American Journal of Law & Medicine

Reproductive autonomy and evolutionary biology: a regulatory framework for trait-selection technologies.


A line of Supreme Court cases culminating in Planned Parenthood v. Casey(1) establish that personal autonomy in reproductive matters is an important (though not absolute) social and legal value. Casey provides, in part, that the Constitution protects each person's autonomy in the realm of personal liberties vindicating the most basic decisions about "family," "parenthood," and "procreation."(2)

Recent insights from evolutionary biology into the procedures and mechanisms by which humans reproduce, however, require an expanded understanding of what family, parenthood, and procreation are all about. So long as the values articulated in Casey guide the incorporation of scientific observations into the legal analysis of laws directly affecting reproduction, evolutionary biology will profoundly affect the extent to which federal law protects an individual's access to reproductive technologies from government intrusion. Specifically, if the basis articulated in Casey for subjecting abortion laws to heightened judicial scrutiny is applied consistently, then the use of technologies to select specific traits in children should receive the same federal protection that afforded abortion.(3)

A number of provocative and process-oriented reproductive technologies, including fertility enhancement (by, for example, artificial insemination, surrogacy, or cryopreservation of embryos) and fertility control (by, for example, contraception, prevention of implantation, or abortion) have already inspired considerable debate in legal and ethical literature. Yet technology increasingly affords women (together, at times, with men) the power to influence the genetic makeup of children, and this presents novel questions with far-reaching implications for the social order.

The actual selection of offspring characteristics, using what might usefully be termed "trait-selection technologies" (TSTS), offers not merely the facilitation or prevention of birth, but rather its refinement. Sperm separation techniques, for example, are being used to skew the chances of having a male or female child. Genetic screening of embryos allows the abortion of fetuses with traits the parent finds undesirable. And gene splicing techniques and therapies4 appear to offer the promise that genes coded for characteristics a parent finds undesirable may soon be replaced with those coded for desired characteristics.

The foregoing technologies focus on the product (that is, the physical result), rather than on the process, of creation and reproduction. Ancient distinctions between reproduction and production are thus disappearing. Such a paradigm shift, from baby as indivisible package to baby as mix-and-match product, raises the specter of "designer" babies -- and this pushes the limits of society's tolerance for diverse reproductive behavior.

Trait selection is neither simply speculative nor fully developed. TSTs are already used to influence the likelihood of a child manifesting certain traits. And the import and scope of TSTs are growing, fueled (in part) by the inexorable progress of ongoing efforts to map the entire human genome.(5) Consequently, the proliferation of TSTs requires a careful inquiry to identify, understand, and evaluate the possible significance of the differences among them.

Part II of this Article thus examines a specific and controversial example of TST: sex selection techniques used to predetermine whether a child is male or female.(6) Evolutionary biology (together, at times, with anthropology) reveals how offspring traits, such as sex, directly affect a parent's reproductive success, and consequently contribute toward the evolution of different "reproductive strategies."(7) Because reproductive strategies are quintessentially matters of family, parenting, and procreation -- matters currently deemed worthy of special federal protection -- trait selection seems logically eligible for similar protection.

But certain limitations must apply. Part III explores a standard by which to delineate appropriate limits of that federal protection. After examining and rejecting two common arguments for the outright prohibition of TSTS (namely that they are condemnably eugenic and bad for the species), this Part ultimately concludes that parents should be allowed to select for any trait,

using any available technique, that is not clearly and significantly damaging to the future child.

Part IV then offers a legal framework, essentially a taxonomic categorization and structure, for analyzing significant similarities and differences among the variety of trait-selection technologies now present or emerging. It proposes an analysis involving three variables on the use of TSTS, one of which accounts for motivation (the Reason a person may pursue TST), and two of which describe implementation (the Method to be employed, and the Time when a trait selection procedure will operate to influence future life). A permutation of these variables yields eight identifiable reproductive contexts. Examining each context in the light of the "not clearly and significantly damaging" standard demonstrates how a government might distinguish among them and determine the relative degrees to which each may properly be regulated.



It is important to note at the outset that the relevance of evolutionary biology to our analysis does not derive simply from its descriptive power. Logic is flawed by the "naturalistic fallacy" whenever one attempts to reason directly from an "is" to an "ought"(8) Such a leap is illegitimate because observations, strictly speaking, contain no normative component.(9) Normative conclusions require the combination of observations and values, to which evolutionary biology may only contribute the former part.

