Evolution is not a fact; it is a theory. Fossils are facts. Living organisms are facts. The vast body of evidence for relationships among existing organisms and those of the past is factual. Evolution is a theory that offers an explanation for organisms living and extinct, but theories are not opinions. Theories can be dissected and presented in the form of the explanans and explanandum of the Covering Law Model, but opinions cannot. One cannot substitute divine intervention for laws in the Covering Law Model. In science, that’s called cheating. Jack and Cy note, “Religion masquerading as science, ironically, has no lasting effect on science, but denigrates religion by replacing the divine with the mundane…”
The theory of evolution is three-tiered. The first level of theory is simply that evolution happens. If relationships exist between species, then, logically, they share a common ancestry and have evolved from a common source. The second level of the theory is how evolution happens. For instance, scientists still lack an understanding of speciation – does it happen gradually over the millennia or in an instant? We don’t know. A third level of theory asks why evolution happens, what drives it, what causes it. We don’t have a scientifically satisfying answer to this either.
Obviously, evolution (irreversible change through time that involves divergence and increasing complexity of self-organizing, self-remembering biological systems) has been happening for the last few billion years on Earth and, given appropriate conditions, is no doubt happening elsewhere in our vast universe. Evolution may be a general property of the universe. On Earth, groups of organisms show different levels of relatedness: different species of maple trees are all more closely related to each other than any are to the oaks, but oaks and maples are more closely related to each other than they are to pines, spruces or firs, which are also closely related to each other as conifers. Oaks and maples share a close common ancestry. Pines, spruces and firs share a close common ancestry. The two groups of trees also share a common ancestry, but it is more distant, more ancient. Given evidence in the form of the characteristics of oaks, maples, pines, spruces and firs, a “family tree” illustrating relationships among these plants can be generated.
On a larger scale, all of the green plants share common characteristics, such as chlorophyll and cell walls that they do not share with animals. All of the complex, multicellular organisms on our planet are called eukaryotes (or eucaryotes) because their cells have membrane-bound nuclei within them where much of their genetic material is housed. Ruth enjoys derivations, so she looked up the origin of “Eukaryote.” “I knew that ‘eu’ was Greek for ‘good’ (or ‘true’),” she says, “but the ‘karyotes’ slays me. It means ‘provided with nuts.’” It doesn’t matter if they are plants or animals; eukaryotic creatures all share this feature, keeping most of their genetic material within the nut-like nucleus. There are no exceptions. This suggests a long, ancient set of relationships derived through evolution, irreversible change and divergence through time. As scientists, biologists are not allowed to dismiss such obvious evidence, regardless of any personal beliefs they may have.
It is possible that life on Earth arose more than once, but possession of characteristics among all organisms, such as the ubiquitous presence of cells, proteins that serve as enzymes, informational molecules such as DNA or RNA provide evidence that forms as diverse as bacteria, mosses, oak trees, earthworms and humans all share a single, very old common ancestry. But Jack Maze adds, “The origin of life is a very contentious issue in biology and the argument for a single origin of life is being questioned. Data gathered by microbiologists, those who study the smallest living creatures, indicates that life arose more than once, resulting in a “pool” of simple organisms from which diverse lineages arose. The idea that life has arisen several times is appealing since it implies that life is the result of the action of natural laws. Also, the argument that life arose only once gives that event the property of a miracle, a completely unique event that is not repeated. Miracles are the result of divine intervention, something to be rejected in offering an account of the natural world.”
The fossil record offers additional overwhelming corroboration that evolution has been going on for a very long time. Many of the species that once inhabited the Earth no longer exist, but they certainly did at one time. Present-day species are related to some of the extinct ones, and this can be clearly demonstrated, with or without DNA evidence. A scientist is not at liberty to ignore such a massive body of relevant data. Creationist views are opinions, not theories. They are not grounded in factual evidence and do not play by the rules of science. Ruth found a definition of religion offered by Prof. Luke Timothy Johnson in a book called, Early Christianity: The Experience of the Divine: “Religion: a way of life organized around experiences and convictions concerning ultimate power.” In science, the only power that is of interest is the explanatory power of theories. There is no ultimate authority.
These observations about evolution say nothing about any particular theory of evolution, but simply that lineages have split over time (phylogenesis is the splitting of lineages, when one species becomes more than one). New forms have come into existence, and their relationships to each other and to older forms can be traced (though not always easily). Apparently, the complexity of life forms has also increased through geologic time. The appearance of a species that is physically simpler than its relatives may not serve as a falsifier for the observation that complexity increases, since the appearance of any new species adds to the overall complexity of life on Earth. This first level of evolutionary theory offers no causal explanation for evolution, but points out that life forms express a larger pattern of relationships, leading to the undeniable conclusion that evolution happens. These patterns are worth exploring further because we wish to understand why and how evolution occurs, what laws of nature drive it and how the outcome of species diversity is expressed. Even after many years of study, we are not really very close to figuring this out.