Evolution: What Every Teenager Should Know is about science and America’s youth. Unlike other subjects that American students are expected to understand and accept, the subject of evolution still creates such controversy that millions of parents avoid exposing their children to it. Many more parents still insist, “It’s just a theory.” There are millions of religious families who regard evolution with skepticism, or even consider it “un-American,” and who would prefer that their children not learn that life on Earth evolved by natural selection. This, in the most scientifically and technologically advanced society the world has ever known, is a sad state of affairs.The life science curriculum in the typical American high school today does not provide a healthy evolutionary perspective. High school biology textbooks typically contain one chapter, sometimes two, on evolution. These summarize evolution in about forty pages of a six hundred-page book. The word “evolution” very rarely appears in any other chapter. This is odd given that evolution accounts for the DNA molecule, the structure and function of cells, reproductive biology, digestion and the whole range of topics covered by every biology textbook. Evolution isn’t a stand-alone subject that can be neatly boxed in a chapter. Restricting it to a chapter or two enables teachers with an anti-evolution mindset to simply ignore the entire concept. Evolution cannot be taught as a stand-alone science; it’s the thread that unifies modern biology.Every Fall, I teach a large undergraduate lecture course at the University of Southern California on human evolution. I ask the students on the first day of class, “How many of you believe in evolution?” More than ninety-five per cent raise their hands. This is cosmopolitan Los Angeles; most of the students come from educated families and privileged backgrounds. The response would be quite different if I took the poll in the rural Midwest or the deep south. Opinion polls show that a third of Americans don’t accept evolution as real, and among the two-thirds who do, many believe that evolution has been guided somehow by a divine power. The desire to insert a role for God into daily life remains powerful even among otherwise enlightened people. My question to the students is actually a trick question, of course. Evolution is not a belief; it’s a reality. If you want to live in denial of evolution, you’re in the same category as people who choose to deny the reality of the Holocaust or the moon landings. Evolution is a historical science, a tool for reconstructing the ancient past, including our own human past. But it is no less a force of nature than gravity.Evolution is a fact. It is also, however, a theory. This requires some explanation. Creationists say, “It’s only a theory, so why can’t our children be taught other theories that explain life on Earth too, like creationism?” This is partly due to a misunderstanding about what the word ‘theory’ means. A theory in our everyday language has a somewhat different meaning that it has in science. I might say I have a theory about why the Lakers will not win the NBA championship this year, or about why a friend of mine from high school no longer stays in touch with me. These are theories in the everyday sense that we use the word; an educated guess, or even just a hunch. This is not the same as a scientific theory. Gravity is one of the fundamental forces of Nature. It is a fact; gravitational force can be predicted, and we know that it accounts for the orbits of the planets as well as many natural processes here on Earth (including the fact that you are sitting in your chair as you read this rather than floating above it). But we still refer to gravity as a theory, because in 1687 Isaac Newton referred to his ideas as such. Today it is an established law of the natural world. Moreover, scientists will sometimes generate theories about something for which little or no evidence exists. One might theorize about whether life exists on a distant moon in our solar system. At present, no solid evidence exists to support or refute those theories. Like gravity, evolution exists to explain a mountain of evidence, all of which points toward the same conclusion.Evolutionary science is not a predictive science in the way that physics is. The future of evolution cannot be predicted, but the past can be explained. Could humans of the distant future evolve useful new adaptive features? Maybe we’ll all have bigger brains, more powerful eyesight, and more agile thumbs from all that texting? As we put layers of technology between the environment and ourselves, we reduce the power of natural selection (texting will likely never be a behavior on which your survival depends). But even if it did, there’s no way to know what we will look like many thousands of years from now.Just because evolution explains the past without predicting the future doesn’t make it any less factual. It is simply documenting history. You can choose to ignore history or pretend to yourself that it’s not true, but that doesn’t change its reality. Suppose I say I don’t believe in George Washington as a real historical figure. You would say that’s ridiculous; he was the Father of the Country, you’ve seen his home at Mount Vernon, portraits of him that hang in art museums, and you’ve read the accounts of his epic Revolutionary War battles at Boston and Trenton. But we have no photos of Washington (cameras were invented a half-century after his death). None of his DNA exists, and since he never bore any children, confirming his identity genetically would be difficult. Perhaps the Founding Fathers, desperately in need of a figurehead to rally the colonists of the young republic, invented a fictional character and dubbed him George Washington.This is silly, of course. Not believing in George Washington makes about as much sense as not believing in American history. But one can choose to live in denial of well-demonstrated real events, and some people do. In the same way, some people choose to live in denial of evolution.American political leaders unfortunately reinforce a denial of evolution, most likely to avoid alienating large segments of their constituency. Several of the 2012 Republican candidates for president vehemently denied the certainty of evolution, and along with other related rejections of science, such as global climate change. Even President Obama stated that the Earth was created in six days, although he acknowledged that this might be a metaphor used in the bible to refer to six much longer units of time. Certain segments of America aren’t going to change their minds about evolution based on a book. But younger people are far more likely to explore and embrace ideas, even ones they were raised to reject. If some younger Americans are persuaded to think for themselves about science and reality with the help of this book, the effort will have been very worthwhile.Evolution: What Every Teenager Should Know is organized as a series of commonly asked questions about evolution. These are actual questions that my teenage son Adam has been asked by his classmates, and we kept notes about them as I began to plan the book. Each question is a prompt for a concise, fact-filled explanation of how evolution works. I discuss the potential conflicts between evolutionary science and religion, and I tackle some of the thorniest questions that doubters ask. I hope the book can serve as a conversation starter with parents, friends, classmates and teachers. That should be the purpose of any provocative book. The reader will also see that evolution need not be at all controversial. It’s really just the study of history - life’s history – and the process that guides it.
