Genetic data show the grizzly bear population in the Greater Yellowstone Ecosystem has grown since the 1980s with no loss in genetic diversity, according to a report by the Interagency Grizzly Bear Study Team.Results indicate that the effective population size of Yellowstone grizzly bears, or the number of individuals that contribute offspring to the next generation, has increased 4-fold over a 25-year period. This provides evidence that Yellowstone grizzly bears are approaching the effective size necessary for long-term genetic viability.