Reproductive value and the marriage bargain

Two recent blog posts on Psychology Today piqued my interest once again in human sexuality and evolutionary psychology.

First came Heidi Reeder’s article a few weeks ago, Sex with friends: are there benefits? In the comments, I gave voice to some of my thoughts, and I penned a blog entry of my own on the subject. Then today I read a thoughtful piece by Jeremy Sherman, entitled Single mid-life female seeks romantic solution. His thoughts mirror the conversations I’ve had with many female friends. As I’ve grown older, I have observed that my options have changed and I’ve been forced to update my expectations accordingly. However, my experience is quite different from that of my single female cohorts.

Reproductive value can be roughly defined as one’s subjective value to the opposite sex on the mating market. In humans, average reproductive value for men and women varies differently by age. Women mature earlier than men, but have fewer years of fertility. Men have a lower peak RV, but have their years of fertility spread across a longer portion of their lifetime. Figure 1 shows my rough estimate of average reproductive values (arbitrary scale) for women and men.

Figure 1. Reproductive value (RV) versus age for women (♀) and men (♂)

Women’s reproductive value (RV) drops off precipitously in their mid-to-late thirties, due to declining fertility. At the same age, men’s RV reaches a plateau and only begins to taper off gradually a few years later. Because women have a more limited range of fertility, they are in higher demand during this period. This is why women’s RV has a higher peak than men’s. On the other hand, because men have more years of fertility, their curve is flatter and more spread out.

I wonder though: do both men and women have about the same total reproductive value over their lifetimes?

Imagine that the area under the curves represents the total amount of reproductive value over time.

Figure 2. Total reproductive value over a lifetime

In Figure 2, the pink shaded area represents a woman’s total reproductive value from puberty until menopause, and the blue shaded area represents a man’s total reproductive value from puberty until infertility. What if the areas under the curves are approximately the same? What would the significance of this finding be?

One way to look at it would be a new appraisal of the institution of marriage. In a comment on Dr.Reeder’s blog entry, I wrote:

Marriage is essentially a compromise and a set of trade-offs. When a young couple gets married, the man earns the woman’s youth in exchange for remaining faithful to her and her children after her fertile years. 

 The above graph provides a graphical representation of this bargain. In essence, we can view marriage as a contractual exchange of each person’s remaining total RV. One could also use graphs like this to gain insight into relationships and conflicts. For example, if the above view is an accurate representation of reality, one would expect that relationships would work best when both partners have approximately the same RV, and that having the same total remaining RV would also be significant. One could also conjecture that incidences of infidelity would be instigated by the partner whose RV (or RV potential) is higher. For women, this should occur more frequently early in life; for men, it should be more common later in life.

Fascinating stuff.  It would be fun to find a rigorous way to actually measure RV and test these theories experimentally.