RNCSE 17 (4)

Reports of the National Center for Science Education
Articles available online are listed below.

The Predictive Power of Evolutionary Biology and the Discovery of Eusociality in the Naked Mole Rat

Reports of the National Center for Science Education
The Predictive Power of Evolutionary Biology and the Discovery of Eusociality in the Naked Mole Rat

Stanton Braude

This version might differ slightly from the print publication.

Anti-evolutionists have asserted that evolutionary biology lacks predictive power (Gish 1979; Johnson 1991; Morris 1974, 1989). They still cite Karl Popper's early suggestion that evolutionary theory is untestable because it cannot be used to make predictions, despite the fact that this view has been rejected by philosophers of science and that Popper himself unequivocally reversed this opinion (1978:344-5). Such assertions that evolutionary theory is unpredictive ignore the power of the comparative method in testing both alternative hypotheses and models of evolutionary processes as well as the pervasive implicit tests of evolutionary theory in every aspect of modern biological science. In this paper I will discuss briefly how biologists across disciplines use evolutionary theory as a foundation for understanding biological systems. Next I will give a few examples of how evolutionary biologists test hypotheses about specific modes of selection and evolution. Finally I will discuss, in detail, an example of the extremely successful predictive power of one evolutionary hypothesis.


Pervasive use of Evolutionary Hypotheses in Biology


"Nothing in biology makes sense except in the light of evolution" (Dobzhansky 1973). Accordingly, biochemists, geneticists, ecologists and medical researchers do not choose their hypotheses randomly. A hypothesis must first be logically consistent to be worth testing. An underlying part of the logic in most biological hypotheses is that the system under study is adaptive, selectively neutral or even maladaptive (but maladaptive in ways that we can understand based on conflicting biological demands or novel circumstances). Maladaptive characters are studied in the context of their unusual nature and the surprise they pose in light of an apparently well adapted biological world. When molecular biologists investigate complex biochemical pathways, gene regulators, or carrier proteins, they are working under the paradigms that the molecules in question serve an adaptive function. Biochemists do not test hypotheses about the beauty of a molecule but about its function (Stryer 1995).

The fact that not all biological systems are adaptive can be confusing, and this confusion has misled some scientists to conclude that evolution is, therefore, irrelevant to understanding particular maladaptive systems. However, evolutionary theory is not limited to explaining adaptations. For example, simple adaptive hypotheses cannot explain senescence, but the study of age-related changes in the potential for future reproduction (reproductive value) and of (pleiotropic) genes that produce a number of different traits has given us the clearest understanding of why senescence has evolved differently in different organisms (Alexander 1987; Charlesworth and Hughes 1996; Williams 1957). Cancer is also best understood as the result of selection working at the cellular level and in conflict with competing selective forces at the individual level (Tomlinson and others 1996).

Biologists across disciplines also indirectly test phylogenetic hypotheses and assumptions when choosing test organisms. When medical researchers want to test the effects of a new drug or treatment, they recognize that the phylogenetic relationship between the model experimental organism and humans is relevant to interpreting results and judging either the efficacy or danger to humans. Results based on rodent studies are given less weight than primate studies because of our more distant common ancestry and the greater divergence that has resulted.


Direct Tests in Evolutionary Biology


Direct tests and predictions about the mode of evolution are conducted daily by evolutionary biologists and population geneticists. However, an arbitrary distinction between micro- and macro-evolutionary processes has been used to devalue tests of evolutionary hypotheses in selection experiments or in insect population cages (where insects can hatch, breed and die for hundreds of generations in the course of an experiment). Population geneticists make predictions and test hypotheses about the mode of evolution. In population cages, petri dishes or growth media, population geneticists test hypotheses about evolutionary change in controlled populations (for example Carson and others 1994; Goodnight and Stevens 1997; Templeton 1996). In wild populations, population geneticists look at gene frequencies within species or populations in order to test hypotheses about relatively recent evolutionary events (for example Crandall and Templeton 1993; Routman and Templeton 1994; Templeton and others 1993).

Ecologists and conservation biologists use evolutionary theory to interpret the relationships we see in wild communities and to predict how those communities will be affected by changes and environmental pressures (for example Georgiatis and others 1994; Losos and others 1997; Templeton and Read 1994). While much of current ecological theory is complex and multivariate, MacArthur and Wilson (1967) were able to make rather simple and testable predictions about the diversity of species on islands of different sizes and distances from mainland. In addition, behavioral ecologists make predictive hypotheses about the trends we expect to see across a wide variety of taxa (Alexander and others 1979; Harvey and Pagel 1991; Martins 1996; Ryan 1990).

In the examples cited above, predictions from and tests of evolutionary theory fit into two general categories: how evolution works in specific cases and circumstances, and what evolution has produced in response to particular circumstances. Ecologists, phylogeneticists, and population geneticists are interested in the subtle details of how evolution works. In testing adaptive hypotheses about how their particular biological system works, other biologists are testing predictions of what evolution has produced. The underlying paradigm is that evolution has generally produced adaptive systems and structures.

The uses of evolutionary theory to make these various predictive hypotheses have also been criticized as being post hoc since we already know what has evolved but cannot do simple experiments and predict what will evolve. This line of reasoning not only ignores all the population cage experiments in evolutionary biology but, if true, would lead to the classification of astronomy as unscientific as well, since we cannot manipulate the cosmos. The multitude of minute, precise predictions about the locations of known planets and stars in tomorrow night's sky are analogous to the specific predictions that are made in comparative tests by evolutionary biologists.

Occasionally, however, more striking predictions are made. In 1845 John Couch Adams and Urbain Jean Joseph Leverrier both predicted the presence of an unseen planet which affects the orbit of Uranus. It was not until the following year that Neptune was discovered as they had predicted.

Richard D Alexander has made a similarly striking prediction based on first principles of the evolution of social behavior. Although common in social insects, eusociality—the social system with a queen and sterile workers—was unknown in any other taxa. Under the appropriate set of conditions, Alexander predicted, evolution ought to produce a eusocial vertebrate, even though eusociality in the naked mole-rat (or any other vertebrate) was unknown at the time.


