"instinct." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica, 2011. Web. 18 February 2011. [1]Arkiveret 3. maj 2015 hos Wayback Machine.
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"instinct." Encyclopædia Britannica. Encyclopædia Britannica Online. Encyclopædia Britannica, 2011. Web. 18 February 2011. [1]Arkiveret 3. maj 2015 hos Wayback Machine.