Human beings are an incredibly social species and along with eusocial insects engage in the largest cooperative living groups in the planet's history. Twin and family studies suggest that uniquely human characteristics such as empathy, altruism, sense of equity, love, trust, music, economic behavior, and even politics are partially hardwired. The leap from twin studies to identifying specific genes engaging the social brain has occurred in the past decade, aided by deep insights accumulated about social behavior in lower mammals. Remarkably, genes such as the arginine vasopressin receptor and the oxytocin receptor contribute to social behavior in a broad range of species from voles to man. Other polymorphic genes constituting the "usual suspects"--i.e., those encoding for dopamine reward pathways, serotonergic emotional regulation, or sex hormones--further enable elaborate social behaviors.
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