The Urogenital Layout

"While on the subject, I will mention another functional absurdity in the male reproductive system, even though I am not aware of its causing medical problems." — George C. Williams, The Pony Fish's Glow, 1997¹

"To paraphrase Robin Williams, it's a sewage pipe running directly through a recreation area." — Jerry Coyne, Why Evolution Is True, 2009²

Summary

Critics make three complaints about the male layout.  The sperm duct loops over the ureter.  The urethra runs through the prostate.  The testes travel from beside the kidneys, through the belly wall, into the scrotum.  Each is an argument from history:  this is the layout expected if the body was modified from an ancestor with internal testes.  The parent article asks three separate questions.  Does the part fail often?  Has anyone drawn a better build and counted what it gives up?  Does history explain the layout?³  The three arrangements answer differently.

1. The vas deferens loop has no measured cost. George C. Williams raised it in 1992, and Richard Dawkins made it famous in 2009. Williams wrote in 1997 that he was "not aware of its causing medical problems." The one harm found needed a surgeon to reroute the ureter first. Embryology agrees with the critics about how the loop forms.
2. The prostate is a real cost, paid late. Tissue enlargement is found in 8% of men in their thirties and 50% at 51 to 60, and there were 94.0 million clinical cases worldwide in 2019, mostly after 65. But the tube through the prostate is also the chamber semen is emptied into, between two closing valves. No one has drawn a layout without it and counted the loss.
3. The testes' route is the critics' strongest case. A man's lifetime risk of a groin hernia is 27 to 43%; a woman's is 3 to 6%. More than 20 million repairs are done each year, and 3 to 5% of full-term boys are born with a testis that has not descended. Why mammals have a scrotum is still debated. Elephants keep their testes inside; dolphins and seals keep theirs low in the abdomen with dedicated cooling. Nathan Lents's alternative, sperm that tolerate body heat, exists in nature, but its cost for a human body has never been measured.
4. The design replies are thin. E. van Niekerk's 2012 paper in the Journal of Creation, the only creationist study found, answers a route the argument's author never proposed. Michael Egnor's storage purpose for the scrotum matches a secular hypothesis but has no numbers. No creationist source found addresses hernia.

Verdict:  one complaint carries a large, measured cost:  the groin hernia that follows the testes' route.  One carries a large cost that falls mostly after the fathering years, with an unpriced alternative.  One carries no known cost.  Neither side has priced a rebuilt layout on every axis.

Part 1: Who makes the complaint

George C. Williams, the evolutionary biologist, is the earliest source found for the sperm-duct argument, in Natural Selection:  Domains, Levels, and Challenges (1992).  The testis, he wrote, moved toward the tail end of the body long before the need for cool sperm arose.  "In fact the economy of duct material was frustrated by each testis taking the wrong path to the posterior. It went dorsal to the ureter, which drains the kidney into the bladder, but the sperm duct goes ventral to the ureter."⁴  His figure drew the alternative:  "testis passing ventral to the ureter."⁴  In 1997 he repeated the argument and added the admission quoted at the top of this page.¹

Richard Dawkins credited Williams and gave the example its popular form in The Greatest Show on Earth (2009).  The duct "takes a ridiculous detour around the ureter," and "If this were designed, nobody could seriously deny that the designer had made a bad error."⁵  When the testes descended, "the vas deferens unfortunately got hooked the wrong way over the ureter."⁵  Dawkins names no medical cost.

Jerry Coyne makes the prostate and hernia complaints, not the duct one.  The urethra "happens to run right through the middle of the prostate gland," and "A smart designer wouldn't put a collapsible tube through an organ prone to infection and swelling."²  The groin canals "leave weak spots in the body wall that make men prone to inguinal hernias," and "No intelligent designer would have given us this tortuous testicular journey."²

S. Jay Olshansky, Bruce Carnes and Robert Butler drew the prostate redesign in Scientific American in 2001.  "An experienced plumber looking at the anatomy of a man's prostate might suspect the work of a young apprentice," they wrote, and then added:  "This configuration may have as yet unknown benefits."⁶

Neil Shubin blames the hernia on history:  "Our propensity for hernias, at least for those hernias near the groin, results from taking a fish body and morphing it into a mammal."⁷  He also grants the scrotum "ample advantages."⁷

Nathan Lents's book Human Errors (2018) has no passage on the testes, prostate, hernia or sperm duct.⁸  His argument is a piece left out of the book and published in Undark.  He calls external testicles "one of the hardest to explain" of the body's features, and proposes that "Evolution could have simply tweaked the parameters of sperm development so the ideal temperature of its enzymatic and cellular processes was the same as the rest of the body's processes."⁹

The "sewer" line.  In the critical literature the "sewer through a playground" image traces to Coyne, who used it for the prostate, paraphrasing the comedian Robin Williams.²  No primary source was found for the comedian's version.  Applied to the birth canal beside the anus, it has one scientific comment on file:  the microbiologist Andrew Greenhill said the closeness "is probably better design than what it initially looks."¹⁰  That is a remark, not a measurement.

