Honestly, a "keep upright" concept could be easily implemented by the ability to mark individual joints as 'vital', and if a 'vital' joint ever make contact with the ground for a member of the population, that member cannot be considered for the next generation. Meaning, for a quadruped, one could mark all joints used in the head/body as vital, and all runs where the creature plops down rather than remaining on its feet aren't evolved from, regardless of distance traveled.
Machine Learning Game
Cooper Perry
Brody Richardson
Not totally sold on the vital joint thing but both of these anons have the right ideas
Something like this can't be hard to code, although I guess I'll start emailing the creator anyways, too lazy