delivered the opinion of the Court.
This appeal raises the question whether the Uniform Parentage Act (UPA), section 19-6-101 et seq., C.R.S. 1973 (1978 Repl. Vol. 8), by not expressly granting a claiming natural father the right to bring an action for a determination of his paternity of a child born during the marriage of the natural mother to another, violates equal protection of the laws under the federal and state constitutions and the equal rights amendment to the Colorado Constitution.1 We hold that the claiming natural father is constitutionally entitled to bring this action and reverse the summary judgment denying him statutory capacity or standing to seek a determination of his paternity.
Plaintiff-appellant R.McG. commenced an action in 1978 in the Denver Juvenile Court against defendants-appellees, J.W. and W.W., on behalf of himself and the minor child, C.W.,2 to establish his paternity of C.W. The complaint alleged that R.McG. is the natural father of C.W., who was born in 1976 to R.McG. and J.W., the natural mother, that at the time of the conception and birth of C.W., J.W. was married to W.W.; that R.McG. is the only man who had sexual intercourse with J.W. at any possible time of conception; that J.W. admitted that R.McG. is the natural father of C.W.; and that blood tests have been unable to exclude R.McG. as the natural father. J.W. and W.W. in their answer denied the alleged paternity of R.McG. and moved for summary judgment on the ground that R.McG. lacked statutory capacity or standing under the UPA to bring the action.3
*348Prior to hearing the motion for summary judgment, the court granted R.McG.’s motion for serological testing of R.McG. and W.W.4 The results of these tests indicated that R.McG. could not be excluded as the father of C.W., and that the probability of R.McG.’s paternity was 98.89 percent.5 The testing laboratory was unable to isolate a sufficient number of lymphocytes from the blood sample of W.W. and requested another blood sample from him, but he refused to comply with the request. In opposition to summary judgment R.McG. filed an affidavit stating that he was the natural father of C.W., and that he and J.W. had intercourse regularly at any possible time of conception; that he and J.W. had planned to divorce their respective spouses and marry each other; that J.W. acknowledged in a sworn codicile to her will and in correspondence that he was the natural father of C.W.;6 and that C.W. had visited almost daily with him until she was 11/2 years old and had developed a close relationship with R.McG.’s three other children.
R.McG. opposed the motion for summary judgment on the grounds that the application of the UPA in a manner that denied him statutory capacity or standing to bring an action for a determination of his paternity of C.W. would violate his right to equal protection of the laws under the federal constitution, U.S. Const. amend. XIV, and under the state constitution, Colo. Const. Art. II, Sec. 25, and also would violate the equal *349rights amendment to the Colorado Constitution, Colo. Const. Art. II, Sec. 29.
The juvenile court rejected the constitutional claims of R.McG. and granted the motion for summary judgment on behalf of J.W. and W.W., holding that R.McG. lacked capacity under the UPA to bring this action. We determine that under the circumstances of this case the failure of the UPA to grant R.McG. the right to bring an action for a determination of his paternity of C.W. violates equal protection of the laws under the federal and state constitution and the equal rights amendment to the Colorado Constitution.
I.
Before the enactment of the UPA, a putative father had no statutory right to commence an action to-establish his paternity. The then existing statute authorized an action by the child’s mother or guardian or the county department of social services, as the exclusive means of establishing paternity. Section 19-6-101, C.R.S. 1973; see People in the Interest of L.B., 19 Colo. App. 101, 482 P.2d 1010 (1976), aff’d, 179 Colo. 11, 498 P.2d 1157 (1972); appeal dismissed mem., 410 U.S. 976, 93 S.Ct. 1497, 36 L.Ed.2d 173 (1973). The UPA was enacted in 1977 and furnishes the statutory framework for the constitutional issues raised on this appeal.
One basic purpose of the UPA is the establishment of the parent-child relationship, section 19-6-104, C.R.S. 1973 (1978 Repl. Vol. 8), and another is the protection of that relationship, section 19-6-103, C.R.S. 1973 (1978 Repl. Vol. 8). Section 19-6-102 defines that relationship as the legal relationship existing between a child and a natural parent, and expressly includes the father-child relationship. The parent-child relationship extends equally to every child and to every parent, regardless of the marital status of the parents. Section 19-6-103, C.R.S. 1973. Section 19-6-104 authorizes the establishment of the paternal relationship between a child and its natural father and recognizes the right of putative fathers to bring an action to establish paternity under the applicable provisions of the UPA.
