" It is a plain matter of biological fact that, as Grisez says, reproduction is a single function, yet it is carried out not by an individual male or female human being, but by a male and female as a mated pair. 50 So, in respect of reproduction, albeit not in respect of other activities (such as locomotion or digestion), the mated pair is a single organism; the partners form a single reproductive principle: they become “one flesh.” In response to Posner, Grisez proposes a thought experiment. Imagine a type of bodily, rational being that reproduces, not by mating, but by some individual performance. Imagine that for these beings, however, locomotion or digestion is performed not by individuals, but only by biologically complementary pairs that unite for this purpose. Would anybody have difficulty understanding that in respect of reproduction the organism performing the function is the individual, while in respect of locomotion or digestion the organism performing the function is the united pair? Would anybody deny that the unity effectuated for purposes of locomotion or digestion is an organic unity? "

― Jean Bethke Elshtain , The Meaning Of Marriage: Family, State, Market, And Morals