Why was the penis bone lost from man?
IN MAY 2001, Scott F. Gilbert and Ziony Zevit published a paper where they proposed a new interpretation of the term “צֵלׇע” (tzela) in the “Genesis” of the “Old Testament”. Contrary to the traditional belief that it referred to Adam’s “rib” from which God created Eve, they suggested that it denoted a bone that, until recently, was largely unknown. This is because the bone had ceased to develop in the human body due to the evolutionary process.
This bone is the baculum, also known as the penis bone or pelvic bone. It once played a role in male erections, but its disappearance has led to a reliance on a combination of muscle activity and blood pressure, which can be either successful or unsuccessful.
According to Gilbert and Zevit’s reinterpretation of the myth, men may feel a sense of nostalgia for this bone that was supposedly removed from their bodies to transform them from Yahweh into a man. The perineal suture is seen as a scar that reminds them of the loss of enduring firmness.
This bone is typically elongated, but in some groups it may be serrated at the tip. It can also be flat or trident-like. It exhibits a great deal of diversity.
Perhaps it was man’s destiny to lose this rigidity. I say “man’s” because women also lost a corresponding bone known as the baubellum or clavicular bone.
The baculum, however, still exists in many other species, most notably dogs. As such, it is more familiar to veterinarians than to andrologists.
“The baculum is a generally striated bone,” explains Dionysios Youlatos, a professor in the Department of Zoology at the Aristotle University of Thessaloniki’s Department of Biology. “It is found inside the penis of male mammals. This bone likely originates from the ossification of connective tissue and is located above the urethra, probably serving a protective function. It is usually elongated, but in some groups it may be serrated at the tip. It can also be flat or trident-like. There is a great deal of variation. It may be straight or keeled (bent), thick or thin, long or short.”
This diversity is also determined phylogenetically. For example, in carnivores it is generally elongated and relatively simple in form. In some rodent groups it may be serrated or triangular. Moreover, the morphology of the pisiform bone, as seen in squirrels or some species of mice, also has a taxonomic significance, meaning it helps distinguish species.
The penis bone is relatively small and its size is proportional to the size of the penis.
One of the largest examples can be found in walruses (often referred to as marine elephants) at the North Pole, reaching lengths of up to 60 cm.
But let’s start from the beginning. The classification of species as we know it today dates back to the 18th century, largely due to the work of Swedish botanist, physician, and zoologist, Linnaeus (Carl von Linné 1707-1778). In modern species classification, one can encounter terms like “primates” or “higher mammals”, which are, as Mr Youlatos points out, “completely anthropomorphic”.
“Once humans were included, they were considered to be a superior class of mammals, hence the name primate,” he explains. “The terms ‘superior’ or ‘inferior’ don’t mean anything biologically. No one is superior or inferior. A species may be more ‘primitive’ based on certain characteristics and another might be more evolved in relation to those same characteristics. But the definitions of ‘superior’ and ‘inferior’ are entirely anthropomorphic and do not belong in biology. Each species is adapted to specific conditions, making it successful in its own right.”
To differentiate between species that have it and those that don’t, Youlatos highlights that the primary criterion is generally bone size.
“The main issue is that it’s a bone located in the penis and is relatively small. An experienced anatomist might not notice it unless they know what they’re looking for. This implies that it might not be absent in organisms where it hasn’t been documented; it could simply be an oversight by the observer who didn’t inspect the specific area. Only through a detailed study of different mammal groups can we definitively confirm its presence or absence.”
Secondly, since mammals, the group in which this bone has been identified, comprise a vast number of species – nearly six and a half thousand according to the latest records – it’s practically impossible to have examined each one anatomically to document the absence or presence of this bone. Most studies include a relatively small percentage, at most 60%.
Primarily, it has been documented in planktivorous mammals. It hasn’t been found in the group known as monotremes, specifically the platypus and echidnas, those primitive mammals that still lay eggs. It also hasn’t been documented in marsupials.
There is a great deal of diversity among planktivorous mammals.
The presence of a pelvic bone has been detected in a group of African shrew mammals known as Afroshorisids, as well as in the Eurasian shrews, a category of mammals we identify as soricomorphs. However, it has only been discovered in aspalaks, not in shrews.”
– Could this discrepancy be due to the observer, as you suggested earlier?
That’s entirely plausible. We have a vast collection of shrews in our museum, and it would be fascinating to delve deeper into this. We’re discussing animals that weigh between 10 and 20 grams. Imagine trying to locate a pelvic bone in a penis that small.
In carnivores, the pelvic bone is also present. Most carnivores, with the exception of hyenas, have a pelvic bone. It’s also found in most bats, except for certain tropical and subtropical groups where its absence has been noted.
This bone can be found in all reptiles, exhibiting immense diversity.
Recently, I read that this bone has been discovered in certain groups of lagomorphs, a class of mammals, in North America. It’s not found in hares or rabbits, but in another class of hare-like animals, the pikas, which resemble rodents more than hares.
There’s a distinction among primates, where a differentiation is also evident. It’s present in most primates, except for certain South American monkeys such as cacao, wakari, and spider monkeys. It’s also missing from the tarsiers of Southeast Asia, small nocturnal primates with large eyes.
This bone is found in all African monkeys and apes. However, it’s absent in one species of Asian monkey residing in Vietnam, the Pygathrix. Yet, it’s only found in one out of every three species. Of course, it’s absent in humans.
– When did it vanish in humans? Can we refer to the species “human” from the time it disappeared onwards?
This question is intriguing because we know it’s not present in modern humans, but it does exist in the chimpanzee (and in the bonobo, albeit reduced, at the tip of the penis, measuring a few millimeters, about 6-15), in the gorilla and in the uracotago.
