I‘M OFTEN ASKED what I do for a living. My answer, that I am a professor at the University of Kentucky, inevitably prompts a second question: “What do you teach?” Responding to such a question should be easy and invite polite conversation, but I usually brace for a negative reaction. At least half the time the person flinches with disapproval when I answer “evolution,” and often the conversation simply terminates once the “e-word” has been spoken. Occasionally, someone will retort: “But there is no evidence for evolution.” Or insist: “It’s just a theory, so why teach it?”

At this point I should walk away, but the educator in me can’t. I generally take the bait, explaining that evolution is an established fact and the foundation of all biology. If in a feisty mood, I’ll leave them with this caution: the fewer who understand evolution, the more who will die. Sometimes, when a person is still keen to prove me wrong, I’m more than happy to share with him an avalanche of evidence demonstrating I’m not.

Some colleagues ask why I bother, as if I’m the one who’s the provocateur. I remind them that evolution is the foundation of our science, and we simply can’t shy away from explaining it. We don’t avoid using the “g-word” when talking about gravitational theory, nor do we avoid the “c-word” when talking about cell theory. So why avoid talking about evolution, let alone defending it? After all, as a biologist, the mission of advancing evolution education is the most important aspect of my job.

TO TEACH EVOLUTION at the University of Kentucky is to teach at an institution steeped in the history of defending evolution education. The first effort to pass an anti-evolution law (led by William Jennings Bryan) happened in Kentucky in 1921. It proposed making the teaching of evolution illegal. The university’s president at that time, Frank McVey, saw this bill as a threat to academic freedom. Three faculty members—William Funkhouser, a zoologist; Arthur Miller, a geologist who taught evolution; and Glanville Terrell, a philosopher—joined McVey in the battle to prevent the bill from becoming law. They put their jobs on the line. Through their efforts, the anti-evolution bill was defeated by a forty-two to forty-one vote in the state legislature. Consequently, the movement turned its attention toward Tennessee.

John Thomas Scopes was a student at the University of Kentucky then and watched the efforts of his three favorite teachers and President McVey. The reason the “Scopes Monkey Trial” occurred several years later in Dayton, Tennessee—where Scopes was a substitute teacher and volunteered to be prosecuted—was in good part due to the influence of his mentors, particularly Funkhouser. As Scopes writes in his memoir, Center of the Storm: “Teachers rather than subject matter rekindled my interest in science. Dr. Funkhouser . . . was a man without airs [who] taught zoology so flawlessly that there was no need to cram for the final examination; at the end of the term there was a thorough, fundamental grasp of the subject in bold relief in the student’s mind, where Funkhouser had left it.”

I was originally reluctant to take my job at the university when offered it twenty years ago. It required teaching three sections of non-majors biology classes, with three hundred students per section, and as many as eighteen hundred students each year. I wasn’t particularly keen on lecturing to an auditorium of students whose interest in biology was questionable given that the class was a freshman requirement.

Then I heard an interview with the renowned evolutionary biologist E. O. Wilson in which he addressed why, as a senior professor—and one of the most famous biologists in the world—he continued to teach non-majors biology at Harvard. Wilson explained that non-majors biology is the most important science class that one could teach. He felt many of the future leaders of this nation would take the class, and that this was the last chance to convey to them an appreciation for biology and science. Moved by Wilson’s words, and with the knowledge that William Funkhouser once held the job I was now contemplating, I accepted the position. The need to do well was unnerving, however, considering that if I failed as a teacher, a future Scopes might leave my class uninspired.

I realized early on that many instructors teach introductory biology classes incorrectly. Too often evolution is the last section to be taught, an autonomous unit at the end of the semester. I quickly came to the conclusion that, since evolution is the foundation upon which all biology rests, it should be taught at the beginning of a course, and as a recurring theme throughout the semester. As the renowned geneticist Theodosius Dobzhansky said: “Nothing in biology makes sense except in the light of evolution.” In other words, how else can we explain why the DNA of chimps and humans is nearly 99 percent identical, and that the blood and muscle proteins of chimps and humans are nearly identical as well? Why are these same proteins slightly less similar to gorillas and orangu­tans, while much less similar to goldfish? Only evolution can shed light on these questions: we humans are great apes; we and the other great apes (gibbons, chimps, gorillas, bonobos, and orangutans) all evolved from a common ancestor.

