In short, we share close genetic relationship with the great apes of Africa, the oldest human skeletons have been found in Africa, and the oldest evidences of human culture, such as poison arrows for hunting, have been found in Africa.
Africa
The oldest evidence of life are single celled organisms that are found in rock and mineral samples. These date back to approximately 3.5-3.8 billion years ago.
The oldest known archaeological remains found in Nigeria date to about 11,000 B.C. It is possible that humans arrived in the region earlier than that, but no remains of their settlements have been discovered.
The oldest know fossilized fungal spores have been found in amber dating back to 225 millions of years ago.
The first and oldest physical evidence of windmills we have discovered so far was found in Greece, used by the Ancient Greeks in the 1st century AD.The oldest known evidence of windmills in literature (but no physical evidence) was mentioned in an Ancient Babylonian book detailing the use of irrigation and wind power for farming, dating back to the 17th century BC.
The oldest known shoes, however, dating at about 7,000 or 8,000 BC, were found in Oregon. They were sandals. However, there is evidence suggesting that humans began wearing shoes long before that.
Europe and Asia
we know about mummification by the evidence found with mummies
The Evidence is that human-related fossils were mostly found in Africa and they were also artifacts related to humans
Many scientists have said so based on the evidence they found.
The oldest humanoid remains that we have found so far are 2.8 million years old.