A Fertile Use of Inductive and Deductive Logic


The roots of Alexander's prediction go back to questions raised by Darwin over 100 years prior. In his chapter titled "Difficulties with the theory" Darwin addressed the problem that sterile workers in social insect colonies pose for natural selection. How could natural selection cause differences between queen bees and workers if the workers are sterile? Darwin guessed that in these cases selection is acting between families or hives.

In 1964 William Hamilton formalized this idea of kin selection and suggested that eusocial colonies with queens and workers have evolved many times in the ants, bees, and wasps because of their unusual genetic system. In these hymenopteran insects, males have one set of chromosomes (haploid) and females have two sets (diploid); this is called haplodiploidy. As a consequence of this genetic peculiarity, sister workers in these insects are more closely related to each other than they would be to their own offspring. Consequently, they contribute to the propagation of a greater proportion of their genes by helping to rear siblings than by producing offspring themselves.

In 1974 entomologist and evolutionary theorist Richard Alexander argued that "subsocial" behavior (that is parental care) and the opportunity for parental manipulation were even more powerful factors in the evolution of social behavior in insects (Alexander 1974). Across taxa, parental behavior correlates much more strongly with eusociality than does haplodiploidy (Andersson 1984; Alexander and others 1991). Alexander's critics argued that if parental care is a crucial precursor to eusociality, we should expect eusociality to have also evolved among the highly parental vertebrates: birds and mammals. Alexander could have pointed out that there are far fewer species of birds and mammals than there are species of insects, or that birds and mammals have only existed for 160 million and 250 million years respectively (Eisenberg 1981; Welty 1979) while insects have existed for 350 million years (Borror and others 1989). Instead he asked himself what characteristics a eusocial vertebrate would have if it had evolved.

Alexander based his answer on his understanding of the selective forces involved in the evolution of insect eusociality and hypothesized a eusocial vertebrate. He created a 12-part model for a eusocial vertebrate, based on this body of theory. He had no idea that a mammal with these characteristics existed.

Alexander predicted that a eusocial vertebrate's nest should be (1) safe, (2) expandable, and (3) in or near an abundance of food that can (4) be obtained with little risk. These characteristics follow from the general characteristics of primitive termite nests inside logs. The nest must be safe or it will be exploited as a rich food source for predators. It must be expandable so that workers can enhance the value of the nest. It must be supplied with safe abundant food so that large groups can live together with little competition over food or over who must retrieve it.

The limitations of the nest characteristics suggested that the animal would be (5) completely subterranean because few logs or trees are large enough to house large colonies of vertebrates. Being subterranean further suggested that the eusocial vertebrate would be (6) a mammal and even more specifically (7) a rodent since many rodents nest underground. The primary food of the hypothetical vertebrate would be (8) large underground roots and tubers because the small grassy roots and grubs that moles feed on are so scattered that they are better exploited by lone individuals and would inhibit rather than encourage the evolution of eusociality.

The major predator of the hypothetical vertebrate would have to be (9) able to enter the burrow but be deterred by the heroic acts of one or a few individuals. This would allow for the evolution of divergent life lengths and reproductive value curves between workers and reproductives. Predators fitting this description would include snakes.

The eusocial vertebrate was also expected to (10) live in the wet-dry tropics because plants there are more likely to produce large roots and tubers that store water and nutrients to help them survive the dry periods. The soil would need to be (11) hard clay because otherwise the nest would not be safe from digging predators. These two characteristics further suggested (12) the open woodland or scrub of Africa.

Alexander described this social vertebrate in a series of guest lectures at North Carolina State University, University of Kansas, University of Texas, Colorado State University, Arizona State University, University of Arizona, and Northern Arizona University at Flagstaff in 1975 and 1976. At Flagstaff, mammalogist Terry Vaughan suggested to Alexander that his hypothetical eusocial rodent was a "perfect description" of the naked mole-rat Heterocephalus glaber. He further described the burrowing East African mammal and suggested that Alexander contact Jennifer Jarvis, an authority on African mole-rats. Jarvis had studied the ecology and physiology of naked mole-rats but at that time nothing was known about their social system. Subsequent field and laboratory observations have confirmed that they are in fact eusocial, as Alexander's model had predicted, and that the other elements of his model are accurate as well (Braude and Lacey 1992; Jarvis 1981; Sherman and others 1991; Sherman and others 1992). This case demonstrates one type of predictive power in modern evolutionary theory.

Evolutionary biologists are making new discoveries every day. To suggest that evolutionary biology is either untestable or unpredictive ignores their vast body of work including the dramatic discovery of eusociality in the naked mole-rat based on clear understanding of the selective forces leading to the evolution of social behavior.




Many thanks to Nancy Berg, Keith Butler and two anonymous reviewers for their valuable comments and suggestions.




Alexander RD. The evolution of social behavior. Annual Review of Ecology and Systematics 1974; 5:326-83.

Alexander RD, Hoogland JL, Howard RD, Noonan KM, Sherman PW. Sexual dimorphism and breeding systems in pinnipeds, ungulates, primates and humans. In: Chagnon N and Irons W eds. Evolutionary Biology and Human Social Behavior: An Anthropological Perspective. North Scituate (MA): Duxbury Press, 1979. p 402-35.

Alexander RD. The Biology of Moral Systems. Hawthorn (NY): Aldine de Gruyter, 1987.

Alexander RD, Crespi B, Noonan K. The evolution of eusociality. In: Sherman P, Jarvis J, Alexander RD, eds. The Biology of the Naked Mole-Rat. Princeton: Princeton University Press, 1991. p 3-44.

Andersson M. The evolution of eusociality. Annual Review of Ecology and Systematics 1984; 15:165-89.

Borror D, Triplehorn C, Johnson N. The Study of Insects. 6th ed. Philadelphia: Saunders College Publishing, 1989.

