Badass Sci Fi Loves Lucy- The Evolution of Opposable (Thumbs)- Part 2
In the previous post, we discussed why Badass Sci Fi loves Lucy (2014) and Lucy (3.2 mya). We also looked at the science in science fiction, and dispelled the 10% brain use myth. Finally, we subjected ourselves to an irresponsibly vague and haphazard lesson on human evolution.
On the other hand, this post deals with facts. Nothing but facts here, expertly culled and compiled into a lucid and reasonable presentation on the magnificence of the human hand and thumb.
At some point, we may even slingshot around the morass of details and tie them back to Lucy (2014) and Opposable (2019). But first, let’s verify some background knowledge. Are you ready for another trip down a rabbit hole? Excellent. Let’s jump right in!
The “Opposable Thumbs aren’t Unique to Homo sapiens” sling.
Okay, yes, there certainly are a few definitions of opposable. For many, the movement of the thumb to the fifth digit (pinky) is opposition. Apposition denotes movement between the thumb and other digits or palm.
With regard to this and the prior post, true opposition, the opposition allowing for both power and uniquely versatile precision grips, and contributing to our higher intelligence and texting ability, is basically this…
No other species on Earth can do that. I mean, seriously, have you seen another species make a GIF?
Novel Anatomy and Physiology of the Opposable Thumb
The human hand is the product of millions of years of evolution brought about by mutations and our ancestors’ increasingly intelligent interaction with, and manipulation of, nature.
Above all, the evolution of the opposable thumb allowed for unprecedented functionality of the hand and subsequent increases in intelligence.
Bones and Joints of the Thumb
Any rigid body’s versatility can be measured by its Degrees of Freedom (DoF), or ability to move in three-dimensional space. For example, the thumb possess 5 DoF; flexion/extension at the InterPhalangeal (IP) joint, and flexion/extension and abduction/adduction at both the MetacarpoPhalangeal (MP) and TrapezioMetacarpal (TM) (CarpoMetacarpal (CMC)) joints.
The other four digits, however, only possess 4 DoF. They cannot move independently at their CMC joints like the thumb.
As a result, the human hand possess an incredible 27 DoF. If there was ever an argument for irreducible complexity, it wouldn’t be the eye, it would be the hand and opposable thumb. But alas, there isn’t.
Science replicated, and surpassed, the functionality of the eye. Just look at your phone. It hasn’t, however, artificially duplicated the functionality of the human hand, no matter the advancement in prosthetics.
Above all, the unique configuration of the thumb’s MP joint (a condyloid joint), and to a greater extent, TM joint (a saddle joint), defy duplication or even complete real world simulation. Indeed, the trapezium‘s unique shape and interface with the thumb’s metacarpal‘s base give the thumb unparalleled maneuverability while masking its true mechanism.
Muscles of the Thumb
But what controls the mechanism? The thumb’s astounding range of motion is controlled by an intricate, precise interplay of 9 muscles; 5 located within the carpus (intrinsic), and 4 originating in the forearm (extrinsic).
As a result, due to the intricacies, the coordination of these muscles makes it difficult to pinpoint each muscles individual action and simulate it artificially.
The thumb is, by far, the strongest and most flexible digit. Imagine a tall, thin Spire or antenna. Thumb muscles lie in a configuration providing maximum stability and freedom to move, much like guy-wires around the antenna.
For example, the three thenar muscles (flexor pollicis brevis, oppenens pollicis, and abductor pollicis brevis), the muscles comprising the meat of your palm, work in concert to flex, abduct, and oppose the thumb. Flexion is further aided by flexor pollicis longus, the strongest muscle in the forearm and one unique to Homo sapiens in its current arrangement.
The thumb’s flexor complex, however, is counterbalanced by only three dorsal, extrinsic muscles (extensor pollicis brevis, extensor pollicis longus, and abductor pollicis longus).
