Narcissism has shifted mate selection from complementary opposites to similarity: modern long-term couples overwhelmingly mirror each other across beliefs, behaviors and traits, seeking validation and narcissistic supply rather than complementary strengths. Large-scale studies (including a meta-analysis and UK Biobank data) found ~97% similarity across hundreds of traits—political, religious, educational, behavioral and personality factors—suggesting people pair with like-minded partners for long-term commitment. This trend undermines the evolutionary benefits of diversity, reduces relationships to autoerotic mirroring, and reflects broader increases in individualism, attention-seeking and avoidance of challenge. Opposites No Longer Attract: How Narcissism Corrupts Mate Selection