The Antiquity of ‘Neo-’

I recently shared some reflections on the concept of the "layered brain." That piece began as a set of preliminary notes for this post, but my musings on the broader cerebral architecture took precedence. Here, I wish to return to my original subject: the neocortex. This specific focus was prompted by a compelling segment in the BBC series Secrets of the Brain, presented last year (2025) by Jim Al-Khalili. As Al-Khalili is a professor of physics, I found the choice of presenter for a neurological survey rather curious at first; however, I now realise that his extensive work in quantum biology provides a natural bridge to the study of complex biological systems. Indeed, viewing the brain through the lens of information theory and thermodynamics offers a perspective that a purely clinical approach might overlook.

As an identifiable structure within the fossil record, we learn that the neocortex is of a staggering age, likely emerging at least 200 million years ago. There is a distinct irony in this antiquity when one considers the term’s etymology. ‘Neocortex’ is a hybridism, grafting the Greek prefix neo- (‘new’) onto the Latin cortex (‘bark’ or ‘rind’). Despite its ancient roots, the name reflects its status as the phylogenetically "newest" or most recently evolved layer of the cerebral cortex. This creates a fascinating temporal paradox: while 200 million years is a vast expanse in the context of human history, it is relatively recent when measured against the three-and-a-half-billion-year odyssey of life on Earth.

The term entered the lexicographical record between 1905 and 1910. Although coined as a neutral descriptive label for the evolutionary age of the tissue, it arrived during a formative period in neuroscience. At the time, the marked expansion and complexity of this structure in humans were frequently interpreted as the biological mandate for human superiority. It was regarded not merely as a mammalian trait, but as the "crowning achievement of evolution," providing the physical basis for our unique capacity for cognition, language, and abstract thought.

However, Secrets of the Brain introduced a complication to this narrative in the form of Morganucodon. This mammaliaform creature first appeared approximately 205 million years ago. Its name, meaning "Glamorgan tooth," pays homage to the area of South Wales where its remains were first discovered. While the soft tissue of the cortex does not fossilise, the impressions left upon the interior of the cranium suggest the presence of a neocortex.

Significantly, Morganucodon preceded the "true" mammals of the modern sense, yet it seemingly possessed this defining feature. This raises a difficult question: is the neocortex truly unique to mammals? The standard academic response remains a hesitant "yes," yet the area is far more contested than the BBC series might suggest. The evidence for neocortical structures in early creatures, combined with the presence of functionally similar regions in birds and reptiles, necessitates a more nuanced evolutionary history. While non-mammals lack the specific six-layered architecture of the neocortex, many possess homologous structures—such as the dorsal ventricular ridge—that perform analogous higher-order functions.

A neutral path through this debate suggests that various ancestral lineages possessed the "mammalian blueprint" for a neocortex, regardless of the divergent evolutionary paths they subsequently followed. What remains certain is that any claims regarding human exceptionalism based solely on this physical structure should be approached with the utmost caution. As we peer into the fossilised echoes of Morganucodon, we find that our "new" brain is, in fact, an ancient inheritance.

Skipping Guts - Addendum 2

Beginning with the idea of expressing gut lengths as a proportion of height (Skipping Guts), I wandered into the idea of a standard (or reference) male and female (Skipping Guts - Addendum). While, to my knowledge, gut length is not mentioned in the reference tables to which I referred, the weights of different organs are.

Based on the International Commission on Radiological Protection (ICRP) standards, the physiological differences between the 70kg "Reference Man" and the 60kg "Reference Woman" are precisely defined to ensure consistency in medical and scientific research. Thus, they supply standardised organ weights (or perhaps I ought to say 'mass', as these values are no doubt applied to astronauts).

Organ Mass Comparisons
The Reference Man (170 cm, 70 kg) generally has larger organ masses than the Reference Woman (163 cm, 60 kg) due to overall body size, though the proportions relative to body weight vary.

Source: ICRP Publication 89

…and one could go on. There are other standards. For example, basal metabolic rate (BMR) also mentioned in ICRP Publication 89 but, having added two addenda to my original post, I will stop here.

A Thin Blue Thread

Human dissection can hardly be described as a dull or tedious pursuit. However, for many students, the encounter with the cadaver can prove onerous, even dispiriting. This is rarely a reflection of the subject matter itself, but rather the pedantry of its presentation. The requirement to memorise an exhaustive catalogue of nomenclature—frequently in an ancient, calcified tongue—can rapidly extinguish any innate curiosity. In contrast, a true study of anatomy should be synonymous with the fascinating and the intriguing.

Within this category of the intriguing, one must include the discovery of the unexpected. This requires a certain intellectual plasticity; one must be sufficiently open-minded to appreciate a find that deviates from the textbook norm. I recall a senior anatomist who, upon being shown a structure resembling a vein coursing along the internal aspect of the left abdominal wall—likely an aberrant epigastric vessel—simply dismissed it with a cursory flick of the forceps. It was a moment where dogma overrode discovery.

Perhaps the most compelling enigma I encountered was a fine, blue synthetic thread embedded within the wall of the right ventricle in the heart of an elderly male cadaver. The mystery lay in the absence of any thoracic intervention; the skin of the chest was entirely devoid of scarring. We were left at a loss. Utilising modern AI tools to review the possibilities, I have since identified a plausible explanation, even if the opportunity for physical verification has long since passed.

The filament was likely nylon or perhaps polypropylene—the latter notably introduced as the surgical monofilament Prolene by Ethicon in 1969. Designed to be inert and non-reactive, these materials can remain sequestered within bodily tissues for decades without eliciting symptoms. As for its presence in the myocardium, venous migration appears the most probable culprit. It seems likely that a fragment of suture material became liberated elsewhere in the body and entered the "highway" of the venous return. Carried through the vena cava to the right side of the heart, it eventually became permanently lodged in the ventricular wall.

Our failure to trace the thread to its source was ultimately a consequence of the rigid boundaries of the dental student syllabus. As their curriculum was strictly confined to the head, neck, and thorax, we never ventured into the abdomen or lower limbs where the point of origin—perhaps a forgotten inguinal or femoral repair—lay hidden. While we will never know for certain, a reasoned hypothesis for such a survival feels infinitely more satisfying than an unresolved mystery. There is, after all, a quiet and haunting poignancy in the find: a thin blue thread of plastic, indifferent to the passage of time, outlasting the very biological life it was designed to support.

...and finally, my last circulation figure

 

This is from the same source as a previous post, being taken from Tortora's Principles of Anatomy and Physiology.

I conclude this series with a figure that differs from those I have posted previously. The only reference to anything anatomical here is to the lungs and capillaries. In so doing this figure raises the question of how to view the human circulation. Do we put the heart at the centre and follow the course of the blood it pumps out? If so, do we first follow it around the systemic circulation or the pulmonary? Or vice versa?

Or do we follow this approach? This figure follows the blood from its place of oxygenation to where that oxygen is delivered and back to where it gets oxygenated again. The heart takes on a more secondary role. Emphasis here is on the oxygen the circulation carries. (Not forgetting the place of carbon dioxide in all this.) The approach I used to take was very much akin to this. The emphasis here is on physiology rather than anatomy.

Coincidentally, this approach returns one to the idea of the simple closed circulation, not least that of fish from whence all forms of vertebrate circulation evolved. One might suggest that the human (mammalian) circulation is really just a single, simple loop that has been twisted into a figure of 8 (or ∞) with the heart at the crossing point.

Please be sure to click the label marked 'The Circulation' to access all related posts. My idea was to illustrate how the same topic can be illustrated in very different ways. View the others to see what I mean.