Bava Kamma 77b ~ Pig x Sheep

בבא קמא עז, ב – עח, א

ואמר רבא זה בנה אב כל מקום שנאמר שה אינו אלא להוציא את הכלאים ...אמר לך ר"א כי איתמר דרבא לטמא שנולד מן הטהור ועיבורו מן הטמא...וטהורה מטמאה מי מיעברא אין דקיי"ל דאיעבר מקלוט 

Rava said this establishes a model and teaches that wherever the term שה [seh] is stated in the Bible, it is meant to exclude a hybrid... R. Eliezer would say to you  - when did Rava state his model?  With respect to a non-kosher animal that was born from a kosher mother and a non-kosher father...But can a kosher animal conceive from a non-kosher animal? Yes, for it has been established that this case refers to a kosher animal that was conceived from a [kosher mutant animal that was] born with uncloven hooves. (Bava Kamma 77b-78a)

A pig in sheep's clothing? Nope. Just a pig.

In toady's page of Talmud we read of a debate regarding the crossbreeding of different species, and the possibility that a non-kosher animal (say, a pig) could fertilize a kosher animal (like a sheep). Here the Talmud seems to suggest that this could not happen, and that when this possibility is raised, it refers to a kosher animal that is breeding with another kosher animal but which looks non-kosher because of a mutation that causes it to have non-cloven hooves. Here is that case:

k= kosher; m= mutant, born with non-cloven hooves

This debate is part of a larger one found in another tractate of the Talmud, Bechorot. Here is part of that discussion:

בכורות ז, א

והאמר ר' יהושע בן לוי לעולם אין מתעברת לא טמאה מן הטהור ולא טהורה מן הטמא ולא גסה מן הדקה ולא דקה מן הגסה ולא בהמה מן חיה ולא חיה מן בהמה חוץ מר' אליעזר ומחלוקתו שהיו אומרים חיה מתעברת מבהמה וא"ר ירמיה דאיעבר מקלוט בן פרה ואליבא דרבי שמעון

...R. Yehoshua ben Levi said: A non-kosher female can never conceive from a kosher male, nor a kosher female from a non-kosher male, nor a large animal from a small animal, nor a small animal from a large animal, nor a domesticated animal from a non-domesticated animal, nor a non-domesticated animal from a domesticated animal, except for R. Eliezer and his disputant [in Chulin 79b], who claimed that a non-domesticated animal can conceive from a domesticated animal...(Bechorot 7a)

Which leads to the question of the day: Can a kosher animal indeed successfully breed with a non-kosher animal? Let's take a look.

When a pig loves a sheep

Pigs have been known to act, well, like pigs, and copulate with sheep. (There's even a video of it, if you are interested). But could this lead to a baby peep, or ship, or whatever you'd like to call it? There are pictures that suggest this may be so, but in actual fact this pig with wool is the rare Hungarian Mangalitza pig, and has no sheep ancestry.  

At the beginning of the twentieth century, Foster Dwight Coburn, a farmer who also served as the secretary of the Kansas Department of Agriculture published Swine in America; a text-book for Breeder, Feeder and Student, and on page 63 he made the following observation: 

There exists in some sections of Old Mexico a type of “hog” represented as the product of crossing a ram with a sow, and the term “Cuino” has been applied to this rather violent combination. The ram used as a sire to produce the Cuino is kept with the hogs from the time he is weaned. A resident of Mexico has given the following description of the Cuino: “The sow used to produce the Cuino belongs to any race, but as a rule to the Razor-Back family, which is the more numerous. There is never any difficulty with her accepting the ram when breeding time comes. The progeny is a pig—unmistakably a pig—with the form and all the characteristics of the pig, but he is entirely different from his dam if she is a Razor-Back. He is round-ribbed and blocky, his short legs cannot take him far from his sty, and his snout is too short to root with. His head is not unlike that of the Berkshire. His body is covered with long, thick, curly hair, not soft enough to be called wool, but which nevertheless he takes from his sire. His color is black, white-black, and white-brown and white. He is a good grazer and is mostly fed on grass with one or two ears of corn a day, and on these he fattens quickly. The Cuino reproduces itself, and is often crossed a second and third time with a ram. Be it what it may, the Cuino is the most popular breed of hogs in the state of Oaxaca, and became so on account of their propensity to fatten on little food.”

