Serotonin, social status and aggression appear to be linked in many animal species, including humans.
http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6VS3-45479ST-FP&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=21284a78f0a799ed0e5dc9222c37b89d

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