All of the Indo-European languages either have gendered nouns or are descended from earlier, attested languages that have gendered nouns. This includes languages that not only were not descended from Latin, but had no contact with Latin during their early formation. Sorry, but it is a fact that gendered nouns go way, way back in the history of the Indo-European languages -- probably all the way back to Proto-Indo-European itself.
Edited to add:I just reread the OP. It appears that the question is why there are genders in the French language specifically. In that case, the reply that they serve no real purpose, but are holdovers in the ancestral Latin language is correct and appropriate. In fact, the professor of French does point out that gender arose before Latin.
My apologies.
Now, back to the regularly schedule off-topic: the relative merits of an Oxford professor vs. Wikipedia.
This message has been edited by Chiroptera, 04-20-2005 10:48 AM