Artificial selection has got to be possible, given we’ve done it to our fruit merely by happenstance over the generations. And our dogs, too.

No, I wasn't clear. I meant for the "it" in my sentence to refer to biologically breaking down plastics, not to refer to artificial selection.

If, for example, wax moth caterpillars can break down polyethylene in small quantities in certain concentrations, then perhaps artificial selection can amplify that effect by expanding the range of concentrations that can be treated that way, or otherwise improving efficiency or volume of processing, etc.