Why Pentadactyl Tetrapods?

Author: Curt Sewell
Subject: Creation Overviews
Date: 11/2/1999


This sheet of “Creation Bits” doesn’t really prove anything, but it gives a typical example of the way that initial mind-set affects the conclusions reached by the two viewpoints — creationist and evolutionist.


One of the favorite “proofs” of evolution theory is the statement that the pentadactyl limb structure indicates a pattern of descent through gradual modification, and that it shows descent from a common ancestor.

Before we go much further, let’s define these terms. “Penta-” means “five,” “dactyl” means “digits, toes or fingers,” “tetra-” means “four,” and “pods” means “feet.” So we’re talking here about four-footed creatures that have five digits on their limbs. This pattern includes many of the mammals, but not all.

Charles Darwin was curious about why this should occur. In his “Origin of Species” he wrote:

“What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of the horse, the paddle of the porpoise, and the wing of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions?”

He went on to speculate that the answer lay in common descent and natural selection.

“The explanation is manifest on the theory of the natural selection of successive slight modifications.”

Darwin used this as an argument for homology, that similar structure is an indication of common evolutionary development. He wrote:

“If we suppose that the ancient progenitor, the archetype as it may be called, of all mammals, had its limbs constructed on the existing general pattern, for whatever purpose they served, we can at once perceive the plain signification of the homologous construction of the limbs throughout the whole class.”

What he meant by this was that some sort of original ancestor had a five-digit limb structure and, as new generations came along, each descendant had its bone pattern modified slightly. After millions of generations had passed, the result would be the diversity of characteristics that we see in creatures around us today. That sounded good to scientists in his day, who were looking for an explanation that didn’t require a divine creator, and who didn’t have the fossil evidences that we have today.

But, as in so many other areas of evolution theory, when the actual facts are examined more closely, they don’t fit the prediction. If Darwin had been right, then we should be able to trace back in the fossil record through the ancestry of various creatures and see a pattern of gradual change. The ancestors of a pentadactyl tetrapod should be pentadactyl themselves. This is not what we find in the fossil record. The earliest mammals were not pentadactyl but rather were “polydactylous,” that is, of multi-digit structure. They had six, seven, or eight digits.

Several paleontologists have written of this discrepancy between fact and theory, including M.I. Coates and J.A. Clack in “Polydactyly in the Earliest Known Tetrapod Limbs,” in Nature, 347 (1990):

  1. 66, and M.I. Coates, “Ancestors and Homology (the origin of the tetrapod limb),” in “ActaBiotheoretica,” 41 (1993): pg. 414. My favorite evolutionist writer is Harvard’s Stephen Jay Gould. Gould is a recognized authority, has an excellent way with words, and often shows a refreshing openness

about the difference between actual evidences and the commonly-accepted ideas presented in elementary textbooks. As an evolutionist, he believes that “Tetrapods had a common ancestor to be sure, …” but wrote, in “Eight Little Piggies,” in the January 1991 issue of Natural History, page 25,

“The conclusion seems inescapable, and an old “certainty” must be starkly reversed. Only three Devonian tetrapods are known. None has five toes. They bear, respectively, six, seven, and eight digits on their preserved limbs. Five is not a canonical, or archetypal, number of digits for tetrapods — at least not in the primary sense of ‘present from the beginning’.”

Now, since there’s no real evidence of ancestral pentadactylism, how would creationists explain the curious fact that so many mammals have five digits? As with so many other actual facts of nature, we point to the obvious intelligence of the designer. For example, look at the many types of cars that have four wheels. They illustrate the simple fact that, for many applications, four is a good number — it works well. Designers utilize a proven principle. We believe that all the creatures around us were created by a super-intelligent Designer. He utilized whatever design he considered best for each given situation, and in a great many cases we’ve only begun to recognize the tremendous complexity shown in those designs. Just as the very existence of a fine watch demands a good watchmaker, so the complicated structure of a living creature demands a super-intelligent Creator.

Paul Nelson, in Bible-Science News, Vol. 32:7, October 1994, pp. 14-18, wrote about the broader principle illustrated by this question of pentadactylism. He showed that each time we consider some bit of evidence we put it into a framework of our accumulated knowledge and belief — what we might call our “world view.” Our interpretation is determined by that knowledge-system. If a person is committed to a framework of materialistic naturalism (like most evolutionists), his belief-system forces him to exclude any trace of intelligent design shown by a creator; he must explain everything in purely material ways, even when they don’t fit the actual evidence! This is why evolutionists insist that the concept of a God is only religious, and thus outside of the domain of science. Evolution is said to be a “fact” that must be believed even if the evidence doesn’t seem to support it.

But the creationist’s world view, or knowledge system, includes the belief that there is a divine Creator who has the power and intelligence to make things in the best way. He was not constrained to follow any set pattern of minor changes from other designs, such as is demanded by Darwinian evolution. Nelson suggested another possibility. He wrote:

“Or the pentadactyl pattern may be God’s “signature,” if you will, intended to reveal a single agent or creator behind the multifarious diversity of life. The creationist system of knowledge, encompassing as it does not only the biological evidence, but the reality of God’s mind and His creative activity in history, can allow for that possibility — and the profound zing of truth that may follow.”