What precisely do you mean by "Ancient Africa"? Are you referring to Egypt, Nubia... Greater Zimbabwe? 21^st century racial apologists of all stripes like to essentialize ancient cultures. But that's a mistake. Ancient Egyptians weren't "black" anymore than Ancient Greeks were "white".

This is profoundly outside my area, so mods, please delete this comment if need be. That said, I just wanted to point to Martin Bernal's Black Athena, which made the argument that much of the Greek and Classical world, and accordingly western culture, was drawn from Egypt. It was a remarkably controversial book; Bernal was writing outside of his usual field, and it immediately entered a divisive political climate. But questions like this are often filtered through the discussion and controversy that book activated.

That said, the 'cradle of civilisation' notion has its own problems. Cultures, even the first 'complex' ones, nearly always had neighbors with whom they exchanged a great deal. The Mediterranean world especially has long been defined as much by its interconnections as by its having played host to singular societies.

I'm sure the chances are that your friends do not subscribe to the types of ideologies I'm about to briefly explain. They're worth mentioning because they're interesting ideologies and the people who believe them fully to extremes are interesting to learn about; oddities are fun.

Although it is certainly not a mainstream idea, there are circles of people both on and offline who believe that most if not all people or aspects of historical eminence today are infact black in origin and there has been a centuries old conspiracy by the white man to eradicate the contributions made by blacks. There is an interesting segment in Louis Theroux's documentary on Black Nationalism in the United States where some members of a jewish sect/group called The Black Hebrew Israelites speak of this conspiracy where a number of historical figures of mostly obvious European/Near East origin are presented and claimed to be black people who are victims of 'damnatio memoriae' by the white race. The kings of England going back through history, all the Egyptians and their accomplishments, Cleopatra, Joan d'Arc, the Vikings, Beethoven are all claimed by this group to have been black.

The followers of these beliefs are obviously on the extreme right wing of politics and are basically groups of black Americans that harbor strong racial separatist or supremacist ideologies. That being said, it is common for people to claim historic lineage or accomplishments for their own nation, group, or race but I won't speculate as to why. Common objects or figures "claimed" by differing groups of non extreme nature are Cleopatra's race, the original descendants of the lands of Palestine (that's a big one), and the first settlers of lands later conquered in full by particular cultures such as Italy and Spain. I hope to have added something interesting to the conversation.