Genetically homogeneous and isolated communities, such as those of the Mirbeck Oak in Portugal, the Red Squirrel in England or the Bromeliad Puya raimondii in the Andes, run the risk of an inbreeding depression rendering organisms even more vulnerable to climate change. However, outbreeding depression is also a danger if inappropriate exogenous material is introduced in order to strengthen the genetic base of a population. Is there an objective way to decide on the right strategy?