Other contemporary neo-Darwinian biologists including Richard Dawkins, Francis Crick, and Richard Lewontin have also emphasized that biological organisms only appear to have been designed.4 They recognize that many biological structures—whether the chambered nautilus, the compound eye of a trilobite, the electrical system of the mammalian heart, or numerous molecular machines—attract our attention because the sophisticated organization of such systems is reminiscent of our own designs. Dawkins has noted, for example, that the digital information in DNA bears an uncanny resemblance to computer software or machine code.5 He explains that many aspects of livings systems “give the appearance of having been designed for a purpose.”6
Nevertheless, neo-Darwinists regard that appearance of design as entirely illusory, as did Darwin himself, because they think that purely mindless, materialistic processes such as natural selection and random mutations can produce the intricate designed-like structures in living organisms. In this view, natural selection and random mutation mimic the powers of a designing intelligence without themselves being intelligently directed or guided in any way.
That’s where the theory of intelligent design comes into play. Intelligent design challenges the idea that natural selection and random mutation (and other similarly undirected materialistic processes) can explain the most striking appearances of design in living organisms. Instead, it affirms that there are certain features of living systems that are best explained by the design of an actual intelligence—a conscious and rational agent, a mind—as opposed to a mindless, materialistic process. The theory of intelligent design does not reject “evolution” defined as “change over time” or even universal common ancestry, but it does dispute Darwin’s idea that the cause of major biological change and the appearance of design are wholly blind and undirected.
Nor does the theory seek to insert into biology an extraneous religious concept. Intelligent design addresses a key scientific question that has long been part of evolutionary biology: Is design real or illusory? Indeed, part of what Darwin set out to explain was precisely the appearance of design. With current materialistic evolutionary theories now failing to explain many of the most striking appearances of design in the Cambrian animals, including the presence of digital information as well as other complex adaptations, the possibility emerges that these appearances of design may not be just appearances after all. The Darwinian formulation of evolutionary theory in opposition to the design hypothesis,7 coupled with the inability of neo-Darwinian and other materialistic theories to account for salient appearances of design, would seem logically to reopen the possibility of actual (as opposed to apparent) design in the history of animal life.
Either life arose as the result of purely undirected material processes or a guiding or designing intelligence played a role. Advocates of intelligent design favor the latter option and argue that living organisms look designed because they really were designed. Design proponents argue that living systems exhibit telltale indicators of prior intelligent activity that justify this claim, indicators that make intelligent design scientifically detectable from the evidence of the living world.
But that, for many evolutionary biologists, is precisely the rub. Because they think of intelligent design as a religiously based idea, they understand that people might want to affirm the intelligent design of life as part of their religious beliefs—but not as a consequence of scientific evidence. Indeed, most evolutionary biologists don’t see how the idea of intelligent design could contribute to a scientific explanation of life’s origins, nor do they see how intelligent design could ever be detected or inferred scientifically from evidence in nature. Exactly how would researchers justify such an inference?
My Story
When I left for my graduate studies in England in 1986, I was asking a similar set of questions. At that time, I wasn’t thinking about the scientific legitimacy of the intelligent design hypothesis as an explanation for the origin of animals. Instead, I wanted to know if intelligent design could help explain the origin of life itself. My questions eventually led me to learn about a distinctive method of historical scientific inquiry. That discovery led me to a method of reasoning that allows for the detection or inference of past causes, including intelligent causes.
A year earlier, in 1985, I had met one of the first contemporary scientists to revive the idea that intelligent design might have played a causal role in the origins of life. Chemist Charles Thaxton (see Fig. 17.1) had recently published a book, The Mystery of Life’s Origin. His coauthors were polymer scientist and engineer Walter Bradley and geochemist Roger Olsen. Their book received acclaim as a groundbreaking critique of current theories of chemical evolution. They showed that attempts to explain the origin of the first living cell from simpler nonliving chemicals had failed and that these theories had specifically failed to explain the origin of the information necessary to produce the first life.
But it was in the book’s epilogue that the three scientists proposed a radical alternative. There they suggested that the information-bearing properties of DNA might point to the activity of a designing intelligence—to the work of a mind, or an “intelligent cause” as they put it.8 Drawing on the analysis of the British-Hungarian physical chemist Michael Polanyi, they argued that chemistry and physics alone could not produce the information in DNA any more than ink and paper alone could produce the information in a book. Instead, they argued that our uniform experience suggests a cause-and-effect relationship between intelligent activity and the production of information.9
FIGURE 17.1
Charles Thaxton. Courtesy Charles Thaxton.
At the time the book appeared, I was working as a geophysicist for an oil company in Dallas where Thaxton happened to live. I met him at a scientific conference and became intrigued by his work. Over the next year, I began dropping by his office to discuss his book and the radical idea he was developing about DNA.
