Nerve fibres of the parasympathetic nervous system arise from the central nervous system. Specific nerves include several cranial nerves, specifically the oculomotor nerve, facial nerve, glossopharyngeal nerve, and vagus nerve. Three spinal nerves in the sacrum (S2-4) also act as parasympathetic nerves.
The word longevity is sometimes used as a synonym for life expectancy in demography - however, the term longevity is sometimes meant to refer only to especially long-lived members of a population, whereas life expectancy is always defined statistically as the average number of years remaining at a given age.
Pair bonds, both social and sexual, in humans are part of complex social networks that emerged as central patterns in human evolution. Pair bonds can involve sexual relationships (and in a cultural sense, romantic attachments) and are probably involved in what most people experience when they think of romantic love. We have extensive social pair bonding across genders and age categories, probably more than any other species.