Unintelligent Design

Biologists such as myself are fond of pointing to the remarkable adaptations generated by natural selection, while benighted religious believers claim that such adaptations are the result of “intelligent design.” Ironically, however, some of the most impressive evidence for evolution – as opposed to special creation — resides in imperfections, including those of our own bodies.

Consider the skeleton. Ask yourself, if you were designing the optimum exit for a fetus, would you engineer a crazy route that passes through the narrow confines of the pelvic girdle? Add to this the tragic reality that childbirth is not only painful in our species, but downright dangerous and sometimes lethal, owing to occasional cephalo-pelvic disproportion — literally, the baby's head being too large for the mother's birth canal — breech presentation, and so forth. This design flaw is all the more dramatic since there is plenty of room for even the most stubbornly misoriented (i.e., breech presentation), large-brained fetus to be easily delivered, any place in that vast non-bony region of a woman’s body below the ribs and above the pelvis. And in fact, that is precisely what obstetricians do, when performing a Cesarean section.

Evolution, however, stubbornly and stupidly insisted on threading its way through the ridiculously narrow pelvic ring, altogether neglecting the simple, straigh-forward solution, which would have been for the vagina to open pretty much anywhere else in the lower abdomen. Why? Because evolution isn’t an observing, creating, all-knowing engineer and designer. Rather, it is a mechanical, mathematically consistent but completely unconscious natural process. Among its constraints is the fact that species aren’t “created” out of whole cloth; rather, they evolve – slowly and imperfectly – from their ancestors.

Human beings are mammals, and therefore tetrapods by history. As such, our ancestors carried their spines parallel to the ground; it was only with our adaptive insistence on upright posture[1] that the pelvic girdle had to be rotated, thereby making a tight birth-fit out of what for other mammals is nearly always an easy passage. An engineer who designed such a system from scratch would get a failing grade, but evolution didn't have the luxury of design, intelligent or otherwise. It had to make do with the materials available. (Admittedly, it can be argued that the dangers and discomforts of childbirth were pre-planned after all, since Genesis gives us God's judgment upon Eve, that as punishment for her disobedience in Eden, "in pain you shall bring forth children.” Might this imply that if Eve had only restrained herself, her vagina would have been where every woman's belly-button currently resides?)

On to men. An especially awkward design flaw of the human body — male and female alike — results from the close anatomical association of the excretory and reproductive systems, a proximity attributable to a long-standing, primitive vertebrate connection, and one that isn't only troubling for those who are hygienically fastidious about their sex lives. In addition, although there is no obvious downside to the deplorable fact that the male urethra does double-duty, carrying both semen and urine, most elderly men have occasion to regret that the prostate gland is closely applied to the bladder, so that enlargement of the former impinges awkwardly on the latter.

In addition, as human testicles descended — both in evolution and in embryology — from their position inside the body cavity, the vas deferens, which connects testis to urethra, became looped around the ureter (which carries urine from kidneys to bladder), resulting in an altogether ridiculous arrangement that would never have occurred if evolution could have anticipated the problem and, like an even minimally competent structural engineer, designed male tubing to run in a direct line.

In this regard, the most dramatic example of a ridiculous, deeply unintelligent and unplanned anatomical detour orchestrated by evolution occurs not in people but in the neck of giraffes. Probably the most famous thing about the giraffe's neck (at least among biologists), is a peculiarity of its innervation, notably its left recurrent laryngeal nerve, which turns out to be a stunning example of extraordinarily dumb design ... once again, precisely what we'd expect in a creature that, like all other creatures, wasn't "designed" at all, but is a ramshackle product of selection acting on the biological material that was historically available.

