There are many puzzling features in mythology, if taken as purely mythology, regarding the so-called gods. I say so-called because to my way of interpreting things, the gods weren't mythological but flesh-and-blood extraterrestrials with advanced technology, especially in the field of bioengineering or genetic engineering. A puzzling feature regarding the 'gods' and related tales, or even tails, are the half-and-halves (my phrase - you probably won't find it lasted in any index in any mythology text). But these half-and-halves, for example there were the Centaurs, Cupid (or Eros), the Harpies, Mermaids or Mermen, the Minotaur, Satyrs, Sirens, the Sphinx, the Chimera, Dragons, the Gryphon (or Griffin - alt spelling), the Hydra, Pegasus and the Questing Beast, are just scratching the surface of the sum total of those represented in our ancient mythologies.
The interesting point is that these hybrids are universal within that collective mythology. That is, they appear across all cultures; all geographies. Anytime something supposedly mythological, is represented everywhere, it's time to sit up and take closer notice that things might not be quite as mythological as things first appear.
Where's the body-on-the-slab-in-the-lab evidence? With no fossil evidence of any such hybrids, perhaps this is where mythology overrides reality. Perhaps it is just a natural pondering to wonder 'what if' human abilities could be combined with some other animal's abilities; or what a composite of one animal's body parts attached to another animal's body parts might achieve.
But then again, maybe that's not the case.
Now clearly, a lot of people, our ancestors, went to a lot of valuable time and effort to create or depict in often quite considerable detail all over the world, the who's who, and what's what, in tens of thousands of paintings, literature, statues, figurines, murals, monuments, carvings, pictograms, hieroglyphs, etc. to what we (their descendents) would call nonsense - purely imaginary entities. But I maintain our ancestors would not go to extraordinary lengths to devote precious resources into making images of beings they knew to be imaginary. Translated, they believed with all their hearts and souls that these beasties, globally numbering in the multi-hundreds, whether 'gods' in various combination's or lesser mortals (human-animal) or purely animal-animal forms, really existed. Multiply that by more multi-hundreds of 'normal' mythological characters that have been honored with thousands of monuments, and well there's apparently a whole ancient expensive and often backbreaking industry devoted to what again, we superior modern descendants of theirs, believe to be nothing at all.
As an exact parallel, 'modern' human have built and erected all manner of monuments, memorials and statutes to really real historical people. Many are on display in all manner of public parks for the pigeons to rest their weary wings on.
Then again, in our modern era, nobody designs and builds cathedrals just to provide work for the construction industry, but rather because the relevant powers-that-be, the instigators and designers and fundraisers of cathedrals firmly believe there is a being who deserves such monuments to be built in his honor. Now the fact that being probably doesn't exist, at least as a supernatural creator deity, but rather just one of many of an advanced race of extraterrestrials is irrelevant. You build the cathedral because you believe that being exists - full stop. Atheists don't build cathedrals. Okay, our smart-as-we-are ancestors believed the half-and-halves really existed.
Now that we've seen some of the puzzling anatomical features associated with the half-and-halves, beasties that are composites of two or more terrestrial life forms, here's a hard as solid rock case study that not only illustrates time and effort but might highlight why human imagination is not at work. There's a very large life-size statue from ancient Assyria housed in the British Museum of a winged, human-headed bull (probably representing Shedu or Lamassu). That would be odd enough, but in this statue of a bull with wings and a human head, you find that the bull is depicted with five legs (please note I can count up to five!). Now, if you were to design from scratch a mythological beastie, one thing I'm pretty convinced of is that you would NOT give it five legs! So, I ask instead, is this statue a representation of one of the 'gods' genetic experiments?
Now before pursuing that tack, we're all aware of the various plants and animals we've artificially selected for via breeding pairs of organisms that have the sorts of characteristics we desire such as leading to faster horses; disease resistant wheat, cuter puppy dogs, etc. Sometimes we interfere at the cellular level to increase the pace of the changes we want. We've all heard of genetically modified food or genetically modified organisms; of DNA from one species being spliced onto the DNA of another species. We've heard of harvesting animal tissues and organs for transplantation into humans. We've come into the era of the designer baby, or at least prospective parents undergo genetic counselling and testing before having children. Having children is no longer hit or miss and take your chances. And it won't be long before babies will be made-to-order if the parents so wish.
Now imagine the genetic tricks a highly advanced, if somewhat amoral race of ET's were to use terrestrial stock to further their genetic research and agenda. Even several hundred, far less thousands of years in advance technologically of us could produce the half-and-halves of our mythologies.
So, were the half-and-halves of our mythologies evidence of genetic and bioengineering experiments by the 'gods', the 'gods' own version of "The Island of Dr Moreau?" If these hybrids are not the wild imaginations of our ancestors, and standard Darwinian natural selection cannot adequately account for them, then it's clear an alternative artificial selection mechanism must be contemplated instead. What on Earth (or off Earth) could be the driving force behind such artificial selection - behind the required bioengineering or genetic engineering required? Well, unless your best guess is better than my best guess, ET, that's who.
