Encounters in the Cosmos between different intelligent species are examined based on the Principle of Mediocrity and the model of intelligence as the result of parallel evolution on different planets. Following the theory of socio-biology : the propagation of genetic material involves ruthless competition between species and subspecies but cooperation within species or subspecies groups. This competitive genetic legacy influences behavior, resulting in murderous hostility towards other species competing directly for resources and living environments. Following Lorentz this results in restrained violence within species battling for dominance or mating privilegesbut deadly violence in battles between different species competing for shared ecological niches. These behaviors may be carried into space by intelligence species with the result that encounters with other intelligent species of completely different evolutionary legacies may result in violent completion for planets or stellar systems deemed suitable for colonization. Such Âgenetic legacy behaviorsÂ may explain the possible nuclear planetary massacre found on mars, where the scenario of an advanced space faring species attacking and destroying a much more primitive species native to Mars may have occurred. If verified, such a scenario would be consistent with competitive genetically inspired behavior that is a legacy of life under much more primitive terms on the advanced raceÂs home planet.