How and if evolution has helped to shape human mating habits is a topic that frequently leads to lively debate. For example, because men produce millions more sperm than women produce eggs, there is a theory that the mating strategy of women will be more focused on protecting and nurturing the relatively few reproductive opportunities she has, whereas men are “pre-programmed” to spread their seed far and wide.
However, this theory is probably simplistic, as it fails to account for a number of other factors. For example, in species where nurturing a newborn requires parental cooperation, monogamy becomes more common. Dr. Helen Fisher has proposed a “four-year” theory, which attributes a spike in divorce rates in the fourth year of marriage to the notion that this is when a child has passed through the most vulnerable phase of their youth and can be cared for by one parent. The “four-year” theory is somewhat flexible. For example, if the couple has another child, the time period may be extended to the infamous “seven-year itch.”
None of this, however, explains those enviable couples who walk hand in hand together through their entire lives into the twilight of their years. It’s also important to remember just how complicated the topic of human affection is. Our culture, our upbringing, and the rest of lives help to change those chemicals and networks. Love’s complexity means that questions about the nature of love will continue to fascinate poets, philosophers, and scientists for many years to come.