Scientists believe there was only one man who left Africa 50,000 years ago and had all his descendants survive. Others that left Africa at that time have no living descendants today.
I started by sending my DNA sample to National Geographic. They tested it, and told me a bit about my ancestors who lived 50,000 to 30,000 years ago. I now know that my ancestors left Africa 50,000 years ago, travelled to the Middle East, and then migrated to Northwest Europe (part of this group became the Vikings and the other part settled in Croatia). The National Geographic performed what is called a "12-marker" test and sent me the results, so I actually have in writing a small part of my DNA code.
I then forwarded the results to the Family Tree DNA project. This web site matches my 12-marker results against its database from other people who sent in a sample. They returned to me a list of 30 people who matched my 12-marker results. The web site says if any of them shared a last name with me, there would be a very good chance we're related. So far, none of the people who match my DNA share my last name or anything close, so I have no good matches.
I ordered a more detail test, a 37-marker test. This test is more accurate. If there are any other positive matches to this test, then I can be sure that I am related to that person within the last few generations. I'll let you know how that goes.