Friday, May 07, 2021

Kidneys Revisited

Some ten years ago I engaged in a sparring match on the question of כליות יועצות, Chazal's statement that the kelayos, apparently the kidneys, give counsel. My sparring partner, Rabbi Dr. Natan Slifkin, asserted that Chazal believed that thought takes place in the kidneys, not in the brain. I argued that this was a metaphor, as the two kidneys incline towards each other as if counseling one another. There were several post on both his and my blog going back and forth. See, for example,

One can also follow the search at

and look at the top results.

But, I recently learned Berachos 61a again:

ת"ר שתי כליות יש בו באדם אחת יועצתו לטובה ואחת יועצתו לרעה ומסתברא דטובה לימינו ורעה לשמאלו דכתיב (קהלת י, ב) לב חכם לימינו ולב כסיל לשמאלו

...תנו רבנן כליות יועצות לב מבין לשון מחתך פה גומר

and a new thought struck me.

I would like to suggest that kelayos are the term that Chazal used to refer to the two hemispheres of the brain. The term is a borrowed term, as the primary reference is to the kidney (first illustration), and only used by extension for the cerebral hemisphere (second illustration). Yet the sacrificial offerings of the kidneys may in turn be seen as symbolic of the two halves of the brain.

As of yet, I have no independent evidence for this hypothesis, but I wanted to put it out there and perhaps someone will find such evidence.


1. "Erasistratus described four ventricles in the brain, noting that the fourth ventricle under the cerebellum communicated with the third, whereas Herophilus seems not to have noticed the third ventricle: this may have been the first description of the cerebral aqueduct (Tsuchiya et al. 2015). He likened the cerebral gyri to the coils of the small intestine and, long before Thomas Willis (1664), he suggested that the extensive cortical surface of the human brain was in some way related to intelligence, …"

2.  "According to the theory of TCM [Traditional Chinses Medicine], the brain is an outgrowth of and is nourished by the kidney. Brain defects and deterioration of the brain may be prevented, limited, or halted by the ingestion of kidney tonics. And, the energy from the kidney, that is called kidney essence, can produce marrow including cerebral marrow, spinal cord, and bone marrow. As Huangdi's Classics on Medicine said: “the brain is sea of marrow” and “kidney stores essence to generate marrow” [15]. The cerebral marrow can nourish the brain and maintain the physiological functions of the brain. If the kidney essence is insufficient, the production of cerebral marrow will be reduced, leading to various symptoms, such as dizziness, amnesia, and retard response.

3. Both the brain and the kidney have a cortex and a medulla.


  1. Assigning the role of thought to organs other than the brain was an almost universal practice in the pre scientific period. It seems that you're trying to argue that Chazal had full knowledge of modern science and just didn't bother correcting the misunderstandings of the time. I've long wondered why segments of the observant world need to believe that Chazal's understanding of the world was any different than that of other intellectuals of their time.

    At the same time as we hold that prophecy ended in the early second Temple period, people insist on ascribing something so similar to prophecy as to be indistinguishable from it to Chazal and to the modern daas Torah.

    Frankly, propagating the concept that there are people with some sort of innate mystical insight into the mind of the divine makes us all look like a bunch of idiots.

    1. I don't know who likes an idiot, but anyone who believes in Kabbalah - as did, say, the Ramban - knows that it is predicated on the seat of knowledge, understanding and wisdom being in the head.

      Moreover, only someone without a working knowledge of Chazal would be unaware that when Rabbi Yehuda Ha
      Nasi was casting aspersions on someone's intelligence, he would say: כמדומה לי שאין לו מוח בקדקדו

      מסכת יבמות דף ט עמוד א ומסכת מנחות דף פ עמוד ב

    2. Adam, "It seems that you're trying to argue that Chazal had full knowledge of modern science"
      -- Some knowledge, not full knowledge.

  2. How would לב מבין fit in to this? That seems to to be the actual heart and not another term for the brain

    1. The heart doesn't bother me. Even were Chazal to have been mistaken, to this day emotion is attributed to the heart because that is where it is experienced. The kidneys doing the thinking, however, is preposterous.

  3. You Are all scientifically obsolete more than our sages
    check up the latest research in science how the the source of intuition are gut microbes, and even intelligence