Reasons to Believe

Facts for Faith, Issue 2

Hume vs. Paley: These "Motors" Settle the Debate

By Fazale Rana and Micah Lott

Machines and motors don't just happen, right? Even the simplest require some thoughtful design and manufacture. This "given" lies behind one of history's best known arguments for God's existence: the "Watchmaker" argument posited by the 18th-century British natural theologian William Paley.

Using the analogy of a watch (which obviously implies the mind and work of a watchmaker), Paley argued that organisms, by the very complex interaction of their precision parts, imply the work of a Master Designer.1 However, 18th-century British philosopher David Hume and 19th-century naturalist Charles Darwin supposedly delivered a one-two "knock-out" punch to Paley's proof.

At least that's how author Richard Dawkins tells the story, when he credits Hume with making atheism "logically tenable," and Darwin with making it possible to be an "intellectually fulfilled atheist."2

Hume argued that cause-and-effect thinking often reflects habits or convention, rather than logic. Later, many accepted Darwin's logical-sounding naturalistic explanation for what Paley saw as "divine design."

Yet in the last 15 years, Michael Denton and several other scientists have turned those tables around. Advances in molecular biology and computer technology indicate that Hume and Darwin were not as effective in challenging Paley's argument as popular opinion has held.3

In the last five years, scientific discoveries about the structural and functional properties of several different types of protein "motors" inside living cells have provided potent evidence for an Intelligent Designer. These discoveries continue to accumulate-and to suggest that Paley's fundamental line of argument still holds, despite Hume and Darwin's hair-splitting.

The analogy's strengths & weaknesses

Hume's critiques of design arguments were several and progressive; we will focus only on the first and foremost of these, as other scholars have effectively challenged Hume's other criticisms.4, 5, 6

Hume curtly dismissed the watchmaker argument, saying that the two things Paley compared-organisms and watches-were too dissimilar for a good analogy. Hume asserted that the strength of an analogical argument depends on the similarity of the two things being compared, insisting that "whenever you depart, in the least, from the similarity of the cases, you diminish proportionably the evidence; and may at last bring it to a very weak analogy, which is confessedly liable to error and uncertainty."7

More recently, atheist B.C. Johnson underscored Hume's anti-Watchmaker argument by saying that Paley did not use a nearly strict-enough criterion for identifying design. For Paley, design was evident when a system contained several parts "framed and put together for a purpose."8 Johnson, in contrast, says "we can identify a thing as designed, even when we do not know its purpose, only if it resembles the things we make to express our purposes."9

Others have argued that organisms are not machines, that those wanting to explain the appearance of design in nature-whether creationists seeking a divine Watchmaker or evolutionists seeking a blind watchmaker-are clearly taking the analogy too far. This third group says the analogy between machines and living systems is nothing more than an explanatory analogy, an illustration that provides a framework to guide research in the life sciences.10

How to determine when a use of analogy is appropriate has been clearly delineated by logician Patrick J. Hurley.11

To build a strong analogy, one must find sufficiently numerous and relevant attributes in both halves of the analogy to establish an analogical relationship that supports the conclusion drawn. An analogy is more firmly established when the analogous systems-for example, living systems and mechanical devices-are diverse and abundant. One must also consider counteranalogies (characteristics that argue against meaningful comparison), as well as the attributes that the analogous systems possess which make them different, distinct or disanalogous.

Molecule motors: helpful & ubiquitous

The merit of Paley's approach, then, rests on how one answers these questions: "Do living systems resemble man-made machines enough to warrant analogy between the two? If so, how strong is the analogous relationship, and thus the conclusions we can reasonably draw from it?"

Thanks to recent scientific advances in our understanding of the proteins that power cellular movement, we are in a far better position to test the analogy than either Paley, Hume, or anyone else since their day.

New biophysical and molecular biology techniques offer a remarkably clear and detailed picture of the parts comprising molecular systems and of how they function. What researchers see is this: At life's most fundamental level, the similarities between these molecular systems and man-made devices are both abundant and intricate.

In the words of one researcher in the field: "Some enzyme complexes function literally as machines, and come equipped with springs, levers and even rotary joints."12 These enzyme complexes can be considered machines by definition,13 and not simply by illustrative analogy.