Part 2: The sperm duct and the ureter

The route

The sperm duct, the vas deferens or ductus deferens, grows from the embryo's mesonephric duct:  "Distal to the epididymis, the mesonephric duct acquires a thick investment of smooth muscle and becomes the ductus deferens."¹¹  The same duct sprouts the bud that becomes the ureter, as The Embryonic Tail, Lanugo, and the Pronephros explains.  The testis forms high on the back wall of the abdomen, near the kidneys, and ends in the scrotum.  A standard embryology textbook states the consequence plainly:  "The mode of descent of the testis explains why the ductus deferens crosses anterior to the ureter".¹¹  So the critics and the textbook agree on how the loop forms.  The question is only what it costs.

What it costs

The duct is "typically 45 cm long" in an adult.¹²  How much of that length the loop adds has not been measured in any source found.  Dawkins judged the added cost of each extra bit of length to be small.¹³

No medical cost was found.  Williams said he knew of none.¹  A search for harm found one case report.  A man with spina bifida had his ureters cut below the crossing in 1973 and brought out to the skin.  As he grew, "The vas deferens on either side was crossing and kinking the ureter."¹⁴  The surgery caused it by leaving the duct hooked over a rerouted tube.  In the natural layout there is no failure rate to report.

The creationist reply

E. van Niekerk, then a mechanical-engineering student, answered Dawkins in the Journal of Creation in 2012.  He makes three points.

First, he says the route comes from embryonic development, "not the evolutionary development or phylogeny (contra Dawkins)."¹⁵  This misses the argument.  Williams and Dawkins agree that development produces the loop.  Their claim is that development itself is inherited.

Second, he says semen must collect secretions from glands "which sit along the way of the ejaculatory duct and urethra,"¹⁵ and that a slack duct lets the cremaster muscle pull the testes up and down to control their temperature:  "the testes can literally be 'given some rope'."¹⁵  Both points answer a duct running straight to the penis.  Williams's alternative changes one thing:  the side of the ureter the testis passes.⁴  A duct on the other side of the ureter would pass the same glands and could have the same slack.  Van Niekerk does not discuss that alternative.

Third, he argues that a longer duct gives its muscular waves more power.  His own figure caption says the force and time values "were realistically, but arbitrarily chosen," so "the values of the power output are also arbitrary."¹⁵  With force and time held fixed, power rises with length by definition.  The parent article reaches the same judgment.

Assessment.  The loop is good evidence for the historical claim, and no evidence for the claim that the body fails.  Neither side has shown that the present route costs anything, or that the alternative would.

Part 3: The prostate around the urethra

What it costs

Enlargement of the prostate, benign prostatic hyperplasia, is very common with age.  S. J. Berry and colleagues pooled ten autopsy studies of more than 1,000 prostates:  "The prevalence of pathological benign prostatic hyperplasia is only 8 per cent at the fourth decade; however, 50 per cent of the male population has pathological benign prostatic hyperplasia when they are 51 to 60 years old."¹⁶  That is the source of Olshansky's "one of every two males."⁶  Tissue changes are not the same as symptoms.  The Global Burden of Disease study counted clinical cases:  "In 2019, there were 94·0 million ... prevalent cases of benign prostatic hyperplasia globally among men aged 40 years and older."¹⁷  The rate peaks at 24,300 per 100,000 men aged 75 to 79.¹⁷  The study counted 1.86 million disability-adjusted life-years and did not estimate deaths.¹⁷

So the cost is large in number, falls mostly after 65, and is counted as disability.  Coyne concedes the timing:  "Presumably this wasn't a problem during most of human evolution, when few men lived past thirty."²

What the arrangement does

The prostate is not a gland that happens to sit on the urethra.  It empties into it.  Amjad Alwaal, Benjamin Breyer and Tom Lue describe the first stage of ejaculation.  "The first step in the emission phase is the closure of bladder neck to prevent retrograde spillage of the seminal fluid into the bladder. This is followed by the ejection of prostatic secretions ... mixed with spermatozoa from the vas deferens ... into the prostatic urethra."¹²  Then "the bladder neck remains closed, whereas the external urethral sphincter is open."¹²  The stretch of urethra inside the prostate is the chamber that is filled and then emptied, with a valve at each end.