In the case of reproduction, these recent observations enter a preexisting context -- one in which a value system has already been articulated.(10) In Planned Parenthood v. Casey, most recently, the Supreme Court reviewed the principles that define the rights of the woman and the legitimate authority of the State respecting the termination of pregnancies by abortion procedures. In the process of doing so the Court (in a plurality opinion of justices O'Connor, Souter, and Kennedy) effectively affirmed the "promise of the Constitution that there is a realm of personal liberty which the government may not enter."(11) The boundaries of that personal liberty, of course, have been and continue to be the subject of considerable debate, as will be the propriety of using substantive due process to vindicate it.(12)

Does that personal liberty include the opportunity, subject to certain restrictions, to use trait selection technology? We know that the personal liberty extends beyond mere freedom from physical restraint,(13) and that it at least protects such things as interracial marriage,(14) the use of contraceptives, (15) and the bearing, begetting, and bringing up of children.(16) This is so, says the Court, because "the Constitution places limits on a State's right to interfere with a person's most basic decisions about family and parenthood"(17) -- decisions "central to personal dignity and autonomy."(18)

With this language the Court attempts to evoke an acknowledgement from the reader, rooted more in faith than logic, that reproductive matters deserve special treatment. This is not truly obvious, else the Court need not rely on the rather tautological formulation that reproductive matters are special because they involve families and parenting. All that establishes is that reproductive matters are special because they are reproductive matters.

No court has ever really done better in explaining why reproduction is so special. The frustration in attempting to explain the seemingly irreducible is matched by the hope that the public would have no better luck in articulating a challenge to the assertion. Because the contours of "reproduction" are so fuzzy, some have interpreted the Supreme Court's decisions in areas of family and parenting as broadly and fully "cement[ing] the right to reproductive autonomy."(19) Nevertheless, the precise extent to which the liberties the Court described in Casey and its predecessors extends to the use of various

reproductive technologies remains unclear.(20) The Court has effectively protected activities affecting whether and when to have a child, but it has not yet had occasion to address the how and what of having a child.(21) Specifically, the Court has not spoken on the extent to which a mother deserves protection from state intervention when she attempts to influence the manifestation of certain traits in her future child.

While the current Court has generally adopted conservative readings of privacy and liberty interests, the Casey decision, as well as Justice Ginsburg's appointment, may reflect a significant change. One may expect the Court, if ever confronted with the questions posed in this Article, to invoke Casey and examine, in part, whether or not a person's decision to use TST constitutes one of the most basic decisions about autonomy, family, and parenthood that she will make in her lifetime. This Article attempts to demonstrate that insights from evolutionary biology are expanding our understanding of what reproduction is all about. If we generally value the liberty to make fundamental decisions about reproduction that are central to personal autonomy, as Casey indicates, then laws designed to prohibit or impede access to TSTs should be subject to heightened judicial scrutiny.(22)

To see why this is so, one may consider a concrete, current, and controversial example in which certain TST is being used: sex selection. One must then explore several fundamental principles of evolutionary biology, which are relevant to any discussion of TST, and discuss how these affect our understanding and approach to sex selection, and illuminate TST issues in general.(23)


Sex selection in humans raises several themes that underlie any discussion of TSTS.(24) It illuminates the ancient and powerful desire to control offspring and exemplifies the rapid, often awe-inspiring, pace of technology enabling trait selection. It also reveals the current and potential demand for such technology, currently paralleled by an increased willingness of practitioners to provide it. Finally, sex selection evidences the extreme polarization of public views developing in response to, rather than in anticipation of, the promise and threats such technology may offer and pose -- creating an environment ripe for unwarranted, premature, and ultimately unconstitutional legislation.

1. Demand: Evidence, Strength, and Prevalence of Sex Preferences

Human history has long revealed a dramatic and undeniably prevalent human desire to control the future, development, and even traits of children. Children have occupied a common and central role in the lives of adults both through time and across races, and the longevity of parent-child relationships, in many cultures, is perhaps unique in the animal kingdom. Most adults feel the biological drive (and often religious obligation(25)) to replicate, and carry a strong commitment to raise their children. Since children become so great a focus of parental intent, purpose, and even meaning, it is thus not surprising that parents seek to influence their development. It is equally unsurprising, given humankind's irrepressible desire to impose order in life, find meaning behind seeming chaos, and harness nature's forces, that men and women have continually sought keys to creation itself

Sex selection is just one context in which this desire has frequently inspired direct action. Through the passing centuries, people have unrelentingly pursued and practiced techniques believed to influence the sex of children. Methods fanciful, cruel, and bizarre evidence the depth and breadth of the desire to do So.(26) Infanticide was for millennia, and in some places remains, a successful (if inhumane) technique for eliminating a child to make room for another of the desired Sex.(27) From a coldly logical perspective, however, post-conceptive techniques are strikingly inefficient since they typically eliminate the unwanted without actually providing the wanted.(28) Consequently, the imaginative focused efforts primarily on preconceptive methods.

