According to the study described HERE, sexism comes from the losers - low-status males, afraid of losing face with other males, who end up bullying females.
Surprised? Read through the various "I-can't-get-a-date" threads on this website, and you'll likely see the common theme that males whose lives have been somewhat less than successful are usually the most vocal about what they think is wrong with women.
True, the researchers used an on-line video game environment for their research, but where else are you going to find dateless males?
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The mere fact that science may not yet adequately explain an object, event, or experience does not mean the immediate explanation should automatically default to a conspiratorial, extraterrestrial, paranormal, or supernatural cause.