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Getting the Monkey off Darwin's Back

Four Common Myths About Evolution

Evolution is poorly characterized by certain commonly used phrases. Properly communicating how evolution works requires careful attention to language and metaphor.

Charles Sullivan and Cameron Mcpherson Smith

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Nearly 150 years after Charles Darwin published On The Origin of Species, the theory of evolution is still widely misunderstood by the general public. Evolution isn't a fringe theory, and it's not difficult to understand, yet recent surveys reveal that roughly half of Americans believe that humans were created in their present form 10,000 years ago (Brooks 2001, CBS 2004). The same number reject the concept that humans developed from earlier species of animals (National Science Board 2000).

But the evidence is clear that no species, including humans, simply "popped up." Each life form has an evolutionary history, and those histories are intricately intertwined. If we don't understand that complex evolution, we will make poor decisions about our future and that of other species. Should we genetically modify humans? How about our food crops? What effects will global warming have on human biology? None of these questions, nor many others of immediate concern to humanity, can be usefully addressed unless we understand the evolutionary process.

In examining how evolution is portrayed in the mass media, we found many problems; chief among them was the use of inaccurate expressions. In this article we examine the commonly-used phrases "evolution is only a theory," "the ladder of progress," "missing links," and "only the strong survive."

These expressions are misleading at best, and simply wrong at worst. Most of these phrases have ancient roots, describing biology as it was understood centuries ago. They lead to a distorted picture of what evolution is and how it works.

Evolution Is Only a Theory

Have you ever heard people challenge evolution by claiming that "it's only a theory?" The Cobb County School District in Georgia did just that when it sought to put stickers on high school biology textbooks stating that, "Evolution is a theory, not a fact, regarding the origins of living things." [1] The problem with this claim rests with two different uses of the word theory. In popular usage the word refers to an unsubstantiated guess or assumption, as when someone theorizes that a light moving across the night sky must be an alien spaceship. When scientists use the word theory, however, they're referring to a logical, tested, well-supported explanation for a great variety of facts. [2] In this sense the theory of evolution is as well supported as the theory of gravitation or other explanatory models in fields such as chemistry or physics. While it's true that much of the evidence for evolution is not obtained by laboratory experiments, as in chemistry and physics, the same can also be said for geology and cosmology.

A geologist cannot travel back in time to observe first hand the formation of Earth's crust, and a cosmologist cannot witness the collapsing of a star into a black hole, but this doesn't mean that scientific theories about the nature of these phenomena are simply unsubstantiated guesses. Some scientific theories do a better job of accounting for the facts than others, and in biology there is no competing scientific theory with more explanatory power than evolution. Biologist Theodosius Dobzhansky put it best when he said, "Nothing in biology makes sense except in the light of evolution."

Many people confuse evolutionary theory with Lamarckism, named for the French naturalist Jean-Baptiste Lamarck (1744-1829). In one sense Lamarck was an evolutionist in that he favored the view that new species had evolved from ancestral species, but he was mistaken about the mechanism by which species change, and about the time required for these changes. Lamarck thought that the mechanism for biological change was the transmission to the next generation of characteristics acquired during the life span of an individual. His most famous example is that of the giraffe. According to Lamarck, the giraffe's ancestors had shorter necks, and they would stretch their necks to reach higher foliage in trees. Their descendants then inherited longer necks because the characteristics of these newly stretched necks of the parents were passed down to their offspring. Moreover, Lamarck thought that the evolution of a new species could occur within a few generations or even one. His position was reasonable for its time, yet it happens to be incorrect.

But acquired characteristics are not passed on. [3] If you lose your arm in an accident, your offspring will not be born with a missing arm. If you lift weights to gain muscle mass, you will not transmit larger muscles to your offspring. Jews have been practicing circumcision for hundreds of generations, yet there is no evidence that this acquired feature is biologically inherited.

The position of modern evolutionary theory (Neo-Darwinism [4]) is that some ancestors of giraffes acquired slightly longer necks through random mutation. These animals could eat food that was a little out of reach of others of their species, and so they tended to be healthier, to live longer, and have a better chance than their fellows at mating and passing on to the next generation their genes for longer necks. Many such incremental changes over a long period of time are required for a new species-or a neck as long as a giraffe's-to arise.

