The Concentration Mechanism: Male Partner Distribution Bifurcation and the Collapse of the Moderate Middle

The majority of the widely-discussed “sex recession” reflects a symmetric rise in virginity affecting both genders equally. A companion paper, however, documented an additional asymmetric component: a post-2012 widening of the male-female gap in sexlessness among the sexually experienced. This study investigates the distributional mechanism underlying that asymmetric gap using the National Survey of Family Growth (NSFG). The analysis focuses on never-married, sexually experienced adults aged 25-34—old enough to have accumulated meaningful partner histories, young enough to reflect contemporary market dynamics, and restricted to those actively in the dating market; similar male-specific redistribution appears in broader sexually experienced samples, indicating the pattern is not driven solely by marital selection. Among this population, I find a male-specific collapse of the “moderate middle”: the share of men with 3-5 lifetime partners fell from 30.3% to 21.5% (-8.8 percentage points) between 2006-2010 and 2015-2017. This loss bifurcated: +4.4 pp shifted to the 1-2 category (exclusion) and +4.4 pp shifted to 6+ (concentration). Women’s distribution remained stable. The upper tail (10+ partners) actually declined slightly for both genders, suggesting concentration operates specifically in the 6-9 range—not through extreme accumulation. Because this redistribution occurs within the middle of the distribution rather than the extreme upper tail, it is poorly captured by standard inequality measures (e.g., Gini coefficients) and to analyses focused on top-end accumulation. This distributional pattern—middle collapse rather than upper-tail growth—has gone unrecognized in prior work. The asymmetric gap decomposes evenly into exclusion and concentration.