[Request] How did legends of dragons (and other such creatures) come to be found in various cultures despite being entire continents away from each other?

Part 1:

I've done a bit of personal research on the overlap of myths and history such as the post that /u/1EnTaroAdun1 referenced. I was working on expanding my previous post so I pulled some relevant sections from that and tried to format them here. It may read choppy as they came from a larger piece and I've not cited these or done background research to the level I normally would. I readily welcome feedback and criticism from actual historians so I can better shape this!

I will also pre-face this by saying I am at best a Wikipedia historian, my write-up will not even come close to being a definitive guide, or replacing the work of historians who devote their academic life to this fascinating field. There is no first-hand research, and I am not a professional in this field, I may get some things flat out wrong. Read on for fun and pleasure only:

Early Trade (More Likely): One concept that attempts to explain common stories, inventions and concepts around the ancient world is that of trade. I like this one as it satisfies the ability for views of snakes/serpents to originate differently but meet a common path from external influence.

The earliest evidence of a strong reference to the modern concept of a dragon is in Ancient Greece around 200 AD. Before that it was mostly discussion of serpents. This theory would then suggest that you don't need an earlier common source than this if it is possible to prove early trade or travel to other regions between this time and the time that we record other civilizations mentioning dragons.

The Roman Empire's reach in that time period can explain European Dragon's (https://en.wikipedia.org/wiki/Roman_Empire#/media/File:Roman_Empire_Trajan_117AD.png).

The Silk Road trade route can explain the shift from serpents to 'Long Dragons' in China.

The debatable part depends on how you classify "American Dragons".

A common rebuttal to this theory would be what about 'American Dragons' like Quetzalcoatl, and this is answered one of two ways:

First, Quetzalcoatl is a feathered serpent (not a winged serpent) and is likely based on either specific regional birds, or possibly species of gliding reptiles11 or simply the combination of snakes and birds (much like the myth of the Unicorn is a combination of two different animal concepts). Ultimately it's a common mistake to classify Quetzalcoatl as a dragon and that there are no dragons in North/Central/South America's history (https://en.wikipedia.org/wiki/List_of_dragons_in_mythology_and_folklore).

However, if you were to really push to say it was influenced by a dragon and wanted to make a leap people have tried to explain it as things like a late surviving Quetzelcoatlus (see my original post) or an artifact of trade stories from Pre-Columbian Trans-Oceanic Contact most likely that of Chinese contact from the Shang Dynasty which would explain why the South American culture has serpents but not 'Dragons'. The other option is Roman Empire contact but it seems less likely as we'd expect a more "Dragon" style figure. (Note: Pre-Columbian Trans Oceanic contract is a hot-button issue and highly contested).

Less Likely Theories: These theories have some available history/science to back them up, but they seem like a real stretch to me.

Ancient Common Ancestry Experience: The overview of this theory is that A) one event happened very early in human history that lead to sharing stories of serpents and eventually shaped the myth. Or B) the events that shaped the myth are more common historically and happened in a few places at a later time. This one seems a bit more of a stretch to me, but it is an interesting concept none the less.

The reason this gets weird is because we don't really know what the 'common point' is for modern humans leaving Africa. There are two fields of thought being the 'Recent Out of Africa Theory' and the 'Multi-Regional Origin Theory'. Our first myth explanation theory hinges entirely on which one is correct. Let's start with the one that doesn't work:

Multi-Regional Origin Theory: If you go back far enough in history we're all from the same common place. Humanities story starts about 4 million years ago in Africa with the first bi-pedal Homini (and the earliest exit from Africa not taking place until 1.7-2 million years ago). The MRO Theory says that modern humans are descended from waves of early Homo leaving Africa at different time points and from multiple clusters of early humans around the world. This means the myth either had to develop really early or in many places for this hypothesis to be true.

The challenge is that for myths to be passed down from such an early period would require some sort of communication, which even 1.7 million years ago was fairly non-existent.

Our best bet is if you go back about 500,000 years to the time period that is roughly considered to be the advent of simple language (proto-language or communicative sounds) you'd be in the time period of H. erectus, H. heidelbergensis and H. neanderthalensis in which the world population was spread (at best) across Africa, parts of Europe and Western Asia.

H. heidelbergensis is believed to have had the auditory sensitivity of modern chimpanezees1 and showed behavior that suggest forms of communication (perhaps non-verbal) such as hunting and the ability to pass on the creation of stone tools.

If H. heidelbergensis or H. erectus had strong enough language to pass along stories they would likely warn their kin about snakes and serpents which were a threat to humans. Since the human population was so small at this time its mathematically possible that many early humans that were alive back then have no presence in today's genetic pool or culture; and so one may not need to influence the entire population that was alive back then, but only be lucky enough to influence the decedents that end up mattering to evolution.

The saving grace for this would be that snakes were common-place enough in most regions that multiple points of origin (and later points of origin) could still have lead to this myth.

Out of Africa Theory: The ROA Theory says that early humans are actually decedents of Homo Sapiens who left Africa quite late. The theory suggests that early Homo Sapiens attempted to leave Africa via a Northern route circa 100,000 - 130,000 years ago and either went extinct or retreated (this is debated by a few finds in Israel and China). Then another migration happened around 60,000 years ago via a southern route (which I think is referred to as the Toba migration?) and this one was more successful and is the batch of early humans we descended from.

I believe one of the core pillars of this concept is that we believe 'Mitochondrial Eve' and 'Y-Chromosomal Adam' are our genetic common routes for all current living humans and we place them as being in Africa around 160,000 years ago. (Oversimplification: To be fair 'Y-Chromosomal Adam' may not have been in that region and his range is from 140,000 - 500,000 years ago you can read more here).

This is interesting because by 60,000 years ago humans were much more advanced. Archaeologists believe we had symbolic language, culture and tradition most of which hinges on the use of red ochre pigment2 and possible ritualistic behaviors such as burying the dead3 (note: highly contested).

In this sub-theory the view would be that early humans leaving Africa around 60,000 years ago used communication to warn each other about threats, snakes being a common threat across regions would have survived as a warning even as groups started to spread out.

These warnings or stories would only have to be carried for 30,000 years before we got to the use of drawn symbols4 or 50,000 years before we go to pictoglyphs5. Given that during that time period all of man kind lived in regions with dangerous serpents its not a huge stretch.

This Theories Conclusion: Ancient man feared snakes. A common place and natural predator some believe we even worshiped or performed sacrifices to serpents as early as 70,000 years ago6. As humans we have a tendency, even in our more recent history to overplay our fears and let them grow larger than life, and to explain the unknown with fantasy. Given that snakes of some variety cover most of the world7 and reptilian megafauna still existed as early humans spawned the globe (The Giant Monitor Lizard and The Quinkana died out 10,000 years after humans reached Australia7, and the other predatory lizards like Komodo dragons, monitor lizards and crocodiles spawn the globe8 it doesn't seem a huge leap that the myths of dragons would spawn from ancient stories and fears.