Molecular motors pervade the cell, performing a wide variety of functions. Some of the most widely recognized and best-understood examples of molecular motors are the systems responsible for cellular translocation.

These include dynein and bacterial flagellar proteins. Also belonging to this list are kinesin, which transports organelles throughout the cell; myosin, which plays a central role in muscle contraction and helps transport organelles throughout the cell;14 and F1-F0 ATPase, a protein involved in harvesting energy for the cell to use.15, 16

Several more molecular motors have recently been identified: Elongation factor G (EF-G), which plays a key role in protein synthesis inside the cell;17, 18 RNA polymerase, which helps transcribe the information contained in DNA into messenger RNA (subsequently used for protein biosynthesis);19 the ABC transporters, a family of proteins responsible for transporting materials across cellular membranes in bacteria and eukaryotic cells;20, 21 and the HSP70 systems, involved in protein translocation through pores in the cell membranes.22

This plethora of newly discovered molecular motors lends weight to scientists' estimates that up to 100 different molecular motor systems exist inside the cell.23

Comparability of parts

The close similarity between bacterial flagella and man-made rotary motors has received much attention. Bacterial flagella possess a half-dozen parts comparable to those of a man-made motors: a rotor, a stator, a drive shaft, bushing, a universal joint, and a propeller24 (see illustrations on opposite page).

Likewise, F1-F0 ATPase has parts virtually identical to an engine block, drive shaft, and three pistons.25 Recently, two stators have been discovered in V-type ATPases.26, 27 These ATPases are similar to F1-F0 ATPase, but play a different role in cells.

The machine-like properties of another molecular motor, myosin, have become more and more clearly evident to biophysicists and biochemists over the last five years or so. Myosin may in fact be the most closely studied and best understood molecular motor to date.

In contrast to bacterial flagella and V-type and F1-F0 ATPases, myosin is not a rotary-type motor. Rather, myosin employs a rigid swinging lever arm complete with a molecular hinge that serves as a pivot point for the swinging lever arm28 (see illustration on page 40).

Until very recently, evidence for myosin's swinging lever arm was indirect.29, 30, 31, 32 Within the last year or so, newly available genetic engineering and biophysical methodologies have given researchers the capacity to detect directly the swing of myosin's lever arm and the swiveling of the myosin hinge.33, 34, 35, 36, 37, 38 Researchers have also directly detected the motion of the myosin light chain upon muscle contraction.39, 40 The myosin light chain wraps around the myosin lever arm, stabilizing it against the stress of muscle contraction.41

Molecule motors rev our devices

The analogy between molecular motors and man-made motors is further strengthened by exciting new work being carried out by researchers seeking to develop nanodevices.42

Nanodevices are extremely small (molecule-sized) mechanisms made by the precise arrangement of molecules. These structures have dimensions less than 1,000 nanometers (1 nanometer = 1 billionth of a meter), and people are pursuing their use in manufacturing, electronics, medicine, biotechnology and agriculture, to name a few applications.

One of the key hurdles preventing nanodevices from becoming a truly viable technology has been our inability to power these devices. An important breakthrough in this area was reported at the Sixth Foresight Conference on Molecular Nanotechnology (in November of 1998).

Scientists working separately (at Cornell University and at the University of Washington in Seattle) have, "like molecular mechanics…unbolted the motors from their cellular moorings, remounted them on engineered surfaces, and demonstrated that they can in fact perform work."43 The molecular motors "borrowed" from cells operate at near 100 percent efficiency-much better than humanly crafted devices.

Reflections of Intelligence

Recent work described as "science at its very best" hints at the superintellect of the Designer responsible for nature's tiny engines.44 A team of researchers from Boston College and a collaborative team from the University of Groningen, Netherlands, and Tohuku University, Japan , have independently designed and synthesized the first single-molecule rotary motors, capable of spinning in a single direction.45, 46 The rotation of the motors is driven by either UV radiation and heat, or through chemical energy.

These synthetic molecular motors are the product of careful, intensely rigorous design and synthesis. The light-and-heat-driven motor depends on the "unique combination of axial chirality and the two chiral centers" in the molecule positioned "just right" in three-dimensional space.47 The chemically-driven motor is dependent upon chirality as well as the fine-tuning of multiple molecular substituents.48

No one could reasonably suggest that these motors happened by accident or as the natural outworking of the laws of chemistry and physics. In fact, the chemically-driven motor, comprised of only 78 atoms, took Boston College's brilliant team more than four years to build.49

And, despite all the effort that went into the design and building of these synthetic molecular motors, each of the two rotates in a cumbersome and step-wise fashion.