Braude S, Lacey E. The underground society. The Sciences 1992; 32:23-8.

Carson HL, Val FC, Templeton AR. Change in male secondary sexual characters in artificial interspecific hybrid populations. Proceedings of the National Academy of Sciences of the United States of America 1994; 91(14):6315-8.

Charlesworth B, Hughes KA. Age-specific inbreeding depression and components of genetic sequence variance in relation to the evolution of senescence. Proceedings of the National Academy of Sciences of the United States of America 1996; 93(12):6140-5.

Crandall K, Templeton AR. Empirical tests of some predictions from coalescent theory with applications to intraspecific phylogeny reconstruction. Genetics 1993; 134(3): 959-69.

Darwin CR. On the Origin of Species. New York: Collier Books, 1859.

Dobzhansky T. Nothing in biology makes sense except in the light of evolution. American Biology Teacher. 1973; 35:125-9.

Eisenberg J. The Mammalian Radiations. Chicago: University of Chicago Press, 1981.

Georgiatis N, Bischof L, Templeton A, Patton J, Karesh W, Western D. Structure and history of African elephant populations: I. Eastern and southern Africa. Journal of Heredity 1994; 85(2): 100-4.

Gish DT. Evolution? The Fossils Say No! San Diego: Creation-Life Publishers, 1979.

Goodnight CJ, Stevens L. Experimental studies of group selection: What do they tell us about group selection in nature? American Naturalist 1997; 150(Supplement):59-79.

Harvey P, Pagel M. The Comparative Method in Evolutionary Biology. Oxford: Oxford University Press, 1991.

Jarvis JUM. Eusociality in a mammal: Cooperative breeding in naked mole rat colonies. Science 1981; 212:571-3.

Johnson PE. Darwin on Trial. Washington: Regnery Gateway, 1991.

Losos JB, Warheit KI, Schoener TW. Adaptive differentiation following experimental island colonization in Anolis lizards. Nature 1997; 387: 70-3.

MacArthur RH, Wilson EO. The Theory of Island Biogeography. Princeton: Princeton University Press, 1967.

Martins E. Phylogenies and the Comparative Method in Animal Behavior. Oxford: Oxford University Press, 1996.

Morris HM. Scientific Creationism. San Diego: Creation-Life Publishers, 1974.

Morris HM. The Long War Against God. Grand Rapids (MI): Baker Book House, 1989.

Popper KR. Objective Knowledge: An Evolutionary Approach. Oxford: Oxford University Press, 1972.

Popper KR. Natural selection and the emergence of mind. Dialectica 1978; 32:339-55.

Routman E, Templeton AR. Parsimony, molecular evolution and biogeography: The case of the North American giant salamander. Evolution 1994; 48(6):1799-809.

Ryan MJ. Sensory systems, sexual selection, and sensory exploitation. Oxford Surveys in Evolutionary Biology 1990; 7:157-95.

Sherman PW, Jarvis JUM, Alexander RD. The Biology of the Naked Mole-Rat. Princeton: Princeton University Press, 1991.

Sherman PW, Jarvis JUM, Braude S. Naked mole-rats. Scientific American 1992; 267(2):72-8.

Stryer L. Biochemistry 4th Ed. New York: Freeman, 1995.

Templeton AR. Experimental evidence for the Genetic-transilience model of speciation. Evolution 1996; 50(2): 909-15.

Templeton AR, Read B. Inbreeding: One word, several meanings, much confusion. In Loeschke V, Tomuik J, Jain SK eds. Conservation Genetics. Basel: Birkhauser Verlag, 1994.

Templeton AR, Hollocher H, Johnston IS. The molecular through ecological genetics of abnormal abdomen in Drosophila mercatorum. Female phenotypic expression on natural genetic backgrounds and in natural environments. Genetics 1993; 134(2): 475-85.

Tomlinson IPM, Movelli MR, Bodmer WF. The mutation rate and cancer. Proceedings of the National Academy of Sciences of the United States of America 1996; 93(25):14800-3.

Welty J. The Life of Birds. 2nd ed. Philadelphia: Saunders College Publishing, 1979.

Williams G. Pleiotropy, natural selection and the evolution of senescence. Evolution 1957; 11:398-411.

About the Author(s): 

Stan Braude
Biology Department
Campus Box 1137
Washington University
One Brookings Drive
St. Louis MO 63130
email: braude@wustlb.wustl.edu


Stanton Braude has been studying naked mole rats in the laboratory and field for the past 15 years. He is currently on the faculty of the International Center for Tropical Ecology at the University of Missouri-St. Louis and at Washington University in St. Louis

(c) 1998, National Center for Science Education

Dealing with Anti-Evolutionism

Reports of the National Center for Science Education
Dealing with Anti-Evolutionism
This version might differ slightly from the print publication.
In November 1995 the Alabama Department of Education required all biology textbooks used in the state to display a disclaimer informing the young reader that

This textbook discusses evolution, a controversial theory some scientists present as a scientific explanation for the origin of living things, such as plants, animals and humans. No one was present when life first appeared on earth, therefore, any statement about life's origins should be considered as theory, not fact.

In March 1996 the governor of Alabama sent all biology teachers a copy of an anti-evolution book, Darwin on Trial, using his discretionary funds. Shortly thereafter the Tennessee legislature debated and ultimately rejected a requirement that

No teacher or administrator in a local education agency shall teach the theory of evolution except as a scientific theory. Any teacher or administrator teaching such theory as fact commits insubordination. (Tennessee HB 2972/SB 3229 1996).

Also during the spring of 1996 Georgia voted down an amendment to an education bill that would "provide that local boards of education may establish optional courses in creationism" and

As part of any science curriculum wherein students are taught concerning the origins of life and living things, including the origins of humankind, teachers shall have the right to present and critique any and all scientific theories about such origins and all facets thereof, including without limitation scientific theories other than evolutionism.

