I recently had a tribe of just men. (by the time I noticed all of the children were male all of my females were too old to produce.) When I got down to 8 tribe members I got the canoe from elsewhere. I eventually got down to as low as 2 male members and three of events in a row were canoe events. My next event after that was a barrel of babies. The tribe is now 40 plus strong. It wouldn't be that high normally because I like to keep the tribes around 25. (I hate large tribes.) It wouldn't be that large except I had a male parent. I prefer female parenting skills because I can control the amount of tribe members better.
But in VV2 and VV3, for me anyway, I notice that when the tribe gets low an event occurs where extra members are produced. In VV2, I hit the gong and all of my eligible females are pregnant. I had about 15 tribe members at the time. Good luck with your events.

One more thing, My tribes was more advanced, all puzzles done, and plenty of food. That may have an effect also.