A layout with the urethra outside the gland would still need the gland's ducts to reach the urethra and a sealed chamber between two valves.  Olshansky's group drew the move but did not describe how either would be kept.  Their own caveat, "as yet unknown benefits," stands unanswered.

One measured result bears on the trade.  Transurethral resection of the prostate, the standard operation for enlargement, cuts a wider channel through the gland.  A 2024 review of 103 randomized trials with 8,521 patients found that "the overall incidence reported was 46%" for retrograde ejaculation, in which semen goes backward into the bladder.¹⁸  This does not price Olshansky's redesign, since the loss comes from damage to the bladder neck and the tissue near the ejaculatory ducts.  It does show that the tissue around the prostatic urethra does work that is easy to lose.

Assessment.  The failure is real and common, but mostly after the fathering years.  The redesign has been drawn, not priced.  The critic's claim that no designer would do this needs an alternative that keeps the emission chamber, and none has been described.

Part 4: The testes, the scrotum and the groin

The route and how it fails

The testes form near the kidneys.  Their move to the groin "is largely a relative movement that results from growth of the cranial part of the abdomen away from the future pelvic region."¹¹  A pouch of the belly lining, the processus vaginalis, pushes through the belly wall ahead of each testis and forms the inguinal canal.  Descent into the scrotum "usually begins during the 26th week," and "By 32 weeks, both testes are present in the scrotum in most cases."¹¹  Around birth, the neck of the pouch normally seals.¹¹

Two things can go wrong.  The testis can stop short.  "Cryptorchidism (hidden testes) is the most common defect in neonates; it occurs in about 30% of premature males and 3% to 5% of full-term males."¹¹  Most descend within months.  If it is not corrected, "these males have a significantly higher risk of developing germ cell tumors".¹¹  Descent fails in other animals too:  in "up to 10% in male dogs," 2% in cats, and 2 to 8% in horses.¹⁹

Or the pouch can stay open.  "The embryologic basis of indirect inguinal hernia is persistence of the processus vaginalis".¹¹

What the hernia costs

The international surgical guideline of 2018 puts the lifetime occurrence of groin hernia at "27–43% in men and 3–6% in women."²⁰  The Oxford record-linkage study of 1976 to 1986 gives 27% and 3% for the lifetime risk of repair.²¹  Repair "is one of the most common surgeries, performed on more than 20 million people annually."²⁰  Planned repair carries a death rate of 0.2 to 0.5%, and emergency repair 4 to 5.5%.²⁰  Before surgery was safe, a strangled hernia could kill, as Coyne says.²  Lents writes that hernias "have killed untold millions over the ages,"⁹ but gives no source for that figure.

Women have an inguinal canal too.  "The round ligaments pass through the inguinal canals and terminate in the labia majora."¹¹  So the sex difference measures the extra cost of the male route, not the cost of having any canal.  On the Oxford figures that is about 24 points of lifetime risk.²²  Two cautions apply.  Hernias peak twice, "at 5 years, primarily indirect and 70–80 years, primarily direct."²⁰  The testes' route explains the childhood, indirect kind directly.  The old-age, direct kind pushes through the canal's floor, and the sources read here do not split the male excess by type.  Krogman blamed upright posture for that weakness, a claim the sibling article The Spine and the Cost of Standing Up tests and finds cannot explain a nine-to-one sex ratio.

What the scrotum is for

The textbook answer is temperature.  The scrotal organs work best "at ca. 4°C below abdominal temperature," according to Karel Kleisner, Richard Ivell and Jaroslav Flegr.²³  Williams put it at "a degree or two," and added "for reasons not entirely clear."¹  The same review states the problem frankly:  of the many hypotheses offered in a hundred years, "none has been able to provide a simple explanation of this phenomenon."²³  One of those hypotheses, Bedford's, holds that the point is to cool the epididymis, the coiled duct where sperm are finished and stored.²³

Lents's alternative, testes inside and sperm that tolerate body heat, is not imaginary.  In most lineages of the Afrotheria, including the elephant, manatee and rock hyrax, the testes stay "at their initial abdominal position near the kidneys".¹⁹  Dolphins, true seals and pangolins keep them in the lower abdomen.  But the same paper notes how those animals manage.  "testicular cooling is achieved by vascular countercurrent heat exchanger systems, as observed in dolphin"; seals use "direct cooling with blood from the hind limbs"; or "testicular cooling may not be necessary, as these species have lower body temperatures".¹⁹  So nature supplies the alternative, and in the cases described it comes with added plumbing or a cooler body.  How the elephant manages is not described in the sources read here, and neither route has been costed for a human.