"Critiques of evolution" or "arguments against evolution" are code-phrases for creation science, stimulated by Supreme Court Justice Antonin Scalia's dissent to Edwards v. Aguillard, the 1987 case that struck down "equal time for creationism and evolution" laws. Another "arguments against evolution" law was debated by the Senate Education Committee of the Ohio state legislature in May 1996. It was ultimately rejected (by a vote of 12-8). The wording directed that

Whenever a theory of the origin of humans or other living things that might commonly be referred to as "evolution" is included in the instructional program provided by any school district or educational service center, both scientific evidence and related arguments supporting or consistent with the theory and scientific evidence and related arguments problematic for, inconsistent with, or not supporting the theory shall be included.

And, as this essay was being written, news arrived to the office of the National Center for Science Education (NCSE) that the Cobb County, Georgia school district had requested MacMillan-McGraw Hill to delete a chapter on the Big Bang and earth's origin in an earth science booklet for fourth graders after parents complained. Newspaper accounts reported that MacMillan would comply.

What's going on here? Clearly, pressure against the teaching of evolution has not abated, and even appears to be on the rise (Gillis 1994; Scott 1994; 1996). What is it about evolution, more than any other scientific theory, that elicits this response? The Alabama disclaimer "no one was present" argument is especially puzzling, as many phenomena studied in modern science are not observed directly. In fact, no one has stood in space and observed the earth making its circuit around the sun through the course of a year, but we do not hear protestations that heliocentrism should be considered just a guess or hunch (the street definition of "theory").

Heliocentrism, as Galileo discovered, was once considered a challenge to religion, because it was thought to conflict with the Bible. The Bible, read literally, assumes the ancient view of the cosmos that the earth is the center of the solar system and the sun revolves around it. Few Americans these days interpret the Bible as a geocentric document, but a healthy percentage still accept a literal reading of Genesis regarding the separate creation of plants and animals as independent "kinds". This belief contrasts starkly with the scientific concept that living species are descended with modification from ancestors that differed from then. Thus evolution, and not theologically-acceptable heliocentrism, is vigorously opposed by an active segment of modern American society.

Anti-evolutionism extends beyond mere biblical literalism, however, as shown by comparing survey data on American religious opinions with survey data on attitudes towards evolution. Polls of adult Americans have consistently shown over the last fifteen years or so that a substantial proportion of us do not think humans evolved (whether other creatures evolved is usually not part of the standard query). In May 1996 the National Science Foundation released results from a telephone survey of 2006 individuals who were asked questions about basic science literacy (Petit 1996). One question was, "Human beings as we know them today, developed from earlier species of animals." Only 44% of Americans answered "True". In 1994 the American Museum of Natural History asked "Human beings evolved from earlier species of animals, true or false" and only 45% agreedùresults virtually identical to the NSF study.

Defining religious conservatism is tricky, as there is no uniform agreement on terms. One term for conservative Christians is "evangelical." Evangelicals are Christians who believe the Bible is inerrant, and that salvation is achieved only through Christ (Hunter 1983). According to Marsden (1987), about 20% of Americans are evangelicals, far fewer than the 44% of Americans who reject evolution.

In a nutshell, there is more anti-evolutionism than there are religious conservatives: anti-evolutionism appeals both to evangelicals as well as Americans who adhere to religiously-moderate faiths. There is an irony here: the "official" theologies of Catholic and mainstream Protestant Christianity are not literalist and have accommodated evolution as the way God created (Scott 1995). NCSE's book, Voices for Evolution (Matsumura 1995), includes a collection of statements from the Roman Catholic Pope, the Episcopalians, Methodists, United Church of Christ, Presbyterians, and the Lutheran World Federation (and several Jewish groups) all expressing respect for science and for evolution as part of science. Nonetheless, even if the ministers, priests and rabbis accept evolution, many people on the other side of the pulpit appear largely ignorant of their own theology!

It is important for those of us trying to teach evolution to recognize that many of our fellow citizens find evolution profoundly disturbing. They have been told or have somehow acquired the belief (sometimes from scientists, unfortunately) that evolution "proves" that there is no purpose to life, that life has no meaning, that they must give up their sense of the divine. According to a respected City University of New York poll, 90% of Americans describe themselves as religious (Goldman 1991). If evolution is presented as antithetical to religion (which is precisely how organizations such as the Institute for Creation Research present it), it is no wonder that a high percentage of Americans reject it. Actually, as suggested by the selections in Voices for Evolution, mainline Christianity can accommodate evolution, though it is doubtful that Biblical literalism can. As teachers and scientists, we need to leave an opportunity for the religious individual to work out the accommodation according to his or her beliefs, and not slam the door by inserting extra-scientific philosophical statements about purpose and meaning into our discussions of evolution. I will discuss this in greater detail below.

The Importance Of Evolution In The Curriculum

Evolution is a necessary part of the science curriculum. A biology or earth science course taught without the inclusion of evolution is an inferior course. Students who take these courses without being told that evolution unifies the data and concepts of the field are being cruelly short-changed. They will leave the course having been misled that science largely consists of the tedious memorization of lists of facts, rather than a tool we can use to help us understand the world of nature. This episodic, atomistic view of science is particularly regrettable: it turns students away from studying science, and perhaps worse yet, defeats our efforts to produce a scientifically literate society.

Evolution needs to be taught, but some teachers will be doing so in a hostile environment. How can teachers present this topic and avoid the potential minefields? Or, since some of the land mines are unavoidable, how can a teacher defuse them?