The evolution of giraffes or other life forms should not be thought of as a singular process. There are at least three independent processes that, when taken together, form our idea of evolution. These are replication, variation, and selection. Replication is essentially reproduction. Variation refers to the random changes-typically mutations-arising in offspring, making them different from their parents. Selection refers to the process whereby those individuals best adapted to their environment tend to be the ones that survive, passing on their genes. These three processes occur every day in nature, and it is their cumulative effect that we call evolution.

If an entirely new scientific theory with more explanatory power is formulated, then Neo-Darwinism will have to be swept aside just as Lamarckism was. Creationism and Intelligent Design don't qualify as competing scientific theories because they're not scientific. They don't offer natural explanations for biological phenomena, but rather supernatural explanations which cannot be tested scientifically. Neo-Darwinism offers a natural explanation to account for the facts of evolution, and rejects supernatural explanations.

When discussing the theory of evolution it's important to realize why it's misleading to say that evolution is only a theory. Evolution is indeed a theory, but it's a theory with a lot of evidence on its side, and with more explanatory power than any competing theory in biology.

The Ladder of Progress

The word evolution is sometimes used to mean progress. People speak of moral evolution when discussing certain cultural changes that have been for the better, such as the increased recognition of the rights of women. Or they speak of technological evolution when comparing present-day technology with that of ancient hunter-gatherers. This sense of the word evolution implies a progressive development toward better or more advanced stages. It is this non-biological sense of evolution that influences people to think of biological evolution as involving ladder-like progress from lower to higher stages.

The idea of an evolutionary ladder of progress has its roots in Classical Greek and Medieval European concepts about the nature of the universe. The most common manifestation is known as the Great Chain of Being, which was most influential in Europe from the fifteenth through the eighteenth centuries. The basic idea of the Great Chain of Being is that God and his creation form a hierarchy which is ordered from the least perfect things or beings at the bottom of the chain to the most perfect at the top, namely, God himself. Simply put, the ranking from bottom to top is as follows: rocks or minerals, plants, animals, man, angels, God.

The Great Chain of Being scheme wasn't designed with evolution in mind since the prevailing idea of the time was that God made all existing species, in their modern forms, long ago. The Great Chain of Being is best described as a method of classification. This idea began to lose support before the Darwinian revolution, but Darwin's ideas and their refinement ultimately broke the links of the Great Chain of Being.

The modern biological understanding of evolution does not involve progress in the sense of a natural upward goal toward which life is striving. [5] Genetic mutations arise randomly.

A study of the DNA of Darwin's finches on the Galapagos Islands (Petren et al. 1999) provides a good example of why the idea of progress makes no sense in evolution. The study's findings suggest that the first finches to arrive on the islands were the Warbler finches (Certhidea olivacea), whose pointy beaks made them good insect eaters. A number of other finches evolved later from the Warbler finches. One of these is the Geospiza ground finch, whose broad beak is good for crushing seeds, and another is the Camarhynchus tree finch with its blunt beak which is well adapted for tearing vegetation.

Even though the seed-eating and vegetation-eating finches evolved from insect-eating finches, the former are not "more evolved" than the latter, or "higher" on some evolutionary ladder. Since finch evolution on the Galapagos Islands was driven primarily by diet, the ground finches simply became better adapted at making a living on seeds, the tree finches on vegetation, and the Warbler finches on insects.

If seeds were to become scarce on the Galapagos Islands, it's conceivable that the seed-eating finches-which are a more recent species-could become extinct, while the insect-eating finches-which have been around much longer-would continue to thrive. The concepts of "higher" and "lower" do not apply to the Galapagos finches or anywhere else in evolution. It is fitness or adaptability relative to the environment that matters. Species cannot foretell the future in order to adapt themselves deliberately to environmental changes, and if the environment changes drastically, those adaptations that were once favorable may turn out to be unfavorable.

Even though biologists reject the Great Chain of Being or any similar ladder-of-progress explanation of evolution, the idea still persists in popular culture. A more accurate analogy would be that of a bush that branches in many directions. If we think of evolution over time in this way, we're less likely to be confused by notions of progress because the branches of a bush can grow in various directions in three dimensions, and new branches can sprout off of older branches without implying that those farther from the trunk are better or more advanced than those closer to the trunk. A more recent branch that has split off from an earlier branch-like a species that has evolved from an ancestral species-does not indicate greater progress or advancement. Rather, it is simply a new and different growth on the bush, or more specifically, a new species that is sufficiently adapted to its environment to survive.

