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Under the common law, there was a presumption that a child born to a marriage was a child of the husband. This presumption could only be overcome by a showing of sterility, impotency, or that the husband had no access to his wife at the time of conception.
In recent years, many states have adopted more relaxed rules, permitting the presumption to be rebutted under other circumstances. In California, the presumption can be challenged by a presumptive father or child for any reason as long as it is raised within two years of the child's birth. In the same period, the mother can challenge it only if the biological father has filled a written declaration acknowledging paternity. In either case, blood testing is used to resolve the paternity dispute. Once the two year period has elapsed, however, the presumption is conclusive, unless the common law grounds can be established.
The "conclusive presumption," found in (California Code] section 7540, states: "Except as provided in Section 7541 [providing for the use of blood tests], the child of a wife cohabiting with her husband, who is not impotent or sterile, is conclusively presumed to be a child of the marriage." Under section 7541, requests for blood tests to rebut the conclusive presumption of paternity must be made within two years of the child's birth and can only be made by the husband, the child, the mother or a "presumed father" as defined in sections 7611 and 7612.
Read full Califronia court decision here:
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