Evolution Happened

First, teachers need to be confident that evolution is state of the art science. A common claim made by anti-evolutionists is that evolution is a "theory in crisis," in the words from the title of a popular anti-evolution book (Denton 1985). Many teachers have not studied evolution, feel unconfident about teaching it, and are susceptible to being swayed by "new" information that "evolution is not as well accepted as it used to be". Evolution is presented matter-of-factly at every decent college or university in this country, including Brigham Young, Notre Dame, and Baylor. It is simply untrue that evolution is being widely challenged by scientists themselves. Help your colleagues to understand that scientists do not debate whether evolution (change through time, descent with modification) took place, though they vigorously argue how it took placeùthe processes, mechanisms and details of evolution. The previously-mentioned Voices for Evolution contains 33 statements from scientific organizations, all of which reassure teachers that evolution is indeed the reigning paradigm explaining how the universe came to be in its present state. Some statements, such as that from the National Academy of Sciences' booklet Science and Creationism, clearly distinguish between evolution as something which should be taught in the science classroom and creation science which should not:

[T]he Academy states unequivocally that the tenets of "creation science" are not supported by scientific evidence, that creationism has no place in a science curriculum at any level, that its proposed teaching would be impossible in any constructive sense for well-informed and conscientious science teachers, and that its teaching would be contrary to the nation's need for a scientifically literate citizenry and for a large well-informed pool of scientific and technical personnel. (Committee on Science and Creationism 1984, p 7-8).

As scientists agree that evolution is a crucial part of science, so also do educators. The National Science Education Standards, released in February of 1996, present evolution as one of the "Unifying Concepts and Processes," as well as listing it prominently in the Content Standards for grades 9-12. Anticipating a tendency for states and districts to pick and choose among the standards rather than truly revise their curricula, the publication states firmly that, "No standards should be eliminated from a category." Perhaps presciently, the Standards chose evolution as a negative example. "For instance, 'biological evolution' cannot be eliminated from the life science standards." (National Research Council 1996, p 112).

"Benchmarks for Science Literacy," the 1993 publication by the American Association for the Advancement of Science's Project 2061: Science for All Americans, cites evolution as an integral part of the science curriculum. Similarly, the California Science Framework and the curricula of most other states require evolution to be presented. (Some disguise it as "change through time," and confuse ontogeny with phylogeny by referring to evolution as "development"). Voices for Evolution includes statements from 30 science education organizations including the National Science Teachers Association, the National Association of Biology Teachers, and the National Science Supervisors Associationùall exhorting science educators to teach evolution and not present creation science. If evolution is a "theory in crisis," somehow the entire science and education establishments are unaware of it.

Know What You Are Talking About!

Now, appealing to authority may often be effective with students, but it is hardly something we wish to encourage! Opponents of evolution rely exceedingly heavily upon (out of context) quotations from authorities like Stephen Jay Gould in their attacks upon evolution. Because "famous scientist X" said something, it supposedly should be accepted. As it happens, when it comes to appeals to authority, the pro-evolution side wins hands down! We have the National Academy of Science, the Nobel laureates, and all the other heavy hitters of big science - but what is more important, we have the science itself. Teachers need to be familiar with the data and theory of evolution, and why this theory has such strong explanatory power. Evolution is accepted by scientists today because it explains more observations than any alternative. Any of a number of basic college level biology and especially evolution textbooks will provide teachers with plenty of evidence for evolution's being the unifying theory explaining observations from biogeography, comparative anatomy, comparative biochemistry, the fossil record, developmental biology, and many other fields.

Define Evolution

A colleague in physical anthropology teaching a small college in the Southeast told me she was teaching a class of freshmen college students and found that none of them had ever studied evolution or even knew what evolution was. When they found out, they found the concept exciting and intellectually challenging, and they clamored for a special course on the topic. Their response, in her words, was "Of course species change through time! You mean that's evolution?!" Sometimes finding out what evolution actually is (or more precisely, replacing erroneous ideas about evolution) in itself reduces students' reluctance to learn about it. A proper definition of evolution is important to helping students understand the concept.

It's been my experience (and perhaps yours too) that most non-scientists think evolution means "man evolved from monkeys," which is an exceedingly narrow definition. It is both scientifically accurate as well as strategically wise to embed evolution within the broadest scientific context possible. Evolution isn't just about humans, or even about living things. Astronomers do, after all, study cosmic evolution. Geologists and geophysicists study the evolution of the planet earth, and evolution is the organizing concept of earth science just as it is for the life sciences. Biologists and biochemists study the change through time of living things. Rejection of evolution doesn't mean merely rejection of "man evolved from monkeys," but rejection of principles relevant (and in some cases crucial) to modern science.

The word "evolution" is defined and used in many different ways, some more useful and accurate than others. Embedding evolution in a wide range of sciences requires a broad definition. What unites astronomical, geological, and biological evolution is the concept of change through time. But "change through time" can also refer to phenomena like the water cycle, or the rotation of the earth around the sun, or the passage of energy through a food chain, or the metamorphosis of insects. Not all change is evolution, so we must distinguish evolution as being cumulative change through time. The evolution of a star from white dwarf to supernova is one such cumulative change.

When we discuss organic evolution, we must be especially precise. Here I part company with many of my colleagues: I do not find the traditional "evolution is changes in gene frequencies through time" to be a useful definition, even if it were modified to be "cumulative changes in gene frequencies through time." Especially at the beginning of a course, who knows what a gene frequency is? The genetically-based definition of evolution is useful in understanding the major constituents of evolution (genetic variation, adaptation, reproductive isolation/speciation), but if a teacher waits until students understand all of the related concepts, it will be the end of the semester. If evolution is to be taught as the organizing principle of biology, we shouldn't wait until the end of the semester to let them in on the secret! I find that even college students lose track of the relationship of evolution to biology using this genetically-based definition, and I am sure high-school students will, also.

What do we want students to know about organic evolution? The "Big Idea" is that living things (species) are related to one another through common ancestry from earlier forms that differed from them. Darwin called this "descent with modification," and it is still the best definition of evolution we can use, especially with members of the general public and with young learners. Descent with modification makes biology make sense. We can study and understand the workings of evolution using genes, cells, fossils, ecology, taxonomy—you name the biological subfield, and evolution is there.