The Missing Link

"Fossils May be Humans' Missing Link" reported the Washington Post on April 22, 1999. The story states that fossils discovered in Ethiopia ". . . may well be the long-sought immediate predecessor of human beings." But almost fifty years earlier, paleontologist Robert Broom published Finding the Missing Link (1950), about his discovery of fossil "ape men" in South African caves. And since 1950, reports of the discovery of "missing links" have been continuous. What's going on? How is it that the "missing link" has been discovered repeatedly?

The problem lies in a false metaphor. When we say "missing link," we invoke a metaphorical chain, a set of links that stretch far back in time. Each link represents a single species, a single variety of life. Because each link is connected to two other links, each is intimately connected to past and future forms. Break one link, and the pieces of the chain can be separated, and relationships lost. But find a lost link, and you can rebuild the chain, reconnect separated lengths. One potent reason for the attractiveness of this metaphor is that it allows for the drama of the quest, the search for that elusive missing link.

But the metaphor is as misleading as it is attractive. The concept that each species is a link in a great chain of life forms was largely developed in the typological age of biology, when species "fixity" (the idea that species were unchanging) was the dominant paradigm. Both John Ray (1627-1705) and Carolus Linnaeus (1707-1797), the architects of biological classification (neither of whom believed in evolution), were concerned with describing the order of living species, an order they each believed was laid out by God (Ray suggested that the divinely specified function of biting insects was to plague the wicked). But while the links of a chain are discrete, unchanging, and easily defined, groups of life forms are not. [6] We generally define a species as some interbreeding group that cannot, or does not, productively breed with another group. But since species are not fixed (they change through time), it can be difficult to be sure where one species ends and another begins. For these reasons, many modern biologists prefer a continuum metaphor, in which shades of one life form grade into another. [7] Life is not arranged as links, but as shades. The metaphorical chain is far less substantial than it sounds.

Thus the chain metaphor is wrong. It doesn't accurately represent biology as we know it today, but as it was understood over four centuries ago. The myth persists because of convenience; it is easier to think of species as types, with discrete qualities, than as grades between one species and another. In school, we learn the specific characteristics of plants and animals; this alone is not a problem, except that we are not often exposed to the main ramification of evolution: that those characteristics will change through time.

Clearly, both the Post article and Broom's book describe the discovery of australopithecenes, African hominids [8] that lived well over three million years ago. Australopithecenes walked upright, like modern humans, but they had large, chimp-like teeth, and smallish, chimp-like brains. Australopithecenes made rudimentary stone tools that are more complex than any chimpanzee's termite-mound probe stick, but far less complex than the symmetrical tools made by early members of our genus, Homo. In terms of anatomy and behavior, some australopithecenes really do appear to be "half human." Additionally, it's widely believed that early Homo descended from some variety of late australopithecene. Broom was right after all, but so was the Post; a "missing link" has indeed been found. It is Australopithecus. But there were many varieties of Australopithecus, as well as Homo, and there is no obvious place to draw a discrete line separating a shade of late Australopithecus from an early grade of Homo. Therefore, it's more accurate to say that we have found some "grade" or "shade," rather than "the missing link." [9]

We can curb the false metaphor by changing our wording. In classes, in textbooks, in discussions with our students, and in press releases (the critical connection between academia and the general public), we have to start saying that we're looking for a missing link, rather than the missing link. Better yet, we should replace the "missing link" stock phrase with something more accurate.

Only the Strong Survive

Around a million years ago, an ape so large that it's now known as Gigantopithecus roamed the bamboo forests of South Asia. Standing nine feet tall, weighing from 600 to 1,000 pounds, and with a bamboo-crushing jaw the size of a mailbox, this was a truly strong creature. But today, all that remains of Gigantopithecus are a few fossil teeth and jawbones, quietly resting in museum vaults.

If only the strong survive, how did early Homo-protohuman bipeds that were in the same area at the same time, and were less than half the size of Gigantopithecus-survive? Wouldn't any clash between these creatures result in the strapping Über-ape annihilating the competition?

Yesterday's giants can be today's museum specimens. If only the strong survive, though, how is this possible? Indeed, how is it that humans are now ascendant on Earth, but, when stripped of tools and culture, we are among the most helpless of animals?

