Since it's no secret that Mew was involved, here's a bonus comic. I did a lot of reading up on the Pokemon universe, and humans did indeed evolve from something. That means that Mew would have carried the DNA of the first human ancestor, which would have had to be a Pokemon. Finding the exact strand, extracting it, and modifying it enough to forcibly evolve *any* species of Pokemon...well that would have taken a lifetime of research.
just let that sink for a minute