For example, everyone teaches some taxonomy in high school and junior high. But how many explicitly teach how the concept of descent with modification makes it possible to group organisms into taxa? Horses and donkeys are similar because they shared a common ancestor quite recently, geologically speaking (in fact, they can still interbreed, though the hybrid is sterile). The horse/donkey group can be grouped with zebras because it shared a common ancestor with zebras, and so on up through genera, families, orders, classes, and phyla. Most of the time taxonomy is taught backwards: organisms are classed together because they are similar. Wrong. They are classed together and they are similar because they shared a common ancestor.

A good example of a confused understanding of evolution is even found in some textbooks. How many times have you seen the peppered moth or other cases of industrial melanism used as an example of evolution? It is an example of change, but fluctuating change. Remember that the frequencies of melanic genes shifted back to their pre-industrial lows after scrubbers were placed on smokestacks and air pollution was reduced. Industrial melanism is an example of natural selection, not of evolution. A good exercise would be to have the students figure out whether industrial melanism could be an example of evolution (as in our definition of "descent with modification.") (Hint: add reproductive isolation and speciation!)

Define "Theory"

Not incidentally, teachers also need to be clear in their minds about what a "theory" is, because (as illustrated in the examples with which I opened this essay) evolution is under attack for being "just" a theory. The problem is that "theory" is used outside of science in a deprecating way as a synonym for guess or hunch.

What is a "fact" and what is a "theory?"

A fact is a confirmed observation. For example, it is a confirmed observation that every tetrapod known has at some stage of its life, a humerus, a radius and ulna, and a distal cluster of bones corresponding to carpals, metacarpals and phalanges. The general public (and even some scientists) use the word "fact" to imply capital T "Truth": unchanging agreement. In science, facts, like theories, may change: it was once a fact (for about 10 years) that Homo sapiens had 48 chromosomes. But other observations were confirmed and explanations found for the erroneous observations, and now we know that there are 46. In general, though, in science we treat facts as statements we don't need to test and question anymore, but rather can use as givens to build more complex understandings.

A theory, in science, is a logical construct of facts and hypotheses that attempts to explain a natural phenomenon. It is an explanation, not a guess or hunch, that one can casually disregard. Theory formationùexplanationùis the goal of science, and nothing we do is more important. A scientist joked that we should applaud the Tennessee law punishing teachers for teaching evolution as a "fact rather than a theory" because "everyone knows that theories are more important than facts!" Theories explain facts, but the general public doesn't know that.

Concerning evolution, then, what's a fact and what's a theory? One hears from many scientists, "Evolution is FACT!!!" The meaning here is that evolution, the "what happened," is so well supported that we don't argue about it, anymore than we argue about heliocentrism versus geocentrism. We accept that change through time happened, and go on to try to explain how. What we mean and what is heard is often different, however. What the public often hears when scientists say "Evolution is FACT!" is that we treat evolution as unchallengeable dogma, which it isn't.

We must learn to present evolution not as "a fact" in this dogmatic sense, but "matter of factly," as we would present heliocentrism and gravitation. Most people consider heliocentrism and gravitation as "facts", but they are not "facts" in my definition of "confirmed observations." Instead, they are powerful inferences from many observations, which are not in themselves questioned, but used to build more detailed understandings.

From the standpoint of philosophy of science, the "facts of evolution" are things like the anatomical structural homologies such as the tetrapod forelimb, or the biochemical homologies of cross species protein and DNA comparisons, or the biogeographical distribution of plants and animals. The "facts of evolution" are observations, confirmed over and over, such as the presence and/or absence of particular fossils in particular strata of the geological column (one never finds mammals in the Devonian, for example). From these confirmed observations we develop an explanation, an inference, that what explains all of these facts is that species have had histories, and that descent with modification has taken place. Evolution is thus a theory, and one of the most powerful theories in science.

We may also speak of "theories" (plural) of evolution, in the sense of the explanations for how descent with modification has taken place. It is conceptually sound to separate evolution as something that did or did not happen from explanations about how, or how fast, or which species are related to which. I'll return to this idea below.

Indeed, teachers have to be sure that students know what theories are and why they are important. Students also must - this is crucial - learn as part of their science instruction that our explanations change with new data or better ways of looking at things. Anti-evolutionists make the statement that "evolution isn't science because you guys are always changing your minds about stuff." This is not a criticism. That's the way a vigorous science works.

Defuse The Religion Issue

People don't oppose evolution because they disagree with the science but because it offends their religious sensibilities. In most communities, at least some students come into a class wary of the "e-word" because somehow they have acquired the idea that acceptance of evolution is incompatible with religious faith. Anti-evolutionists, in fact, make a special point of proclaiming that one is either an evolutionist or a creationist, falsely dichotomizing the issue. Although it is not the job of public school science teachers to teach theology, when students come to class with their fingers stuck into their ears and their eyes closed, it is necessary to figure out a way to get the fingers out and the eyes open.

Most Catholic and mainline Protestant denominations have accepted evolution as the way God brought the world about, and this is also true of the theology of all but the most conservative Jews. Although it would be inappropriate for a teacher to encourage students towards or against any religious view, it is appropriate to inform them, in a comparative sense, of the existence of more than one religious perspective on creation and evolution. Because students are not tabulae rasae when they come to class, a constructivist approach is a useful way to help them build their understanding of this important fact.

Teachers have told me they have had good results when they begin the year by asking students to brainstorm what they think the words "evolution" and "creationism" mean. As expected, some of the information will be accurate and some will be erroneous. Under "evolution," expect to hear "Man evolved from monkeys" or something similar. Don't be surprised to find some variant of, "You can't believe in God" or some similar statement of supposed incompatibility between religion and evolution. Under "creationism" expect to find more consistency: "God"; "Adam and Eve," "Genesis," etc. The next step in constructing student understanding of concepts is to guide them towards a more accurate view. One goal of this exercise is to help them see the diversity of religious attitudes towards evolution.

After one such initial brainstorming session, one teacher presented students with a short quiz wherein they were asked, "Which statement was made by the Pope?" or "Which statement was made by an Episcopal Bishop?" and given an "a, b, c" multiple choice selection. All the statements from theologians, of course, stressed the compatibility of theology with the science of evolution. This generated discussion about what evolution was versus what students thought it was. By making the students aware of the diversity of opinion towards evolution extant in Christian theology, the teacher helped them understand that they didn't have to make a choice between evolution and religious faith.