It may have been the most popular pig breed in Oxaca, but it was still rather an oddity in the US; newspapers found them interesting, as evidenced by two reports, from 1902 and 1908 about sheep-pig hybrids.  

The Minneapolis Journal, September 24, 1902, from here.

Los Angeles Herald. October 3, 1908, from here.

Species and interbreeding

Despite these reports, it would seem that the rule suggested by R. Yehoshua ben Levi is correct. Different species cannot successfully interbreed, because, well, because that's the definition of a species, as the Oxford English Dictionary makes clear:

A group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. The species is the principal natural taxonomic unit, ranking below a genus and denoted by a Latin binomial, e.g., Homo sapiens.

So although it is a tautology, you get the idea: a species by definition can only breed with other members of its own species. If a pig and a sheep could breed and have offspring, they'd be members of the same species. But they are not. Pigs belong to genus Sus, and the species Scrofa, whereas sheep belong to the genus Ovis and the species Aries. Pigs have 38 chromosomes, and sheep have 54.  So they cannot cross-breed.  (Lions and tigers both have 38 chromosomes, so they can cross breed, and produce a liger.)

But it's not as simple as that.  Even if you don't have the same number of chromosomes, you can still sometimes breed outside your species. Horses have 64 chromosomes and donkeys have 62. Yet they can cross breed, resulting in a mule (if mom was a horse) or a hinny (if mum was a donkey), although these are nearly always sterile. Horses belong to the genus Equus and the species ferus, and donkeys belong to the same genus but to a different species, africanus.  Yet they can interbreed.  Which raises the question: should a horse and a donkey be re-classified as belonging to the same species? But that would be odd, because they look so different and act in very different ways.

These kinds of questions  are perplexing, and have challenged the world of biology since the time of Carl Linnaeus (d. 1778) who gave the world a way of categorizing and naming all living things called binomial nomenclature. Briefly it goes like this: the grey wolf belongs to the genus Canis and the species lupus.  Dogs belong to the same genus, Canis, and are a subspecies of wolves, so their scientific name is Canis lupus familiaris (which I suppose makes it a trinomial nomenclature).  We belong to the genus Homo and the species sapiens, whereas chimpanzees belong to a different genus and species, Pan troglodytes. Anyway just what gets a creature into one species class or another is a really challenging question, one that is still being played out in the scientific literature. There's even a 320 page book from the University of California Press in which the author "provides a new perspective on the relationship between philosophical and biological approaches" to the concept of a species. For now, though, R. Yehoshua ben Levi's generalization found in Bechorot is pretty close to the Linnaean taxonomy we use today.  We can also conclude that the general rule of the Talmud from today's daf, that a kosher animal could not successfully breed with a non-kosher one, is a pretty good rule of thumb.

“Every living thing loves its like,
and every person his own sort.
All creatures flock together with their kind.”

— Ecclesiasticus, 13:15.

Next time on Talmudology: Is garlic good for you? 

 

Bava Kamma 60b ~ Quarantine and Social Isolation

בבא קמא ס, ב

ת"ר דבר בעיר כנס רגליך

Our Rabbis taught: When there is an epidemic in the town keep your feet inside your house (Bava Kamma 60b.)

Social Isolation

There is a long history of isolating those with disease, beginning with our own Hebrew Bible:

 (כל ימי אשר הנגע בו יטמא טמא הוא בדד ישב מחוץ למחנה  מושבו.  (ויקרא פרק יג, מו

As long as they have the disease they remain unclean. They must live alone; they must live outside the camp (Lev. 13:46).