The answer, of course, is that strength can be measured in many ways. Brawn is one measure; brain is another. But this distinction is often lost in popular culture. When we say "the strong," or even "the fittest," most people immediately think of competition between individuals. These individuals, we imagine, are pitted against one another in some evolutionary arena, where they fight for survival and mates. The strongest survive, pass on their genes, and propagate their lineage. The loser, and its entire lineage, goes extinct.

But this notion of single combat in a single arena of competition is too simple. In reality, there are dozens of arenas, dozens of problems any organism must face in life. Perhaps direct competition with other individuals is one, but every day individuals are kicked from one arena to the next. If the river dries up, you're now in the Arena of Water Conservation. If the temperature suddenly drops, you're pushed into the Arena of Heat Conservation. If the properties of the vegetation you eat begin to change, you're now in the Arena of Metabolic Versatility.

In short, survival is much more complex than is implied by the single-arena concept of combat between individuals. Life forms struggle against a wide array of factors, and often against more than one factor at a time. In biology, these factors are known as selective pressures.

Selective pressures also change. A certain selective pressure can be particularly hard-pressing for a period, shaping the course of evolution, but later that pressure may ease, and another concern becomes primary. And since the environment is always changing, no species can ever be sure what selective pressures it will have to cope with tomorrow. Indeed, such conscious anticipation of the future is precluded for most species (could deer have anticipated the invention of guns?), and evolution is entirely reactive, shaping species according to past and present environments, but never "looking" into the future. [10]

We humans, and all life forms, exist and struggle not in any single arena, but in an immense web of selective pressures that is incomprehensibly complex and ever-changing. Survival is much more involved than simply beating down your immediate peers.

Why does the single-combatant, evolutionary arena myth persist? The answer is probably deeply intertwined with renaissance values of individualism too complex to examine here [11] but it is clearly related to nineteenth-century Social Darwinism. Social Darwinists grafted Darwin's basic ideas about biological evolution to human society and economy. To them, progress could only be made by eliminating imperfections from humanity, and this was best done by competition. That competition, neatly summarized by Herbert Spencer's term "survival of the fittest," was taken to mean the competition between individuals. It is significant that today's reality-TV programs are steeped in this metaphor, in which the concept of survival via ruthless individual competition is paramount.

The best way to curb this myth is to teach that brute strength does not guarantee long-term success. In fact, no single characteristic does. More importantly, we need to describe why there is no single key to long-term success, because we never know how our selective environment is going to change. For humanity, then, the only hope for success, for survival, is in remaining flexible and adaptive. Real strength is in adaptability, which comes from genetic and cognitive variation.

Conclusion

A picture of evolution based on the common myths we've outlined is a mosaic of confusion. It's very important to remedy this confusion, because how we think of ourselves, and every other species on Earth, is directly related to how we understand evolution. We can either see ourselves as separated from a natural world that simply serves as a theater for our evolution,12 or as one of many coevolving species of life on Earth. The former view is more likely to persist if we continue to describe evolution using obsolete or faulty expressions. The latter view, which is accurate, will be promoted by a better use of language, and by acknowledging what we have learned about biology in the past 150 years. [13]

Solutions for conveying this accurate view must include more careful use of language and metaphor to explain exactly what evolution is, and how it happens.

