Posted by jlwile on May 31, 2010
A student recently sent me a question based on a statement made in Dr. Jerry Coyne’s book, Why Evolution is True. Since there doesn’t seem to be much written about it for a general audience, I thought I would summarize the issue. Here is Dr. Coyne’s statement:
One of my favorite cases of embryological evidence for evolution is the furry human fetus. We are famously known as “naked apes” because, unlike other primates, we don’t have a thick coat of hair. But in fact for one brief period we do – as embryos. Around sixth months after conception, we become completely covered with a fine, downy coat of hair called lanugo. Lanugo is usually shed about a month before birth, when it’s replaced by the more sparsely distributed hair with which we’re born. (Premature infants, however, are sometimes born with lanugo, which soon falls off.) Now, there’s NO NEED for a human embryo to have a transitory coat of hair. After all, it’s a cozy 98.6 degrees Fahrenheit in the womb. Lanugo can be explained ONLY as a remnant of our primate ancestry: fetal monkeys also develop a coat of hair at about the same stage of development. Their hair, however, doesn’t fall out, but hangs on to become the adult coat. And, like humans, fetal whales also have lanugo, a remnant of when their ancestors lived on land.1 (emphasis mine)
Note the strong words by Dr. Coyne. Embryos have “no need” for such hair, and thus its presence can “only” be explained as a remnant of our primate ancestry. Not surprisingly, Dr. Coyne is wrong on both counts.
Let’s start with the first mistake Dr. Coyne makes. He seems to think that the only reason a human embryo would need hair is for insulation. Since the embryo is obviously kept at a constant temperature in its mother’s womb, there is no need for insulation, so there is obviously no reason for it to have hair. This, of course, is amazingly narrow thinking, as hair can have functions other than that of insulation. For example, in adults, hair provides sensory information. Not surprisingly, this kind of narrow thinking led Dr. Coyne to the wrong conclusion about lanugo.
Perhaps Dr. Coyne should have asked a few embryologists to look at his book before he published it. If he had, he would have learned that lanugo has a very important function in the human embryo. To learn about the function of lanugo, however, you must first learn about something else embryos have during the same stage of development: the vernix caseosa. This name comes from two Latin words that mean “cheesy varnish,” and it is a waxy coating made from dead skin cells and oil produced by the embryo’s sebaceous glands.
While it sounds pretty gross, this “cheesy varnish” serves at least three very important functions for the embryo. As Tortora and Grabowski say in their book, Principles of Anatomy and Physiology,
This substance covers and protects the skin of the fetus from the constant exposure to the amniotic fluid in which it is bathed. In addition, the vernix caseosa facilitates the birth of the fetus because of its slippery nature and protects the skin from being damaged by the nails.2
So what does this have to do with the lanugo that Coyne highlights in his book? Well, the “cheesy varnish” that is so important to the embryo is produced slowly, and since there is a lot of motion in the womb, it could be easily pulled off the skin in its initial stage of formation if there weren’t something to hold it in place That’s the job of the lanugo.
Indeed, if you look at a developing human embryo, you find that the “cheesy varnish” first accumulates where there is a lot of lanugo.3 It then spreads out, coming into contact with other patches that are spreading out from other regions of lanugo. So lanugo performs a very important function in the development of the vernix caseosa: it anchors this important “cheesy varnish” to the skin while the varnish is being formed.
Of course, this fact is taught in most classes that deal with embryology in depth. For example, students at the University of Michigan Medical School are taught:
The fine hair on a newborn infant is known as lanugo. It helps to anchor vernix caseosa (“cheese-like varnish”), a waxy substance that protects the fetus from maceration by the amniotic fluid.
Dr. Mark Hill at the University of New South Wells describes lanugo hair as follows:
From about the third month lanugo hair (Latin, lana = wool) hair is initially formed and it has a role in binding vernix to skin.
Indeed, this is such a well-known fact that review materials for the U.S. Medical Licensing Exam discuss it. For example, Philip R. Brauer in his review book, Human embryology: the ultimate USMLE step 1 review says:
Vernix caseosa is a culmination of sebaceous gland secretions and dead epidermal cells, and the lanugo hair helps retain it on the outer skin surface.4
Now remember, Dr. Coyne stated that the “only” explanation for lanugo hair in human embryos is as a remnant from our primate ancestry. Of course, we know that is not correct. Lanugo hair is present in human embryos because it serves an important purpose: Without lanugo, the embryonic skin would not form the protective layer that it needs while in the womb.
This, of course, is exactly what you would expect in a creationist framework: embryonic structures form for a reason, not because of some leftover vestige of an imagined evolutionary process. As is usually the case, then, the more you learn about science, the stronger the case for creationism becomes.
1. Jerry A Coyne, Why Evolution is True (Viking), 2009, p. 80.
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2. Gerard J. Tortora and Sandra Reynolds Grabowski, Principles of Anatomy and Physiology (John Wiley and Sons, Tenth Edition), 2003, p. 154.
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3. Susan Tucker Blackbur, Maternal, fetal, & neonatal physiology: a clinical perspective (Saunders, Third Edition), 2007, p. 530.
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4. Philip R. Brauer, Human embryology: the ultimate USMLE step 1 review (Hanley & Belfus), 2003, p. 95.
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