The UPA, however, makes no provision for a male claiming to be the natural father of a child to bring an action to establish his paternity under the circumstances present here. Section 19-6-107 of the UPA, insofar as pertinent to this case, provides:
“(1) A child, his natural mother, or a man presumed to be his father under section 19-6-105(1)(a) . .. may bring an action:
“(a) At any time for the purpose of declaring the existence of the father and child relationship presumed under section 19-6-105(1)(a), ...; or
“(b) For the purpose of declaring the nonexistence of the father and child relationship presumed under section 19-6-105(1)(a) . . . only if the action is brought within a reasonable time after obtaining knowledge of *350relevant facts, but in no event later than five years after the child’s birth. After the presumption has been rebutted, paternity of the child by another man may be determined in the same action, if he has been made a party.”
Under section 19-6-105(1)(a) a man is presumed to be the natural father of a child if he and the child’s natural mother are or have been married to each other and the child is born during the marriage. Section 19-6-105(2) provides that this presumption and other statutory presumptions of paternity may be rebutted by clear and convincing evidence, and a presumption is rebutted by a court decree establishing paternity in another man.
The juvenile court, relying on the interpretative rule of expressio unius est exclusio alterius, reasoned that since section 19-6-107(1) expressly provided that certain categories of persons may commence an action in paternity, including a presumed father under section 19-6-105(1)(a), the legislature thereby intended to prohibit anyone outside the specifically designated categories, such as a claiming natural father not married to the natural mother, from commencing a paternity action in connection with a child born to the natural mother during her marriage to another.
II.
R.McG. argues the juvenile court’s construction denying him statutory capacity or standing to establish that he is the natural father of C.W. violates equal protection of the laws under the Fourteenth Amendment to the United States Constitution and Article II, Section 25, of the Colorado Constitution,7 and, in addition, violates the equal rights amendment to the Colorado Constitution, Colo. Const. Art. II, Sec. 29. We agree with R.McG.’s argument. The UPA, as construed by the juvenile court, denies R.McG. equal protection by impermissibly discriminating between natural mothers and claiming natural fathers, and such statutory classification is not substantially related to an important governmental interest. A fortiori, we also determine that the denial of statutory capacity or standing to R.McG. is based on a gender classification that violates the equal rights amendment to the Colorado Constitution, which prohibits the denial or abridgement of equality of rights on the- basis of sex. Colo. Const. Art. II, Sec. 29.
“Gender-based distinctions ‘must serve important governmental objectives and must be substantially related to achievement of these objectives’ in order to withstand judicial scrutiny under the Equal Protection Clause.” Caban v. Mohammed, 441 U.S. 380, 99 S.Ct. 1760, 60 L.Ed.2d *351297 (1979); see Craig v. Boren, 429 U.S. 190, 97 S.Ct. 451, 50 L.Ed.2d 397 (1976); Reed v. Reed, 404 U.S. 71, 92 S.Ct. 251, 30 L.Ed.2d 225 (1971). No one questions the interest of the state in preserving the integrity of family units already in existence and fostering child rearing in harmonious family settings. See section 19-1-102, C.R.S. 1973 (1978 Repl. Vol. 8). These interests are important and within the power of the state to implement. The controversy here is not with governmental ends but rather with the choice of means to achieve those ends:
“ . . . [T]he unquestioned right of the State to further these desirable ends by legislation is not in itself sufficient to justify the gender-based distinction .... Rather, under the relevant cases applying the Equal Protection Clause it must be shown that the distinction is structured reasonably to further these ends . .. [Sjuch a statutory ‘classification must be reasonable, not arbitrary, and must rest upon some ground of difference having a fair and substantial relation to the object of the legislation, so that all persons similarly circumstanced shall be treated alike.’” Caban v. Mohammed, 441 U.S. at 391, 99 S.Ct. at 1767, 60 L.Ed.2d at 306.
We, therefore, must analyze the pertinent provisions of the UPA under this intermediate standard of judicial scrutiny applicable to gender-based classifications.
Section 19-6-107(1) (a) grants statutory standing to a child, her natural mother and a presumed father to establish the father-child relationship. Were the restrictive standing provisions to end there, it is at least arguable that the statutory classification, although under-inclusive in its omission of a claiming natural father, might satisfy substantially the governmental interest by insulating a continuing family relationship from the potentially disruptive effects of a judicial determination of paternity in another. However, it is unnecessary for us to resolve that question because constitutional infirmities are evident in section 19-6-107(1)(b), which permits the natural mother to undo the state’s interest in preserving family stability by seeking both a declaration of non-paternity in the presumed father and a declaration of paternity in the non-family natural father. Section 19-6-107 (1) (b) does not condition the natural mother’s right to seek a declaration of paternity in a non-spousal father upon the failure of her existing marriage to the presumed father, or the presumed father’s desertion or non-support; the statute requires only that the natural mother’s action be commenced within five years after the child’s birth.