Given that it’s present in the chimpanzee, gorilla, orangutan, gibbon, and caiman, it implies that the bone was present in this evolutionary lineage. Considering that chimpanzees and humans as groups diverged about six million years ago, based on the fossil record and primarily on molecular and genetic studies, it’s likely that it disappeared sometime after this separation.
Because this bone is typically small and exhibits low ossification, it’s challenging to fossilize. The scientific literature does not report the existence of a baculum (penis bone) in hominid fossils. Therefore, it’s extremely challenging to determine with certainty when this bone was lost.
The term anthropoids refers to a family within the diverse primate families, typically associated with the group known as the great apes. This group includes three species of orangutans in Asia, two species of gorillas and two species of chimpanzees in Africa, as well as humans, who are now spread across the globe.
– What is its purpose and why was it lost?
The precise function of this bone remains unclear. It is thought to be linked to various functions. Some suggest it provides mechanical support to the penis. Others associate it with overcoming vaginal resistance, preventing urethral compression, or stimulating female genitalia during vaginal penetration.
Some theories propose that the presence of the baculum aids in sperm transport. Most studies suggest that this bone facilitates prolonged penetration. These theories, of course, are all interconnected.
Research indicates that in primates and carnivores, where most of the studies have likely been conducted, the presence of the baculum is linked to intense sexual competition and specifically to pre-copulatory and post-copulatory sexual selection. It has been found, particularly in primates, that its presence and robustness correlate with a prolonged duration of penetration, which enhances reproductive success by delaying the female’s availability for subsequent mating.
This bone is primarily found in primate groups that exhibit polygamous or seasonal breeding systems and are characterized by intense competition. Conversely, in other primate groups where such pressures or competition are absent, the bone appears to be somewhat reduced.
These observations have led to several theories attempting to explain the absence of the baculum in humans. It’s important to note that, according to urologists, this bone only occurs in certain rare pathological conditions.
Firstly, relative to body mass and size, and compared to similar primates, humans have a relatively large penis.
The loss of the baculum is primarily attributed to sexual selection. It is a trait determined by this process. Some speculate that males capable of maintaining a strong and prolonged erection without the support of an internal bone were selected. These males would theoretically appear healthier and stronger to females.
This is a hypothesis proposed by Richard Dawkins.
One theory suggests that males with a softer, more flexible penis were favored in the evolutionary process. The flexibility could allow a wider range of erotic positions and movements, potentially increasing physical arousal in females. The presence of a bone might have hindered acrobatic courtships and been more prone to injury.
Another theory posits that as social or reproductive systems evolved towards monogamy or polygyny (i.e., harems), males gained more control over females. This could have led to the preference for a non-elongated bush and a corresponding penile bone. Otherwise, the penis might have been overly conspicuous or highly vulnerable.
– Could this interpretation merely be a projection of our current values onto the history of evolution?
Yes, it’s possible. The assertion that monogamy now dominates human populations and the Western lifestyle is actually incorrect. In reality, monogamous systems account for a small fraction of human societies, perhaps 15-20%. Most human societies function, or have functioned, within different social structures, such as polygyny or polygamy, which are quite distinct from monogamy. Therefore, it’s likely that current evolutionary theories do not accurately explain why the penile bone gradually diminished and ultimately disappeared.
A recent 2021 study speculates that the penile bone likely disappeared due to changes in male aggression and cognitive perception in humans. Over time, a long, exposed penis, potentially containing a bone, could be easily injured, leading to numerous complications, not only from the injury itself but also from subsequent issues such as sepsis during recovery. Consequently, any male sustaining such injuries would likely withdraw from sexual activity for an extended period. Awareness of the risk of a prolonged absence from the sexual arena could result in fewer opportunities to pass on genes to the next generation, possibly leading to the evolution of biological systems without this bone.
– Could this be an example of neoteny? (i.e. Neoteny (the slowing of normal development, resulting in the retention of embryonic or juvenile traits in adulthood)
This might be the case because certain traits that we possess, such as our jaws and large skulls—which accommodate our large brains—are considered neotenic. This neoteny might have facilitated the rapid evolution of our species.
Regrettably, I have not found any relevant literature on the subject. Neotenic studies are generally a challenging field because the deviations from normal development seen throughout the animal kingdom, which have led to numerous differentiated groups, raise many overarching questions. For example, how is neoteny sustained? Why does it occur in some groups but not in others? And so forth.
– What do we know about the female clitoral bone?
Our knowledge on this subject is rather limited. Generally, at least among primates, there seems to be a correlation between the presence or absence of both bones in males and females. The clitoral bone, or the baubellum, appears to be absent in a larger proportion of primates than the penile bone. However, it’s relatively small—much smaller than the coccyx. Exceptions do exist, such as in female lemurs, who possess a fairly large clitoral bone that is almost half the size of the male’s penile bone.
– What is your opinion on the publication that claimed that Eve was not ultimately made from Adam’s rib, but from his penile bone?
I can’t say for certain. To my knowledge, the penile bone was first documented in the 17th century, which makes the claim rather dubious.
However, if we consider the Semitic nomadic pastoral populations in the Middle East during the Bronze Age—when the Old Testament was supposedly written—the animals they would have interacted with include guard dogs, which do have a penile bone. On the other hand, their primary livestock were artiodactyls—goats and sheep—which lack a penile bone. Given that this bone is absent in the animals they regularly slaughtered and deboned, why would they interpret its absence as Adam’s rib?
In conclusion, I find the claim in this post highly speculative. Having read Gilbert & Zevit‘s 2001 paper, it seems somewhat far-fetched to me. Of course, I’m not an expert in biblical history, which is the expertise needed to properly evaluate this claim.
