I was going to say your professor must be
quite the remarkable man indeed if he can identify what 'tribe' one comes from by looks alone.
While many people are familiar with the most common physical traits of various continental "subdivisions" (eg Kenyan, Ghanaian etc) I think to know all the common physical attributes of the hundreds of tribes within Africa is a long shot.
When I think of South Africa alone, one who lives there can easily can determine who is pedi, twana, zulu, sotho, xhosa etc.. whereas another from the outside looking in would likely see these neighbours as all the same. Or Zimbabwe.. the Ndebele, Shona, Shangane etc..
Again, while not impossible, if your professor claims that he himself can do it by sight alone.. well... I, personally, would be surprised if he could name all the 'tribes' of Africa, let alone identify them all
Zulile