I don’t believe in Santa Claus—but if he and his reindeer landed on my roof one Christmas Eve, I just might change my mind. As the old adage goes, “Seeing is believing.”
Evolutionary biologists often make use of this maxim to argue that biological evolution is a fact. They point out that we can see evolution happening right before our eyes and this should be all the proof of biological evolution that anyone needs. One recent example of evolution in action was reported in Science.1 Collaborators representing a number of American institutions observed green (or Carolina) anole lizards, located on islands off Florida’s coast, evolving over the span of 15 years (about 20 generations) in response to an invasion of brown (or Cuban) anoles.
Both lizards occupy the same ecological niche, but in the early 1990s, researchers observed green anoles perching higher up in trees when confronted with growing brown anole numbers. To determine if the invasion was the direct cause for this change in habitat, the researchers studied six islands occupied by green anoles only. They measured the lizards’ perch height and then released brown anoles on three islands, with the remaining three serving as control sites.
The researchers observed that as brown anole numbers increased, the green anoles’ average perch height increased. On the other hand, no change in perch height was observed on the control sites. The researchers discovered that on all three test sites the toe pads of the green anoles became larger as perch height increased. The bigger toe pads made it possible for the green anoles to perch higher up in the trees. This adaptation was due to genetic changes in the green anoles, not to developmental plasticity. According to Yoel Stuart, lead author of the study, “We did predict that we’d see a change, but the degree and quickness with which they evolved was surprising.”2
In many respects, this is a remarkable piece of scientific work. It helps alleviate a frustration evolutionary biologists often experience. It is difficult for these scientists to directly test the theoretical framework of biological evolution because direction observation (let alone monitoring) of evolutionary changes is rare. In the absence of direct observation, evolutionary ideas are debated based on theoretical analysis and inferences drawn from various comparative studies—but the ideas can never be experimentally confirmed or rejected.
The rapid evolution of the green anoles represents a rare opportunity to test a hypothesis advanced in the 1950s by famous evolutionary biologist E. O. Wilson. He suggested that when two closely related species co-occur and compete for resources, evolutionary divergence will result. The green anole study confirms Wilson’s hypothesis.
I often find that such studies raise concerns for Christians. After all, if seeing is believing, then how can we deny the reality of biological evolution when we can observe evolution happening before our eyes? And if evolution is a fact, does it eliminate the need for a Creator to explain the origin and history of life?
Not necessarily. We must distinguish between evolutionary change (driven by genetic variation filtered, iteratively, by selection) and the evolutionary paradigm, which argues that this mechanism is sufficient to explain life’s origin, history, and diversity. Just because evolutionary change is observed, or even inferred, doesn’t mean that the evolutionary paradigm has been established. To see how my argument plays out, think of evolutionary changes as falling into one of five categories.
- Microevolution refers to changes happening within a species. A textbook example would be peppered moths changing wing color in response to rising pollution levels in the UK.
- Speciation describes the scenario in which one species can give rise to a closely related sister species. A classic example is the evolution of the finches on the Galapagos Islands from an ancestral finch species that arrived to this archipelago from South America. Upon arrival, the ancestral finch evolved into a variety of species that vary primarily in body size and beak size and shape.
These two types of evolutionary changes have been observed repeatedly and, in my opinion, are noncontroversial. The change in the green anoles falls between the categories of microevolution and speciation.
- Microbial evolution refers to transformations in viruses, bacteria, archaea, and single-celled eukaryotes—such as the acquisition of antibiotic resistance in bacteria, the ability of viruses to hop from one host to another (e.g., SARS and HIV), and the emergence of drug-resistant strains of the malaria parasites. Microbial evolution would also include horizontal gene transfer between microbes that accounts for the evolution of pathogenic bacteria from nonpathogenic strains (e.g., E. coli O157:H7). Again, I don’t find microbial evolution particularly controversial.
- Macroevolution includes putative changes that require that evolutionary processes have genuine creative potential. Examples would include humans evolving from a primate ancestor, whales evolving from a terrestrial wolf-like mammal, and birds evolving from theropods. Whether or not macroevolution has occurred defines the creation-evolution controversy. I am skeptical that macroevolution is a real process that has shaped life’s history. (To read representative articles that explain my skepticism, go here, here, and here.)
- Chemical evolution refers to the processes that presumably generated the initial life-forms. According to this model, chemical selection transformed a complex chemical mixture of simple compounds into protocellular entities that evolved to yield the first true cells. (I would refer readers to Origins of Life, a book I coauthored with Hugh Ross, for a detailed rationale for my skepticism about chemical evolution.)
For the evolutionary paradigm to be true, macroevolution and chemical evolution must be unequivocally established. And they simply haven’t been. Thus, seeing shouldn’t necessarily lead to believing. We have to be careful about interpreting what we experience.