The contrast between these synthetic molecular motors, assembled by some of the finest and most creative organic chemists in the world, and the elegance and complexity of molecular motors found in natural cells is striking. Considering the efforts of scientists working to develop nanoscale devices, one cannot help but marvel at the elegance of the "originals."

Beating the criterion

Nearly 15 years ago, Michael Denton recognized the closeness of the analogy between the internal workings of the cell and human artifacts.50 As research progresses in molecular biology and biophysics, the evidence for an Intelligent Designer mounts. Some of the most convincing "hints" of design come from the protein assemblies that function precisely as motors inside cells.

The work of nanodevices and single-molecule synthetic motors indicates that molecular motors found in nature meet even the strict requirement for design set by atheist B.C. Johnson. As micro-engines, they indeed resemble, in abundant, precise detail, "the things we make to express our purposes."51

The analogy between man-made devices and the biological molecular motors studied by researchers in the last give years fits the criteria for "strong" analogy. The similarities among the parts of man-made machines and the parts of biological rotary and lever-arm motors are both precise and abundant.

Biological motors reveal diversity of form and function. As new motors are identified and as the structural details of existing biological motors are better understood, the range of diversity continues to expand. Again, the facts argue for strong analogy.

Finally, the degree of disanalogy between man-made motors and biological motors has greatly diminished as a results of the work on nanodevices and single-molecule synthetic motors. While for some enzyme assemblies, as we currently understand them, the designation "motor" must still be considered an "explanatory analogy"-albeit a strong one-the various parts of the bacteria flagellar proteins, the F1-F0 and V-type ATPases, and myosin make them strict analogs to the man-made motors.

We may consider them motors by definition. The fact that the analogy between biological molecular motors and man-made machines is so strong, so close, means that certain conclusions are logically warranted.

Since we know that machines require design, we are compelled, then, to believe that these molecular motors require design. And if life's most basic components require design, then life itself argues for an Intelligent Designer.

This argument for divine design contrasts sharply with "god-of-the-gaps" reasoning. The inference of an Intelligent Designer is based not on the lack of knowledge about these living systems, but rather on the abundance of information and understanding. Through the latest scientific advances, God has given us a perspective on His creation that was unavailable to both Paley and Hume.

Current findings permit us to rephrase the famous opening to the book that opened the debate: Paley's Natural Theology:

In crossing a heath, suppose I pitched my foot against a stone, and were asked how the stone came to be there. For anything I knew to the contrary, I might suppose that it had lain there forever. But suppose I found a rotary engine or a device with a lever arm sitting there in the heath, and were asked how it came to be there. I should hardly think the answer I gave for the stone to be a sufficient explanation for either of these machines. I would know that someone, somewhere had constructed these devices.

In the same way, as we delve into the innermost workings of the cell and encounter rotary motors and machines with lever arms, we can be sure that they are the handiwork of a Designer.


1 William Paley, Natural Theology: Evidences of the Existence and Attributes of the Deity, Collected from the Appearances of Nature (1802; reprint, Houston: Thomas Press, 1972).

2 Richard Dawkins, The Blind Watchmaker: Why the Evidence of Evolution Reveals a Universe Without Design (New York: W.W. Norton, 1986), 6.

3 Michael Denton, Evolution: A Theory in Crisis (Bethesda, MD: Adler & Adler, 1986), 339-42.

4 David Hume, Dialogues Concerning Natural Religion in Hume on Religion (New York: Meridian Books, The Word Publishing Company, 1963), 99-204. Hume makes other critiques, many of which point out the need to combine the design argument with other arguments to arrive at a true Creator God. The Dialogues themselves are fairly accessible, but a nice summary and exposition can also be found in John L. Mackie's The Miracle of Theism: Arguments for and Against the Existence of God (Oxford: Oxford University Press, 1983).

5 Michael J. Behe, Darwin's Black Box: The Biochemical Challenge To Evolution (New York: Simon & Schuster, Touchstone, 1996).

