Complexity:
There very well may be something in the game to "stir things up" as you say. Last night I had an illicit breeding between 1 male I had only bred once (8m) and a semi-retired female 10 f. They had not been together before nor were they working in the same area, neither one were even adept parents. What's very strange is I have 2 female master parents both of whom are working in his area (both over 50). I ended up with a 10m so nothing special with the child.
Have you noticed various actions between the villagers, like arguing, complaining and teaching? I'm starting to think that not only is there an "intelligence" rating (some villagers are just hopeless learning anything), but also some sort of "status" rating for each villager. For example, Britney's post above...suppose her 10M didn't have enough "status" so his number wasn't used? 18/2=9 she could have had a female child with just herself? Just a thought there.
I've also oopsied a couple of times and dropped a villager on another and they had a baby right there at the research table. That's when I discovered they don't need to actually go inside the "Lovely Hut" to have a baby. I was quite irritated about that.
I don't think having a skill at master has anything to do with the selection of the child. In my 2nd tribe my 2M came with running. He was an esteemed elder at 46. He has fathered 23 of my 57 children so far. Those mothers that were mastered in a skill had a higher chance of a baby born with some skill in the one they were mastered in since he was mastered in Farm/Build/Research. Perhaps master parenting is relevant? I really don't want to go there except at the last minute. It would completely disrupt my breeding program.
I hate to admit this, but I haven't solved all the puzzles in either of my tribes yet.
How have you managed to get so many elders? I have 3 in my first tribe and 4 in the 2nd.
Britney:
Yes it does make sense, but it could be also the male wasn't used at all. However, a 9 is at the outer edge of possibility with those numbers as well.