The promiscuity gene is a genetic variant of the DRD4 gene. It provides with the instructions to make the dopamine receptor D4. The DRD4 variation is due to a repeat in the gene that controls the structure of the dopamine receptor. These repeat sizes vary between individuals, ranging from 2 to 11 repeats.

The DRD4 seven-repeat version (7R) has reduced function as it cannot bind dopamine as effectively. Individuals with repeat sizes greater than 7 (called +7R) are more likely to be sexually promiscuous and report more than 50% more extra-pair partners, compared to individuals with lower repeat sizes.