Here's the deal: The laryngeal nerves, present in vertebrates generally, branch off from the larger vagus nerve and connect the brain to the muscles of the larynx. (Forget, for the moment, that giraffes are probably the quietest of any large mammal; they do vocalize a little, albeit faintly.) In all mammals, the recurrent laryngeal nerves depart from the vagus at the level of the aortic arch, the spot where the aorta, initially ascending from the heart and continuing via the carotid arteries to nourish the head and neck, dives posteriorly to provide blood flow to the rest of the body. This arch of the aorta makes a hairpin, 180-degree loop; this is no problem for the right recurrent laryngeal nerve, which, being on the "correct" side, goes directly up to the larynx, along the trachea. But its left counterpart is forced to curve under the aortic arch before heading larynx-ward — a bit anatomically inconvenient but not a major problem in most vertebrates including human beings, since this literally loopy path only necessitates a few extra inches of length. Herein lies both an interesting dilemma for long-necked creatures as well as an object lesson in evolution's often erroneous "design."

Among fish, the recurrent laryngeal nerves (left and right) follow a straight path from the brain, along the heart and then to the gills; pretty much the same, we can predict with near certainty, in short-necked early mammals, although the left version, stuck on the downward curving side of the aortic arch, would have had a slightly longer, loopier route. But among those critters that evolved long necks – all the better to get leaves high on acacia trees — with the heart essentially sinking low into the thorax and the larynx staying relatively high in the throat, the poor left recurrent laryngeal nerve was forced to perform a ridiculous detour during embryonic development: emerging from the brain, going southward so as to loop just below the ever-retreating aortic arch, then literally heading upward again, along the trachea to reach the larynx. In the case of modern giraffes, this absurd arrangement now necessitates a nerve that's about 15 feet long (7.5 feet down and then back up), whereas if it had simply been routed directly, its entire length would have been perhaps six inches.

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And why? Just like our own evolution, that of giraffes wasn't laid out a blank drawing-board; rather, it proceeded from their immediate antecedents, whose evolution proceeded from theirs, going back to a common ancestral fish, whose left recurrent laryngeal nerves were perfectly reasonable, thank you. (By the way, don't expend all your recurrent laryngeal sympathy to giraffes: There were other vertebrate descendants of fish — notably, the sauropod dinosaurs — whose 45-foot-long necks would have necessitated a lot more nerve: roughly 90 feet.)

Back to our own species, for a final example, although many more are available: The primitive vertebrate system, still found among some of today's chordates, combined both feeding and respiration, just as excretion and reproduction used to overlap, and still do in many species. Water went in, food was filtered out, and passive diffusion sufficed for respiration. As body size increased, a separate respiratory system was added, not de novo but by piggybacking onto the pre-existing digestive plumbing.

By consequence, access to what became the lungs was achieved only by sharing a common anteroom with incoming food. As a result, people are vulnerable to choking. The Heimlich maneuver is a useful innovation, but it wouldn't be needed if evolution only had the foresight to design separate passages for food and air, instead of combining the two. But here as in other respects, natural selection operated by small, mindless increments, without the slightest attention to any bigger picture or anything approaching a wise, benevolent over-view. And it still works that way.

It must be emphasized that the preceding does not constitute an argument against evolution; in fact, quite the opposite. Thus, if living things (including human beings) were the products of special creation rather than of natural selection, then the flawed nature of biological systems, including ourselves, would pose some awkward questions, to say the least. Granted, God isn’t typically conceived as giraffe-like. But if God created "man" in his image, does this imply that He, too, has comparably ill-constructed knee joints, a poorly engineered lower back, a dangerously narrow birth canal, and ridiculously ill-conceived urogenital plumbing? A novice engineer could have done better.

The point is that these and other structural flaws aren't "anti-evolutionary" arguments at all, but rather cogent statements of the contingent, unplanned, entirely natural nature of natural selection. Evolution has had to make do with an array of constraints, including — but not limited to — those of past history.

We are profoundly imperfect, neither more nor less than all other creatures, and in these imperfections reside some of the best arguments for our equally profound natural-ness.

[1] Interestingly, although there are numerous hypotheses as to why our ancestors evolved bipedalism – i.e., the adaptive payoff of being upright beings — that issue is currently unresolved.

David P. Barash is an evolutionary biologist and professor emeritus of psychology at the University of Washington. His most recent book is Through a Glass Brightly: using science to see our species as we really are, just published by Oxford University Press.