Although a little brainy for me, this excerpt from a longer article on anxiety explains the importance of the sensory system in deciphering environmental threats (that which provokes evolutionarily beneficial fear and the less beneficial anxiety). When we think about the unbalanced sensory system of the individual with ASD, we begin to understand why anxiety or an “exaggerated fear response” leads to behaviors of aggression, running away, social isolation,refusal to eat certain foods, etc. To be fair, this behavior would be beneficial if the stimuli being processed was in fact a real threat or danger to the individual (being in a room with closed doors could in some contexts be a threat to one’s physical safety- but maybe not when that room is a classroom) . Far too often, we as practitioners/parents are left thinking “What just happened?”, “Why did he do that?”.
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Check this out.

“Organisms develop mechanisms to adapt to their changing environment (Tinbergen 1963; Seligman 1970; Mayr 1974). They use exquisitely designed sensory systems to receive environmental cues and respond appropriately, favoring cues that aid survival and reproduction, while avoiding those that indicate danger (Hollis 1982; Domjan 2005)… Perhaps the most crucial of these functions is the ability to recognize a threat: an increase in temperature, a poisonous fruit, or the scent of a predator. Individuals that fail to detect and avoid threats are likely to experience injury or death; thus, the machinery governing threat response must be precise (Plutchik 1980). Fear and anxiety are complex behaviors that represent responses to environmental threats. These two behaviors differ in that fear is a response to a real or clearly identifiable threat and functions to remove the individual from a harmful situation (Belzung and Philippot 2007). In contrast, anxiety is a contrived or exaggerated fear response (Chaffey et al. 2002) and often proceeds in the absence of a truly threatening stimulus. This important distinction has led most psychologists and evolutionary biologists to regard fear as an appropriate and adaptive response (Barlow and Durand 2011), and anxiety as psychologically unhealthy and often associated with unwarranted physiological stress across multiple organ systems (Kessler et al. 2005).”

Link to the full article: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3505513/