George Gaylord Simpson Prize

Chase Brownstein

Chase D Brownstein, Daniel J MacGuigan, Daemin Kim, Oliver Orr, Liandong Yang, Solomon R David, Brian Kreiser, Thomas J Near, The genomic signatures of evolutionary stasis, Evolution, Volume 78, Issue 5, 1 May 2024, Pages 821–834, https://doi.org/10.1093/evolut/qpae028

Some lineages on the Tree of Life are hundreds of millions of years old yet contain only a handful of species that display very little variation in shape, size, ecology, and other aspects of their biology. These lineages, first called ‘living fossils’ by Charles Darwin, have fascinated paleontologists and evolutionary biologists since the start of both fields. Yet, the existence of living fossils has remained controversial. The debate over the existence of living fossils has centered around whether ‘living fossils’ are accidents of history, surviving on isolated islands or rivers buffeted from the worst effects of extinctions long past, or whether their bizarre evolutionary history is governed by intrinsic biological mechanisms. 

In our 2024 paper, The Genomic Signatures of Evolutionary Stasis, we demonstrate that several lineages of ‘living fossil’ fishes, the gars, sturgeons, and paddlefishes, have exceptionally slow rates of molecular evolution relative to other jawed vertebrates. These rates are so slow that sister species of gars that last share common ancestry over 10 million years ago show no differences in over a third of the over 1000 sequences that we examined! This stagnant rate of change in the DNA sequences of these living fossils is paired with their capacity to hybridize across deep divergences. For example, we document a case of fertile hybrids being produced in the wild by two gar species that last share a common ancestor over 100 million years ago, making it the most ancient split in animals, plants, or fungi known to produce fertile hybrids in nature. These results suggest that an intrinsic mechanism – slow rates of evolution across the genome – is responsible for evolutionary stasis in these living fossils.