If you go far back enough in the history of humans, eventually we all lead to a single related population. All humans share a common ancestor (our great-great-great-great plus seven thousand more greats grandma) and we can trace our cousins’ and our family lineage to some common relative (like how 1/2 a percent of the world can trace their ancestry back to Genghis Khan). We can trace all of today’s living species to common ancestors that existed millions of years ago in a similar fashion. Time Tree is a tool that summarizes scientific literature to tell you the point in geologic time that a single lineage split into two – say, when the human and chimpanzee lineages split from a shared ancestor.
I'll leave the science involved for others to debate. However, if you would like to read more, look at the article by Courtney Stepien at http://bioforthewin.com/2013/01/30/time-tree/.
My thanks to newsletter reader Chad Milliner for telling me about this article.