This is really a great help. Thank You!

My tribe is still very young and only ten children have been born yet. I only had one exception until now. I will list them and maybe it will help to figure out how the exceptions occur.

(m=male; f=female)

m8 + f2 = f5 (average: 5)
m8 + f2 = f4 (av: 5)
m12 + f24 = f19 (av: 18)
m25 + f5 = m9 (av: 15)
m12 + f24 = m17 (av: 18)
m23 + f4 = f14 (av: 13,5)
m12 + f5 = m7 (av: 8,5)
m25 + f4 = m14 (av: 14,5)
m9 + f19 = f14 (av: 14)
m25 + f14 = m18 (av: 19,5)