ARE WE ENTERING A SIXTH MASS EXTINCTION? AGE SELECTIVITY OF MODERN EXTINCTIONS

There is growing debate on whether the earth has entered a sixth mass extinction. Most previous research has focused on the rate of modern extinctions compared to that known from the fossil record. Here we compare the age selectivity of modern extinctions with mass extinctions and background extinctions in the fossil record. We evaluate age selectivity using logistic regression to quantify the relationship between extinction risk and genus age. While genus age is measured similarly in all time intervals, extinction risk is a binary outcome for fossil groups and an estimated probability for modern groups, with the latter calculated to make fossil and modern analyses as comparable as possible. To estimate extinction risk for modern data, we used assessments of threatened species from the International Union for Conservation of Nature (IUCN) Red List. For Phanerozoic background and mass extinctions, we compiled data from the Paleobiology Database supplemented with the Sepkoski Compendium. We find that with respect to genus age selectivity, modern extinctions are significantly more similar to mass extinctions in the fossil record than to background extinctions.