What mechanism can it be that results in the production of homologous organs, the same 'patterns' in spite of their not being controlled by the same genes? I asked this question in 1938, and it has not been answered.
Evolutionary biologist Gavin de Beer,
Homology: An Unsolved Problem (Oxford: Oxford University Press, 1971).
Itís been nearly 150 years since the publication of Charles Darwinís influential book, On the Origin of Species, and the theory of evolution remains the focus of intense public controversy. So, whatís all the controversy about?
Itís hard to tell, sometimes. Public debate over this issue usually generates more heat than light. There is no shortage of headline grabbers willing to “go public” with confrontational statements on one side or the other. The media sometimes makes the situation worse. Television news in particular tends to rely on “sound bite” coverage of sharply divided opinions that are easy to describe. This makes for exciting viewing, but is not always helpful in finding answers to the real questions in the origins debate.
This focus on media-ready “good guys” and “bad guys” completely misses some of the real (and more interesting) scientific controversies about evolution. We hope this book will help you understand what contemporary Darwinian theory is, why many scientists find it persuasive, and why other scientists question key aspects of it.
Actually, we shouldnít refer to the theory as “it.” As you will discover in the pages that follow, Darwinís theory is not a single idea. Instead, it is made up of several related ideas, each supported by specific arguments. We hope to help you understand what these ideas and arguments are and what different scientists have to say about them in light of current scientific evidence.
The approach we are using in this book is called “enquiry-based” education. This approach allows you, the student, to follow the process of discovery, deliberation, and argument that scientists use to form their theories. It allows you to evaluate answers to scientific questions on your own and form your own conclusions. Our goal in using this approach is to expose you to the discoveries, evidence, and arguments that are shaping the current debates over the modern version of Darwinís theory, and to encourage you to think deeply and critically about them.
Why use the enquiry-based approach?
The enquiry-based approach to education has a number of advantages. First, by enabling you to think critically about scientific theories and ideas, the enquiry-based approach will prepare you to be a better, more informed citizen. You will soon be asked to decide on many political and personal issues that involve science—debates about stem-cell research, decisions about personal medical care, and issues of environmental policy. Teaching scientific ideas openly and critically not only helps prepare you for possible careers in science, but it helps you learn to make informed decisions about such issues.
The second advantage to enquiry-based education is that students typically enjoy science more when itís taught this way. Scientific conclusions donít just pop up fully-formed from a lifeless collection of facts, so why would we teach science that way? Instead, the enquiry-based approach teaches about the arguments scientists have had, and are having, about current theories in light of the evidence. This allows you to do what scientists do—think and argue about how best to interpret evidence.
Third, many science educators are convinced that students gain a better understanding of a subject if they are taught about the arguments that scientists have in the process of formulating their theories. For this reason, the educational standards of several countries now encourage this approach.
In the United Kingdom, for example, the National Curriculum for Key Stage 4 Science has previously recommended that pupils “should be taught how scientific controversies can arise from different ways of interpreting empirical evidence,” and currently recommends “that pupils should be taught how uncertainties in scientific knowledge and scientific ideas change over time, and about the role of the scientific community in validating these changes.” United States federal education policy calls for teaching students about competing views of controversial scientific issues. As the U.S. Congress has stated, “[W]here topics are taught that may generate controversy (such as biological evolution), the curriculum should help students to understand the full range of views that exist.”*
Controversies in science are nothing new. As recently as the early 1960s, for example, most geologists accepted the “geosynclinal theory” as the explanation of how mountain ranges form. After a significant period of controversy, most scientists came to accept the theory of plate tectonics because it provided a better explanation for a larger number of scientific observations. Yet without understanding the arguments that led to the acceptance of plate tectonics, it is very difficult to understand the theory itself or its current standing in the scientific community.
Today we continue to have important unresolved scientific controversies in many branches of science. In climatology, for example, scientists disagree over what global warming is, whether it is a natural phenomenon or a man-made problem, how big a problem it presents, and what (if anything) should be done about it. In theoretical physics, scientists disagree over the meaning and importance of string theory.
This book is one of the first textbooks ever to use the enquiry-based approach to teach modern evolutionary theory. It does so by examining the current evidence and arguments for and against the key ideas of modern Darwinian theory. We hope examining the evidence and arguments in this book will give you a deeper understanding of the theory and help you to evaluate its current status.
But are there really any scientific controversies about the modern theory of evolution?
Throughout this book, you will discover that there are, indeed, important scientific controversies about the key claims of evolutionary theory and about the arguments that are used to support them. We have written this book, in part, so that you could learn about the controversial aspects of evolutionary theory that are discussed openly in scientific books and journals but which are not widely reported in textbooks.
As we said before, Darwinís theory is made up of several ideas, each with supporting arguments. For each argument in Darwinís case, we will begin by explaining the argument, and examining the evidence in support of it. (We call this the Case For.) Then, we will spend some time examining the claims and evidence that lead some scientists to question the argument. (We call this the Reply.) We then look at the current state of the discussion in a section called Further Debate.
Throughout the book, you may notice that the Reply section is often longer than the Case For section. There is an important reason for this. The Case For is the version taught in most school textbooks, and you should, therefore, already be familiar with it to some extent. The Reply section has not yet been presented in most school textbooks. The Reply is sometimes longer simply because it often takes more time to explain an unfamiliar concept or idea.
Whenever there is disagreement over a particular point, we have tried to give arguments from the best people we could find on both sides of the question, rounding up the most qualified proponents and critics that we could.
Ah, yes: the critics. Who are these people, anyway? The main thing you need to know is that “the critics” are not necessarily the same from chapter to chapter. A scientist quoted in the Case For section of one chapter may very well be quoted as a critic two chapters later. As you will find out throughout this book, there are qualified, respected scientists on both sides of each argument.
Finally, you should know something about us, the authors. Two of us are biology professors doing research on evolution-related topics. Two of us are philosophers of science who have specialised in studying the logic of evolutionary arguments. One of us is a technical/curriculum writer. All of us happen to have reservations about various aspects of contemporary evolutionary theory, but we all think that students should learn more—not less—about this theory than they presently do. So, while we present criticisms of the theory that many biology books donít present, we also explain and develop the arguments for contemporary Darwinian theory in more detail than other standard textbooks.
One final word. We donít want you to simply accept this book as the last word on this subject any more than weíd want you to uncritically accept the word of other textbooks that present only the case for Darwinian evolution. Thatís the beauty of open enquiry—and of science, itself. Thatís also an example of the kind of critical thinking that we hope this book will encourage. Look at the evidence, listen to the arguments, and think for yourself.
So, whatís the story on evolution? Thatís what we want to explore. Letís get started!