If an award of joint custody or of sole custody to either parent would result in substantial harm to the child, the court shall award custody to another person with whom the child has been living in a wholesome and stable environment, or otherwise to any other person able to provide an adequate and stable environment.

Acts 1986, No. 966, §1; Acts 1989, No. 546, §1; Acts 1993, No. 261, §1, eff. Jan. 1, 1994.