One might loosely term preconceptive methods of influencing the sex of a child as "biologic" or "symbolic." The biologic methods involve prescribed behavior during (or timing of) copulation or specific variations in the female diet. In contrast, symbolic methods are magical and mysterious.

Early biologic methods capitalized upon supposed correlations between offspring sex and the vigor of copulation,(29) the side of the body providing the semen or egg,(30) the method of breathing during orgasm,(31) the timing of the female orgasm relative to that of the male,(32) and even properly timed bites on a woman's ear.(33) Some people even recommended raping one's wife to produce a male, on the theory that the more "male" a man acted, the greater the likelihood of fathering a boy.(34) Dietetic theories also proliferated, culminating during the Middle-Ages in more than a few women partaking in a ceremony involving the consumption of lion's blood, followed by copulation under a full moon while an abbot prayed for a child of the desired sex.(35) Later dietetic theories extolled the role in sex selection of fish, seeds, sugars, peas, lettuce, cheese, salt, sweets, and even the testes of certain animals.36 Early symbolic methods for preselecting sex correlated gender with the side of the bedpost on which one's trouser's were hung, the maintenance of appropriate flowers in the windowsill, cross-dressing prior to intercourse, and prescribed songs sung (or objects taken) in bed.(37)

Because none of these methods proved particularly reliable, however, they stand more as a testament to frustrated and grasping demand than as an indication of a corresponding supply. That demand continues to this day. While it may not be as strong in the United States as it is in India or China,(38) the demand is strong nonetheless. Studies of sex preferences in the United States, spanning over 50 years, reveal a continuing preference for a male child as the only child, or, alternatively, as the first child.(39) A recent study of women alone, for example, indicated that they would prefer to birth 161 boys for every 100 girls in a one-child context.(40) Similarly, their preferences would yield 171 to 100 first-born boys to girls in the multi-child context.(41) Significantly, studies have revealed an increasing willingness to pursue and to use sex selection procedures.(42)

The wide variety of reasons why people might prefer to have their next child be of one sex or another only contributes to the aggregation of demand. Individual parents may have "sequential" or "compositional" goals.(43) Sequential goals concern preferences to have children of one sex before the other sex. Compositional goals concern the preferred ratio of sexes within the family. These latter goals may include the desire to have more, or to have exclusively, offspring of one sex, to complement a child of one sex with another of the other, or to have a child of a sex opposite to that shared by a string of children.(44)

Parental preferences can span the spectrum of the fact-based, practical, stereotypical, and irrationally prejudiced. Parents' sequential or compositional goals may derive from associating with each sex different degrees of economic potential, status, or parentally-desired personality and behavioral traits.(45) Actual (or only subjectively perceived) superiority of boys, for example, in earning potential, or prevalence in girls, for example, of milder childhood demeanor, may affect the formulation of these goals. In other instances, parents may simply prefer the symmetry of having one child of each sex, or wish to diminish the chances of bearing a child with sex-linked diseases, such as Down's syndrome, Tay-Sachs disease, or more than 400 others.(46)

2. Supply: Technological Advances Enable Actualization of Sex Preferences

As is now well-known, the egg, supplied by the female, always carries an X chromosome. A male's sperm carries either an X or Y chromosome. An egg fertilized by an X chromosome yields a girl; the Y chromosome leads to a boy. Since this was discovered in 1924, researchers have scrutinized human conditions and behavior for clues to controllable factors that might skew the sex ratio; sex selection research began in earnest.(47)

Postconceptive techniques enable sex selection both in vivo (in the body) or in vitro (out of the body). Currently available in vivo techniques require discovery of the sex of a developing embryo or fetus (by ultrasound, chorionic villi sampling, or amniocentesis)(48) and subsequent abortion if it is of the "wrong" (more accurately, "dispreferred") sex. Postconceptive in vitro techniques, in contrast, require the selection, and implantation in a woman, of one of several eggs fertilized in a laboratory.

Preconceptive techniques also may be in vivo or in vitro. Preconceptive in vivo theories prevalent today involve coital timing and manipulation of diet, hormones, and cervical mucus acidity. Preconceptive in vitro techniques require separation of X- from Y-bearing sperm, as much as possible, followed by artificial insemination of the woman using the "enriched" semen, in which the ratio of X- to Y-bearing sperm has been skewed in favor of the desired sex.