This statutory scheme creates more than a difference in treatment of natural mothers and fathers. It establishes contrary treatment. Although a statutory classification under the intermediate level of scrutiny need not be tailored precisely to the interest sought to be achieved, it must at least mesh substantially with the purpose that the statutory classification is designed to accommodate. The statutory classification and corresponding difference in treatment created by section 19-6-107(1) fail to pass *352constitutional muster under equal protection doctrine. Section 19-6-107(1) exemplifies a gender-based classification predicated on an overbroad generalization that a mother has a legitimate interest in establishing a determination of paternity in a non-spousal father, while such father has no interest in establishing a determination of paternity in himself.8 See, e.g., Caban v. Mohammed, supra; Stanley v. Illinois, 405 U.S. 645, 92 S.Ct. 1208, 31 L.Ed.2d 551 (1972); cf. Quilloin v. Walcott, 434 U.S. 246, 98 S.Ct. 549, 54 L.Ed.2d 511 (1978) (unwed father, who never sought custody of eleven-year-old minor child, was granted full hearing on his interest in child, but his interest cannot prevent child’s adoption by natural mother’s husband). Under the circumstances present here, the claiming natural father, no less than the mother, must have the right to establish the significant relationship of paternity as to the child he has allegedly sired.
The gender-based inequality of section 19-6-107(1) is compounded by the statutory presumption of section 19-6-105(1)(a). Although the UPA makes all presumptions rebuttable by clear and convincing evidence, section 19-6-105(2), C.R.S. 1973 (1978 Repl. Vol. 8), only presumed fathers would have the necessary standing to rebut the presumption under the restrictive categories of section 19-6-107(1). R.McG., in spite of a threshold showing of 98.89 percent probability of his paternity of C.W., is effectively precluded not only from establishing his own claim of paternity but also from rebutting the statutory presumption of paternity in W.W.
Under the circumstances of this case, the rebuttable presumption of paternity in W.W., the husband of the natural mother, is converted into a conclusive presumption against the claiming natural father. Thus, the statutory scheme denies the claiming natural father, R.McG., judicial access to establish a constitutionally significant relationship, Stanley v. Illinois, supra, while simultaneously granting the natural mother practically unencumbered judicial access to establish that same relationship if she so desires.
Procedure by presumption is permissible, but when that procedure “forecloses the determinative issues . . . [and] explicitly disdains present realities in deference to past formalities, it needlessly risks running roughshod over the important interests of both parent and child.” Stanley v. Illinois, supra. We hold that so long as the UPA grants a natural mother judicial access for a period of years to seek a determination of paternity against the natural father of a child born during the marriage of the natural mother to another, equal protection of the laws under the *353United States and Colorado Constitutions mandates that a claiming natural father be granted judicial access and Standing to establish his paternity of that child during that same period of time.
Because we have found that section 19-6-107(1) falls short of satisfying the intermediate level of judicial scrutiny applicable to gender-based classification under equal protection doctrine, it necessarily follows that section 19-6-107(1) fails to satisfy the stricter judicial scrutiny standard applicable to the equal rights amendment of the Colorado Constitution, Colo. Const. Art. II, Sec. 29. See People v. Green, 183 Colo. 25, 514 P.2d 769 (1973).
III.
The natural mother and her husband, J.W. and W.W., citing Griswold v. Connecticut, 381 U.S. 479, 85 S.Ct. 1678, 14 L.Ed.2d 510 (1965), contend that granting R.McG. standing to pursue his claim for a declaration of paternity will violate their constitutional right of privacy emanating from the due process clause of the Fourteenth Amendment. The privacy interest implicated in Griswold was that of reproductive autonomy. See Carey v. Population Services International, 431 U.S. 678, 97 S.Ct. 2010, 52 L.Ed.2d 675 (1977); Eisenstadt v. Baird, 405 U.S. 438, 92 S.Ct. 1029, 31 L.Ed.2d 349 (1972). That privacy interest belongs to the individual and not to the family as a unit, e.g., Planned Parenthood v. Danforth, 428 U.S. 52, 96 S.Ct. 2831, 49 L.Ed.2d 788 (1976), and it is not involved in the posture of this case. Moreover, whatever interests of J.W. and W.W. might be impacted by the continuation of R.McG.’s claim, those interests certainly are no greater than the interest of R.McG. in establishing his paternity of C.W., and the interest of C.W. in determining her biological parentage and the rights incident thereto. See Caban v. Mohammed, supra; Stanley v. Illinois, supra; In re Lisa R., 13 Cal.3d 636, 119 Cal.Rptr. 475, 532 P.2d 123, 119 Cal. Rptr. 475, cert. denied, 421 U.S. 1014 (1975). Therefore, we find the argument of J.W. and W.W. unpersuasive.
IV.
