In addition to these studies, other research has looked at the influence of specific genes on longevity. For example, research has shown that the heritability of human longevity is high based on a population-based study of Danish twin pairs born between 1870 and 1900. Furthermore, the angiotensin gene polymorphism has been associated with variation in blood pressure in a Japanese population. Finally, polymorphisms in factor VII gene alleles display sex-specific effects on fibrinogen levels.