 6 Hugh Ross, Beyond the Cosmos, rev. ed. (Colorado Springs, CO: NavPress, 1999), 73-75.

 7 Hume, 166.

8Hume, 117.

9 B.C. Johnson, Atheist Debater's Handbook (Buffalo, NY: Prometheus Books, 1981), 45.

10 David Depew, "Intelligent Design and Irreducible Complexity: A Rejoinder," Rhetoric and Public Affairs 1 (1998): 571-78.

11 Patrick J. Hurley, A Concise Introduction To Logic, 6th ed. (Belmont, CA: Wadsworth Publishing, 1996), 494-96.

12 Steve M. Block, "Real Engines of Creation," Nature 386 (1997): 217.

13Webster's Third New International Dictionary defines a machine as: "1) an assemblage of parts that are usually solid bodies but include in some cases fluid bodies or electricity in conductors and that transmit forces, motion and energy one to another in some predetermined manner and to some desired end." "2) an instrument (as a lever) designed to transmit or modify the application of power, force or motion."

14 Lubert Stryer, Biochemistry, 4th ed. (New York: W.H. Freeman, 1995), 391-416.

15 William S. Allison, "F1-ATPase: A Molecular Motor That Hydrolyzes ATP with Sequential Opening and Closing of Catalytic Sites Coupled to Rotation of Its g Subunit." Accounts of Chemical Research 31 (1998): 819-26.

16 Matti Saraste, "Oxidative Phosphorylation at the fin de siècle," Science 283 (1999): 1488-93.

17 R.A. Cross, "A Protein-Making Motor Protein," Nature 385 (1997): 18-19.

18 Marina V. Rodnina et al., "Hydrolysis of GTP by Elongation Factor G Drives tRNA Movement on the Ribosome," Nature 385 (1997): 37-41.

19 Michelle D. Wang et al., "Force and Velocity Measured for Single Molecules of RNA Polymerase," Science 282 (1998): 902-7.

 20 Michael J. Welsh, Andrew D. Robertson, and Lynda S. Ostedgaard, "The ABC of a Versatile Engine," Nature 396 (1998): 623-24.

21 Li-Wei Hung et al., "Crystal Structure of the ATP-Binding Subunit of an ABC Transporter," Nature 396 (1998): 703-7.

22 Cindy Voisine et al., "The Protein Import Motor of Mitochondria: Unfolding and Trapping of Preproteins Are Distinct and Separable Functions of Matrix Hsp70," Cell 97 (1999): 565-74.

23 James A. Spudich, "How Molecular Motors Work," Nature 372 (1994): 515-18.

24 Behe, 69-72.

25 Hugh Ross, "Small Scale Evidence of Grand-Scale Design," Facts & Faith 11, no. 2 (1997): 1.

26 E.J. Boekema et al., "Visualization of a Peripheral Stalk in V-Type ATPase: Evidence for the Stator Structure Essential to Rotational Catalysis," Proceedings of the National Academy of Sciences, USA 94 (1997): 14291-93.

27 E.J. Boekema et al., "Connecting Stalks in V-type ATPase," Nature 401 (1999): 37-38.

28 Steven M. Block, "Fifty Ways to Love Your Lever: Myosin Motors," Cell 87 (1996): 151-57.

29 James D. Jontes, Elizabeth M. Wilson-Kubalek, and Ronald A. Milligan, "A 32° Tail Swing in Brush Border Myosin I on ADP Release," Nature 378 (1995): 751-53.

30 Michael Whittaker et al., "A 35-Å Movement of Smooth Muscle Myosin on ADP Release," Nature 378 (1995): 748-51.

31 Jeffery T. Finer, Robert M. Simmons, and James A. Spudich, "Single Myosin Molecule Mechanics: Piconewton Forces and Nanometre Steps," Nature 368 (1994): 113-19.

32 Roberto Dominguez et al., "Crystal Structure of a Vertebrate Smooth Muscle Myosin Motor Domain and Its Complex with Essential Light Chain: Visualization of the Pre-Power Stroke State," Cell 94 (1998): 559-71.

33 A.F. Huxley, "Support for the Lever Arm," Nature 396 (1998): 317-18.

34 Yoshikazu Suzuki et al., "Swing of the Lever Arm of a Myosin Motor at the Isomerization and Phosphate-Release Steps," Nature 396 (1998): 380-83.

