Reckless behaviour is <i>not associated</i> with lack of fear, as reckless behaviour is not uncommon among normal human adults with fear intact (also the aforementioned drug does more than inhibiting fear).<p>If one is going about life &quot;without thinking or caring about the consequences of an action&quot;, that is more a sign of being unintelligent (quite often a case of native intelligence being hampered by such strong emotions as ideological feelings) than merely being fearless.<p>Animals (especially early primate ancestors of humans) do not have fully developed intelligence, so it not unsurprising that they unlike us require primitive emotions such as fear to survive as a species.