Soon, every topic and lecture in my class was built on an evolutionary foundation and explained from an evolutionary perspective. My basic biology for non-majors became evolution for non-majors. It didn’t take long before I started to hear from a vocal minority of students who strongly objected: “I am very offended by your lectures on evolution! Those who believe in creation are not ignorant of science! You had no right to try and force evolution on us. Your job was to teach it as a theory and not as a fact that all smart people believe in!!” And: “Evolution is not a proven fact. It should not be taught as if it is. It cannot be observed in any quantitative form and, therefore, isn’t really science.”

We live in a nation where public acceptance of evolution is the second lowest of thirty-four developed countries, just ahead of Turkey. Roughly half of Americans reject some aspect of evolution, believe the earth is less than ten thousand years old, and that humans coexisted with dinosaurs. Where I live, many believe evolution to be synonymous with atheism, and there are those who strongly feel I am teaching heresy to thousands of students. A local pastor, whom I’ve never met, wrote an article in The University Christian complaining that, not only was I teaching evolution and ignoring creationism, I was teaching it as a non-Christian, alternative religion.

There are students who enroll in my courses and already accept evolution. Although not yet particularly knowledgeable on the subject, they are eager to learn more. Then there are the students whose minds are already sealed shut to the possibility that evolution exists, but need to take my class to fulfill a college requirement. And then there are the students who have no opinion one way or the other but are open-minded. These are the students I most hope to reach by presenting them with convincing and overwhelming evidence without offending or alienating them.

Some students take offense very easily. During one lecture, a student asked a question I’ve heard many times: “If we evolved from monkeys, why are there still monkeys?” My response was and is always the same: we didn’t evolve from monkeys. Humans and monkeys evolved from a common ancestor. One ancestral population evolved in one direction toward modern-day monkeys, while another evolved toward humans. The explanation clicked for most students, but not all, so I tried another. I asked the students to consider this: Catholics are the oldest Christian denomination, and so if Protestants evolved from Catholics, why are there still Catholics? Some students laughed, some found it a clarifying example, and others were clearly offended. Two days later, a student walked down to the lectern after class and informed me that I was wrong about Catholics. He said Baptists were the first Christians and that this is clearly explained in the Bible. His mother told him so. I asked where this was explained in the Bible. He glared at me and said, “John the Baptist, duh!” and then walked away.

To truly understand evolution, you must first understand science. Unfortunately, one of the most misused words today is also one of the most important to science: theory. Many incorrectly see theory as the opposite of fact. The National Academy of Sciences provides concise definitions of these critical words: A fact is a scientific explanation that has been tested and confirmed so many times that there is no longer a compelling reason to keep testing it; a theory is a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence generating testable and falsifiable predictions.

In science, something can be both theory and fact. We know the existence of pathogens is a fact; germ theory provides testable explanations concerning the nature of disease. We know the existence of cells is a fact, and that cell theory provides testable explanations of how cells function. Similarly, we know evolution is a fact, and that evolutionary theories explain biological patterns and mechanisms. The late Stephen Jay Gould said it best: “Evolution is a theory. It is also a fact. And facts and theories are different things, not rungs in a hierarchy of increasing certainty. Facts are the world’s data. Theories are structures of ideas that explain and interpret facts.”

Theory is the most powerful and important tool science has, but nonscientists have perverted and diluted the word to mean a hunch, notion, or idea. Thus, all too many people interpret the phrase “evolutionary theory” to mean “evolutionary hunch.”

Not surprisingly, I spend the first week of class differentiating theory from fact, as well as defining other critical terms. But I’m appalled by some of my colleagues who, despite being scientists, do not understand the meaning of theory. As I was preparing to teach a sophomore evolution class a few years ago, a biology colleague asked how I was going to approach teaching evolution. Specifically, he asked if I would be teaching evolution as a theory or a fact. “I will teach evolution as both theory and fact,” I said, trying hard to conceal my frustration. No matter. My colleague simply walked away, likely questioning my competence to teach the class.

ONCE I LAY DOWN the basics of science, I introduce the Darwinian theories of evolution. Charles Darwin was by no means the first or only to put forth evolution; others came before him including his grandfather, Erasmus Darwin, who wrote about descent with modification. Later, while Charles was amassing evidence in England for natural selection, one of the most eloquent scientific theories ever, Alfred Russel Wallace was also developing the same theory during his travels in Indonesia. But it was Charles Darwin alone who advanced the theory of descent with modification, with his bold idea that all species belong to the same tree of life and thus share a common ancestor. He also gave us sexual selection theory, which explains how evolution is shaped by competition for mates as well as choice of mates. Too often only natural selection and descent with modification are emphasized in introductory biology classes. I also cover Darwin’s theories of gradualism (including the nuance of punctuated equilibrium); descent from a common ancestor; multiplication of species; and sexual selection. I emphasize that five of the theories explain the patterns of evolution, while natural and sexual selection are the mechanisms that drive evolution.

