 በትውልድ ውስጥ ተጨማሪ ዝርያ ሲፈጠር የዘር ምድቡ እያነሰ እያነሰ መጣ፣ የአንድ ቋንቋ ቤተሰብ ሰዎች ሁሉ ተመሳሳይ ገጽታ እስኪኖራቸው ድረስ።
As further inbreeding occurred through the generations, the gene pool grew smaller and smaller, to the point that people of one language family all had the same or similar features.