In a blog reply Lents listed "sloths, elephants, and most marsupials" as having abdominal testes.²⁴  Marsupials are wrong:  "In marsupials, we find a well-developed scrotum that is, however, prepenial".²³

Coyne proposed another build:  testes that "formed directly outside the body."²  That skips the canal, and with it the indirect hernia.  It also needs a blood supply and a duct that start outside the belly wall.  In the actual embryo the testis's vessels "form when the testes are located high on the posterior abdominal wall".¹¹  No one has described how Coyne's build would supply them.

Assessment.  This is a large, measured cost, and the route that causes it is exactly what the historical argument predicts.  Two alternatives exist.  One, internal testes, is found in living mammals;  where its workings are described, it comes with extra cooling or a cooler body.  The other, testes formed outside, has been named but not described.

Part 5: The design replies

Van Niekerk (2012) is the only creationist study found of any part of this layout.  Part 2 explains why it fails as a reply, though it does name real functions.

Michael Egnor, a neurosurgeon writing for the Discovery Institute, an intelligent-design group and not a young-earth one, answered Lents in 2018:  "Sperm are produced and stored in a cooler external environment for the same reason we refrigerate food; for preservation, until it's needed."²⁵  This matches Bedford's secular hypothesis, which adds weight to it.  But Egnor gives no measurement, does not address the hernia, and hedges:  "I suspect so, but maybe it is a design flaw."²⁵

Don Batten and Tas Walker of Creation Ministries International put the prostate under the Fall:  "Degeneration with old age is not a design fault (prostate problems in some men are a case in question). ... None of these bad things were part of the original design but are a consequence of the Fall of man."²⁶  That fits the age pattern, since enlargement is uncommon in young men and common after 50.  But Coyne makes the same point about age in other words, and the Fall claim cannot be tested.

Answers in Genesis, the Institute for Creation Research, Jerry Bergman and David Menton:  no text by any of them on the sperm duct, the prostate or groin hernia was found in the searches made for this article.  The general ICR position is Randy Guliuzza's:  "There is no objective test for poor design."²⁷  A 24-point excess in lifetime hernia risk is an objective measurement, and a reply has to meet it.

Objections and responses

"The vas deferens loop proves evolution, so the article concedes the point."  It concedes that the loop fits a history of descent from ancestors with internal testes.  The article's question is narrower:  whether the loop is a costly defect.  On that, Williams, who raised it, says it is not known to cause harm.

"The hernia is caused by upright walking, not by the testes."  Women walk upright too and have a canal of their own, yet men have about nine times the rate.²⁰  Childhood hernias, which are mostly indirect, follow the testes' path.

"Hernia is a disease of old age, like the prostate, so it falls under the Fall."  The indirect kind peaks at five years old, before any wear.  The age answer covers the direct kind at best.

"Internal testes would be better, since elephants have them."  Perhaps.  But a human version has not been drawn, let alone costed, and Lents's claim that evolution "could have simply tweaked" sperm development is a guess about what is easy for biochemistry.

"The prostate reply is special pleading:  a designer could have built the emission chamber differently."  Possibly.  The point is that the critic has not shown how.  The one redesign on paper, Olshansky's, keeps silent about the chamber, and its authors grant "unknown benefits."

Issues and unanswered questions

• The hernia cost is not answered by any creationist source found. This is the weakest point for the design side. A reply would need to show that the scrotal route buys something measurable, such as fertility or sperm quality, that outweighs the hernia burden. Or it could show that the earlier body had a stronger wall, which cannot be tested.
• The scrotum's function is unsettled. That weakens both Lents's view that the cool temperature is a fluke and Egnor's confident purpose.
• The direct-hernia share of the male excess was not found. If most of the gap is in direct hernias, the testes' route explains less of it.

Verdict

The vas deferens loop has no measured cost.  Its author admitted as much, and the one harm found was made by a surgeon.  It supports common descent, and it is not a defect anyone has shown.

The prostate around the urethra carries a large late-life cost:  50% tissue prevalence at 51 to 60 and 94.0 million clinical cases worldwide.  The arrangement does work, since the prostatic urethra is the chamber semen is emptied into.  The only redesign has not been described in enough detail to price.

The testes' route is the critics' strongest case.  It is the leading explanation for why men's lifetime groin-hernia risk is 27 to 43% against women's 3 to 6%, though how much of the gap it explains depends on the unmeasured share of direct hernias.  Internal testes exist in living mammals, so an alternative is real.  But the examples described in the sources read here pay for it with cooling systems or cooler bodies, and the cost for a human is unknown.

No layout here has been priced on every axis by either side.  The design reply is weakest on the hernia, where it has said nothing at all.

Sources