Once the two essential strands of the class have been presented—the basic tenets of science and evolutionary ­theory—it’s time to tie the two together and thread them through the rest of the semester. I choose examples that will catch the class’s attention, such as the plight of the ivory-billed woodpecker, also known as the Lord God Bird due to its magnificent appearance. The story of the bird’s decline from habitat loss and hunting, and the failed efforts to save it from extinction, is riveting and heartbreaking. It pulls students in as we discuss how evolution can explain why this North American bird is so similar to a group of large South American woodpeckers, as well as Old World “ivorybills.” Students have to generate hypotheses that explain this phenomenon, and determine what evidence is needed to support or refute their hypotheses. They use a fact-gathering approach, plus all the Darwinian theories, to explain how and why these similar groups of big woodpeckers, many with sturdy white bills, live on three continents. Both scientific approach and evolutionary theory are now intertwined—an approach that is, in my opinion, essential for the teaching of biology at all levels. It does not shy away from public resistance to evolution education but stares it directly in the eye. To this end, I include a section on human evolution, a topic that, somewhat surprisingly, is avoided by many who teach evolution.

Rarely do I have a Kentucky student who learned about human evolution in high school biology. Those who did usually attended high schools in large urban centers like Louisville or Lexington. Given how easily it can provoke parents, the teaching of human evolution is a rarity in high school, so much so in Kentucky that it startled me when I first arrived. I had naively assumed it was something all students learned. I was fortunate to have attended Omaha Central High School in Nebraska, where the science teachers were excellent, and inspiring as well. They never sidestepped controversial ­topics relevant to their science. One teacher in particular—Creighton Steiner, the equivalent of my Funkhouser, and whom I regret not thanking in time before his passing—taught biology, earth science, and anthropology. One semester of his anthropology class was devoted entirely to human evolution. Steiner’s fascination with evolution ignited my passion for the subject. He was the first person to tell me about the age-old clash between science and religion, and how evolution was now at the heart of the conflict. He helped me realize that defending science and evolution is an obligation.

Human evolution is the greatest of all stories. It explains how we came to be. To weave the story of our ancestors and their evolutionary contributions to our existence is an exciting part of the semester. Australopithecus, Homo habilis, Homo erectus—I want my students to know these amazing beings, as well as the many more that have been discovered since my school days. The story of our evolutionary history captivates many of my students, while infuriating some. During one lecture, a student stood up in the back row and shouted the length of the auditorium that Darwin denounced evolution on his deathbed—a myth intentionally spread by creationists. The student then made it known that everything I was teaching was a lie, and stomped out of the auditorium, slamming the door behind him. A few years later during the same lecture, another student also shouted out from the back row that I was lying. She said that no transitional fossil forms had ever been found—despite my having shared images of many transitional forms during the semester. Many of her fellow students were shocked by her combativeness, particularly when she stormed out, also slamming the door behind her. Most semesters, a significant number of students abruptly leave as soon as they realize the topic is human evolution.

My classes provide an abundance of examples of how evolutionary theory explains biological phenomena, with evolutionary medicine surfacing toward the end of the semester. I focus on four basic points: our evolutionary legacy influences present-day health problems; overuse of antibiotics is causing pathogens to evolve resistance; treating conditions (fever, coughing, sneezing, diarrhea, vomiting) as symptoms of an illness can harm our health, while treating these conditions as adaptations and leaving them to run their course (unless they’re acute) can benefit our health; and how the ecological phenomenon of “corridors” (not washing hands, openly sneezing and coughing, shaking hands, unprotected sex) causes pathogens to spread easily, permitting them to evolve greater virulence, while maintaining “barriers” (washing hands, covering your mouth when sneezing and coughing, not shaking hands, using condoms) causes pathogens to evolve lower virulence.

If mild fever evolved as an adaptation to “cook” pathogens, and coughing, sneezing, and diarrhea evolved to expel them, then it is unwise to use medications to suppress these adaptations. Similarly, if a virulent strain can kill a host and escape to another via a corridor, greater virulence evolves. If, however, a barrier prevents spread of this pathogen, the most virulent die along with their host, leaving only less virulent forms to survive.

Evolutionary medicine brings the significance of evolution home. Students realize that not understanding evolution can have severe consequences to their health. If everyone understood that pathogens evolve (not develop) resistance to antibiotics when used excessively and unnecessarily, we would have fewer problems with ineffective antibiotics and highly resistant pathogens.

