Marriage is intrinsically related to human sexuality. The bonding associated with marriage has a physical origin in sexuality and therefore we will begin with an essay on sexuality and the human brain.
The center of human sexual behavior in both males and females is the human brain. Sex is about chemicals that work within the brain. The feelings of attraction and attachment that are so basic to human life take place due to various activities in the brain. When the human being is studied in her uniqueness, the complexity of the brain becomes of paramount importance.
Human sexuality is related to the sexuality of other primates, but is distinct just as the human brain is distinct. This means that we have to study the brain to understand human behavior. Although there are an enormous number of chemicals surging through the human body/brain three are most significant in the discussion of sex and marriage. Dopamine is a chemical called a neurotransmitter that rewards behavior that is exiting or risky. It is not rational; it rewards behavior regardless of the wisdom or propriety of the behavior. Dopamine produces a high that is pleasurable and addictive. And dopamine is produced in abundance from puberty onwards. Unfortunately the full development of the brain especially the frontal cortex is not complete until the mid-twenties. So from puberty to the mid-twenties young adults are being urged by their brain chemistry to take risks that they have no internal way of evaluating, good, bad, worthwhile etc. Not only is this a serious concern for that period of life, but for the whole of life because the brain is always being molded by behavior and experience and this molding is pronounced during the teen years so that risky and ill-advised choices begun during adolescence become a habitual way of experiencing life.
Besides dopamine two other neurotransmitters we need to be familiar with are oxytocin and vasopressin. Both may exist in both sexes, but oxytocin is very prominent in females and vasopressin in males. They are bonding agents. They connect the brain with a sexual partner. Oxytocin in females also bonds them with their children. The bonding part of the brain is different from the pleasure centers of the brain. However sex is definitely about bonding and not only about pleasure. Many studies indicate that the combination of bonding and pleasure produces a great sense of well-being. On the other hand, when people either engage in sex for pleasure alone or when they bond and break up often, they actually experience frustration and, frequently, depression and anxiety. The greatest sexual satisfaction is reported by people in long-term commitments.
Adolescents who engage in short-term bonding or hooking up with no interest at all in the partner, often mold their brains in such a way that later on they cannot experience long-term bonding and commitment, perhaps because the synapses which are for that purpose have shrunk. Adults who engage in such behaviors usually began such behaviors in adolescence. As the chemical bonds are broken immediately or in a short time, the ability to make new connections lessens. Further the pleasure experienced by the dopamine decreases calling for more and more risk to replace the reduced experience of excitement. Eventually there is a great deal of pain and unhappiness that requires a great struggle to overcome. Perhaps a great deal of dissatisfaction with contemporary mores will cause people to look again at the perennial philosophy which lies at the foundation of traditional beliefs about marriage and sexuality. As Dr. J. McIlhaney et al put it:
The important thing to recognize is that the desire to connect is not just an emotional feeling. Bonding is real and almost like the adhesive effect of glue—a powerful connection that cannot be undone without great emotional pain. J. S. McIlhaney et al, Hooked: New science on how casual sex is affecting our children, [Chicago, IL: Northfield Publishing, 2008], p.37 cf. Naomi I. Eisenberger and Matthew D. Lieberman, "Why Rejection Hurts: A Common Neural Alarm System for Physical and Social Pain" Trends in Cognitive Sciences 8, No 7 : 294—300.
To summarize: by nature males and females bond sexually and find maximum satisfaction in a committed relationship that is stable in all ways. Since sex also tends to produce children, nature favors this stability for the offspring as well. Therefore the three qualities of marriage according to traditional thinking correspond exactly: they are permanence [commitment], unity [bonding], and children [offspring]. What modern studies have shown is that the brain is not wired for multiple partners, but for one. So far this concerns only the basis of marriage in nature itself. Now we will look to the spiritual qualities as well. For more information on any of the above topics see: McIlhaney, Joe S. Hooked, [Chicago IL: Northfield Publishing, 2008], Passim.