Chapter 9: Evolution
Theories of Evolution
The word ‘evolution’ means a process of change. We speak of the evolution of technology, culture, art, and so on: these things change over time. In biology, the term evolution refers to the process in which features of living organisms change from one generation to the next. This sort of change obviously does occur, at least to some extent. Offspring don’t look exactly like their parents. However, not everyone agrees about how much change can occur or has occurred.
In the mainstream scientific community and in popular culture, the prevailing account of biological evolution is usually called the theory of evolution, though in fact it consists of numerous theories in genetics, paleontology, and other sciences. To avoid confusion, I will adopt the same nomenclature; but readers should bear in mind that “the” theory of evolution is actually a medley of several distinct theories, pieced together by scientists working in a variety of disciplines. Chemists, molecular biologists, and geneticists together give an account of the processes by which hereditary features are transmitted with variations from parents to offspring; paleontologists try to map out a coherent history of the evolutionary variations that have occurred in the past; geologists and ecologists try to explain why those variations occurred in terms of environmental changes throughout Earth’s history, and so on.
Many details of evolutionary history are debated, and there are unresolved problems with certain aspects of the theory, as we’ll see. Nevertheless, the prevailing consensus in the scientific community is that the theory of evolution is correct in its two central claims, namely:
- All living things on Earth descended from a common ancestor, presumed to have been a single-celled organism that lived billions of years ago. (This doctrine is called universal common descent.)
- The offspring of that first organism have evolved over billions of years through processes of genetic recombination, mutation, and natural selection. Genetic recombination and mutation introduce new hereditary features; natural selection steers evolution by eliminating features that are disadvantageous. (Each of these processes will be explained and discussed later in the chapter.)
Those central claims of the theory of evolution are, for the most part, undisputed in the mainstream scientific community today. In the Christian community, on the other hand, the theory of evolution is about as controversial as any theory can be, and for good reason. If you believe in the truth and authority of the Bible, as I do, you probably aren’t eager to embrace a theory that seems outright contradictory to the story of creation recorded in the book of Genesis. We must take care, however, not to confuse the true, divinely-inspired message of scripture with our own fallible understanding of that message. The opening chapters of Genesis are difficult to understand fully, and close examination of the text reveals a number of subtleties that might indicate a deeper meaning than is apparent at first blush. As we’ll see in chapter 10, the biblical account of creation was already a controversial topic long before the rise of modern science. Since the time of the early church, Christians have held a variety of different views about the meaning and significance of the Genesis creation story.For example, many Christian leaders, apologists, and theologians in the early church—including Justin Martyr (AD 100 - 165), Irenaeus (AD 130 - 202), Clement of Alexandria (AD 150 - 215), Origen (AD 185 - 254), and Augustine (AD 354 - 430)—argued that the “days” described in the creation story represent something other than 24-hour days. See chapter 10 for more details. Similarly, Christians today have diverse opinions concerning the theory of evolution, ranging from full acceptance to complete rejection of practically every aspect of the theory.
Many Christians interpret the scriptures to mean that God created all species of plants and animals just a few thousand years ago in a series of events that took place over the span of four literal days (the 3rd through 6th days of creation). This view, called young-earth creationism, is obviously incompatible with the two central claims of the theory of evolution, and for this reason some young-earth creationists reject the theory of evolution completely. Other young-earth creationists accept some aspects of evolutionary theory. They believe that God created a few biological species supernaturally and then used natural processes to diversify the varieties of life to a limited extent, creating new species or subspecies that still closely resemble their first ancestors.
At the opposite end of the spectrum, some Christians fully accept the theory of evolution, suggesting that God ordained evolutionary processes to create all of the diversity of life on this planet. That view is sometimes called evolutionary creationism. Evolutionary creationism is one type of old-earth creationism—the view that God created the world billions of years ago (or more than a few thousand years ago, at least). Not everyone who accepts old-earth creationism accepts the theory of evolution, however. Many old-earth creationists reject certain aspects of the prevailing theory of evolution. Some have proposed ways of modifying the theory in order to render it compatible with their understanding of scripture. For example, some believe that God used evolutionary processes to create animals but that he created human beings in a separate, supernatural event.
We’ll consider each of those views in chapter 10. In the present chapter, however, I will refrain from promoting and defending my own opinions on these matters. Instead, this chapter will focus on explaining and examining the theory of evolution itself. We’ll examine the theory’s historical development, its central tenets and principles, the types of evidence adduced to support it, and its problems and limitations. This will put us in a better position to consider various Christian perspectives on the theory and its relation to the biblical account of creation, which will be discussed in the next chapter.