Similar architecture, language, culture, even boatbuilding.
At some point there must have been a global civilization, prior to what is currently documented.
The moot point here is "There MUST HAVE BEEN a global civilization"
The favourite line of the fringe fraternity (sorry Snychronomy, not calling you a fringe, but if you are, it applies to you)
The fringe fraternity will never state with firmness anything on their pet fringe theories.
it will always be
It could have been
it might have been
it must have been
Is there any evidence for a global civilization?
No. No body has found out any such evidence that is conclusive.
Only thing that exists is similarities.
Quetzalcoatl was a creator god hood, The White Tezcatlipoca, the god of light, mercy and wind.
In Asian and South Asian mythology Nagas were a class of lower deities/beings/entities. they were not creator godhoods.
South Asian Serpent worship mainly derives from Hinduism.
The Middle east had the Mesopotamian underworld deity Ningishzida, and many prehistoric snake cults.
The basic idea of worshipping snakes was the human misconception that snakes were immortal due to their ability to shed their skin and live on. This gave rise to numerous snake cults in many places, even unrelated.
Major snake worship was
1. In Hinduism with the worship of Nagas.
2. In Greek/Roman Mythology as The caduceus, which was the staff of Mercury/Hermes, iris(Hera's messenger) and had a staff with two intertwined snakes and these two snakes stood for commerce & negotiation, as such Mercury was the god of the merchants, trader & commerce guilds. it has nothing to do with snake worship. it is just symbology.
3. In Greek Mythology, as The Rod of Asclepius. Difference between The Caduceus andThe Rod of Asclepius is that The Rod of Asclepius has only one snake on it. The reason why only one snake is shown on it is because of the nature of the snake shedding its skin and renewing itself. It is not worship in fact, but sorts of symbology.
Many have mistaken The Caduceus with The Rod of Asclepius. It is just because they don't know the difference.
Mankind worshipped nature which included the natural forces and the fauna.
It was not that all mankind worshipped nature in the same manner.
Different civilization/cultures worshipped nature differently, their worship/belief/religion/cults having evolved differently.
Assimilation of beliefs between cultures is common during the migration, intermingling, trade and contact between them.
But putting a theory of a Global Civilization as the source of serpent worship is too far fetched and without evidence other than similarities.