Bio-behavioral synchrony is a potential mechanism for mate selection in humans

Abstract

The decision with whom to form a romantic bond is of great importance, yet the biological or behavioral mechanisms underlying this selective process in humans are largely unknown. Classic evolutionary theories of mate selection emphasize immediate and static features such as physical appearance and fertility. However, they do not explain how initial attraction temporally unfolds during an interaction, nor account for mutual physiological or behavioral adaptations that take place when two people become attracted. Instead, recent theories on social bonding emphasize the importance of co-regulation during social interactions (i.e., the social coordination of physiology and behavior between partners), and predict that co-regulation plays a role in bonding with others. In a speed-date experiment of forty-six heterosexual dates, we recorded the naturally occurring patterns of electrodermal activity and behavioral motion in men and women, and calculated their co-regulation during the date. We demonstrate that co-regulation of behavior and physiology is associated with the date outcome: when a man and a woman synchronize their electrodermal activity and dynamically tune their behavior to one another, they are more likely to be romantically and sexually attracted to one another. This study supports the hypothesis that co-regulation of sympathetic and behavioral rhythms between a man and a woman serves as a mechanism that promotes attraction.

Figure 1

The experimental setting. A man and a woman meet for a speed date while their behavior and physiology are being recorded, providing 1200 physiological data points (sampled at 4 Hz) and 3000 behavioral data points per date for each subject (sampled at 10 Hz). The room design, as well as the ambulatory recording equipment, enabled participants to freely interact, for an ecologically-valid estimation of bio-behavioral measures, naturally occurring during a romantic date. After the date, participants rate their romantic interest and sexual attraction to the partner. We measured the association between physiological synchrony and behavioral attunement during a date, and the romantic and sexual ratings after the date.

Figure 2

Increased electrodermal synchrony during a date is associated with increased romantic interest. (A) Dyadic electrodermal synchrony between partners in a date (x-axis), is associated with increased mutual romantic interest (y-axis), multilevel model analysis: β = 2.83, p = 0.006; Pearson r = 0.51, 95% confidence interval = [0.23, 0.72], p < 0.001, BF₁₀ = 73.23, N = 42 dates, combined across three experimental runs (run 1, N = 15 dates, run 2 N = 14 dates, run 3 N = 13 dates). (B) The results in each experimental run.; Mutual romantic interest is calculated as the sum of the man’s and the woman’s ratings of romantic interest in each other (see “Methods”).

Figure 3

Coupling of electrodermal activity and behavior during a date indicates the date-outcome. (A) The date outcome was calculated based on the romantic interest of both partners. After each date, subjects rated the romantic interest in their partner on a scale of 1 to 5. Based on the median of the ratings, participants who rated their partner with a score of 3 or above were considered interested. (B) The dates’ outcome as a function of motor attunement (x-axis) and electrodermal synchrony (y-axis). Electrodermal synchrony and motor attunement are positively associated (Pearson’s r = 0.304, 95% confidence interval = [0.05, 0.57], p < 0.027). Moreover, a multilevel model analysis shows that both electrodermal synchrony (β = 2.75, p < 0.001) and motor attunement (β = 4.39, p = 0.003) are significant predictors of mutual romantic interest. With a leave-one-out linear regression classifier, the model correctly classified 71% of the successful dates (‘both interested’, in yellow) and unsuccessful dates (‘no one interested’, in red). Correctly predicted dates are marked with a black circle. (C) A linear regression showing the association between bio-behavioral coupling (i.e., electrodermal synchrony and motor attunement, x-axis) to ratings of mutual romantic interest (y-axis) (Pearson’s r = 0.56; p < 0.001, BF₁₀ = 220.96). The dashed line depicts the threshold between successful and unsuccessful dates that enables optimal prediction of the date outcome, calculated with Receiver Operating Characteristic (ROC) curve (see “Methods”).

Figure 4

Women are more sexually attracted to synchronous men. We computed the correlation between participants' individual synchrony scores and their level of sexual attractiveness. The x-axis depicts mean electrodermal synchrony scores across men’s dates, while the y-axis depicts women’s sexual desire. Higher synchrony scores in men are associated with increased women’s sexual desire (Spearman r = 0.68, 95% confidence interval = [0.24, 0.93], p < 0.004, Bonferroni alpha = 0.025, BF₁₀ = 7.55). Horizontal error bars depict the standard error of men’s mean synchrony, while vertical error bars depict the standard error of women’s mean sexual desire (see “Methods” section). For visualization: colors represent low synchronizers in purple (the lowest 25% synchrony scores of men), medium synchronizers in indigo (25–75% synchrony scores of men), and super synchronizers in green (top 25% synchrony scores of men).

Figure 5

Cross-correlation values at different time-lags indicate dominance in leadership. In this graphical scheme, when summing across all time-lags in a cross-correlation analysis in a specific window, either the woman leads the dyadic interaction, or the man. When most of the mass of the cross-correlation function is on the negative side (left plot), the woman is the dominant leader in this time window. When most of the mass is on the positive side (right plot), the man is the dominant leader in the time window. We computed the dominance in leadership per each sliding window to assess the turn-taking in interactive leadership, for participants’ motion and physiology.