As a result, if you do a simple pressure test on the thumb, you’ll find it generates much more force flexing than extending. For example, in a thumb war, it’s much easier to pin than escape a pin. Therefore, the evolutionary advantage of the opposable thumb is to forcibly grip, not release. Choke on that.
I’m sorry. That was rude.
Tendons of the Wrist and Hand
Finally, let’s take a look at the complex of tendons and fascia that stabilizes the thumb’s associated effectors.
Tendons, ligaments, and fascia of the forearm, wrist, and hand form an exquisite system engineered by the evolutionary interplay of form and function.
On the surface, however, it’s a deceptively simple and elegant design; a network of opposing pulleys channeled through a stabilizing, guiding ring of fascia.
The antebrachial fascia is a deep, fibrous membrane covering and stabilizing muscles in the forearm.
But near the wrist, it thickens and incorporates with other ligaments and tendons, forming a band, much like an incredibly wide, strong, and tight ‘What Would Jesus Do’ wristband. This is the flexor retinaculum and extensor retinaculum.
The retinaculum provides a stable channel to guide tendons traveling from the forearm to the hand. Anteriorly, it forms the roof of the carpal tunnel.
In addition to the anatomical, reality-based functions of the retinaculum, it also serves as a portal to a fictional universe.
The Carpal Wormhole and the Vanderbilt Cuff
The Black Box
To this day, the structure, nomenclature, and function of the contributing components in the retinacular matrix spurs debate. For instance, where are the lines of differentiation between the antebrachial fascia, transverse carpal ligament, and palmaris longus? No one can say with 100% certainty. No one…with 100% certainty.
I submit the retinacular complex is a veritable ‘black box’ in human, and specifically thumb, anatomy and physiology.
Firstly, efferent nerves carry instruction to muscles. However, no muscle acts upon the thumb without first integrating with retinaculum (Except the adductor pollicis, but even that is debatable). The three thenar muscles originate in the retinaculum.
Secondly, the retinaculum contains no muscle tissue, and its vaguely differentiated connective tissue makes pinpointing motor pathways unreliable.
As a result, we have inputs and outputs separated by a sheathed, convoluted intermediary relay. A black box.
The Vanderbilt Cuff
Certainly, Dr. Stanley Ivan Vanderbilt knew these constraints when receiving his second Spark. But he couldn’t effectively untangle the retinaculum for a human. How was he supposed to modify it to attach an opposable thumb to a cat’s paw? Two Opposable thumbs? On each paw?
Regardless, the directive arrived; successful attachment of the TOOTs (Tactical Opposing Opposable Thumbs). Vanderbilt identified the main obstacle. Little did he know, however, successful completion of the directive would pose obstacles far greater.
The device, the component enabling successful actuation of the TOOTs, would be forever known as the Vanderbilt Cuff. This one, simple, intuitive, oversized What-Would-Jesus-Do wristband would catalyze artificial punctuated quantum hyper-evolution and make Dr. Vanderbilt the epicenter of a multi-species, transgalactic war.
But if you don’t believe me, check out Opposable. $2.99 or the first 4 chapters free!
In our next post, we’ll discuss the effects of attaching opposable thumbs to a feline and prove individuals DO evolve, not just populations. In other words, more fictional science, the foundation of science fiction.
Until next time, don’t bother me. I’m calling Scarlett Johansson to tell her I couldn’t fit her in this post.
Most supplemental information gathered here…
Most diagrams gathered here…
Visakha K. Nanayakkara1, Giuseppe Cotugno2, Nikolaos Vitzilaios1, Demetrios Venetsanos1, Thrishantha Nanayakkara3* and M. Necip Sahinkaya1
By Me – I created this from Gray's Anatomy plate 415 using Gimp, Public Domain, https://commons.wikimedia.org/w/index.php?curid=1595018
By Henry Vandyke Carter – Henry Gray (1918) Anatomy of the Human Body (See "Book" section below)Bartleby.com: Gray's Anatomy, Plates 414, 415, 418, 419, , 425, 427, 1233, Public Domain, https://commons.wikimedia.org/w/index.php?curid=527313