(צו את בני ישראל וישלחו מן המחנה כל צרוע וכל זב וכל טמא לנפש. (במדבר ה, ב

Command the people of Israel to remove from the camp anyone who has a skin disease or a discharge, or who has become ceremonially unclean by touching a dead person (Num. 5:2).

These are examples of social isolation, that is, individual and community measures that reduce the frequency of human contact during an epidemic. Here, for example, are some of the ways that social distancing was enforced during the Spanish flu epidemic of 1918-1918, an outbreak that killed about 40 million people worldwide:

... isolation of the ill; quarantine of suspect cases and families of the ill; closing schools; protective sequestration measures; closing worship services; closing entertainment venues and other public areas; staggered work schedules; face-mask recommendations or laws; reducing or shutting down public transportation services; restrictions on funerals, parties, and weddings; restrictions on door-to-door sales; curfews and business closures; social-distancing strategies for those encountering others during the crisis; public-health education measures; and declarations of public health emergencies. The motive, of course, was to help mitigate community transmission of influenza.

The teaching in tomorrow's page of Talmud emphasizes not the isolation or removal of those who are sick, but rather the reverse - the isolation of those who are well.  Of course the effect is the same: there is no contact between those who are ill and those who are well, but since there are usually many more well than there are sick, the effort and social disruption of isolation of the healthy will be much greater.  

“Implementation of social distancing strategies is challenging. They likely must be imposed for the duration of the local epidemic and possibly until a strain-specific vaccine is developed and distributed. If compliance with the strategy is high over this period, an epidemic within a community can be averted. However, if neighboring communities do not also use these interventions, infected neighbors will continue to introduce influenza and prolong the local epidemic, albeit at a depressed level more easily accommodated by healthcare systems.”

— Glass, RJ. et al. Targeted Social Distancing Design for Pandemic Influenza. Emerging Infectious Diseases 2006. 12: (11); 1671-1681.

It is not hard to see a relationship between expelling those who are ill and denying entry to those whose health is in doubt.  In the 14th century, when Europe was ravaged by several waves of bubonic plague that killed one-third of the population, many towns enacted measures to control the disease. Around 1347 the physician Jacob of Padua advised the city to establish a treatment area outside of the city walls for those who were sick.  "The impetus for these recommendations" wrote Paul Sehdev  from the University of Maryland School of Medicine, "was an early contagion theory, which promoted separation of healthy persons from those who were sick. Unfortunately, these measures proved to be only modestly effective and prompted the Great Council of the City to pursue more radical steps to prevent spread of the epidemic." And so the notion of quarantine was born. Here is Sehdev's version of the story:

In 1377, the Great Council passed a law establishing a trentino, or thirty-day isolation period . The 4 tenets of this law were as follows: (1) that citizens or visitors from plague-endemic areas would not be admitted into Ragusa until they had first remained in isolation for 1 month; (2) that no person from Ragusa was permitted go to the isolation area, under penalty of remaining there for 30 days; (3) that persons not assigned by the Great Council to care for those being quarantined were not permitted to bring food to isolated persons, under penalty of remaining with them for 1 month; and (4) that whoever did not observe these regulations would be fined and subjected to isolation for 1 month. During the next 80 years, similar laws were introduced in Marseilles, Venice, Pisa, and Genoa. Moreover, during this time the isolation period was extended from 30 days to 40 days, thus changing the name trentino to quarantino, a term derived from the Italian word quaranta, which means “forty."

The precise rationale for changing the isolation period from 30 days to 40 days is not known. Some authors suggest that it was changed because the shorter period was insufficient to pre- vent disease spread . Others believe that the change was related to the Christian observance of Lent, a 40-day period of spiritual purification. Still others believe that the 40-day period was adopted to reflect the duration of other biblical events, such as the great flood, Moses’ stay on Mt. Sinai, or Jesus’ stay in the wilderness. Perhaps the imposition of 40 days of isolation was derived from the ancient Greek doctrine of “critical days,” which held that contagious disease will develop within 40 days after exposure. Although the underlying rationale for changing the duration of isolation may never be known, the fundamental concept embodied in the quarantino has survived and is the basis for the modern practice of quarantine.

