Long juvenile period. A 10yo human child with living parents has a greater chance of surviving to breeding age than the same aged child with dead ones. Also, a

Long juvenile period. A 10yo human child with living parents has a greater chance of surviving to breeding age than the same aged child with dead ones. Also, a reproductive pair with living post reproductive (but still not decrepit) parents can breed at a higher rate as they are can delegate some childcare to them.