After many years of teaching about evolution and natural selection, it continues to surprise me how many misconceptions exist about how the process works. If you do a web image search for “human evolution,” the following image is likely to appear (Figure 2.16).
What is wrong with this picture? First, it implies that humans evolved from chimpanzees, which is incorrect. Although, as primates, we share a common ancestor very far back in time, we split from other primates, including our closest relatives, the nonhuman apes, several million years ago. This image also suggests that evolution is gradual and progressive; that it is intentional and directional; and that there is an end to it—a stopping point. As you will be learning, evolution takes place in fits and starts, depending on the physical environment, changes in climate, food supply, predation, reproductive success, and other factors. It is also not intentional, in the sense that there is no predetermined end; in fact, if environmental conditions change, species can evolve in different directions or even go extinct. Evolution also does not necessarily progress in the same direction over time. One example is the eel-like creature Qikiqtania wakei that lived 375 million years ago. It was originally a fish that evolved to walk on land, then evolved to live back in the water. Early tetrapods like Qikiqtania were likely spending more and more time out of the water during this period. The arrangement of bones and joints in their fins was starting to resemble arms and legs, which would have allowed them to prop themselves up in shallow water and survive on mudflats. Qikiqtania’s skeletal morphology, however, suggests that it then evolved from having rudimentary fingers and toes back to fins that allowed them to again swim in open water (Stewart et al. 2022).
There is also the misperception that natural selection can create entirely new anatomical structures out of thin air in response to changes in environmental pressures. For example, when asked if they can think of ways in which modern humans are continuing to evolve biologically, students often postulate that, as a result of climate change, humans might rapidly develop gills, webbed hands and feet, and learn to breathe underwater in response to rising sea levels. Unfortunately, natural selection can only act on slight variations in anatomy that are already present, and we have no rudimentary physiological system for breathing underwater. Given that natural selection can only act upon existing variation, humans have evolved in such a way that many parts of our bodies are prone to injury. Our knees are one example. The anterior cruciate ligament (ACL) in our knees is “vulnerable to tearing in humans because our upright bipedal posture forces it to endure much more strain than it is designed to” (Lents 2018, 23). When our ancestors made the transition from quadrupedalism to upright walking, we shifted from four bent legs to two straight legs, relying more on our bones than our muscles to support our weight. This is functional for normal walking and running in a straight line, but sudden shifts in direction and momentum, combined with the sizes and weights of modern humans, result in tears in an ACL that is simply not strong enough to bear the stress. If evolution had the capability to engineer a knee from scratch, it would look quite different, and any ligaments involved would likely be larger, stronger, and more flexible. For an interesting look at what anatomically modern humans might look like if we had evolved to withstand the stresses our bodies undergo in our present environment, see “This is what the perfect body looks like – according to science,” which was proposed by biological anthropologist Alice Roberts (Harrison 2018).
Another misperception about evolution is that some species are “more evolved” than others. Every species currently alive on the planet today is the result of millennia of natural selection that has rendered current members of that species well-adapted to their respective environments. Humans are no more “evolved” than fruit flies or yeast. What sets us apart are our cultural and technological abilities, which have allowed us to successfully survive in a wide variety of physical environments, many of which are now becoming too hot, too wet, or too dry to sustain human life without a great deal of technological intervention (IPCC 2022).
There is also some confusion about what “fitness” actually means and a failure to grasp that it changes as environmental conditions change. Evolutionary “fitness” is different from physical fitness. “Fitness” in evolutionary terms refers to an individual’s ability to survive and reproduce viable offspring who also survive and reproduce. Evolutionary fitness and reproductive success are highly dependent on specific environmental conditions, which can shift over time, greatly affecting the relative fitness of individuals in a population. Recent research on the impacts of climate change on dragonflies will serve to illustrate the point (Figure 2.17).