Notes

1. The entire disclaimer reads: "This textbook contains material on evolution. Evolution is a theory, not a fact, regarding the origin of living things. This material should be approached with an open mind, studied carefully, and critically considered." This led to a lawsuit, Selman v. Cobb County School District. On January 13, 2005, a federal judge found this policy unconstitutional.
2. See, for example, "What's Wrong with 'Theory not Fact' Resolutions." National Center for Science Education. 7 December 2000. Available here.
3. However, a recent study on fruitflies suggests that some genetic instructions that are not encoded in the DNA may be passed on to offspring by way of material encompassing the DNA (Lin et al. 2004).
4. Developed in the 1930s, Neo-Darwinism (also called the Modern Synthesis) integrates Darwin's theory of natural selection with the theory of genetic inheritance first proposed by Gregor Mendel and subsequently refined by later biologists.
5. Biologists disagree about whether there is an evolutionary tendency toward complexity, primarily because there is no consensus on how complexity should be defined and measured.
6. The species concept is introduced in Strickberger (1985:747-756), but also see Mallet (1995) for the need to review how we define species.
7. Lions and tigers once coexisted naturally in India, and although they are outwardly very different, they can mate to create tigons or ligers. Since such hybrids were never found in nature, however, it is known that lion and tiger did not interbreed naturally. Thus, genetically, lion and tiger can be classified as one species, but behaviorally, they differed enough to be considered separate species by biologists, and in nature this difference was maintained by the animals themselves (Wilson 1977:7).
8. Hominids are large primates that walk upright. Those of the genus Australopithecus (which predate the human lineage Homo) are referred to as australopithecenes. They appear over 4 million years ago. Many hominid varieties have existed, but Homo sapiens sapiens is the only living hominid.
9. The link metaphor also suggests that any given species is represented by only one chain, as when we see a diagram of hominids, first knuckle-walking, then hunched over in a half-stand, then upright as modern man. This depiction does not show several other bipedal hominid varieties to which we are related, such as the robust australopithecenes (appearing over 4 million years ago, disappearing about 1 million years ago) or the Neanderthals (who appear around 300,000 years ago and are extinct by c.30,000 years ago). The depiction suggests that there was one, unbroken chain, from quadruped to biped, but actually there have been bipeds that have gone extinct (as well as quadrupeds that exist today).
10. Humanity, of course, is uniquely proactive. We can imagine the future, and we prepare for it by controlling our evolution with all sorts of social and biological methods. Social methods include complex kinship and marriage rules that ensure gene flow among different populations. Biological methods include mass vaccination programs against polio and smallpox.
11. See for example Shanahan (2004), an interesting comment in Commager (1965:82-83), and Butterfield (1965:222-246).
12. We suggest that this view of humanity contributes to wasteful use of resources; for example, humanity has chronically overfished nearly every fishery ever discovered; see Jackson et al. (2001).
13. It's not sufficient to constantly explain away old, inaccurate expressions: we must develop new ones. What is the use in keeping old metaphors or phrases that do not point to reality? For example, we may say "The Bush of Evolution" or "The Labyrinth of Evolution,' rather than 'The Ladder of Evolution." A good way to find such new metaphors may be to create a Web site where anyone could suggest them, and, after a time, select new ones to start incorporating into our common speech. Perhaps poets, being familiar with the power of image and metaphor, could be helpful.

References

Brooks, D.J. 2001. Substantial numbers of Americans continue to doubt evolution as explanation for origins of humans. The Gallup Organization. Available online here.

Broom, R. 1950. Finding the Missing Link. London: Watts & Co.

Butterfield, H. 1965. The Origins of Modern Science. New York: MacMillan.

CBS News Polls. 2004. Creationism trumps evolution. CBSNEWS.com. Available online here.

Commager, H.S. 1965. The Nature and Study of History. Columbus, Ohio: Charles E. Merrill Books.

Dobzhansky, Theodosius. 1973. Nothing in biology makes sense except in the light of evolution. The American Biology Teacher 35:125-129.

Jackson, J., M. Kirby, W. Berger, K. Bjorndal, L. Botsford, et al. 2001. Historical overfishing and the recent collapse of coastal ecosystems. Science 297:629-637.

Lin, Q., Q. Chen, L. Lin, and J. Zhou. 2004. The Promoter Targeting Sequence mediates epigenetically heritable transcription memory. Genes & Development 18: 2639-2651.

Mallet, J. 1995. A species definition for the modern synthesis. Trends in Ecology and Evolution 10:294-299.

National Science Board. 2000. Science and Engineering Indicators. Washington, D.C. US Government Printing Office. Available online here.

Petren, K., B.R. Grant, and P.R. Grant. 1999. A phylogeny of Darwin's finches based on microsatellite DNA length variation. Proceedings of the Royal Society of London B266: 321-329.

Shanahan, T. 2004. The Evolution of Darwinism: Selection, Adaptation and Progress in Evolutionary Biology. New York: Cambridge University Press.

Strickberger, M.W. 1985. Genetics. New York: Macmillan.

Suplee, C. 1999. Fossil find may be that of humans' immediate predecessor. The Washington Post, April 23. pp. A3, A11.

Wilson, E.O. 1977. Sociobiology. Harvard, Massachusetts: The Belknap Press of Harvard University Press.