use speech to communicate abstract concepts, and engage in the reasoning that produces nuclear power plants, modern biotechnologies, and books about moral philosophy. Normal brain development produces children who are curious about themselves and the rest of the universe. Human curiosity, in partnership with reason, education, and communication, fuels humankind’s cultural advancements in art, science, technology, and social living in the global community. Purposefully denying students the opportunity to learn what science has to say about the interrelatedness of all components of the biological world, confusing them about the nature of science, and discouraging their questions or skepticism about dogmatic teachings are hostile to the human spirit. Each of these hindrances to normal human development is especially egregious when carried out by persons who themselves have not made the effort to learn what evolutionary theory actually is, and what it is not.

Plato’s Cave and Learning about Biological Evolution

Consider now a simple exercise to aid students and teachers in discussing evolution in the classroom and to help anybody learn or teach about evolution. Plato (428/427–348/347 BCE) can help us, not because he knew about biological evolution, but because he knew about human nature. In Book VII of Plato’s Republic, Socrates famously describes what can happen to any of us when challenged by new ideas or when introducing others to new ideas.[19] Allow me to paraphrase and take some liberty in interpreting Plato’s Allegory of the Cave for the advantage of students and teachers of evolution.

One sunny day, a person enters a cave to find inside a group of “prisoners” tied in chairs facing one wall of the cave. They cannot even turn their heads from side to side and have spent their entire lives like this. Moving before them on the wall of the cave are dark, indistinct images of animals, people, and implements of all kinds. The intruder examines the situation and discovers a line of puppets and other objects hanging from a stone ledge behind the prisoners; behind the puppets burns a fire whose light is interrupted by the puppets before it illuminates the wall facing the prisoners. So, for the prisoners’ entire lives, reality has been the shadows cast by puppets. Recognizing a teachable moment, the intruder unties one of the prisoners, shows her the puppets and the fire, and then leads her up out of the cave into the sunlight. Entrance into the above-ground world of sunlight is painful to her eyes. But after some time, the former prisoner adapts to the light and soaks up the wonders and beauty of the sunlit world. Anxious to tell her cave-bound family members and friends what she has discovered, she returns to the cave. But to her surprise and dismay, her words are met with hostility and ridicule. Her family and friends believe she has lost her mind.

The pain we experience when moving from a dark place into the sunlight, and the hostility we receive from those living in darkness are risks of education. Pain and hostility are normal responses to new ideas that upset our previous world views. Caves are comfortable. They are neither too hot nor too cold; they remain predictably about the same all of the time. Each of us has some personal caves in which we live or to which we retreat. When new information makes us feel uncomfortable or angry, it may be revealing a personal cave to us. Our job then is two-fold: to decide whether our cave is based on something negative such as fear, prejudice, or ignorance; and to decide whether we will risk leaving the comfort of the cave to move toward the light of reason and education.

Since discovering Plato’s Allegory of the Cave 25 years ago, I have used it regularly and successfully in university biology courses to aid in teaching and learning about controversial topics, including human cloning, human embryonic stem cell research, scientific origin of life studies, and biological evolution. Students who have read or heard Plato’s cave allegory report feeling more open-minded and willing to challenge themselves with new ideas. Finally, it is as important for teachers to acknowledge that they have their personal caves as it is for them to encourage students to identify their own caves and begin stepping out of them.

Acknowledgment

Designer and photographer Janna Claire Sidwell created the illustrations for this chapter.

Notes

1 - Gallup. On Darwin’s Birthday, Only 4 in 10 believe in Evolution. http://www.gallup.com/poll/114544/darwin-birthday-believe-evolution.aspx.

2 - Time. Can You Believe in God and Evolution. http://www.time.com/time/magazine/article/0,9171,1090921-1,00.html.

3 - Brown University. Case Histories of Speciation I&II. http://biomed.brown.edu/Courses/BIO48/23.Cases.html.