A teacher in Minnesota told me that he had good luck sending his students out at the beginning of the semester to interview their pastors and priests about evolution. They came back somewhat astonished, "Hey! Evolution is OK!" Even when there was diversity in opinion, with some religious leaders accepting evolution as compatible with their theology and others rejecting it, it was educational for the students to find out for themselves that there was no single Christian perspective on evolution. The survey-of-ministers approach may not work if the community is religiously homogeneous, especially if that homogeneity is conservative Christian, but it is something that some teachers might consider as a way of getting students' fingers out of their ears.

A less constructivist but not necessarily ineffective approach is to begin by properly separating "evolution" as something that occurred (change through time) from the processes and mechanisms - the causes - of evolution. Define evolution as an issue of the history of the planet: as the way we try to understand change through time. The present is different from the past. Evolution happened, there is no debate within science as to whether it happened, and so on. Then, list (for later discussion) a number of causes or processes which might explain in whole or in part, how this change through time might have taken place. Stress that this is where debating takes place. List both currently-debated and also rejected explanations, such as Lamarckism, saltation, Darwinian natural selection, neodarwinism, non-Darwinian evolution, and so on. At the end of the list (and I recommend using a transparency or writing the list on the blackboard), include "Supernatural Causation". Explain that some people think that change through time is caused directly or indirectly by a supernatural being, including God, the Hero Twins (Navajo), or some other supernatural power. At this point you then state because this is a science class, and science is limited to explaining through natural forces, we cannot discuss supernatural causation here.

I have used this approach at the college level and seen a remarkable development: the fingers start coming out of the ears. Just by mentioning the fact that some people believe God was responsible for change through time, you are recognizing the view of many Christian and Jewish students, even though you are not going to discuss it further (you're not a theology teacher!) Many religious students have never been exposed to a continuum of religious views, and in a very real sense, you are giving them an opportunity to listen to you and not shut you out. Note that you are not to promote theistic evolution: the schools must be religiously neutral. The purpose of this exercise is to give the student some critically important information so that he or she will be more willing to listen to the scientific information you will present.

Similarly, it is useful to separate "creationism" into two parts. Most Americans define "creationism" as "God created," and when creationism is juxtaposed with evolution, the translation made is that "evolution = God-didn't-create." This is the perspective promoted by anti-evolutionists, of course, but it is an unnecessary dichotomy. As discussed above, mainline Christian and Jewish theology accept evolution as the way God created. The other type of "creationism" tries to more specifically answer the question, "what happened?" Special creation, the view of biblical literalists, is that everything in the universe was created all at one time, in its present form. From my experience in dealing with the general public on this issue (radio talk shows are very educational...), most Americans are willing to accept that change through time has taken place, but they very much want to retain God as the creator.

Whether God created is of course, not a scientific question, because science is restricted to explaining natural phenomena using only natural processes. But science can tell us a great deal about "what happened," and the evidence powerfully leads us to conclude that change has taken place and not that everything appeared in its present form.

Helping students understand that evolution, like all scientific explanations, deals only with proximate, never ultimate cause, allows them to accommodate their religious views to evolution, if they so choose. Much resistance to evolution is overcome by allowing the religious student to retain his or her faith in God the creator, while still accepting the scientific evidence for descent with modification.

"But I don't believe in evolution"

There will doubtless be students who refuse to accept evolution. That's all right. Remember, the job of you and your colleagues at the K-12 level is to help students understand the consensus view of a discipline, whether it is history, literature, mathematics, or science. No one said a student has to "believe" in a spherical earth, and in fact, a teacher in a small mountain community in Appalachia told me that she had a brother and sister who would walk out of the class when she discussed a heliocentric solar system! It's the job of the teacher to instruct, not to indoctrinate. All you are asking is that the student learn the subject. Whether he agrees with what is being taught is up to him. Although you'd feel silly telling students, "Well, kids, today we're going to discuss the theory of heliocentrism, but you don't have to believe it!," tension is often reduced when you reassure students that all you're expecting of them is to learn the material (they have to pass the test, after all). Whether they accept the modern scientific consensus that evolution occurred is up to them.

Counter The "Equal Time"/"Fairness" Sentiment

School boards in every state have been pressed by citizens to include creationism in the science curriculum because "you already teach evolution, so it's only fair to teach creationism too." The idea of "balancing" evolution with creationism, giving "equal time" out of "fairness" is an approach that resonates with Americans. It is, in fact, the strongest argument creationists have raisedùnot because of logical soundness, but because Americans value fairness and equality.

Science is not a democratic process

We decide which explanation (theory) is superior based on its power to explain successfully, not on how popular it is. Heliocentrism was not a popular idea 300 years ago - ask Galileo - but it is now the standard explanation for the relationship of the earth to the sun because it explains so many more observations than any other theory. The theories of kin selection and parental investment derived from sociobiology are not "popular" views, but if they continue to explain social behavior successfully, they will be utilized.

If scientists could vote to choose theories, I'd vote for Lamarckism! It's a lot more humane and useful than natural selection! But the world doesn't work that way. The laws of nature work as they will, irrespective of human wish or will. The explanations scientists accept are the ones that work, and Lamarckism doesn't work. The special creationism explanation that the universe was created all at one time in its present form doesn't explain nature nearly as well as the evolutionary explanation that the universe has had a history and that change has taken place. Thus, special creation has been discarded as a scientific explanation.

"It's only fair!"

It is not "fair" to mislead students by pretending that discarded ideas are still viable. We do not present geocentrism and heliocentrism as if they are currently contending theories. We only confuse students by presenting special creation and evolution as if both were equally scientific and as if scientists were still trying to decide between them.