More talmudic health measures during an epidemic

In addition to staying indoors, tomorrow's page of  Talmud recommends two other interventions during a plague:

ת"ר דבר בעיר אל יהלך אדם באמצע הדרך מפני שמלאך המות מהלך באמצע הדרכים

Our Rabbis taught: When there is an epidemic in the town, a person should not walk in the middle of the road, for the Angel of Death walks in the middle of the road...

 ת"ר דבר בעיר אל יכנס אדם יחיד לבית הכנסת שמלאך המות מפקיד שם כליו

Our Rabbis taught: When there is an epidemic in the town, a person should not enter the synagogue alone, because the Angel of Death deposits his tools there...

It probably won't surprise you to learn that neither of these two measures is discussed in the medical literature, and in fact if there's an epidemic in town, you probably shouldn't go to shul at all. Nevertheless, the first suggestion made by the rabbis - to isolate yourself from others during an epidemic - is a basic part of public infection control. You'd be wise to listen.  

שולחן ערוך יורה דעה הלכות מאכלי עובדי כוכבים סימן קטז סעיף ה 

עוד כתבו שיש לברוח מן העיר כשדבר בעיר, ויש לצאת מן העיר בתחלת הדבר, ולא בסופו. וכל אלו הדברים הם משום סכנה, ושומר נפשו ירחק מהם ואסור לסמוך אנס או לסכן נפשו בכל כיוצא בזה

Initial growth of an infectious contact network. Colored rectangles denote persons of designated age class, and colored arrows denote groups within which the infectious transmission takes place. In this example, from the adult initial seed (large purple rectangle), 2 household contacts (light purple arrows) bring influenza to the middle or high school (blue arrows) where it spreads to other teenagers. Teenagers then spread influenza to children in households who spread it to other children in the elementary schools. Children and teenagers form the backbone of the infectious contact network and are critical to its spread; infectious transmissions occur mostly in the household, neighborhood, and schools. From Glass, RJ. et al. Targeted Social Distancing Design for Pandemic Influenza. Emerging Infectious Diseases 2006. 12: (11); 1671-1681.

Bava Kamma 55a ~ Does a Goose have a Scrotum?

בבא קמ נה,א

אמר שמואל אווז ואווז הבר כלאים זה בזה ... מאי טעמא ? אמר אביי זה ביציו מבחוץ וזה ביציו מבפנים

Shmuel said "a domestic goose and a wild goose are kilayim with one another"...what is the reason [to classify them as two distinct species]? Abbaye explained, the male wild goose has testicles that are external, but the male domestic goose has testicles that are internal...(Bava Kama 55a)

The Emden goose, a species of domestic goose.

The Koren Talmud on Wild and Domestic Geese

In today's Daf Yomi page of Talmud, we enter a brief discussion of the biblical prohibition of כלאים - kilayim - which is the prohibition of cross breeding two different species, be they plant or animal.  According to the great talmudic sage  Abbaye (died c. 339 CE), cross breeding a domestic goose and a wild goose is forbidden as well, because they seem to be two different species as evidenced by their anatomy: "the male wild goose has testicles that are external, but the male domestic goose has testicles that are internal."  Here is the background note found in The Koren Talmud. 

Today, these two types of birds are treated as one species. The wild goose is classified as the Anser anser, also known as the greylag goose, and the domestic goose is classifeid as the Anser anser domestica. Although the differences between them are not always apparent, they do differ in several ways, such as in their appearance, voice, and behavior. In terms of their appearance, they differ in color, as the wild goose is usually gray and the domestic goose white, and the neck of the domestic goose is shorter than that of the wild goose.
Another difference is that the male organ of the wild goose is more recognizable than that of the domestic goose. As for laying eggs, the wild goose lays fewer eggs than the domestic goose, which can lay more than ten eggs at a time.

