Sex is a type of Species. Species is related to Alien. Alien is related to Life. Dying requires Life. 
Sibling is a type of Animal. Twin is a type of Sibling. Twin is a synonym of Counterpart. 
Sex --IsA--> Species <--RelatedTo--> Alien <--RelatedTo--> Life <--HasPrerequisite-- Dying 
Animal <--IsA-- Sibling <--IsA-- Twin <--Synonym--> Counterpart 