Jason Snell explains how you can generate images of generic people with Image Playground using skin tones and collections of pseudo-people as foundation:

This is where it gets a little weird: Rather that building a person, Memoji style, you choose from three different collections of thumbnails, which are the various Appearances that might come up when you generate an image. They appear to be weighted by gender, so the leftmost is (mostly?) women, the rightmost men, the middle more of a grab bag—but there’s a lot of variation between each collection of Appearances.

What a strange interface.