All of this is very helpful indeed, but it does not address the claim that was made by Abbaye and which Rashi clarifies: "ביצי הזכרות ניכרין באווז הבר מבחוץ"  - that the testes of wild geese may be seen outside of the body.  Is that the case? Let's see what the geese experts have to say.

The Handbook of Bird Biology

The avian urogenital system. From  Lovette IJ. and Fitzpatrick JW. The Handbook of Bird Biology, Wiley-Blackwell 2016, 198.

Here are the ornithologists at the Cornell Lab of Ornithology on the location of bird testes:

Oval or elliptical in shape, avian testes are paired and lie within the body cavity at anterior end of each kidney.

In most birds the the intestinal, urinary, and generative canals open into a cavity called the cloaca.  However the Cornell Handbook notes that a few species including ostriches, ducks and geese, have a more advanced copulatory organ, the cloacal phallus. "Although often called a 'penis', this structure differs from the mammalian equivalent: since it lacks an internal urethra, sperm must travel along the external surface of the phallus." Good to know.

The Manual of Ornithology: Avian Structure and Function

The authors of the 1993  Manual of Ornithology are an interesting duo: on is a professor of biology, and the other, a radiologist. Here is their description of  where bird testes are located:

Male birds have paired testes within the abdominal cavity just anterior and ventral to the lobes of the kidneys. During much of the year the testes may be difficult or impossible to find because of their small size, but during the breeding season the testes may grow to several hundred times their non-breeding size, resembling two bean-shaped organs lying next to the kidneys on the dorsal abdominal wall...Some birds experience a nightly drop in body temperature that allows sperm development in males.  In other species the male develops a cloacal protuberance, a swelling of the terminal end of the vas deferens.  This functions like a mammalian scrotum, holding the developing sperm away from the high temperatures within the abdomen. 

To be clear: there are no testes on the outside of the body, as Abbaye claims; the closest we get to this is a small swelling during the mating season. 

Goose Production

The last reference book we will look at is Goose Production, published in 2002 by Food and Agriculture  Organization of the United Nations. Chapter Five addresses the male (and female) reproductive system found in geese:

There are two bean-shaped testicles inside the body cavity which produce both spermatozoa and male hormones. They are highly vascularized and change in size and position according to whether the gander is sexually active or not...the copulatory organ of the gander is very well developed. It is invaginated, spiral-like, and is about 15cm in length.

To recap: Geese testes are only located within the body cavity. No birds - geese included - have a scrotum, though sometimes the cloaca may swell to hold the maturing sperm.  And of course there is no difference between the natural and wild goose in any of these anatomical facts.

So what Did Abbaye mean?

What then, are we to make of Abbaye's testicular error? A couple of options spring to mind:

1. The translation of  אווז - avaz - as a goose is wrong, and he was referring to another species. The problem with this is (1) there is no dispute as to the translation and identification of this word and (2) even if Abbaye was referring to another species of bird, in no species do the testes reside in any place other than snugly inside the abdomen.

2. The geese in Abbaye's time were different.  There is no way to determine if this claim is true, though based on what we know about evolution it would be a pretty remarkable evolutionary change in the space of less than  two millennia.  Wait a minute, you say: what about the article two days ago in The New York Times with the title 'Evolution Is Happening Faster Than We
   Thought'? Perhaps two millennia is enough time for a change like this to occur?  Well, it is true that certain evolutionary changes may happen more quickly than scientists had previously expected, but this only happens "as long as natural selection — the relative benefit that a particular characteristic bestows on its bearer - is strong." One place where this happens is within our cities, where, for example, the temperature can be much higher or the ambient light much brighter, than in the surrounding countryside. However no such selective pressure is known to have occurred for geese living betwen Abbaye's time and our own.  Absent this evolutionary pressure, the suggestion that the internal anatomy of geese has changed is without any merit. 

