Mapping Human History contained a conjecture about human ancestry that was disputed when the book was published. The book claimed that the most recent common genealogical ancestor of everyone living on the Earth today must have lived just 2,000 to 3,000 years ago, a number that geneticists thought much too small. However, a more formal version of the conjecture was proven by the author, working with coauthors Douglas Rohde and Joseph Chang, in a September 30, 2004, article in Nature. They modeled the human population as a set of randomly mating subpopulations that are connected by occasional migrants. If the size of the population is n, then the time to the most recent common genealogical ancestor is a small multiple of the base-2 logarithm of n, even if the levels of migration among the populations are very low. Using a model of the world’s landmasses and populations with moderate levels of migration, the authors calculated that the most recent common genealogical ancestor could have lived as recently as AD 55.

These results lead to some highly counterintuitive conclusions. In the generations before that of the most recently common genealogical ancestor, more and more people are common ancestors of everyone living on Earth today. At a time 2,000 to 3,000 years before the appearance of the most recent common genealogical ancestor, everyone in the world is either an ancestor of everyone living today or an ancestor of no one living today. Thus, everyone living today has exactly the same set of ancestors who lived 5,000 to 6,000 years ago, even though those ancestors are represented in very different proportions on a person’s family tree.

In an article published in the Los Angeles Times on the day the movie of The Da Vinci Code was released, Olson pointed to several other consequences of the analysis in the Nature paper. If Jesus has any descendants living in the world today, then almost everyone in the world is descended from Jesus. Furthermore, if a person living today has four or five grandchildren, so that his or her genealogical lineage is unlikely to go extinct within a few generations, that person is virtually guaranteed to be an ancestor of all humans in the Universe who will be living 2,000 to 3,000 years from now,

Olson is married to Lynn Olson, a long-time education journalist who is currently a senior program officer with the Bill and Melinda Gates Foundation. They have two children.

Steve Olson's web page