The unusual suspects: A systematic search for the molecular and cellular correlates of human aggression

Decades of research have uncovered several molecules and cell types (i.e., biomolecules) associated with aggression, violence, and hostility (AVH). In this systematic review, we aimed to identify which of these biomolecules have been predominantly studied in relation to AVH in human adults, and to obtain a general sense of the direction of the effects reported for each identified biomolecule. Eighty-one studies (out of 2914 initial abstracts) were included in the review, totaling 198 effects and 29,565 participants. Hormones, particularly testosterone and cortisol, were by far the most studied biomolecules (57.58 %), followed by cytokines (14.14 %), proteins (9.09 %), and neurotransmitters (4.55 %). Out of all extracted statistical effects, 15.1 % reported a negative association, 45.5 % reported no association, and 39.4 % reported a positive association between AVH and the biomolecules, although this pattern varied substantially for individual biomolecules. We also identified some research on biomolecules pertaining to the immune system, which could turn out to play crucial roles in advancing our understanding of AVH. These quantitative insights into the current state of biochemical research on AVH in human adults provide a basis for shaping a broader and more integrative research agenda for studying AVH.