WHEN CLOCKS (AND COMMUNITIES) COLLIDE: ESTIMATING DIVERGENCE TIME FROM MOLECULES AND THE FOSSIL RECORD

Traditionally, deep time was the domain of paleontology. Origination time could be assessed only through reference to first appearance data in the rock record. This changed almost from the beginnings of modern molecular biology, when it was realized that molecules could be used to calculate divergence times between living species. Early studies relied on immunological distance information, and the underlying rationale was simple: because evolution involves changes to the genetic code, and because these changes accumulate over time, we should expect the number of accumulated changes (the molecular distance) between living taxa to increase as their time of divergence becomes older (Zuckerkandl and Pauling, 1962). By inferring a rate of evolution of the genetic code, we can place absolute time estimates on divergence points.