[goobatrooba]

While humans and the first basis of culture evolved in Africa, many of the key cultural/technological innovations happened outside Africa, notably the invention of agriculture and pastoralism which happened 3-6 times independently (modern Turkey, China (possibly twice) and South America, possibly in addition also in Iran and India).

So if you look at Africa it stayed for the longest times with hunter & gatherer cultures until neolithic settlers came back into Africa from modern Turkey.

Moreover Africa in large parts is either moist or desert/savannah, both of which do not help preservation. And there are simply much fewer archaeologists going around Africa.