The first part of Thaxton’s argument made sense to me. Experience does indeed seem to affirm that (specified or functional) information typically arises from the activity of intelligent agents, from minds as opposed to mindless, material processes. When a “tweet” appears on your smart phone’s Twitter feed (if you’re into that kind of thing), it clearly originated first in the mind of a person who created a Twitter account, scripted the “tweet,” and then sent it out across the Internet. Information does arise from minds.
But Thaxton went further. He acknowledged that most branches of science didn’t consider intelligent activity as an explanation because, he thought, intelligent agents don’t usually generate repeatable or predictable phenomena and because they are difficult to study under controlled laboratory conditions. Nevertheless, Thaxton argued that scientists might propose an intelligent cause as a positive scientific explanation for some events in the past, as part of a special mode of scientific inquiry he called origins science. He noted that scientific disciplines such as archaeology, evolutionary biology, cosmology, and paleontology often infer the occurrence of singular, nonrepeatable events and that the methods used to make such inferences could help scientists identify positive indicators of intelligent causes in the past as well.
Here I wasn’t initially so sure. Thaxton’s ideas about a distinctive method of science concerned with origins, or at least with the past generally, seemed intuitively plausible. After all, evolutionary biologists and paleontologists do seem to use a method of investigation different from that employed by laboratory chemists. Nevertheless, I wasn’t exactly sure what those methods were, how they were different from those used in other sciences, and whether using them in any way justified considering intelligent design as a scientific hypothesis.
So the next year when I left Dallas, Texas, for Cambridge, England, to pursue my studies in the history and philosophy of science, I had a lot on my mind. Is there a distinctive method of historical scientific inquiry? If so, does that method of reasoning and investigation justify a scientific reformulation of the desi
gn hypothesis? In particular, does the intuitive connection between information and the prior activity of a designing intelligence justify a positive (historical) scientific inference to intelligent design? Does it make intelligent design detectable?
Historical Scientific Method and the Design Hypothesis
In my research, I discovered that historical scientists often do make inferences with a distinctive logical form. This type of inference is known technically as an abductive inference.10 During the nineteenth century, American logician C. S. Peirce characterized this mode of reasoning and distinguished it from two better-known forms, inductive and deductive reasoning. He noted that in inductive reasoning, general rules are inferred from particular facts, whereas in deductive reasoning, general rules are applied to particular facts in order to deduce specific outcomes. In abductive reasoning, however, inferences are often made about past events or causes based on present clues or facts.11
To see the difference between these three types of inference, consider the following argument forms:
Inductive argument:
A1 is B.
A2 is B.
A3 is B.
A4 is B.
An is B.
All A’s are B.
Deductive argument:
MAJOR PREMISE: If A has occurred, then B will follow as a matter of course.
MINOR PREMISE: A has occurred.
CONCLUSION: Hence, B will follow as well.
Abductive argument:
MAJOR PREMISE: If A occurs, then B would be expected as a matter of course.
MINOR PREMISE: The surprising fact B is observed.
CONCLUSION: Hence, there is reason to suspect that A has occurred.
Note the difference between deductive and abductive forms of inference. In deduction, the minor premise affirms the antecedent variable (“A”), while the conclusion deduces the consequent variable (“B”), an anticipated outcome. In this sense, deductive inferences look forward to something that will happen in the future. A classic illustration of deductive reasoning has this character:
MAJOR PREMISE: All men are mortal.
MINOR PREMISE: Socrates is a man.
CONCLUSION: Therefore, Socrates is a mortal (i.e., he will die).
In an abductive argument, the minor premise affirms the consequent variable (“B”) and its conclusion infers the antecedent variable (“A”)—the variable referring to something that went before, either logically or temporally. Abductive reasoning, thus, often affirms a past occurrence. For this reason, forensic or historical scientists such as geologists, paleontologists, archaeologists, and evolutionary biologists often use abductive reasoning to infer past conditions or causes from present clues. As Stephen Jay Gould notes, historical scientists typically “infer history from its results.”12
For example, a geologist might reason as follows:
MAJOR PREMISE: If a mudslide occurred, we would expect to find felled trees.
MINOR PREMISE: We find evidence of felled trees.
CONCLUSION: Therefore, we have reason to think that a mudslide may have occurred.
In the deductive form, if the premises are true, the conclusion follows with certainty. The logic of the abductive arguments is different, however. Abductive arguments do not produce certainty, but instead merely plausibility or possibility. To see why, consider the following variation of the preceding abductive argument:
MAJOR PREMISE: If a mudslide occurred, we would expect to find felled trees.
MINOR PREMISE: We find felled trees.
CONCLUSION: Therefore, a mudslide occurred.
or symbolically:
MAJOR PREMISE: If MS, then FT.
MINOR PREMISE: FT.
CONCLUSION: Therefore, MS.
Notice that unlike the first version of the abductive argument in which the conclusion was stated tentatively (“We have reason to think that a mudslide may have occurred”), in this version the conclusion is affirmed definitively (“A mudslide occurred”). Obviously, this latter form of argument has a problem. It does not follow that, because the trees have fallen, a mudslide necessarily occurred. The trees may have fallen for some other reason. A hurricane may have blown them down; perhaps an ice storm occurred and the trees fell under the weight of accumulating ice; or loggers may have cut them down. In logic, affirming the consequent variable of a minor premise (with certainty) constitutes a formal fallacy—a fallacy that derives from the failure to acknowledge that more than one cause (or antecedent) might produce the same evidence (or consequent).
