The Ecphorizer

Sexual Decay in H. Sapiens
A. Fish, Ph. D.

Issue #03 (November 1981)

Why does romantic love cool off? Science comes up with the answer!

In a recent paper1, Alden and Mullens reported the results of a survey of terminated human sexual relationships, which indicated that sexual desire (referred to by the authors as "romantic love") decreases

...'romantic love seems to have a half life, much like radioactive decay.'

exponentially after inception, typically decaying to a nonmeasurable level in 6 to 18 months. The researchers advanced the hypothesis that "romantic love seems to have a half life, much like radioactive decay."

[quoteright]The present research2 supports that hypothesis, and further extends it by suggesting an exact quantification for the decay process. It shows that

T=G- sqrt 2 over 2 [a]

where T is the half-life of sexual desire for the species under study and G is the same species' natural gestation period. In H. Sapiens G is 273 days; therefore T is 193 days and 58 minutes. In the laboratory, this is called the Lust Extinction Factor. The right hand expression in formula (a) is derived from standard theories of exponential change in dynamic systems3. Regression analysis shows that formula (a) exhibits a chi-square test fit to Alden and Mullins' empirical data to a 0.96 confidence factor, well within standard limits for theoretical validity4.

The role of G in formula (a) is of interest. The present research suggests that this is a constant deeply embedded in the evolution of social animals. Referring again to H. Sapiens in the prototypical mating pair (before adculturation) sexual desire commonly results in fertilization, followed after the period G by parturition. The breeding population maximizes its survival rate by evolving responses such that the female transfers her attentions from the impregnating male to the neonate during this process. To adapt to this transfer, breeding males evolve a simple Wallenden-Kirchstein decay curve in their sexual behavior, as expressed in formula (a).

In conclusion, the foregoing theory is offered as an explanation for frequently expressed, but hitherto unanalyzed, observations such as, "the honeymoon is over," "after a few weeks they're all the same," and "you don't love me any more." Research is continuing in an effort to elicit the exact dynamics of the lust-to-boredom transition.


1. Alden, J., and Mullens, P., "The Goodbye Syndrome: Terminated Human Relationships," in Sexual Abstracts 135:12-20 (Oct. 1977).
2. Supported in pert by Grant No. INB-354-81-002 from the Institute of Mating Behavior of the National Scientific Foundation.
3. Wallenden, A., and Kirchstein, H., Elementary Statistical Models Brooklyn University Press, 1975, pp. 655-693.
4. Piltdown, M., "Fitting Facts to Formulas," in Research Management Review, Spring 1978.
Reprinted, in abridged form, from the Journal of Determinate Behavior 8 June 1981, pp. 745-756. Reprinted by permission. 

We are indebted to Dr. Fish for having forwarded the latest results from his laboratory. We hope this will be the start of a trend, by which we bring you monthly news scoops from the fast-breaking world of scientific research.

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