But then it all ceased to be; then they all went away, either literally (as I suspect) or within the human imagination (and if so, why?).
One thing I'm convinced cannot adequately for the massive range of our mythological hybrids are fossils. Fossils cannot explain the half-and-halves. There aren't going to be too many buried skeletons of a lion minus its head that just happens to have a human skull in the immediate vicinity to explain the Sphinx. And what about the odds of finding the skull of a falcon minus body that just happens to rest next to a headless human skeleton and thus explain several of the Egyptian 'gods'?
Now clearly some of these half-and-halves beasties are going to ultimately prove to be mythical - figments of the human imagination invented for reasons now lost and buried by the sands of time. Some cases are probably of real beasties we all know today but embellished for reason or reasons unknown and probably unknowable. There's going to be cases of linguistic misinterpretations or misunderstandings or errors in translations. Then too there's going to be cases of someone who told someone who told someone who told someone who told someone over many miles and probably generations before the tale was written down. The 20th generation retelling of an 'eyewitness' account explains some of the half-and-halves.
But are the mythological half-and-halves all really products of pure human imagination and embellishments and 20th generation retellings? If that be the case, why are there no more recent equivalents, in the multi-hundreds, in our 'modern' (say within the last 300 years of fictional literature, later films and TV) apart from those taken directly from our mythological ancient history like Mermaids? Nearly all 'modern' literature's creations are human (Sherlock Holmes, James Bond, Harry Potter, and Captain Kirk as examples - even if they do come from another planet like Superman or Mr. Spock). The Creature from the Black Lagoon was humanoid; ditto the Wolfman who at no time was represented as being a wolf's head on a human body or vice versa. Frankenstein's Monster was still human, even if patched together. Dracula may have been able to shape-shift into a bat, but he never was actually half-human and half-bat - ditto Batman. Even Donald Duck was still a duck; Mickey Mouse was just a clothed talking mouse. Some of the Egyptian gods were represented as half-and-halves, but The Mummy wasn't! So, if all is assumed to be human imagination, then there's this discrepancy between way back then and recent history. The one obvious 'modern' exception is the well known novel "Island of Dr. Moreau."
The "Island of Dr. Moreau" was originally a novel published in 1896 by H.G. Wells with film adaptations in 1933 (as the "Island of Lost Souls"), 1977, and 1996. It basically deals with vivisection and an obsessed scientist who conducts profane experiments in evolution, eventually establishing himself as the self-styled demigod to a race of mutated, half-human abominations. This all takes place on a remote island, the inhabitants being those experimental animals being turned into strange looking humans by one Dr. Moreau - the obsessed mad scientist in question. I'm just substituting the ancient 'gods' for the more modern Dr. Moreau; the so-called mythological half-and-halves for those modern fictional experimental animals turned into abominations.
That 'modern' novel aside, you may think the ancient mythological menagerie - if entirely imaginary - exhibits quite an intense range of the human imagination in the creation of half-and-halves. I'd beg to differ. There's an immense array of potential half-and-halves possibilities that apparently have never been realized, or at least popularized. The whole plant and invertebrate communities have largely been ignored, which may make sense from the biological reality of a genetic engineering standpoint. I do realize that Hollywood has rectified this with several versions and sequels to "The Fly" and B-Grade films like "The Wasp Woman", and probably several other B-Graders in that vein. But 1) those cinema features were relative rarities in terms of modern half-and-halves images and 2) there was never any possibility of mistaking those films for anything else other than social commentary and/or entertainment, just like the novel by H.G. Wells.
Anyway, as to what might have been imagined by our ancient ancestors, but never really was, though I do seem to recall a mythological human head on an octopus body, but that was about it when it came to the invertebrate and plant kingdoms - no lobster heads on a human body; no human heads on a slug; and as for humanoid rose bushes - forget it!
However, when talking real modern half-and-halves, one would be remiss not to mention Mothman, a winged hominoid with glowing red eyes, associated with the Point Pleasant area of West Virginia around the period of November 1966 through December 1967. Mothman's been the subject of several books, dozens of articles, and at least one motion picture ("The Mothman Prophecies" - 2002). However, there have been no sightings since. Perhaps Mothman's a purely imaginary half-and-halves case, one never before or after seen. Maybe.
Finally, there might be a really real modern version of the 'gods' and their half-and-halves. If UFO / alien abductions are to be believed, taken at face value, (somewhat backed up and supported by animal mutilation cases), then the alien 'gods' - collective now called the 'Greys' - are still manipulating human genetics and further progressing with the evolution via artificial selection (breeding) of the human species, as well as their own, for the apparent objective is nothing less than a human-alien (or human-grey) hybrid. That this is implausible, well, recall from mythologies around the world those human-animal hybrids like the Satyr, Sphinx, Minotaur, Mermaid, and a host of others.
Science librarian; retired.