35 Ian Dobbie et al., "Elastic Bending and Active Tilting of Myosin Heads During Muscle Contraction," Nature 396 (1998): 383-87.

36 Fumi Kinose et al., "Glycine 699 is Pivotal for the Motor Activity of Skeletal Muscle Myosin," The Journal of Cell Biology 134 (1996): 895-909.

37 Thomas P. Burghardt et al., "Tertiary Structural Changes in the Cleft Containing The ATP Sensitive Tryptophan and Reactive Thiol Are Consistent with Pivoting of the Myosin Heavy Chain at Gly699," Biochemistry 37 (1998): 8035-47.

38 Katalin Ajtai et al., "Trinitrophenylated Reactive Lysine Residue in Myosin Detects Lever Arm Movement During the Consecutive Steps of ATP Hydrolysis," Biochemistry 38 (1999): 6428-40.

39 J.E.T. Corrie et al., "Dynamic Measurement of Myosin Light-Chain-Domain Tilt and Twist in Muscle Contraction," Nature 400 (1999): 425-30.

40 Josh E. Baker et al., "A Large and Distinct Rotation of the Myosin Light Chain Domain Occurs Upon Muscle Contractin," Proceedings of the NationalAcademyof Sciences, USA 95 (1998): 2944-49.

41 Susan Lowey, Guillermina S. Waller, and Kathleen M. Trybus, "Skeletal Muscle Myosin Light Chains Are Essential for Physiological Speeds of Shortening," Nature 365 (1993): 454-56.

42 Robert F. Service, "Borrowing from Biology to Power the Petite," Science 283 (1999): 27-28.

43 Service, 27. 44C. Wu, "Molecular Motors Spin Slowly But Surely," Science News 156 (1999): 165.

45 T. Ross Kelly, Harshani De Silva, and Richard A. Silva, "Unidirectional Rotary Motion in a Molecular System," Nature 401 (1999): 150-52.

46 Nagatoshi Koumura et al., "Light-Driven Monodirectional Molecular Rotor," Nature 401 (1999): 152-55.

47 Koumura et al., 154.

48 Kelly et al., 150-152.

49 Anthony P. Davis "Synthetic Molecular Motors," Nature 401 (1999): 120-21.

50 Denton, 339-42.

51 J. P. Moreland says there are major problems with Johnson's understanding of the nature of a scientific criterion, and that for this reason his criterion for design is unreasonably difficult to meet. That these molecular motors are able to meet a design criterion that is unreasonably challenging only further shows the high degree of design present in these motors. See Moreland's Scaling the Secular City: A Defense of Christianity (Grand Rapids, MI: Baker Book House, 1987), 67-70.


Axial Chirality: The left-handed or right-handed orientation of a molecular in space, along one of the molecular axes.

Bacterial flagella: Whip-like appendages that extend from the surface of bacteria and work to propel the bacteria through its environment.

Biophysical methodologies: Techniques used by researchers to characterize the physical properties and physical behavior of biological systems.

Biosynthesis: The general collection of processes inside cells that lead to the production of biomolecules.

Chiral center: The left-handed or right-handed orientation in space of chemical groups that are bonded to a central atom.

Enzymes: Proteins that assist the chemical process that takes place inside cells.

Eukaryotic cells: Cells having a nucleus and internal membrane structure; eukaryotic cells make up fungi, plants and animals.

Genetic engineering: The manipulation of genes and their sequences to produce desired properties in biological systems and/or molecules.

"God-of-the-gaps" argument: An argument for God's existence that relies on human inability to explain a phenomenon (usually complex) through the use of natural processes.

Molecular motors: Protein/enzyme complexes that generate movement in the cell.

Naturalism: The view that the material, physical universe is the only reality, that all phenomena in the universe can be explained solely on the basis of the laws of physics, chemistry, and biology.

Organelles: Subcellular particles or membrane bound structures inside cells that perform specific cellular functions.

Organic chemistry: The area of chemistry that studies substances made out of carbon.

Protein: A complex molecule found in and produced by living organisms. Proteins take part in essentially every cellular process and function. Proteins are made up of one or more of the same or different polypeptide chains. Polypeptides are chain-like molecules that fold into a precise 3-D structure; this structure determines the protein's function.

Protein synthesis: The collection of processes occurring inside cells that result in the production of proteins.