Extreme climate cycles in the Northern Hemisphere over millions of years altered the evolutionary history of the hemisphere’s conifer trees, encouraging the formation of new species that are millions of years younger than their counterparts in the Southern
Hemisphere, according to a new study. In an analysis of the fossil remains and genetic makeup of 489 of the world’s roughly 600 living conifer species, scientists found that while the majority of conifers belong to ancient lineages, most of those found in the Northern Hemisphere emerged in just the last 5 million years. Scientists suggest that the migration of trees species and changes to range sizes in response to glacial cycles resulted in isolated populations and the introduction of new species. “Extreme climatic shifts through time may have favored the replacement of older lineages with those better adapted to cooler and drier conditions,” said Andrew Leslie, a Yale researcher and co-author of the study, published in the Proceedings of the National Academy of Sciences. In the Southern Hemisphere, meanwhile, fragmented habitats and mild, wetter habitats likely helped the older conifers survive with greater diversity.