Even so, the presence of downed timber might indicate that a mudslide has occurred. Thus, amending the above argument to conclude: “We have reason to think that a mudslide may have occurred” does not commit a fallacy. Even if we may not affirm the consequent with certainty, we may affirm it as a possibility. This is precisely what abductive reasoning does. It provides a reason for considering that a hypothesis—and often a hypothesis about the past—might be true, even if one cannot affirm the hypothesis (or conclusion) with certainty.13
The Method of Multiple Competing Hypotheses
To address this limitation in abductive reasoning and to make it possible to strengthen inferences about the past, the nineteenth-century geologist Thomas Chamberlain developed a form of reasoning he called “the method of multiple working hypotheses.”14 Historical and forensic scientists employ this method when more than one cause or hypothesis can account for the same evidence. They use it to adjudicate between competing hypotheses by comparing them to see which one best explains not just one piece of evidence but, usually, a wider class of relevant facts.
For example, consider how this method of reasoning was used to establish the hypothesis of continental drift as the best explanation for a wide range of geological observations. During the early 1900s, a German geologist and meteorologist named Alfred Wegener became fascinated with the way the African and South American continents fit together on the map like pieces of a jigsaw puzzle.15 He proposed that the continents had once been fused together as a single giant continent that he called “Pangea,” which later separated and drifted apart.
Initially, many geologists ridiculed Wegener’s idea. They thought that—given the vast distances separating the continents—the matching shapes were most likely just a coincidence. Wegener’s critics dismissed his theory of continental drift as “delirious ravings,” “Germanic pseudo-science,” or a “fairy tale.”16 But Wegener cited other evidence that he thought continental drift could explain that the coincidence hypothesis could not. He noted that fossil forms discovered on the east coast of South America matched those on the west coast of Africa in corresponding places and sedimentary strata. This fact seemed too coincidental to him to be explained away by chance alone. Nevertheless, other geologists attempted to explain matching fossil forms an ocean apart not as the result of the movement of the continents, but instead as the result of the migration of flora and fauna—either across oceans or over ancient land bridges.17 This introduced a third hypothesis into the mix, one that, in conjunction with the coincidence hypothesis, could explain each of the same facts that Wegener’s hypothesis could.
Later, however, an additional set of facts came to light—one that helped scientists to decide between the competing hypotheses. During World War II, the United States Navy surveyed the seafloor topography and measured the earth’s magnetic field across the oceans. These magnetic surveys showed parallel stripes of magnetized rock, each with the same polarity on either side of mountain ridges running down the middle of the ocean floor at equal distances from the mid-oceanic mountain ranges.18 Geologists also learned that magma was continually seeping out at the middle of these mid-oceanic mountain ranges. They discovered that as the magma cools, it “acquires” a characteristic magnetic signature reflecting the polarity of the earth’s magnetic field at that location at the time of its cooling. When ships towing sensitive magnetometers measured this “remanent magnetization,” scientists learned that the
magnetization of the seafloor alternated between sections of “normal” and “reverse” polarity as the magnetometer was towed away from a mid-ocean ridge in each direction. This led to the discovery of a famous symmetrical “piano key” pattern on each side of a mid-ocean ridge, seen in Figure 17.2.
To explain this symmetrical pattern of alternating magnetism, geologists proposed that the magnetic stripes were formed as the result of the seafloor spreading away from the mid-ocean ridge as magma was extruded and cooled in the presence of earth’s changing magnetic field—in other words, that the continents were literally drifting apart. This hypothesis not only explained the symmetrical pattern of magnetic stripes but also other relevant evidence. Although the other hypotheses could explain (or explain away) the fit of the continents and/or the similar pattern of fossilization across the oceans, only continental drift (driven by seafloor spreading) could explain the magnetic seafloor stripes and these other pieces of evidence. Consequently, as the result of its superior explanatory power, a decisive case for continental drift was soon established, strengthening a merely plausible abductive inference about the past movement of the continents by showing that this inference provided the best (and only adequate) explanation of all the relevant facts.19
FIGURE 17.2
This diagram shows the symmetrical pattern of alternating magnetic stripes of either “normal” or “reversed” polarity on either side of a mid-ocean ridge. Because this “piano key” pattern could only be explained by plate tectonics and seafloor spreading, it contributed to the widespread acceptance of those theories within contemporary geology.
Contemporary philosophers of science such as Peter Lipton have called this method of reasoning “inference to the best explanation.”20 Scientists often use this method when trying to explain the origin of an event or structure from the past. They compare various hypotheses to see which would, if true, best explain it.21 They then provisionally affirm the hypothesis that best explains the data as the one that is most likely to be true.
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