3. Abbaye was wrong.  Abbaye was descended from a family of priests, and after the death of his parents was raised by an uncle and a kindly foster mother.  As a young man Abbaye spent some time in poverty: he worked at night irrigating agricultural canals so that he could be free during the day for study. Eventually his fortune changed and he became a wine trader and a farmer with tenants of his own. But there is no record of his having worked closely with animals, and animal husbandry would be an unlikely occupation for the head of the rabbinic academy in Pumbedita, a position that he occupied for the last five years of his life. It is very likely then, that wise as he was, Abbaye simply had no factual experience on which to base his claim that wild and domesticated geese have different male sexual organs. It is always best to speak with authority only about that which you are certain is correct.  Abbaye was certainly in authority as a great leader of a great rabbinic academy. But being in authority, and being an authority are by no means the same. That's a great lesson to remember.

Testes of pheasant during the reproductive season.  From here.

Bava Kamma 50 ~ Ten Tefachim to Death

משנה, בבא קמא נ, ב

החופר בור ברה"ר ונפל לתוכו שור או חמור חייב אחד החופר בור שיח ומערה חריצין ונעיצין חייב א"כ למה נאמר בור מה בור שיש בו כדי להמית עשרה טפחים אף כל שיש בו כדי להמית עשרה טפחים היו פחותין מעשרה טפחים ונפל לתוכו שור או חמור ומת פטור ואם הוזק בו חייב

If a man digs a pit on public ground and a bull or a donkey falls into it, he is liable for damages. Whether he dug a pit, or a ditch, or a cave, trenches, or wedge-like ditches, he is liable for damages that his digging caused. If so why is pit mentioned in the Torah? It is to teach the following: just as a standard pit can cause death because it is ten tefachim [handbreadths] deep, so too for any other excavation to have sufficient depth to cause death, it must be ten tefachim deep. Where, however, they were less than ten tefachim deep, and a bull or a donkey fell into them and died, the digger would be exempt.  But if then animal was only injured by falling into them, the digger would be liable. (Mishnah, Bava Kamma 50b.)

The Highest Fall Survived (without a parachute)

According to The Guinness Book of Records, Vesna Vulovic  holds the world record for the highest fall survived without parachute. And how high was that? Really, really high:

Vesna Vulovic (Yugoslavia) was 23 working as a Jugoslavenski Aerotransport hostess when she survived a fall from 10,160 m (33,333 ft) over Srbsk, Kamenice, Czechoslovakia (now Czech Republic), on 26 January 1972 after the DC-9 she was working aboard, blew up. She fell inside a section of tail unit. She was in hospital for 16 months after emerging from a 27 day coma and having many bones broken...She never suffered any psychological trauma as a result of the incident, and never experienced any fear of flying. She is still alive today, and flies with some regularity. However, Vulovic does not consider herself lucky. Thirty years after the crash, in an interview she said:  ''I'm not lucky. Everybody thinks I am lucky, but they are mistaken. If I were lucky I would never have had this accident and my mother and father would be alive. The accident ruined their lives too."

In my years as an emergency physician I saw countless patients with injuries from falls. Most injuries were relatively minor, but several of my patients died. Is there a minimum height below which a fall would result in a trivial, or at least a non-fatal injury? Based on my experience, the answer is an unequivocal no.  A fall from any height, however low, can result in a serious or fatal injury, and that includes a fall from standing. But that's just my experience. What does the medical literature say? Does it agree with the assertion of the Mishnah that a fall below 10 tefachim (about 76 cm or 30 inches) cannot result in a fatal injury? Let's take a look...

