The fourth section of Gary N. Fugle’s book Laying Down Arms to Heal the Creation-Evolution Divide looks at the value of biological evolution. It is hard for the non-scientist, and even many scientists who are not conversant with biology, to appreciate the depth and importance of the evolutionary theory in biology.
[O]nce the idea of evolutionary change is considered, we find that it has enormous power to explain much of what we see in the biological realm. This explanatory power pervades all levels of biology, extending from the origin of cell organelles to complex interactions within ecosystems. With evolution in mind, phenomena in one area of biology after another become understandable like they never were before. Biologists are able to repeatedly exclaim, “Aha! I get it! Now that makes sense.” It is because of this sweeping power to make sense of the natural world that evolution is regarded as one of the few unifying principles in the biology discipline. (p. 129)
Now some biologists will claim that this level of explanation removes God from the picture. Fugle’s response, along with that of other Christian scientists, is a sense of awe in understanding God’s methods of creation.
If you wonder why scientists find the evidence persuasive, read this section of Fugle’s book. He runs through a discussion of body plans and embryology; moves to fossils, with sequential ordering and transitional forms; considers biogeography and the dispersion of forms and species; and concludes with evidence embedded in the genetic coding of DNA. This gives a flavor of the range of evidence for evolution available. It is important to realize however, that the evidence for evolution is so pervasive that no short book can do justice to the sum total. Fugle includes a range of examples, but it would be a mistake to think that this is more than just the tip of the iceberg.
An outline of a few of the examples:
Whales provide a particularly significant example illustrating a number of the lines of evidence for evolution. Mainstream science leads to the conclusion that whales evolved from land mammals over the last 65 million years or so. Almost every line of evidence for evolution is illustrated by the whale.
The whale fin has the same external hydrodynamic structure as fish but the bone structure found in vertebrates, especially mammals with a humerus, ulna, radius, carpals. Whales also have vestigial pelvic bones.
The embryos of many whales develop hind limb buds that are reabsorbed, as well as external ear lobes, also reabsorbed. “Baleen whale embryos start with nostrils toward the tip of the snout, but, as development progresses, changes in the shape and size of skull bones cause the nostrils to migrate to their final place at the top of the head to form the blowhole.” (p. 144)
The fossil record shows a progression of whales with disappearing rear legs and nostrils at various locations along the snout. Transitional forms abound. The ankle bones of ancient whale precursors have a structure similar to that of even-toed hoofed animals.
The genome project confirms these connections. Whale and dolphin DNA is most similar to the hippopotamus, then cow, sheep, deer and giraffes. All consistent with evolution from an even-toed hoofed precursor. All of these connections could simply be “the way God chose to do it,”creating a succession of unrelated species, but this does not seem as satisfactory as the explanatory power of evolution … as the mechanism God chose to use in creation.
Vestigial structures provide a powerful line of evidence for evolution. The pelvic bones of whales are one example. Moles born blind for life … “also have the basic form of an eye, including a bony eye socket, eyelids, a structural “eyeball,” and even a lens, but a functioning retina for sight is not formed.” (p. 140) “Flightless beetles grow perfectly formed wings that remain permanently locked away under their fused wing covers.” (p. 141) These structures make sense in the context of evolutionary theory, but little sense if we assume spontaneous creation.
Continental drift. Fossils of marsupials, large reptiles, and seed bearing trees are found on Antarctica – in an inhospitable environment today, but similar to those found in Africa and South America. “This is really a rather remarkable confirmation of continental drift and evolutionary theory since no marsupials, reptiles, or trees could possibly have lived on Antarctica if it was always located where it is today.” (p. 189)
The majority of mammals have a useful protein-coding gene for an enzyme (L-gulonolactone oxidase or “GULO”) that allows them to synthesize their own ascorbic acid molecules. However, almost all primates (i.e., tasiers, all monkeys, the great apes, and humans) lack the ability to make ascorbic acid. … It may seem logical to assume that since most primates don’t manufacture ascorbic acid they simply lack the gene for making it. This is not the case! Instead, the DNA of the deficient primates contains a nonfunctional mutant copy of the GULO gene. This dysfunctional DNA sequence is clearly recognizable as the gene for ascorbic acid synthesis, due to the overall matching pattern of DNA bases, but there are noticeable errors in the sequence that interfere with normal production of the GULO enzyme. (p. 199)
Sure, God could have simply created primates with the dysfunctional DNA, but why should we prefer this explanation?
