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Homology, dermatomes, and pentadactyl limbs

Moe Q. contacted us with a question about dermatomes, raised in her science class at school.

Public domain, Grant 1962 663.pngDermatomes

Figure 1. Dermatomes are regions/bands of skin along the length of the body that are innervated by different sets of nerves, arising from different levels of the spinal cord, different roots of the cervical (C), thoracic (T), lumbar (L), and sacral (S) regions (Grant, An Atlas of Anatomy, J.C.B, 1962).

See also, The Splendid spine in Standing upright for creation.

I had a Q on evolution and the bible if you don’t mind.

My teacher said dermatomes make little sense regarding the arrangement, unless we confess that we used to walk on 4 legs and [that] evolution is true. What do you think? This link shows a dermatome which seems random [link removed as per feedback rules]. This link shows dermatome which seem organised if we crawl like animals [link removed as per feedback rules]. What do you think?

Thank you

CMI-UK/Europe’s Philip Bell responds:1

Dear Moe,

All claims, like those of your teacher, are based on the following assumption: large-scale evolution has occurred, so the arrangements we observe in biology must confirm it. With this starting belief, evolutionists predict that there will be similarities between living things, e.g. between different vertebrates: fish, amphibians, reptiles, mammals, and birds. In this case, the similar dermatome arrangements in different creatures are believed to be confirmation of evolution (human dermatomes are shown in fig. 1).

Whatever the level of complexity of the organ or body system under consideration, evolutionists are incredulous that any intelligent scientist would allow for a common designer as an explanation. From their point of view, having ruled out purposeful design, all sorts of ambitious evolutionary ‘explanations’ are perfectly reasonable.

Take the pentadactyl limb for example. In ourselves, the arm and hand are composed of the humerus (upper arm), radius and ulna (lower arm), and the bones of the five-digit hand (carpals, metacarpals and phalanges). Similarly in the human leg and foot (femur, tibia and fibula, tarsals, metatarsals, etc.). This same pattern is seen in the dog’s leg, bat’s wing, bird’s wing, dolphin’s flipper, etc.; although the comparison is not always neat and tidy, the similarities are undeniable. Evolutionists rule out design, so some sort of evolutionary explanation must account for what is observed. Seldom (if ever) is the question asked, “Could the evidence I’m looking at be pointing to a different explanation of origins?” And this applies to dermatomes just as much as to pentadactyl limbs. While I’ve not gone into the arrangements of dermatomes in humans (fig. 1) compared to other vertebrates, the same principles apply.

CC BY-SA 4.0human-arm
Figure 2. Bones of the pentadactyl limbs of three vertebrates.

If the latter question (in blue) is permitted—which it must be, if science is to be genuinely empirical, not merely driven by ideology—different options have to be considered. In the case of similar pentadactyl limbs or similar dermatome arrangements we should ask, “Are these similarities evidence of common ancestry or evidence of common design?”

Professor Günter Wagner, Yale School of Medicine, evolutionary geneticist and expert on homology.

However, you might be wondering how we could scientifically choose the option that best fits the data, the facts of biology? One way would be to study the gross anatomy (physical appearance), but that could be used to reach either conclusion (common ancestry, or common design). What about the genetics, the coded instructions underlying the anatomy? Do the digitally-coded DNA programs for making these similar things (limbs or dermatome arrangements) tell the same story? They have to if common evolutionary ancestry is true, for the simple reason that DNA codes for proteins, which are built into the structures you see.

In fact, it is here that there is a big fly in the ointment, one which stubbornly obstructs even the most ambitious evolutionary arguments. A big embarrassment for true believers in evolution is that quite different genotypes are associated with seemingly homologous phenotypes. That is, the genetic instructions frequently do not align with the body parts that are built from them. Worse, similar looking things in biology can be coded for by quite different proteins (which is a little counterintuitive, but it’s a fact). Am I just pointing to a few exceptions to the rule? Unfortunately, from the point of view of the evolutionists, not at all. But don’t take my word for it. Listen to what leading expert and evolutionist Dr Günter P. Wagner confessed in his major book on the subject, Homology, Genes, and Evolutionary Innovation:

“The more comparative molecular work that is done on various species, the more examples of homologous organs with mechanistically different modes of development become known. … Continuity of morphological characters is not subscribed by continuity of genetic information.”2

Which means, morphology (how things look) frequently doesn’t correlate with (agree with) genetic information, the coding on the DNA. Günter also admitted:

“This seems to be a pretty depressing situation if one thinks that homology should somehow be related to the evolution of development and motivates the notion that homology may be an illusion … However, on closer inspection, the pattern of development is not entirely random …”2

He means that it is “a depressing situation” for him and his fellow evolution-believers. And note that he is clutching at straws with his last statement, that “the pattern of development is not entirely random”. In other words, he is admitting that the relationship between genes and body parts often seems so random that it simply doesn’t fit the prediction of evolution at all—see this useful article: Homology made simple.

I hope this answer is helpful.

Yours sincerely,

Published: 20 February 2024

References and notes

  1. This is a partially edited version of the private response. Return to text.
  2. Wagner, G. P., Homology, Genes, and Evolutionary Innovation, Princeton University Press, Princeton, N.J., p. 90, 2014. Return to text.

Helpful Resources

The Wonder of Science
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