Observing the kernel of one walnuts it is almost inevitable to notice it resemblance to the human brain: two hemispheres, a surface full of folds (gyri and sulci), a protective shell. It’s an example of pareidoliathe tendency to recognize familiar shapes even where there is no functional link.
The shape of the nut resembles that of the brain
From a structural point of view, the kernel has characteristics that resemble the miniature human brain:
- Two “hemispheres”: the seed is divided into two lobes separated by a thin membrane, evoking the longitudinal fissure that divides the cerebral hemispheres.
- Convoluted surface: the irregular folds recall sulci (sulci) and convolutions (gyri) of the cerebral cortex. In the human brain these structures increase the surface area available for neurons in a limited space.
- Protective shell: the woody endocarp (the innermost part of the fruit in contact with the seed) functions as a mechanical barrier that protects the lipids contained in the seed, a bit like the skull protects the brain.
Of course, this is a purely morphological similarity. Yet, in the past it was interpreted in a symbolic key: the shape of the kernel was considered an indication of its presumed beneficial properties for the brain, according to an analogical approach typical of pre-scientific medicine.
From Signature Theory to modern nutrition
In the Middle Ages and Renaissance, doctors and natural philosophers were convinced that nature had written a visible code in plants and foods: if a fruit resembled an organ, it was destined to heal it. This idea took the name of Doctrine of Signatures (or Theory of Signatures), and was systematized in the 16th century by the Swiss doctor Paracelsus. According to this doctrine, the walnut, having a shape similar to the brain, must have been useful for nourishing the brain. Although today science has overcome this intuitive approach and the Signature Theory is to be considered pseudoscience, in the case of walnuts the intuitive tradition finds partial confirmation in nutritional data because walnuts are one of the richest plant sources of alpha-linolenic acid (ALA)an essential fatty acid from the family of Omega-3. Correct integration of these fats guarantees the fluidity necessary for the transmission of synaptic signals and the correct functionality of the receptors. In addition, nuts contain vitamin Ea powerful antioxidant that can protect neurons from premature aging. Minerals such as magnesium and zinc also play important roles: the magnesium is involved in synaptic plasticity, i.e. the brain’s ability to form new connections, while it zinc regulates the transmission of signals between neurons. The potassium keeps the electrical potential of nerve cells stable.
The brain is an organ with a very high energy consumption and particularly vulnerable to oxidative stress: the combination of polyunsaturated fats and antioxidants makes walnuts (and in general all dried fruit) a nutritionally interesting food in the context of a varied and balanced diet, which is by far the most important indication.