Many genes are duplicated in the genome. These can be modified leading to beneficial new capacities or disabled without affecting the viability of an animal. Evolutionary theory predicts that beneficial mutations will be selected, but inactivated genes will also be carried along for the ride. They experience little selective pressure, either negative or positive. “With the pseudogenes as a nonfunctional passenger, there are no constraints on additional mutations in nucleotide bases and these should accumulate steadily through ancestral lineages without consequence to individual organisms.” (p. 200) One such example is a missing 11 base pair sequence in a version of the SHMT pseudogene in gibbons, orangutans, chimpanzees, gorillas and humans. “The SHMT pseudogene in other primate species is not missing this distinctive set of eleven bases.” (p. 202) The conclusion is that this eleven base pair segment was lost in a common ancestor to these “great apes” after divergence from the other primates. This supports a tree of connection derived from a wide variety of data.
Ring Species. Consider Ensatina eschascholtzii salamanders in Oregon and California. Populations in Oregon interbreed freely, and as the populations move down the Sierra Nevada and the coastal mountains they interbreed freely with neighboring populations. When they overlap again in Southern California the populations cannot interbreed. They are biologically distinct entities. This isn’t “macroevolution” (a category distinction that isn’t really recognized in biology) but it is an illustration of the development of new species through the accumulation of evolutionary change.
For that matter Chihuahuas and Great Danes would likely be considered separate species if we only had these two varieties of dogs. It is the varieties between that connect the two in one family.
And this leads us to …
Macro and micro evolution. There really is no significant distinction between macro and micro evolution, except the amount of time involved. This doesn’t mean we have all the answers In fact, according to Fugle “It has never been certain that we understood all the natural mechanisms needed to explain the grand story of life.” (p. 219)
This is still true, but much progress has been made in the last several decades.
Duplicate genes provide a mechanism for evolution that has only recently been recognized. “In the past, we typically viewed mutations primarily as disruptions in currently functioning systems. But a mutation in a duplicated gene can occur without harming an organism because the original gene still functions and gives rise to the normal protein product.” (p. 219) A duplicate gene can be modified stepwise to give rise to a related, but distinct protein product providing a new functional capacity to an organism. Many active enzymes are similar, but fulfill different functions.
We are also learning that “a relatively small number of genes direct crucial embryonic events.” (p. 220) Changes in these genes can have interesting consequences. Hoxc8 is a gene that produces a product that prevents formation of limbs in snakes. This gene is present in lizards, but the product is not expressed. In another example, Giraffe necks are the result of an extended developmental period for the requisite process, not a distinctively new process.
The take-home message is that genetic-changes that alter the regulation of developmental steps are the likely source of many major evolutionary changes. This means that organism differences may not be so much the presence or absence of particular genes but rather the regulation of where, when, and how existing developmental genes are expressed. It is highly significant that these processes contrast with the typically perceived evolutionary progression of small, accumulated steps. (p. 221)
Major transfers of DNA between organisms likely played a major role in primitive forms of the Precambrian and Cambrian periods as well. We see remnants of these events in the DNA of modern plants and animals.
All of these mechanisms add to our understanding of evolutionary biology and counter some of the skepticism that mutation could lead to new organisms. There may also be other mechanisms not yet fully understood. But the patterns are clear. Biology isn’t a finely tuned machine, but a mesh of potentially interchangeable or malleable components constrained by basic chemistry and physics.
I’ve summarized only a small part of the evidence Gary Fugle outlines in this section (at 94 pages, the longest section of the book) and he’s provided only an overview of the vast amount of evidence for evolutionary biology. There are genuine reasons why scientists believe that the earth is very old and life is interconnected via evolutionary mechanism. Evolution is not a theory in trouble. The value of evolutionary theory is not the elimination of God (despite the claims of a few scientists and the fears of more Christians) but the coherent story that emerges from the evidence of the natural world. It is truly awe inspiring.
Evolutionary theory is the framework through which everything makes sense.
If evolution isn’t true we are left with an enormous number of facts and observations, but no story that puts them together.
What evidence do you find convincing?
If you don’t find the evidence convincing, what would it take to convince you of the strength of evolutionary theory?
If you wish to contact me directly, you may do so at rjs4mail[at]att.net