Methods for separating sperm, however, considerably antedated techniques for evaluating the success of those methods. Mass impregnation followed by observation of the sex ratio at birth, obviously, was and is rather impractical. But in 1964 a researcher developed a technique to stain Y-bearing sperm with a material that fluoresces under ultraviolet light, thereby enabling researchers to assess visually the success of various sperm-separation techniques.(49) The promise offered by this evaluative technique spawned additional quests for sperm separation methods.

With the 1971 discovery that the X-bearing sperm is 3%, larger than the Y-bearing, and that the X-bearing swims more slowly (though further), researchers developed processes designed to separate sperm by size, weight, or motility. In the most successful technique, sperm is introduced to the top of a test tube containing three increasingly dense layers of the protein albumin. If a woman wants to conceive a boy (the method is rather less effective in selecting for girls) she is inseminated with the Y-enriched fluid from one end of the tube, to which the faster Y-bearing sperm have travelled.(50)

While the method is not perfect, the most recent data indicate that the method can skew the probability of conceiving a boy from roughly 50% to approximately 72%.(51) To put this in perspective, this would skew the sex ratio for selected offspring from roughly 1:1 to 3:1 if those employing the technique consistently selected for the same sex.

TST supply increases steadily. Studies now indicate that practitioners, many of whom were previously reticent to provide trait-selection services, are increasingly willing to supply sex selection procedures to those who request them.(52) At least 70 clinics in the U.S., for example, already offer sperm separation for the purposes of sex preselection.(53) Swiftly-advancing TSTs afford increasing access to objects of longstanding desires. In addition to the sex selection methods described above, these technologies allow a woman, for example, to learn basic genetic information about the human embryo when it is only three days, that is 8 cells, old.(54) Such information may as easily reveal the sex as disclose the presence of genes coding for particular traits, deleterlous or otherwise.

Demand, supply, and a concomitant market are generally not problematic (at least in the short term) so long as private desires confront only public acquiescence. But in sex selection, as with trait-selection and technologically-facilitated reproduction in general, beliefs frequently run strong -- and at odds with each other.(55) With increased public discourse in the social science and medical literature, positions have become increasingly polarized, with diminishing numbers of neutral observers.(56) While some have argued eloquently for nearly blanket reproductive freedom,(57) others have begun extensive calls for the outright prohibition of sex selection through criminal and civil penalties.(58) Two such state prohibitions have already been passed.(59)


To explore how evolutionary biology may contribute to our understanding of human reproduction, and hence illuminate the contours of reproductive autonomy, one must first examine certain fundamental principles the field considers to be strongly-supported working hypotheses.(60) So that it may be immediately clear: evoking biology as relevant to human affairs is not the same as saying biology should be automatically dispositive of any issue. Description is not prescription, and observing the influence of biological mechanisms does not lead ineluctably to the conclusion that the existence of these are unquestionably good.(61)

Although many questions concerning the evolution of life remain unanswered, remarkable advances in our knowledge of these processes, especially those driving social evolution, have been made in recent years. It is regrettable, but perhaps understandable, that public understanding and acceptance of the achievements in this field have fallen so far behind: its theories and prediction often seem counter-intuitive, its facts are unfamiliar, and its implications are startling, far reaching and, at times, unwelcome. In order to evaluate what relevance this new knowledge may have for legal analysis, it is critical to understand its basic ideas and findings.

Three basic principles of evolutionary biology provide the ground rules by which all living creatures, including humans, must play.(62) Each ultimately bears on an analysis of trait selection in the human context.

1. The Basic Mechanism of Evolution Is Natural Selection, Operating at the Level of the Gene

Individuals in a population of a sexually-reproducing species are not identical. If an individual possessing a certain trait has a higher probability than those around it of surviving long enough to reproduce, then that trait will be more likely, commensurately, to be passed on to the next generation.(63) "Natural selection," at base, means that if the trait remains advantageous over time, the percentage of individuals within that population that bear the trait will increase.(64) In many ways, an organism is thus simply a vehicle, made by the complex collaboration of a "parliament" of genes, for transporting copies of genes from one generation to the next.(65) It is, in essence, a fleeting meeting place of genes on a trajectory through time.

It is, however, technically incorrect to summarize the process of natural selection as "survival of the fittest."(66) Personal survival and longevity is relevant, from a Darwinian perspective, only to the extent that it facilitates the entry of genes into successive generations. Natural selection may thus be more accurately described as the pressure to maximize "inclusive fitness." Inclusive fitness" is a measure, essentially, of the proportion of a population, in a given future generation, that will carry copies of your various genes after your death. …

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