Remember Darwin and Wallace: great minds can and do think independently but in parallel.
A real-life example: the famous Tribble of Star Trek, as created by David Gerrold. Robert Heinlein, long before Star Trek in 'The Rolling Stones' came up with a creature, the Martian flat cat, similar to the Tribble in its general morphology and fecundity. As it turned out, both writers were beaten to that punch by Elizabeth Parker Butler's 'Pigs is Pigs,' a 19th Century story of guinea pig proliferation run amuck.
The 'p' word, according to Mr. Gerrold's memoir of his Star Trek experience, did come up, but Heinlein, when given a copy of the Gerrold script, did not consider that the case and himself mentioned the Butler tie-in.
So an idea-pet overbreeding-made the basis for three different tales with three very different outcomes. If you haven't seen 'The Trouble With Tribbles' read 'The Rolling Stones' or read 'Pigs is Pigs,' I won't spoil the experiences for you. It could, for a clever teacher or professor, still in a great search about the boundaries of originality and plagiarism!)