They didn't reliably even have social class or status in common, at least not in the era when trade volumes were highest. A number of prominent Muslims were known to have been enslaved; one such was Omar ibn Said, taken around 1800, who left quite a narrative and made many petitions for his release; there are others from Senegambia and areas inland that are known as well, from many walks of life. (See the other slave narratives on that page with Said's, on the right hand sidebar.) The Nigerian Hinterlands Project has itself traced a great many families of enslaved people, and found that they ran the gamut--some very poor taken into servitude, some enemies of powerful people, some powerful people themselves, and many just in the wrong place at the wrong time when a raiding party moved through. I'll see if there is a good systematic treatment of origins, but if anyone would know it would be Paul Lovejoy (Transformations in Slavery) or John K. Thornton (A Cultural History of the Atlantic World).

If you're interested in accounts of individual experiences, Olaudah Equiano wrote a narrative about his experiences in the transatlantic slave trade. Jeffrey Brace and Venture Smith also wrote similar narratives.

I will second some of the other comments here and recommend Randy Sparks's "Two Princes of Calabar." It is about two wealthy African slave traders from the Bight of Biafra who were tricked and sold into slavery. Both men were educated, spoke English, and able to draw upon their connections with influential Britons to become free--very different from most other slaves. The book is a great read too.