“Whales can tell us new stories of how species can evolve into different forms,” said Dr. Janke, also a professor of evolutionary biology at Senckenberg Biodiversity and Climate Research Centre, and Goethe University in Frankfurt am Main, Germany.
The idea that species can intermingle is new, even to scientists, said Scott Edwards, an evolutionary biologist at Harvard University, who was not involved in the new study.
“Ten years ago, most evolutionary biologists would have assumed that a species is a species, especially when they look phenotypically distinct,” Dr. Edwards said. Recent research has shown that humans, too, are the product of species intermingling. There are varying levels of Neanderthal and Denisovan DNA across the human population.
Dr. Janke said he was also struck by the wide range of genetic diversity he saw within whale species. Genetic diversity helps animals survive change. “The whaling moratorium, where they stopped whaling in 1978, came just in time to prevent this biodiversity from being genetically more monotonous,” he said. “If that had been the case, it would have been difficult to envision how the species could survive.”
The DNA samples in the study were taken mainly from biopsies collected with remote darting; the gray whale samples came from Alaska, where the Museum of Fairbanks secured samples from deceased animals, Dr. Janke said.
This study is the first genome-scale comparison of so many baleen whales, but it won’t be the last. A team at the American Museum of Natural History in New York and the University of California, Riverside, is preparing an even more detailed analysis of more animals and species.
“We were mildly scooped by this,” conceded John Gatesy, the senior scientist leading the museum study. He praised the work of the European scientists and said his own research will add subtleties but not conflict with their major findings.
Dr. Gatesy said he was most interested in the confirmation that this study provides of the intermingling of species. “This is pretty strong genomic evidence for hybridization among multiple lineages in baleen whales, which is pretty exciting, I think,” he said.
To a whale biologist, he said, the idea of two whale species mixing is as mind-bending as the image of a chimp mating with a gorilla.
Blue and fin whales, for instance, differ in size, color and body shape. “The thought of them breeding and reproducing is fun to think about,” Dr. Gatesy said.