To explain evolutionary legacy, I point out that our physiology evolved for a hunter-gatherer diet and is not adapted for the modern Western diet, which is one reason obesity, diabetes, and other health issues are a growing problem. I also point out that a significant percentage of my students experience lower back problems—a seemingly odd phenomenon for such a young crowd. The explanation is that the vertebrate spine evolved 500 million years ago as a horizontal support structure from which internal organs hung (essentially a suspension bridge to oppose the forces of gravity). But seven million years ago, our ancestors evolved into upright walking creatures with vertical spines. Our spines no longer offset the pull of gravity, leaving our internal organs to push on our lower extremities. With the horizontal support structure gone, we are left to deal with lower back pain, ruptured disks, hemorrhoids, hernias, and varicose veins.

AFTER A SEMESTER filled with evidence of evolution, capped off with a dose of evolutionary medicine, one might expect that every last student would understand it and accept it as fact. Sadly, this is not the case. There are those who remain convinced that evolution is a threat to their religious beliefs. Knowing this, I feel an obligation to give my “social resistance to evolution” lecture as the final topic.

This lecture lays down the history of the antiscience and anti-evolution movements, the arguments made by those opposing evolution, and why these arguments are wrong. I make it clear that one can accept evolution and maintain their religious beliefs. They are not mutually exclusive. Among the religious groups and organizations that support the teaching of evolution are the Episcopal Church, Lutheran World Federation, United Methodist Church, Presbyterian Church, United Unitarian Universalists, Roman Catholic Church, and the American Jewish Congress. In fact, 77 percent of all American Christians belong to a denomination that supports the teaching of evolution, and several high-profile evangelical Christians are ardent defenders of it, including former President Jimmy Carter and Dr. Francis Collins, director of the National Institute of Health. Even Pope John Paul II acknowledged the existence of evolution in an article he published in The Quarterly Review of Biology, in which he argued that the body evolved, but the soul was created. Pope Francis has made it clear that he accepts evolution as well.

This lecture should put students at ease knowing that religion and science need not be at odds. Of all the lectures I give, this one provokes the most discussion after class. And yet it often results in students expressing concern that I might not be saved. I never say anything about my personal religious beliefs, yet it is assumed I am an atheist. One student told me she hoped I could find God soon. When I again pointed out that John Paul accepted evolution—and he certainly wasn’t an atheist—the student countered that Catholics aren’t Christians. Several simply let me know they will be praying for me and praying hard. One student explained that as a devout Catholic he had no choice but to reject evolution. He accused me of fabricating the pope’s statements. When I explained that he could go to the Vatican website for verification or call the Vatican to talk to a scientist, he insisted that there was no such information available from the Vatican. He then pointed his finger at me and said the only way he would believe me is if Pope John Paul II came to my class to confirm these quotes face-to-face. The student then stomped out, again slamming the auditorium door behind him.

The thing about teaching is we are never sure we are making a difference. We never know how many students have been reached. What I have never come to grips with is that no matter how hard I try to be the best teacher I can, I will fail to connect with some students. Every time a student stomps out of my auditorium slamming the door on the way, I can’t help but question my abilities. Based on evaluations from the 24,000 students I’ve taught, 8 percent of my students simply detest me, but 90 percent love my class. That makes me one of the most hated and loved professors at the university.

I’m occasionally told my life would be easier if I backed off from my relentless efforts to advance evolution education. Maybe so. But to shy away from emphasizing evolutionary biology is to fail as a biology teacher. I continue to teach biology as I do, because biology makes sense only in the light of evolution.

And it’s a message that sometimes gets through. There’s one student I can remember in particular, who took my freshman seminar on evolutionary medicine. He was an ardent evangelical Christian who believed in the literal truth of biblical creation. The seminar was very hard on him, and he struggled with the information, questioning and doubting everything we read. Several years later, our paths crossed, and we stopped for what turned out to be a long, easy chat. Now a doctor, he explained to me that, at the time, he was so upset with my seminar that he attended a number of Creationists’ public lectures for evidence I was wrong. He said he found himself embarrassed by how badly these individuals perverted Christian teachings, as well as known facts, to make their argument. He wanted me to know that he came to understand he could be a Christian and accept evolution. Then he did something that resonates with any teacher: he thanked me for opening his eyes, turning his world upside down, and blurring the line between black and white. O

Hear a conversation with James J. Krupa about his experience teaching evolution.