Behavioral psychologists argue that mutism is a child's adaptive response rather than pathological. 

A child who has an innately shy and hesitating temperament may be more prone to developing an anxiety disorder — this follows the route of how one’s biological basis influence oneself.  However, the relational, environmental, and situational experiences of that child will also influence likeliness and course of development of said child’s anxiety disorder. 

(Reference: Anstendig)

Selective Mutism may be ADAPTIVE rather than PATHOLOGICAL

Children with selective mutism appear frozen and inactive due to behavioral inhibition. 

In social situations which may be unfamiliar or lead to increased emotional arousal , the individual’s sympathetic nervous system may take inhibitory control over behavior and ability to speak. This may lead to that individual exhibiting characteristics of Selective Mutism. 

(Reference: Wong)

Observed Behavior of Children with SM in social sitations

To conclude, the paralleling biological and social similarities of the characteristics of Selective Mutism and anxiety disorders may indicate a strong relationship between their etiologies. 

Those who develop SM and those who develop an anxiety disorder(s) demonstrate similar behavioral characteristics in similar environmental conditions/situations. 

Extrapolations from observed Strong Relationship between SM and Anxiety Disorders (via biological and social similarities)

In this theory, Selective Mutism is portrayed as an unconscious, language-based form of behavioral inhibition or as a defense mechanism. This perspective is significant because it frames selective mutism as a symptom of anxiety, rather than consciously manipulative behavior. (Reference: Wong)

New York University

There are many theories which attempt to explain the etiology of Selective Mutism. This concept node and its child relation nodes will explore theories for SM through these following lens/frameworks: 

1) Psychodynamic Theory
2) Behavioral Theory 
3) Social phobia and Social Anxiety 
4) Family Systems Theory 
5) Dissociative Identity Theory 
6) Post-traumatic Stress Theory
7) Developmental Psychopathology Theory 

A table from 'Wong, Priscilla. "Selective Mutism: A Review and Integration of Etiology, Comorbities, and Treatment." paper has provided a table that may be helpful (see image; cred: Wong, Theories on the Etiology of Selective Mutism). 

Theories on the Etiology and Emergence of Selective Mutism 

Anstendig, Karin D. “Is Selective Mutism an Anxiety Disorder? Rethinking Its DSM-IV Classification.” Journal of Anxiety Disorders, vol. 13, no. 4, July 1999, pp. 417–434, doi.org/10.1016/S0887-6185(99)00012-2, https://doi.org/10.1016/s0887-6185(99)00012-2. Accessed 6 June 2023.

The concept node "Behavioral Theory of Selective Mutism" included information from Anstendig. The information is denoted by the intext citations. 

Anstendig, Karin D. “Is Selective Mutism an Anxiety Disorder? Rethinking Its DSM-IV Classification.” Journal of Anxiety Disorders, vol. 13, no. 4, July 1999, pp. 417–434, doi.org/10.1016/S0887-6185(99)00012-2, https://doi.org/10.1016/s0887-6185(99)00012-2. Accessed 6 June 2023.

Wong, Priscilla. “Selective Mutism: A Review of Etiology, Comorbidities, and Treatment.” Psychiatry (Edgmont (Pa. : Township)), vol. 7, no. 3, Mar. 2010, pp. 23–31, www.ncbi.nlm.nih.gov/pmc/articles/PMC2861522/. Accessed 2 June 2023.

The "Definition and Diagnostic Criteria of Selective Mutism" relation node included paraphrase information regarding the criteria and definition of Selective Mutism. 

Wong, Priscilla. “Selective Mutism: A Review of Etiology, Comorbidities, and Treatment.” 

The Psychodynamic theory emphasizes the concept of unresolved conflict. In the case of Selective Mutism, this theory supposes that the individual has 
1) an oral and/or anal fixation and may be maintaining a family secret or some kind of family-related discomfort (such as abuse, divorce, death, a life threatening experiences, frequent house moving), and/or
2) have displaced anger towards a family member (such as a parent), or is involved in a family relationship characterized by dependence, ambivalence, and an excessive need to control -- the neurotic relationship between the parent and the child with SM may carry over to the child's interactions with others, and/or
3) is regressing to a nonverbal stage in their development. 

The Selective Mutism is hence viewed as a coping mechanism to deal with that anger and anxiety from this repression, representing the behavior as a way to punish the individual's parents and other family members. 

This theory has very little empirical data to support this model, and hence is a theory that is currently losing validity. 

Psychodynamic Theory of Selective Mutism

Behavioral Theory of Selective Mutism 

This theory of Selective Mutism, proposed by Black and Uhde, views the phenomenon of Selective Mutism through the lens of social phobia. 

Their proposed theory is as follows: Selective Mutism is a variant of social phobia, characterized by excessive social anxiety; under this model, Selective Mutism is seen as the severe end of the spectrum for childhood speech inhibition and social anxiety.  

Black & Uhde's argument is based upon their collected data which shows higher instances of Selective Mutism in families with a family history of Social Anxiety. 

(To learn more about Black & Uhde's theory, or to view the study containing their data, please move to the relation node titled 'Black & Uhde's Evidence Supporting Social Theory & Social Anxiety of Selective Mutism')

(While some researchers support this theory, there has been another study which challenges the notion that Selective Mutism is a variant and can be explained by social anxiety and social phobia. To learn more about this, please move to the relation node titled 'Evidence Challenging Black & Uhde's Social Theory & Social Anxiety of Selective Mutism') 

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