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The Case for Evolution It is often argued by champions of Creationism that evolution is only a theory, as if it were only the opinion of a certain group, and that other opinions have a right to be expressed and taught to school children. Although evolution, like all scientific knowledge, is indeed provisional, subject to correction and extension as further knowledge accumulates, it is more than a theory. Evolution is so fundamental to the understanding of modern biology, geology, and cosmology, that the whole structure of these sciences would collapse if it were to be shown to be fundamentally incorrect. Our understanding of biological evolution is based on the concept of natural selection, formulated independently about 150 years ago by Charles Darwin and Alfred Wallace. Simply stated, natural selection says that any population consists of individuals with different degrees of expression of a variety of characteristics. When the environment changes, those individuals with the set of characteristics best suited to the new environment will survive in higher numbers, and therefore produce more progeny, than the others. The difference need not be great; an edge of as little as a few percent greater survival is enough, given sufficient time, to produce a new species. Biologists have understood long ago that Darwin’s formulation was in error in several details. Perhaps most significantly, it is currently understood that the process is a more holistic one, that an evolving species not only responds to a changing environment, but it also brings about changes in the environment. So, in a sense, it is not so much the species that evolves as the whole ecosystem of which it is a part. Even with corrections, however, the fundamental outlook of classical evolutionary theory continues as the foundational paradigm in science, with major influence in philosophy and theology. The traditional evidence for biological evolution comes from four sources: the fossil record, isomorphism, embryology, and the evolution of marsupials. Fossils are the petrified remnants of living beings, most typically bones and teeth of animals, but including plants and other organisms of all types. The strata within which fossils are found can be dated by the presence of other specimens of known age or by radioactive dating. Digging down through layers of sedimentary rock, then, amounts to descending backward in time. The fossil record shows that certain species are found back to a certain time and then not at all before that, indicating that the species first appeared at that time and presumably developed from another species. Other species appear at a certain time and then at a later time completely disappear, again indicating its development from a predecessor and possibly its replacement by a successor. An objection which is frequently posed is that intermediate forms between a species and its successor, “missing links,” are rarely found, supposedly showing that the second species did not develop from the first, but had an individual special creation. To the contrary, however, the normal process of evolution is a series of spurts and stabilizations. When an environmental challenge arises, nature tries all sorts of variations to see which will present the best adaptations to the changed circumstances, discarding the misfits and trying further variations on the successful ones. This process is relatively rapid, so it is not surprising that very few of these individuals become fossilized. After a good adaptation is settled on, there is a much longer process of consolidation and stabilization, with many more individuals over a much longer time, resulting therefore, in more fossils. The argument from isomorphism comes from the observation that the members of related groups have the same basic structure over a variety of species much differently adapted. Among vertebrates, for example, there is a spinal column and brain and four limbs, the familiar pattern among human beings and other mammals. In birds, the front limbs are adapted into wings. In fish the limbs are adapted to fins. The presence of a basic pattern in such a wide variety of species argues for a common origin in their evolutionary history. The evidence from embryology is based on the fact that early embryos of widely divergent species look almost exactly alike—humans, apes, pigs, etc. In their earliest stages of development, the embryos of these species go back to the form of their earliest ancestors. Furthermore, vestigial remains, like the tailbone of human beings (the coccyx), again go back to early ancestors. Marsupials are mammals without placentas and usually with a pouch (like the familiar kangaroo). Marsupials bear young in the usual way of mammals, but the young crawl up the mother’s abdomen and enter the pouch, at the base of which are nipples for nursing. Marsupials developed at a time when what is now Australia was still attached to southwest Africa in the continent of Pangaea. After Australia became detached, placental mammals on the rest of Pangaea developed into the wide variety of animals we know, and the placentals largely (not entirely) replaced the marsupials. A similar development did not take place in Australia. (The placentals presently in Australia were all introduced by humans.) Instead, marsupials adapted to fill the corresponding niches elsewhere filled by placentals, so that one finds marsupial rats, marsupial wolves, etc. It is hard to imagine any explanation for this phenomenon apart from evolution. So the case for evolution is strong. Still, the argument thus far leaves out an important piece. Is the evolutionary process--not only biological, but cosmological and geological as well--simply the result of chance? Many scientists have taken exactly this position. Other scientists, along with many philosophers and theologians, have followed the lead of Teilhard in seeing a profoundly spiritual and sacred dimension in the evolutionary process. The divine creator is seen as embedded profoundly in the evolutionary process, a process which now has shifted into the realm of consciousness, and in which we human beings play so important a part. Our creativity is part of the divine creativity. Evolution has come into our own control, and with our own hands we can share in this ever-old yet ever-new process of creation. Dom Roberti |