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This article was originally published as a chapter in the book “Design and Catastrophe: 51 Scientists Explore Evidence in Nature"
Having spent 40 years in the practice of surgery, much of that performing microsurgery,[1] I have often pondered the amazing structure of the human body that allowed the fine patterns of dexterity that produced the Mona Lisa, carvings of Chinese ivory figures, elaborately illuminated Bibles of medieval times, the hand assembly of microprocessors, and many other intricate works. This ability to perform manual tasks involving fine movement differentiates the human from all other primates. Accomplishments such as the concert performance of Chopin’s Etude in G# minor, op. 25, no. 6, or the performance of brain surgery are a universe beyond the technical ability of even the smartest ape.
Currently, presupposed concepts based in evolutionary biology dominate the field of human neurophysiology. The cognitive advantage of the human brain has been attributed to its large size,[2] in particular encephalo-cortical mass, which is genetically controlled. A gene, strangely called “microcephalin,” regulates human brain size.[3],[4] The large functional representation occupied by the human hand, especially the thumb and index finger in the parietal lobe cortical areas, adds adjunctive support to this concept but does not explain why it happens.
Furthermore, the functional anatomy of the human hand is designed for precise movements that are impossible for other primates. The longer and fully opposable thumb of the human is the chief example, producing the “pincer” or pen-grip used in art, writing, surgery, etc., something not possible for the chimpanzee.[5] The independent complex movement of fingers required for piano playing and other dexterous activities enjoyed by humans is not seen among apes, nor is it required for their daily existence. There is no evolutionary advantage to the appreciation of Beethoven’s Fifth, let alone the ability to play it.
The sensory end-organ density of human fingertips partly explains its large representation on the post-central parietal cortex of the brain. Sensory discrimination is at least as important as motor function in the performance of fine movement, as is the rapid feedback of position and stretch receptors in muscles and joints, rapidly informing the brain, especially the cerebellum, of exact spatial positioning, accurate to fractions of a millimeter in some cases.
The world of neuroanatomy was recently updated in an amazing way when in late 2018 the Australian neuroanatomist, Professor George Paxinos, announced the discovery of a new cerebral nucleus at the base of the human brain.[6] Paxinos, a world leader in his field, found the structure he called the “endorestiform nucleus” through close study of thousands of thin slices of brain tissue. To date, after studying a number of mammals, including primates, Paxinos and his team have found this nucleus to be unique to humans. Moreover, the nucleus has neural connections with many other parts of the brain, indicating that it is most likely a coordination center for fine motor function, an attribute exclusive to Homo sapiens.
While Paxinos remains a supporter of evolutionary theory, his discovery gives rise to some interesting questions. One of these is based on the fact that a brain nucleus contains the cell bodies of many neurons. Its presence means that something cellular has been added to the basic primate “cerebral blueprint,” if we can use that term. But like the fossil record, there seems to be no “intermediate forms” of this structure—it just appears in the human brain and in no other. Perhaps in no better anatomical way does it differentiate us from the apes. So the obvious question is, How did it get there?
There are many other functional differences between the brains of humans and other mammals. These include higher cognitive functions such as consciousness, speech, artistic and musical appreciation, empathy, logical thinking including inference, hypothesis formation, memory, and ideation, to mention a few. The learning process in humans is therefore far more complicated than the behavior patterns of other species. Another unique feature is that human learning is transmissible to others, chiefly owing to speech, the fine motor functions of writing, and our color stereoscopic vision that permits the latter. Some of these attributes appear to have no evolutionary survival advantage. In my experience, this bears witness to a privileged position of Homo sapiens granted by a higher Power.[7]
The unique, functional anatomy of Homo sapiens differentiates us so widely from other, even superficially-similar mammals, that it is perhaps best expressed by this statement: “Then God said, ‘Let us make mankind in our image’” (Gen. 1:26).
NOTES
[1] DG Pennington, MF Lai, AD Pelly. Successful replantation of a completely avulsed ear by microvascular anastomosis. Plastic & Reconstructive Surgery 1980; 65:820–823.
[2] CC Sherwood, AL Bauernfeind, S Bianchi, MA Raghanti, PR Hof. Human brain evolution writ large and small. Progress in Brain Research 2012; 195:237–254.
[3] The null mutation of the gene microcephalin produces a genetic abnormality of small brain size called “microcephaly.” Recently in utero infection with the Zika virus has been implicated in causing microcephaly in the fetus, presumably by causing mutation of microcephalin.
[4] HN Nguyen, X Qian, H Song, G-l Ming. Neural stem cells attacked by Zika virus. Cell Research 2016; 26:753–754.
[5] Although there are claims that chimpanzees and other apes have opposable thumbs and even opposable first toes, their function is for crude but strong grip, an advantage in climbing trees. Chimpanzees may even use crude tools, but their neuroanatomy precludes the precision movements of the human hand.
[6] L Mannix. Aussie brain-mapper discovers part of brain that lets you play piano. The Sydney Morning Herald; November 22, 2018, Science. https://www.smh.com.au/national/aussie-brain-mapper-discovers-part-ofbrain-that-lets-you-play-piano-20181122-p50hlm.html [accessed June 25, 2020].
[7] C Goldstein. Baptizing the devil: evolution and the seduction of Christianity. Nampa (ID): Pacific Press; 2017.
David G. Pennington is an emeritus associate professor of plastic and reconstructive surgery at Macquarie University, and he was formerly head of the department of plastic surgery at Royal Prince Alfred Hospital. He currently practices as an expert medico-legal consultant in plastic surgery. He is a medical graduate of the University of Sydney (MBBS) and holds surgical fellowships in the Royal College of Surgeons of Edinburgh and the Royal Australasian College of Surgeons. He was the first person in the world to replant a human ear using the microsurgical technique and is a recognized expert in the field of microsurgical reconstruction. He has fifty peer-reviewed publications in various fields of plastic and reconstructive surgery. He is currently a reviewer for the Australian Journal of Plastic Surgery and was a contributor and editor of the textbook ByDesign Biology.