United Kingdom
Seen August 12th, 2019
Posted August 7th, 2019
Guys, it appears some post on Tumblr has pointed out what the theme between the Alola starters is - and it's ALCHEMY! Credit goes to this person here for pointing it out:

So far, the obvious one here is Litten whose head marking and eyes together form the symbol for sulfur and brimstone, associated with its Fire typing.

Rowlet's leaf bowtie apparently resembles one of the alchemic symbols meaning "night", which ties into the fact that owls are nocturnal creatures.

And finally, Popplio's nose and snout resemble a notable alchemic symbol for Water, fitting its type.

Now that we know the apparent theme (or not?) it will be interesting to see how alchemy themes will come into play with the designs of the evolutions.
Interesting point. There is another well known alchemical symbol which is the green lion consuming the sun which obviously could have ties with Solgaleo.

For reference: