We granted this appeal from the denial of a petition for habeas corpus in order to consider the impact of the 1988 amendment to OCGA § 17-7-131 on the validity of Son Fleming’s death sentence.1 For the reasons that follow, we conclude that the new statute reflects a societal consensus against the execution of mentally retarded defendants. Executing a mentally retarded defendant would therefore constitute cruel and unusual punishment prohibited by the Georgia Constitution. We remand this case for a determination of whether Fleming has presented sufficient evidence to warrant a jury trial on the issue of mental retardation.
In 1977, Son Fleming and two other defendants were convicted of murdering a police officer. Fleming was sentenced to death. In the action below, he alleged that newly discovered evidence demonstrates that he is mentally retarded.2 This evidence indicated that in 1966 Fleming suffered gunshot wounds and applied for Social Security disability benefits. He was declared totally disabled and awarded benefits. Documents from his Social Security file indicate that the basis for the disability determination was not the gunshot wounds, but rather the evidence that he was mentally retarded, organically brain damaged and psychotic. Because he was unable to handle his financial affairs, his wife was made the payee for his benefits. He continued to receive benefits until he was incarcerated for murder.
In 1988 the legislature passed an amendment to OCGA § 17-7-*688131. Under the amended statute, the jury in a capital trial must decide at the time of the trial on guilt or innocence of the defendant whether the .defendant is “guilty but mentally retarded.” OCGA § 17-7-131 (c) (3). If the defendant is found to be guilty but mentally retarded, “the death penalty shall not be imposed and the court shall sentence the defendant to imprisonment for life.” OCGA § 17-7-131 (j). The amendment is to be effective “in the trial of any case in which the death penalty is sought which commences on or after July 1, 1988.” Id. On its face the statute does not apply to Son Fleming, who was tried more than ten years ago.
1. Fleming contends that, in spite of the language in the statute giving it prospective application, constitutional guarantees of due process and equal protection require that the statute be given retroactive effect. He argues that the distinction between those cases that have been tried and those that have not is arbitrary and capricious: it discriminates without rational basis between Fleming and other equally culpable mentally retarded defendants in violation of due process and equal protection. We disagree. '
According to Fleming’s argument, the legislature could never enact a statute that would ameliorate or repeal a prior sentencing provision unless the new law were given retroactive effect. The Constitution contains no such requirement. See United States v. Sorondo, 845 F2d 945 (11th Cir. 1988). Where a criminal statute does not discriminate on racial grounds or against a suspect class, equal protection and due process concerns are satisfied if the statute bears a “reasonable relation to a proper legislative purpose” and is “neither arbitrary nor discriminatory.” United States v. Holmes. 838 F2d 1175, 1177 (11th Cir. 1988) (quoting Nebbia v. New York, 291 U. S. 502, 537 (54 SC 505, 78 LE 940) (1934)).
The amendment to OCGA § 17-7-131 does not improperly discriminate among classes of defendants. It distinguishes between cases that have been tried and those that have not. This classification is neither arbitrary nor discriminatory. The legislature had to choose some effective date. And, although the legislature certainly could have selected another effective date, such as the date of the offense or the date of sentencing, our responsibility is not to determine whether the legislature selected the best of possible alternatives, but rather to decide whether the legislative decision is a rational one. Holmes, supra, at 1178. We conclude that it is. The classification bears a reasonable relationship to a legitimate legislative concern for the finality of criminal convictions. Thus, we conclude that Fleming’s equal protection and due process claims are without merit.
2. Fleming next argues that the passage of the amended statute renders his death sentence disproportionate under OCGA § 17-10-35 (c) (3). He argues that no case will again come before this Court for *689direct review of a death sentence imposed on a mentally retarded person. He says that his sentence is therefore disproportionate to that imposed against similar defendants in similar cases in Georgia.
OCGA § 17-10-35 (c) (3) does not require this Court to undertake a de novo proportionality review whenever new information about the defendant is discovered or whenever a new legislative enactment changes the penological landscape. We do not reach the issue of whether there may be some circumstances under which a second proportionality review would be appropriate. It clearly would not be proper, however, to undertake a proportionality review of Fleming’s case at this time. This is true because there has been no judicial determination that Fleming is mentally retarded. If he is not, there is no reason to conduct a second proportionality review. If he is retarded, our holding in Div. 3, below, is sufficient to correct any proportionality problem.
3. Fleming next argues that his sentence violates the guarantee against cruel and unusual punishment found in the Eighth Amendment to the U. S. Constitution and in Art. I, Sec. I, Par. XVII of the Constitution of Georgia of 1983.
Both the Georgia and the federal constitutions categorically prohibit inflicting cruel and unusual punishments. A punishment is cruel and unusual if it “ ‘(1) makes no measurable contribution to accepted goals of punishment and hence is nothing more than the purposeless and needless imposition of pain and suffering; or (2) is grossly out of proportion to the severity of the crime.’ ” Wyatt v. State, 259 Ga. 208, 209 (378 SE2d 690) (1989)(quoting Coker v. Georgia, 433 U. S. 584 (97 SC 2861, 53 LE2d 982) (1977)). Further, the constitutional standard reflects society’s view of what punishments are cruel, and prohibits those that “disgraced the civilizations of former ages, . . . mak[ing] one shudder with horror to read them.” Dutton v. Smart, 222 Ga. 35 (148 SE2d 396)(1966); Whitten v. State, 47 Ga. 297 (1872). In other words, whether a particular punishment is cruel and unusual is not a static concept, but instead changes in recognition of the “ ‘evolving standards of decency that mark the progress of a maturing society.’ ” Penry v. Lynaugh, 492 U. S. _, at _ (109 SC 2934, at 2953, 106 LE2d 256) (1989) (quoting Trop v. Dulles, 356 U. S. 86, 101 (78 SC 590, 2 LE2d 630) (1958) (plurality opinion)).
To ascertain how society currently views a particular punishment, this court, like the U. S. Supreme Court, considers objective evidence. Such evidence may include information gathered from polls or studies, data concerning the actions of sentencing juries, etc. See, id., 109 SC at 2953. However, legislative enactments constitute the clearest and most objective evidence of how contemporary society views a particular punishment. Id. Those enactments may change from time to time and as they do those changes amount to evidence *690of the shifting or evolution of the societal consensus.
In Penry v. Lynaugh, supra, the United States Supreme Court decided that the execution of mentally retarded people is not “at present” prohibited by the Eighth Amendment to the U.S. Constitution. Penry, 109 SC at 2955. This decision was based in great part on the absence of any “national consensus” against executing the mentally retarded. In contrast, the objective evidence indicates that a consensus against execution of the mentally retarded does exist among Georgians.
Recently, the Georgia Senate passed a resolution urging the Board of Pardons and Paroles to give special consideration to commuting the sentences of mentally retarded offenders that had been sentenced to death, citing the poll and stating, “. . . executing a retarded offender destroys public confidence in the criminal justice system.” Senate Resolution 388. Further, this state’s elected representatives, voicing the will of the electorate, have spoken on the subject and have declared that if a defendant is found to be mentally retarded, “the death penalty shall not be imposed and the court shall sentence the defendant to imprisonment for life.” OCGA § 17-7-131 (j). The legislative enactment reflects a decision by the people of Georgia that the execution of mentally retarded offenders makes no measurable contribution to acceptable goals of punishment.3 Thus, although there may be no “national consensus” against executing the mentally retarded, this state’s consensus is clear.
The “standard of decency” that is relevant to the interpretation of the prohibition against cruel and unusual punishment found in the Georgia Constitution is the standard of the people of Georgia, not the national standard. Federal constitutional standards represent the minimum, not the maximum, protection that this state must afford its citizens. Harris v. Duncan, 208 Ga. 561 (67 SE2d 692) (1951). Thus, although the rest of the nation might not agree, under the Georgia Constitution, the execution of the mentally retarded constitutes cruel and unusual punishment.
This holding does not mean that the Georgia Constitution prohibits execution of retarded persons per se. We merely hold that it prohibits cruel and unusual punishment. Our conclusion that the societal consensus in Georgia opposes execution of retarded persons does not mean that such consensus may not change thus altering what comes within the meaning of cruel and unusual punishment.
*6914. Having so decided, we must now apply the Georgia constitutional standard to the case at hand. As noted above, there has been no judicial determination that Fleming is mentally retarded. We must therefore decide by what procedure that determination will be made.
When a defendant who was tried before the effective date of the OCGA § 17-7-131 (j) alleges in a petition for habeas corpus that he or she is mentally retarded, the habeas corpus court must first determine whether the petitioner has presented sufficient credible evidence, which must include at least one expert diagnosis of mental retardation, to create a genuine issue regarding petitioner’s retardation.4 The court, in its discretion, may hold a hearing on the issue, or may make the determination based on affidavits, depositions, documents, etc. If, after examining the evidence, the habeas corpus court finds that there is a genuine issue, a writ shall be granted for the limited purpose of conducting a trial on the issue of retardation only. This trial shall be held in the court in which the original trial was conducted. Petitioner shall be entitled to a full evidentiary hearing on the issue of retardation. The determination shall be made by a jury using the definition of retardation enunciated in the statute. See OCGA § 17-7-131 (a) (3). The petitioner will bear the burden of proving retardation by a preponderance of the evidence. The jury shall not be bound by the opinion testimony of expert witnesses or by test results, but may weigh and consider all evidence bearing on the issue of mental retardation. If the jury returns a verdict that the petitioner is mentally retarded, the petitioner’s sentence shall be vacated and he shall be sentenced to life imprisonment.
In summary, we conclude that the execution of mentally retarded offenders violates the Georgia constitutional guarantee against cruel and unusual punishment. We reverse the judgment of the court below to the extent that it held otherwise. In all other respects the judgment below is affirmed.
Judgment affirmed in part, reversed in part and remanded.
All the Justices concur, except Marshall, C. J., and Smith, J., who dissent as to Divisions 3 and 4 and the reversal and remand.Fleming attempts to raise several other issues in this petition. We limit our review to an examination of the impact of the newly amended statute on the validity of Fleming’s death sentence because this is the only issue that has not been previously decided and could not reasonably have been raised in Fleming’s previous petitions for habeas corpus. See OCGA § 9-14-51; Smith v. Zant, 250 Ga. 645 (301 SE2d 32), cert. denied 464 U. S. 807 (1983).
The documents declaring Fleming to be mentally retarded, etc., were not discovered by his attorneys until recently. They had been in his Social Security file labeled as follows:
This communication should be made part of the patient’s file. Under no circumstances should the report be read or given to the patient.
Because opinion polls may produce widely varying results, we do not rely on polls to establish a societal consensus. We note, however, that a Georgia poll found that while 75% of Georgians favor capital punishment, 66% oppose the death penalty for the retarded, 17% favor the death penalty for the retarded, and 16% feel that their answer would depend on how retarded the person is. See Penry, 109 SC at 2955.
The procedure is remedial in nature and will not apply to defendants tried after the effective date of the statute.