There's no cause and effect like "my parents consumed a lot of plastic, so I will be able to digest them", if that's what you're asking.
For humans to evolve to be able to eat & digest plastics, we'd probably have to be in a situation where we'd die or be unable to reproduce if we didn't. There's probably been some interesting research around gluten/lactose tolerance that might be related (or maybe not).
> For humans to evolve to be able to eat & digest plastics, we'd probably have to be in a situation where we'd die or be unable to reproduce if we didn't.
That's really not how it works. If you get dumped into a desert you don't become able to eat sand.
You first need to luck out on the ability to digest the thing, before it can become an evolutionary advantage. Because we're so big and we evolve so slowly, the thing in question would have to be a micro-organism colonising our guts. But we consume so little microplastics compared to our size and the rest of our feeding that it's unlikely to happen.
There are much better odds for large seaborne life e.g. seabirds, as not only do they ingest a good amount of plastics (macro and micro both) it accumulates and becomes deadly as they can ingest pieces large enough that they can't excrete or vomit the bits, and it fills their stomach. Likewise sea turtles for instance.
For humans to evolve to be able to eat & digest plastics, we'd probably have to be in a situation where we'd die or be unable to reproduce if we didn't. There's probably been some interesting research around gluten/lactose tolerance that might be related (or maybe not).