4 - Barluenga, M., et al. 2006. “Sympatric Speciation in Nicaraguan Crater Lake Cichlid Fish.” Nature 439: 719–23; Carson, H.L., 1982. “Evolution of Drosophila on the Newer Hawaiian Volcanoes.” Heredity 48: 1–25; Witte, F., et al., 2008. “Major Morphological Changes in a Lake Victoria Cichlid Fish within Two Decades.” Biological Journal of the Linnean Society 94: 41–52. An excellent, short description of examples of speciation written by a biology professor for his evolutionary biology course at Brown University uses these sources.

5 - Ridley, M. 1996. Macroevolutionary Change. In Evolution, 2nd ed. Cambridge: Blackwell Science, Inc., 582–609.

6 - Dawkins, R., 1996. The “Alabama Insert:” A Study in Ignorance and Dishonesty. In Charles Darwin: A Celebration of his Life and Legacy. Montgomery: NewSouth Books.

7 - Gee, H., et al. 2009. Land-Living Ancestors of Whales. 15 Evolutionary Gems. http://www.sesbe.org/sites/sesbe.org/files/file/EVOLUTIONARY_GEMS.pdf.

8 - Reuters. 2009. China Finds Bird-Like Dinosaur with Four Wings. http://www.reuters.com/article/idUSTRE58R1ST20090928.

9 - University of Chicago. Meet Tiktaalik roseae: An Extraordinary Fossil Fish. http://tiktaalik.uchicago.edu/meetTik.html; Gee, H., et al. 2009. From Water to Land. 15 Evolutionary Gems. http://www.sesbe.org/sites/sesbe.org/files/file/EVOLUTIONARY_GEMS.pdf; Gibbons, A. 2009. “Breakthrough of the Year: Ardipithecus ramidus.” Science 326: 1598–9.

10 - Presbyterian Church USA. Theology and Worship; Evolution Statement. http://www.pcusa.org/theologyandworship/science/evolution.htm.

11 - United Methodist Portal. Methodism Supports Teaching of Evolution. http://www.umportal.org/article.asp?id=3869.

12 - Catholic Answers. Adam, Eve, and Evolution. http://www.catholic.com/library/Adam_Eve_and_Evolution.asp.

13 - Clergy Letter Project. Statement on Evolution. http://www.clergyletterproject.net/.

14 - Pennisi, E. 2009. “Darwin Applies to Medical School.” Science 324: 162–3.

15 - Wang, H., et al. 2009. “Programming Cells by Multiplex Genome Engineering and Accelerated Evolution.” Nature 460: 894–8.

16 - Boldt, J. and O. Müller. 2008. “Newtons of the Leaves of Grass.” Nature Biotechnology 26: 387–8. The authors argue for an extended dialogue among synthetic biologists to develop a code of ethics for their discipline that reflects an understanding of how synbio activities impact society and nature as a whole.

17 - Matsumura, M. and L. Mead. 2007. Ten Major Court Cases about Evolution and Creationism. National Center for Science Education. http://ncse.com/taking-action/ten-major-court-cases-evolution-creationism.

18 - Galilei, G., 1615. Letter to the Grand Duchess Christina of Tuscany. In Discoveries and Opinions of Galileo. New York: Random House, Inc, 1957.

19 - Plato. ca. 380BC. The Collected Dialogues, Republic Book VII. eds. E. Hamilton and H. Cairns. Princeton: Princeton University Press, 1989, 514–18.

Discussion Questions

1. How would you rate your knowledge about biological evolution?
2. Did you learn about evolution in high school? If so, do you believe your teacher(s) were well qualified to teach it? If not, why do you believe evolution was not taught in your high school?
3. Most students likely to become biomedical researchers, genetic engineers, or synbio technicians are not required to study evolution or ecology in their university curricula. Do you think this situation is all right?
4. Do you believe that students in all majors at the university ought to receive some formal training in evolution? Why or why not?
5. If you belong to or attend a church, do you know what your church’s position on evolution is? If so, do you agree with it?
6. Have your views/feelings about biological evolution evolved during your life? If so, how?
7. Do you agree with the author that knowledge about evolution is good for the country and for the physical and spiritual well-being of its citizens?