Phylogenies are usually dated by calibrating interior nodes against the fossil record.
This relies on indirect methods that, in the worst case, misrepresent the fossil information.
Spalding and her postdoc advisor Jonas Frisén had a hunch that a pulse of radioactive carbon created by above-ground nuclear tests during the Cold War could help solve the riddle.
“A geopolitical phenomenon—this Cold War bomb testing—has, in a way, put a date stamp on everything and everybody,” Spalding says.
Our bodies are prolific artists, creating new cells throughout the body.
Some cells, like those found in skin, hair, and the lining of the gut, are produced and discarded on a regular basis, like doodles on scrap paper. Kirsty Spalding was one of the scientists who doubted that assessment.
In particular, an acceleration of evolutionary rates at the base of Poaceae followed by a deceleration in the descendants strongly biases methods that assume an autocorrelation of rates. Meanwhile, molecular dating analyses of angiosperms (flowering plants) are abundant in recent literature and, despite differences in methodology, independent estimates converge on a date for the split between the two major groups of flowering plants (eudicots and monocots) between roughly 130 and 170 Ma (Bell et al. The conflicts between different sets of calibration points, methods and genomes highlight the importance of considering multiple sources of evidence when attempting to estimate evolutionary events that happened in distant geological time.