Pictured here is a male dragonfly, who, you will notice, has distinctive black markings on its wings. This is due to melanization. Males control breeding, and those with more ornamentation tend to attract more mates and to successfully ward off male competitors. Higher levels of melanization, however, have negative consequences for males in warming climates. The black markings absorb heat, elevating body temperatures, which can cause overheating, reduce male fighting ability, and even lead to death (Moore et al. 2021). Females are not as adversely affected because they spend more time in shaded areas, while males are more often flying in sunlit areas, fending off rivals. However, as highly melanized males become less viable, wing coloration is undergoing selection in males. In other words, what constitutes being “fit” for males has changed, favoring those who have fewer of the black markings and, therefore, are less negatively impacted by warming temperatures. Note that natural selection acts on individuals, “selecting” those who happen to be fit for particular environmental conditions at a particular point in time. Evolution, though, happens at the level of the population. If the climate continues to warm, populations of dragonflies who inhabit warming areas will increasingly exhibit less ornamentation in males.
Lastly, natural selection can only act on characteristics that influence reproductive success. Deleterious traits that have nothing to do with one’s ability to reproduce and successfully rear offspring to reproductive age will continue to be passed on. For example, the author of this chapter is a natural redhead, and redheads are predisposed genetically to a number of conditions that can negatively affect health (Colliss Harvey 2015), but some of these conditions are not diagnosed until later in life. One example is Parkinson’s disease (Chen et al. 2017), which is a degenerative neurological disorder. The average age of diagnosis of Parkinson’s is 60 years of age, meaning redheads may encounter such a diagnosis well past childbearing age, having already passed on the genetic predisposition. Thus, Parkinson’s disease cannot be selected out from the redhead family tree.
Dig Deeper: Teaching Evolution Around the World
Evolution is recognized as a central organizing principle for all scientific disciplines and accepted without controversy among scientists and educated people around the world. The United States has historically been the exception (Lerner 2000). In some parts of the U.S. the teaching of evolution to K-12 students continues to evoke controversy, related to politics and religion. The problem is compounded by the degree of control individual states and local school boards exercise over curriculum in the nation’s public schools (Lerner 2000).
The debate over teaching evolution in schools in the United States first came to a head in 1925 after several states attempted to legislate a ban against its teaching. The state of Tennessee eventually did pass such a ban, and the American Civil Liberties Union (ACLU) offered to defend any science teacher who agreed to break the law. John Scopes, who taught in a small, rural Tennessee school, continued to teach evolution, resulting in the “Scopes Monkey Trial,” one of the most famous media trials in American history (Figure 2.18). The entire nation listened to its broadcast live on the radio and read about it daily in hundreds of newspapers. Scopes was defended by Clarence Darrow, the most famous lawyer in the country at the time; Scopes was eventually convicted, though the conviction was later overturned. The pro-Evolution movement benefited greatly from Darrow’s questioning of those on the anti-Evolution side, whose responses were perceived negatively by well-educated listeners in northern cities. The teaching of evolution was also bolstered by a Supreme Court decision in 1947 overriding states’ rights to make decisions on church-state issues and by the launching of Sputnik, the first Soviet (Russian) satellite, in 1957, making science education a national priority. During the 1960s to 1970s, creationism and intelligent design began to take hold as courts ruled in favor of “academic freedom” (Pew Research Center 2019). Since that time, states, and even local school boards, have pushed for the removal of evolution from science curriculum and textbooks or for teaching evolution on equal footing with concepts such as creationism and intelligent design (Masci 2019).
Partly in response to chronically low scores by students in the United States on international measures of ability in science, math, and reading (Desilver 2017), development of the Next Generation Science Standards (NGSS) for K-12 education began in 2011 and were implemented in 2013 in public schools across the nation (nextgenscience.org). The standards were developed collaboratively by The National Research Council (NRC; a branch of the National Academy of Sciences), the National Science Teachers Association, the American Association for the Advancement of Science, and Achieve, an independent, nonpartisan, nonprofit education-reform organization dedicated to working with states to raise academic standards and graduation rates. Twenty-six states also partnered together in the development of the standards. However, due to a number of issues, including funding and support for teachers, adoption of the standards has varied by state. States were also allowed to alter the curriculum. One of the main issues in several states with the original curriculum was the teaching of evolution (Pew Research Center 2014). One prominent aspect to note is that the NGSS do not specify that human evolution be taught, and high school standards do not require teaching about all of the forces of evolution, only mutation and natural selection.