We are not unmindful that the continuation of this paternity proceeding might affect the relationship of J.W. and W.W. However, a prohibition of the proceedings will produce at least equally adverse consequences to the claiming father. Also, we are aware of the potential consequences that these proceedings might create for the minor child. In that regard we note that the juvenile court appointed a guardian ad litem to protect the child’s interests, and the guardian ad litem’s position consistently has been that R.McG. should not be denied standing to establish his claimed parentage of C.W. In fact, after the court granted summary judgment, the guardian ad litem requested the court that it permit the action to continue on behalf of the child so that biological parentage and other rights of the child, such as inheritance and support, might be determined. That request *354was denied. The guardian ad litem’s position reflects a candid admission that the best interests of the child, under the circumstances of this case, are not necessarily coextensive with those of J.W. and W.W., and are extremely difficult to determine.
In summary, we hold that where, as here, the statutory scheme allows a natural mother to seek a judicial declaration of paternity in the natural father in connection with a child born to the natural mother during her marriage to another, the equal protection guarantee of the federal and state constitutions as well as the Colorado equal rights amendment require that a claiming natural father be accorded standing to file and proceed with his claim for a judicial declaration of paternity in himself with respect to a child born to the natural mother during her marriage to another.
The judgment is reversed and the cause is remanded to the juvenile court with directions to vacate the summary judgment and to proceed in a manner consistent with the views expressed herein.
JUSTICE DUBOFSKY specially concurs.
JUSTICE LOHR dissents.
The case was transferred to this court from the court of appeals pursuant to section 13-4-110(1)Ca), C.R.S. 1973.
Section 19-6-110, C.R.S. 1973 (1978 Repl. Vol. 8), provides that the child whose paternity is in dispute shall be made a party to the action, as well as the natural mother, each man presumed to be the father under section 19-6-105, and each man alleged to be the natural father, if subject to the jurisdiction of the court.
The juvenile court appointed a guardian ad litem for the protection of the interests of the minor child, C.W. Section 19-6-110, C.R.S. 1973 (1978 Repl. Vol. 8).
The juvenile court resolved the motion for summary judgment in terms of R.McG.’s statutory capacity to seek a declaration of paternity. The parties in their briefs often posture their arguments in terms of R.McG.’s standing. Although in some cases the distinction between capacity and standing may be important, see Friendly Village v. Silva & Hill Construction Co,, 31 Cal.App.3d 220, 107 Cal. Rptr. 123 (1973), that distinction is not significant to our determination of this case. Standing problems may be analyzed in terms of two inquiries: (a) whether the party alleges that the challenged action has caused him injury in fact; and (b) whether the interest sought to be protected is arguably within the zone of interests encompassed by the statute or constitutional guarantee in question. E.g., Association of Data Processing Service Organizations v. Camp, 397 U.S. 150, 90 S.Ct. 827, 25 L.Ed.2d 184 (1970); Wimberly v. Ettenberg, 194 Colo. 163. 570 P.2d 535 (1977).
Section 19-6-112, C.R.S. 1973 (1978 Repl. Vol. 8), provides for blood grouping tests and their receipt into evidence, as set forth in section 13-25-126, C.R.S. 1973 (1979 Supp.). Under section 13-25-126(1)(c)(iv) the presumption of legitimacy is overcome if the court finds that the conclusions of all the experts, as disclosed by the evidence based upon the tests, show that the husband or wife is not the parent of the child.
The probability of R.McG.’s paternity of C.W. was calculated by comparing (a) the probability that a mating of a random male in the population of the same race as the putative father with a female of the mother’s phenotype would produce an offspring of the child’s phenotype, and (b) the probability that a mating of a male of the putative father’s phenotype with a female of the mother’s phenotype would produce such an offspring.
In the codicil to the will of J.W., she swore that her present husband, W.W., did not have sexual intercourse with her at any time during which C.W. could have been conceived, and W.W. is not and could not be the father of C.W.; J.W. also swore that the only person with whom she had sexual intercourse during the time C.W. could have been conceived was R.McG., and to the best of J.W.’s knowledge R.McG. is the father of C.W. The codicil also contained a request that R.McG. be appointed guardian or custodian parent of C.W. in the event J.W. died while C.W. was an unmarried minor.
Equal protection of the laws is a constitutionally recognized right included within the due process clause of Article II, Section 25 of the Colorado Constitution. See Vanderhoof v. People, 152 Colo. 147, 380 P.2d 903 (1963); Trueblood v. Tinsley, 148 Colo. 503, 366 P.2d 655 (1961); People v. Max, 70 Colo. 100, 198 P. 150 (1921).
Gender as the basis of statutory differential in treatment is also apparent in section 19-6-122, C.R.S. 1973 (1978 Repl. Vol. 8), which provides that any interested party may bring an action to determine the existence or nonexistence of the mother and child relationship. A claiming natural mother, of course, would qualify as an interested party under this section.