This series of posts is intended as a basic introduction to the science of evolution for non-specialists. You can see the introduction to this series here. In this post we revisit what a “theory” is in science, and discuss how evolution, as a theory, is expected to have core ideas that are well established, but also extend from that core to test hypotheses at a more speculative frontier.
Weizsäcker’s book The World View of Physics is still keeping me very busy. It has again brought home to me quite clearly how wrong it is to use God as a stop-gap for the incompleteness of our knowledge. If in fact the frontiers of knowledge are being pushed back (and that is bound to be the case), then God is being pushed back with them, and is therefore continually in retreat. We are to find God in what we know, not in what we don’t know; God wants us to realize his presence, not in unsolved problems but in those that are solved.
Dietrich Bonhoeffer, Letters and Papers from Prison
When we began this series over a year ago, we started with a discussion of what a theory is in the scientific sense: a broad explanatory framework supported by experimental evidence, that makes accurate predictions, that has not (yet) been falsified through experimentation. Since that time we have traced the outlines of evolution as a scientific theory – discussing its origin with Darwin’s travels, discussing its mechanisms, and tracing the history of life on earth, including our own. We have also seen how evolution has withstood new evidence provided through scientific advancements, such as in paleontology and genetics. Though scientific theories always remain provisional, evolution as a scientific theory is so well established that its basic contours (species are related through common ancestry, natural selection is a significant player in speciation, et cetera) are no more likely to be overturned than those of other well-established scientific theories.
All theories, however, have frontiers – where their theory-like structure slowly gives way to a more hypothesis-like one. Demarcating the line between theory and hypothesis is also an attempt to draw a line on a gradient, but nonetheless it is a feature of all theories to expand into areas where less is known. As theories expand, some of what was once at the hypothetical frontier moves towards the well-established core – namely, those hypotheses that were accurate, or at least accurate enough to be refined through experimentation. In this series, we have seen historical examples of this process occurring. For example, in Darwin’s time, the idea that humans are related to other forms of life through common ancestry was much less well established than it is today, and was very much towards the “hypothesis” side of the equation. Human common ancestry was clearly predicted by Darwin’s work with other species, and supported by the lines of available evidence (such as the anatomy and physiology of humans compared to living great apes). Despite these evidences, however, in 1859 the science of human evolution had a long way to go – and it would be decades in coming, as we have seen. Eventually, the idea that humans are a lineage nested within the great apes would become entirely uncontroversial for scientists, given the accumulated evidence. This idea, then, moved from what was once the frontier of evolutionary theory to the core – a natural progression for an accurate hypothesis.
So, it is not a surprise that a scientific theory will address areas that are poorly understood: indeed, it is expected that theories, as they expand, will naturally have a frontier where the science is far from settled. Accordingly, we expect evolutionary theory to have its areas that are being actively researched and thus are more hypothetical than theoretical (in the scientific sense of those terms). For evolution, there are many such areas of active inquiry, where no single hypothesis has yet outcompeted its rivals – and no survey of evolutionary theory would be complete without at least a sketch of some of these areas.
Scientific frontiers and Christian apologetics
One challenge that faces us when examining frontier areas of evolution is that many Christians have had exposure to such topics exclusively in the context of antievolutionary apologetics. In such cases, it is common for the arguments to have the following basic structure: discuss a genuine scientific controversy from a frontier area of evolution, and then inappropriately use it in an attempt to cast doubt on evolution as a whole. This approach, though sadly common, misses the mark for two reasons: it fails to appreciate that a field of science is expectedto have areas that are well supported as well as areas that are more speculative; and that in speculative areas, the presence of competing hypotheses does not imply that the more theoretical base that allows the hypotheses to be made in the first place is somehow suspect.
Nowhere in Christian antievolutionary apologetics is this approach more prominent than for the first frontier area of evolution that we will examine: abiogenesis, or the proposed transition between nonliving matter and the first life on earth. Strictly speaking, abiogenesis is not part of evolutionary theory, in that evolution is the theory of how life changes over time, not how life may have arisen from non-life. As we will see, however, there is good evidence that this distinction is yet another attempt to draw a line on what is in fact a gradient between “non-living” and “living”. Regardless of these careful distinctions that a scientist might make, however, in the popular Christian antievolutionary literature the mystery of abiogenesis is reason enough to doubt evolution as a whole. Hopefully, the scientific problem with this approach is by now obvious – unsolved problems at the frontier are expected, and the natural result of a productive theory. Of course, there is also an apologetics problem with this approach: should a hypothesis at the frontier find experimental support, it will shift towards the theoretical core over time. If an apologetics argument is based on the expectation that such a hypothesis is false, then that argument will lose even what meager force it may have once had, to the detriment of the apologetic it was designed to support. Bonhoeffer famously rejected this approach, and we would do well to follow suit.
In the next post in this series, we’ll examine the reasons why evolutionary theory leads us to hypothesize that life had a singular, chemical origin deep in earth’s history.