The situation regarding teaching evolution has changed greatly in recent years. A 2007 survey found that only one in three public high school biology teachers in the United States presented evolution consistently with the recommendations of the nation’s leading scientific authorities, and 13% of these teachers emphasized creationism as a valid scientific alternative to modern evolutionary biology (Plutzer, Branch, and Reid 2020). A repeat of the survey in 2019 demonstrated marked improvement in the amount of time teachers devoted to teaching evolution, as well as more teacher training and preparedness to teach evolution. Such improvements were attributed to the need to meet the Next Generation Science Standards, as well as continuing outreach by the National Science Teaching Association, the National Association of Biology Teachers, and the National Academy of Sciences in producing classroom resources and providing professional development opportunities to advance the inclusion of evolution in the nation’s classrooms.
Public acceptance of evolution has also substantially improved in recent years (Miller et al. 2022). National samples of American adults have been asked at regular intervals since 1985 to agree or disagree with the following statement: “Human beings, as we know them today, developed from earlier species of animals (Miller et al. 2022)” During the last decade, the percentage of U.S. adults agreeing with this statement increased from 40% to 54%—a majority for the first time. This level of acceptance of evolution in the United States is atypically low for a developed nation. In a study of the acceptance of evolution in 34 developed nations in 2005, only Turkey—at 27%—scored lower than the United States (Miller, Scott and Okamoto 2006). There are also distinct differences among members of the U.S. population in terms of acceptance of evolution, with 68% of those ages 18–24, 58% of those with college degrees, and 65% of those who have taken four or more college-level science courses the most accepting of evolution. An increasing number of parents also report changing their unfavorable views of evolution due to helping their children with science homework and science fair projects.
Approaches to teaching evolution vary across the globe, with considerable differences within and between nations. One example is the United Kingdom, home of Darwin and Wallace. There, evolution is not introduced until ages 14–16, which is considered quite late by some educators. And, although evolution is taught in biology classes, it is addressed as a separate topic, rather than integrated into the curriculum as a foundational concept. As in the United States, there is also considerable variation between public and private schools, and between religious and secular institutions, in their treatment of the topic and the inclusion of alternative viewpoints, such as creationism (Harmon 2011). There are similar differences across the European Union, including within different populations in member countries.
There are also differences in the teaching of evolution across many predominantly Muslim nations. Salman Hameed, Professor of Integrated Science and Humanities at Hampshire College and Director of the Center for the Study of Science in Muslim Societies (SSiMS), whose research focuses on the acceptance of evolution among Muslims, has uncovered a great deal of variation among Muslims regarding beliefs about evolution. He points out that there is no central position within Islam regarding evolution, leaving it up to governments, textbook authors, and other entities to decide whether, and how, to address evolution in education. Saudi Arabia, Oman, Algeria, Morocco, and Lebanon all ban the teaching of evolution on religious grounds. Other Islamic nations, including Egypt, Malaysia, Syria, and Turkey, include evolutionary concepts like natural selection in their science curriculum but refrain from discussing human evolution (Asghar, Hameed, and Farahani 2014).
Impeding acceptance of evolution in science classes around the world is the adoption of textbooks from the E.U., the U.K., and the U.S. that include examples that are not culturally relevant to local populations (Harmon 2011). One classic example Hameed cites is that of the peppered moths in England whose predominant color pattern evolved from mostly white to mostly black due to pollutants darkening the tree bark of their habitat during the Industrial Revolution. Historical examples like this have little relevance for 21st-century students who grew up in non-Western countries and know little of England’s history or of the species that live there. It also privileges Western science over local science, to which many individuals in former European colonies and territories object (Jones 2017). Hameed suggests customizing textbooks to include local fossils and species whenever possible (Harmon 2011).
