From the article (Excoffier's hypothesis):
"A small number of those fledgling people then migrated to Asia. As the population expanded, separate groups formed in different areas...Some ancestral genes could have been carried out of Africa, while being lost within Africa. That would explain why Asians carry much older stretches of DNA than Africans do."
That would seem it would also explain the shovel-shaped incisors. They were present in the ancestoral population in Africa, but later lost.
I have never heard of any sizeable (>2-3%) numbers of shovel-shaped incisors in Africa. I am still confused. I understand the Lapps or some group in that area had a slightly higher percentage, but the real mother-lode is in the Mongolian group, and in Peking Man. Help?!?