Scientists have long thought there is only one species of elephant in Africa. But earlier this year, DNA evidence suggested African elephants may well come from two separate and distinct species. For commentator Gwen Acton, that finding is just the latest example of a thorny problem. She says the lack of a clear way to define species creates a predicament not only for scientific research, but also for conservation efforts. Commentator Gwen Acton is a biologist at Harvard University's Museum of Comparative Zoology.