Purpose: People engage in green consumption for many reasons, both conscious and unconscious. This paper aims to draw on evolutionary psychology to propose that hard-wired mating strategies encourage both men and women to increase their green consumption in the presence of members of the opposite sex. Design/methodology/approach: Observations were conducted on 324 students who purchased cold drinks in disposable cups from a college café. The students were offered the choice of adding 20 cents to their purchase for a bio-degradable cup. Findings: Overall, 160 students agreed to pay the premium for a bio-degradable cup, with green purchases 46 per cent higher among women and 61 per cent higher among men when facing a cashier of the opposite sex. Originality/value: The findings suggest that the activation of mating cues prompts students to display prosocial, altruistic behavior and/or to engage in conspicuous consumption (i.e. agreeing to pay more for the sustainable product). The study was conducted in the field using naïve participants and demonstrates the application of evolutionary psychology to green marketing. It also adds to what is a surprisingly small literature on the effect of employee-customer gender mismatch.