“At autopsy, classic findings in falls from height include aortic lacerations and vertebral compression fractures, as well as ring fractures of the skull base...Severe head injuries most frequently occurred in falls from heights below 10m and above 25m, whereas in the group that fell from 10 to 25m, few head injuries were seen and they rarely were the cause of death. ”

— Turk, EM. Tsokos, M. American Journal of Forensic Medical Pathology 2004;25: 194–199

The Epidemiology of Falls

Falls are very common. In the US they make up about a third of the injuries that lead to an ED visit in the each year - that's close to eight million visits.  In keeping with my experience, national data shows that only about 1% of all fall injuries that come to the ED are profound.  And here's another interesting finding that is in keeping with my own clinical experience: it's close to impossible to predict what kind of injury a person will have based on the height of the from which the victim falls. In a paper that examined over six-hundred fatal falls that occurred in Singapore, the authors noted that  

...there was much variability in the injury severity scores, in relation to the height of fall... Thus, a subject who had fallen through a height of 10 m, with primary feet impact, could have sustained complete traumatic transection of the thoracic aorta, with haemorrhage into the pleural cavities but little else by way of serious injury; while another, similar, subject could have fallen through 20 m and had sustained multiple head, thoracic and abdominal injuries...

In fact theses authors had a very hard time coming up with a model that describes the height of fall and indicators of injury severity other than to give this rather useless nugget: "Our findings suggested that the height of fall was significantly associated with ... the extent of injury." Well thanks. But it's one thing to fall 10m or more (that's over 30 feet for those if you not on the metric system). What about falls from less lofty heights?

Falls Down the Stairs, and Falls from Standing

Let's start with falls down the stairs. German forensic pathologists published a paper in Forensic Science International that addressed this aspect of falls in 116 fatal cases.  The most frequent victim was a man between 50 and 60 years old, and brain and skull injuries were the most common cause of death. About 8% broke their spines as they fell and (shocker) many were intoxicated. So stairs can kill.  

What about falls from standing? Well back to the German forensic pathologists, who this time published a retrospective analysis of 291 fatal falls. Of these, 122 -that's 42% - were falls from standing. About 80% of these ground-level falls were not immediately fatal, and the victim survived anywhere from three hours to almost a year post injury. Almost 60% of the men and 11% of the women who sustained a fatal ground-level fall were (shocker again) intoxicated.  So there we have it. The medical literature demonstrates that falls from standing can certainly be lethal.  Especially after kiddush.

From Thierauf A. et al. Retrospective analysis of fatal falls. Forensic Science International 2010. 198. 92–96. Forgive the English. It wasn't their first language.

The US federal government has also weighed in on the matter. OSHA, the Occupational, Safety and Health Administration has a ruled that a duty to erect fall barriers to protect employees only applies when the fall will be more than 6 feet (1.8m).  

“Each employee who is constructing a leading edge 6 feet (1.8 m) or more above lower levels shall be protected from falling by guardrail systems, safety net systems, or personal fall arrest systems. ”

— 29 CFR 1926.501

Back to the Mishnah

The Mishnah rules that only a pit more than 30 inches (ten tefachim) deep is lethal should someone  - or some animal - fall in. We have seen that this has no medical validity. But that doesn't really matter for a legal system.

Consider the legal limit for alcohol allowed when driving. In my home state of Maryland, it is 0.08%, (though of course your ability to drive safely is impaired at levels considerably lower). So what happens if a driver is stopped and his blood alcohol content is 0.07%? Well, it's simple: he is not legally impaired and so may continue to drive.  Is this an indictment of the Maryland drunk driving laws? Not really. Maryland, like all other states, sets its blood alcohol limit; if a driver is close, but below the limit, no penalty follows.

Jewish law too, has to set limits and measures, below which legal penalties do not apply.  The Mishnah's ruling that a pit is only fatal if it is more than 30 inches deep is a legal one - not a medial one.  It works to set limits and insure public safety. A person who digs a pit only 9.5 tefachim deep is not legally liable, and a pit that is a full 10 tefachim deep is certainly rarely lethal if a person accidentally falls in.  But for the sake of public safety a ruling  - arbitrary though it is - had to be made.  So be careful when you dig your pit in a public thoroughfare.