The Texas Family Code provides that the best interest of the child shall always be the primary consideration of the court in determining issues of possession and conservatorship. TEX. FAM. CODE ANN. 153.002 (Vernon 1996). There is a strong presumption that the best interest of a child is served if a natural parent is awarded custody. Brook v. Brook, 881 S.W.2d 297, 299 (Tex. 1994). This presumption is codified in section 153.131 of the Texas Family Code. Section 153.131(a) provides a parent shall be appointed as managing conservator unless the court finds that appointment of the parent would not be in the best interest of the child because it would significantly impair the child's physical health or emotional development. See TEX. FAM. CODE ANN. 153.131(a) (Vernon Supp. 2000); Lewelling v. Lewelling, 796 S.W.2d 164, 166 (Tex. 1990) (discussing section 14.01(b) of the family code, the predecessor to section 153.151). To rebut the presumption, a nonparent must affirmatively prove by a preponderance of the evidence that appointment of the parent as managing conservator would significantly impair the child, either physically or emotionally. In the Interest of Hidalgo, 938 S.W.2d 492, 497 (Tex. App.-Texarkana 1996, no writ). The parental presumption imposes a heavy burden on the nonparent. Lewelling, 796 S.W.2d at 167. The nonparent must offer evidence of specific actions or omissions of the parent that demonstrate an award of custody to the parent would result in physical or emotional harm to the child. Id. The link between the parent's conduct and harm to the child may not be based on evidence which raises mere surmise or speculation of possible harm. In the interest of M.W., 959 S.W.2d 661, 665-66 (Tex. App.-Tyler 1997, no writ). When determining the fitness of a parent, the material time to consider is the present. May v. May, 829 S.W.2d 373, 377 (Tex. App.-Corpus Christi 1992, writ denied). While evidence of past misconduct may be relevant to a parent's fitness, it may not, by itself, be sufficient to show present unfitness. Id. Further, evidence that the nonparent would be a better custodian of the child is not sufficient to rebut the parental presumption. Lewelling, 796 S.W.2d at 167.