Fridge Logic: Gumba, Gumby's mother, and his aunt, Gumbetta, both look a bit more humanlike than Gumby, his father or his sister. They have a human mother, who is sometimes shown. Gumbetta is also married to a human man, and their children are even more humanlike (scarily so...); but since Gumba -ahem- procreated with a clay man, their children ended up very non-human again. All the genetics make sense. May also double as Fridge Horror, but YMMV.