Although human remains transmit ritual impurity, if they are missing a bit they may not transmit a certain kind of ritual impurity called tumat ohel. Which brings us to the case of a skull with a hole in it. How much needs to be missing for the skull to be incapable of causing others to become impure?
ובגולגולת ב"ש אומרים כמלא מקדח וב"ה אומרים כדי שינטל מן החי וימות
Concerning the deficiency in the skull: Beit Shammai say that it must be missing a piece like the size of a drilled hole, and Beit Hillel say: It must be missing an amount that if removed from a living person, he would die.
But just how big is Bet Shammai’s “size of a drilled hole?” In tomorrow’s daf (38a) we learn that it is the size of “the small drill hole, used by physicians” (בקטן של רופאים). So around the first century BCE there were physicians going around drilling holes (of various sizes) into the skulls of the living. Why on earth would they do such a thing, and just how common was this practice?
Trephination - a hole drilled into the skull
Let’s start by introducing you to a word you may not have heard of. Trephination. It is the art of boring holes into people’s heads, and is also known as trepanning. The word is ultimately derived from the Greek trypanon, which was the instrument used to bore these head-holes. That is what the Talmud refers to as “the small drill hole, used by physicians” (בקטן של רופאים). Trephination, the removal of a piece of the skull of a living individual without penetration of the underlying soft tissues goes back a long, long way. In fact it is the oldest surgical procedure known to humanity, and it predated Bet Shammai by at least 4,000 years.
Trephinated skulls from ancient Israel
Archeologists in Israel have discovered a many trephinated skulls. According to Prof I. Hershkovitz from the Department of Anatomy at Tel-Aviv University these include trephined skulls from a 7th century BCE. at Tel Duweir, a trephinated skull found in a tomb near Timna, roughly dated between the 6th century B.C.E. and the 3rd century C.E, and a skull from the Hellenistic-Roman period in Acco. Two trephinated skulls from the Middle Bronze Age I (~2,200-2,000 BCE) were found in Jericho, one from the Early Bronze age was found in Azor, and a trephinated Iron Age skull was found in Yavneh. But the very earliest skull found around the Land of Ancient Israel was uncovered in a a large cemetery at Wadi Hebran in the Southern Sinai. It belonged to a man aged between 35 and 40, who was buried around 4,000 BCE; that’s over 6,000 years ago. So yeah, trephination is a really old procedure.
Around the world with trephination
Evidence of trephination is by no-means unique to ancient Israel. Trephinated skull have been found in Peru, India, and Africa (where it is still practiced). The procedure was practiced in several different and geographically remote populations, which demonstrate that it independently evolved in each. Why would that happen?
In 2015 the neurosurgeon Miguel Faria suggested the following as an explanation. Neolithic man would have noticed that while massive blunt head injuries were invariably lethal, milder head injuries were not. There might be an extended period of unconsciousness to be sure, but some victims would, having been left for dead in the back of a cave, “miraculously” recover and become “undead.” Today we would call this period a “coma”, and, so the claim goes, it would have been supposed that “something in the head had to do with undying.” Then this:
“..an opening in the head, trephination, could be “the activating element,” the act that could allow the demon to leave the body or the good spirit to enter it, for the necessary “undying” process to take place. If deities had to enter or leave the head, the opening had to be sufficiently large…The head was chosen for the procedure, not because of any particular intrinsic importance or because of magic or religious reasons, but because of the unique and universally accumulated experience observed by primitive man in the Stone Age with ubiquitous head injuries during altercations and hunting. Otherwise, the pelvic bone or femur could have served the same purpose. We must recall that even the much more advanced ancient Egyptian, Mesopotamian, Hindu, and even Hellenic civilizations believed the heart to be the center of thought and emotions, not the brain. In fact, the association of the heart with emotions lingered to the present age.
And so it was that the procedure came to be practiced across the world. This may also explain how it also ended up being used in ancient Israel, and trickled down into a teaching about ritual impurity cited by Bet Shammai.