How many hands could a “person” have?
Depends on your definition of a “person.”
In science fiction and fantasy, our characters don’t have to be human, or they might be human with enhancements or different genetic characteristics. On Earth, most vertebrate land animals have four limbs. Even snakes evolved from lizards. Why? How many hands, or fingers, or toes, could a human have?
“The condition of having no more than five fingers or toes—in this context, ‘most species’ means a subgroup of jawed vertebrates—probably evolved before the evolutionary divergence of amphibians (frogs, toads, salamanders and caecilians) and amniotes (birds, mammals, and reptiles in the loosest sense of the term). This event dates to approximately 340 million years ago in the Lower Carboniferous Period. Prior to this split, there is evidence of tetrapods from about 360 million years ago having limbs bearing arrays of six, seven and eight digits. Reduction from these polydactylous patterns to the more familiar arrangements of five or fewer digits accompanied the evolution of sophisticated wrist and ankle joints–both in terms of the number of bones present and the complex articulations among the constituent parts.” (Michael Coates, associate professor in the department of Organismal Biology and Anatomy at the University of Chicago and co-editor of Evolution & Development, https://www.scientificamerican.com/article/why-do-most-species-have/
In evolution, it’s far easier to lose properties than to create something that didn’t previously exist. So snakes lost all their digits, horses evolved to use only one digit which forms a hoof, and others utilize two or three digits.
What strikes me as interesting in the chart is that the first creature in the tetrapodomorpha branch, Eustenopteron, has six fins, not four. Two are lost by the appearance of Tiktaalik. Could that option still exist in our genome? One scientist, Yacine Kherdjemil, demonstrated that by reproducing the fish-type regulation for the hoxa11 gene, mice develop up to seven digits per paw, i.e., a return to ancestral status https://www.sciencedaily.com/releases/2016/10/161005132654.htm. Chart at right from https://earthsky.org/earth/elpistostege-ancient-4limbed-fish-fin-origin-human-hand?
There’s no particular evidence to prove that four limbs are better than six or eight. “You could consider it somewhat arbitrary,” said Edward Daeschler, associate curator at the Academy of Natural Sciences in Philadelphia. Land vertebrates all share the same basic design, but could it be different? Absolutely.” (https://www.livescience.com/33284-what-if-first-animals-crawl-out-sea-six-legs.html)
Some believe six or eight limbs are simply less practical, that the extra legs would get in the way. On the other hand, there’s no reason why an extra pair of limbs couldn’t function both as legs and as arms as needed. Wouldn’t that be cool? I used that approach in my sentient insect species, the Rakshi, who appear in my third book, Salvation’s Star, (to be released sometime this spring depending on COVID-19). Scientists also claim insects with an exoskeleton couldn’t evolve to be as large as a human, because the exoskeleton couldn’t sustain that much weight. Though it’s never occurred on Earth, there’s no reason an animal on another planet couldn’t have developed both a skeleton and an exoskeleton.
Most appearances of extra limbs or digits are genetic anomalies or defects. However, another hint of what might have been, or what might still be possible for humans, comes from research by Yacine Kherdjemil, who demonstrated that by reproducing the fish-type regulation for the hoxa11 gene, mice develop up to seven digits per paw, i.e., a return to ancestral status. https://www.sciencedaily.com/releases/2016/10/161005132654.htm
If a story that takes place on Earth, I find it harder to become fully immersed in plots that defy science. While I’ll admit I enjoyed the X-men movies, I never could develop a deep affinity for an array of characters, each of whom mysteriously developed genetic mutations independent of each other, and so many different mutations at one time. Nature doesn’t work that way.
That said, taking a look at the mutations independently, some are certainly plausible. Wings? Birds developed from the same common ancestor as humans. Apelike characteristics? Apes are closely related to humans. Invisibility? Never heard of any Earth creature who could pull that off other than through camouflage. The X-man would work better for me if there had been an evil mastermind at center stage who was manipulating the genome to create the mutations. Maybe a feline gene could have explained Wolverine’s ability to extend his claws.
But who am I to question an icon of fantasy who made millions?