There is another question regarding the "fairness" approach: How should educational curricula be determined? Most of the time, we agree that the consensus scholarship of history, literature, art, or science should be presented to Kindergarten - 12th grade students. We do not teach astrology with astronomy because professional astronomers (and physics teachers) tell us that astrology is not considered good scholarship. Biologists, geologists, astronomers and other scientists tell us that evolution should be taught, and creation "science" should not. The proponents of creationism in the curriculum are a political pressure group outside of the educational and scientific communities. A good defense against the "fairness" argument is to point out that we do not determine scholarship depending on what a political pressure group wants, otherwise we would teach Holocaust revisionism along with standard World War II history, and give equal time in medical school to the ideas that AIDS is caused by viruses and AIDS is a curse sent from God.

"Teach both creationism and evolution to promote critical thinking"

Often teachers are encouraged by parents or others to present creationism with evolution for pedagogical reasons: supposedly, presenting nonscience with science and "letting the children decide" will improve their reasoning skills. It makes more sense to have students practice critical thinking by evaluating ideas that are truly in contention. Few teachers would have students evaluate the "scientific" evidence for flat-earthism (there is some, with emphasis on the quotation marks!) versus spherical-earthism "and let the children decide." Again, the creationists make an issue of whether evolution occurred, rather than how. The scientific debates concern the latter, not the former.

It is possible to use creationism and evolution as foils in a discussion of the nature of science, but this may well result in a student's taking offense at what may appear to be criticism of his or her religion. It is better to avoid this, for many reasons.

Evaluating the creation science literature requires far more background than students have, or will haveùand maybe even than the teacher has. Most teachers would not ask students to evaluate whether balloon angioplasty or by-pass surgery should be used to treat heart failure, and that question deals "only" with medicine, one field in biology. Consider that organic evolution (not to mention astronomical and geological evolution) relies on data from biochemistry, comparative anatomy, the fossil record, biogeography, and many other fields. The vast majority of students are not well enough versed in even one of these areas to critically evaluate it. The amount of time devoted to evolution in most classes is pitifully small as it is, although the consensus of science educators and scientists is that it should be the organizing principle of biology and geology, and be referred to regularly throughout the semester. Few teachers who favor teaching the "two models" would be willing to spend enough time teaching about evolution so that students could see why the creationist arguments are faulty.


Teachers should teach evolution, but in many classrooms they encounter much opposition, mirroring the rejection of evolution by large percentages of the population. There are three approaches discussed here to help teachers deal with anti-evolutionism.

First, be informed about the nature of science, and the science of evolution.

Second, understand the religiously-based opposition to evolution, and consider ways to defuse it. Before students can learn evolution, they must be willing to learn, and many come into class thinking that evolution is incompatible with their religious views. In some cases, this will indeed be the case, and nothing a teacher can say will change it. In this situation, it is best to remind the student that the job of the teacher is to communicate the consensus view of the field, and the job of the student is to learn it. Whether the student accepts what he learns is up to him. For most students, becoming aware of the plurality of religious views towards evolution allows them to accommodate their views to the science you are presenting.

Finally, there is much pressure on teachers to teach creationism along with evolution in the science class because doing so is "fair," or, perhaps, "good pedagogy". Neither is the case: students should learn state of the art science, not outmoded views which have been rejected as science. Also, we do not determine curricula based on the desires of a pressure group, but based on the consensus of scholars in the field.

But teachers themselves need to take the initiative, because ultimately, the buck stops in the classroom, with the teacher. Many teachers teach science without having had training in the subject, or with only inadequate training. Especially at the elementary level, many teachers have "science phobia." These teachers are especially reluctant to teach evolution, for obvious reasons. They need better knowledge of the content of science, but they also need encouragement to teach a controversial issue. There are many knowledgeable teachers who are teaching evolution, and teaching it well. You have a responsibility to mentor those who are not, and I encourage you to do so.

Evolution is the organizing principle of biology and geology, and it needs to be taught if we are to produce new scientists as well as have a scientifically literate society. There is help for teachers willing to teach this "controversial subject," from organizations like the National Association of Biology Teachers, the National Center for Science Education, and also - most importantly - from colleagues.

[Originally published in The Paleontological Society Papers Oct 1996; volume 2, LEARNING FROM THE FOSSIL RECORD, edited by Judy Scotchmoor and Frank K McKinney. ]


[Anonymous]. American Museum of Natural History announces results of nationwide survey on science literacy. NY: Office of Public Affairs, American Museum of Natural History, 1994.

[Anonymous]. Only 25% of American adults get passing grades in science survey. Los Angeles Times 1996 May 24, p A22. Committee on Science and Creationism. Science and creationism. A view from the National Academy of Sciences. Washington (DC): National Academy Press, 1984.

Denton M. Evolution, a theory in crisis. Bethesda (MD): Adler and Adler Publishers, Inc, 1985.

Gillis AM. Keeping creationism out of the classroom. Bioscience 1994:44(10):650-6.

Goldman AL. Portrait of religion in US holds dozens of surprises. New York Times 1991 Apr 10: A1.

Hunter JD. American evangelicalism: Conservative religion and the quandary of modernity. New Brunswick (NJ):Rutgers University Press, 1983.

Marsden GM. Evangelical and fundamental Christianity. In: Eliade M, editor. The Encyclopedia of Religion. Volume 5. NY: Macmillan, 1987. p 190-7.

Matsumura M. Voices for evolution. 2nd ed. Berkeley (CA):National Center for Science Education, 1995.

National Research Council. National science education standards. Washington (DC): National Academy Press, 1996.

Petit C. Americans flunk science basics. San Francisco Chronicle 1996 May 24: A1.

Project 2061. Benchmarks for Science Literacy. NY: Oxford University Press, 1993.

Scott EC. The Struggle for the schools. Natural History 1994 Jul: 10, 12-3.

Scott EC. . Science and Christianity are compatibleùwith some compromises. The Scientist 1995 Jan 9: 12.

Scott EC. Monkey business. Creationism regroups to expel evolution from the classroom. The Sciences. 1996 Jan/Feb: 20-5.