1. Introduction

Five years after she married Gerald D., a wealthy oil executive, Carole D., a former international model, met Michael H., and in an extramarital affair, conceived a child with him.  Michael H. et al. v. Gerald D., 491 U.S. 110 (1989).  After the child, Victoria D., was born, Carole confirmed by genetic testing that the little girl was Michael’s.  Separating from her husband, she, Victoria, and Michael, moved to St. Thomas, Virgin Islands, where they lived together as a family unit.  Several months later, Carole left Michael for a third man, Scott K.  For the next several years, Carole and Victoria maintained contact with all three men, living with each at different times of the year.  Finally, Carole reconciled with Gerald, who acknowledged Victoria as his child, despite genetic evidence to the contrary.  Michael H. filed suit, seeking visitation rights with his biological daughter against the wishes of Gerald.  He argued that fatherhood was a fundamental and protected constitutional right.  The state court awarded Michael limited privileges to see Victoria, but Gerald appealed. 

On appeal to the U.S. Supreme Court, Michael was denied any contact with Victoria whatsoever on the grounds of the so-called paternity presumption rule, a century old law, enacted originally in 1872, providing that “[t]he issue of a wife cohabiting with her husband, who is not impotent, is indisputably presumed to be legitimate.”   By California law, unless the parents disputed a child’s paternity within a two year period of time, the child’s paternity was irrefutably determined to be the husband’s.  Victoria was deprived of her biological dad, and Michael, of fatherhood.

The paternity presumption rule has an equally unkind side for the duped husband.  After two years had passed, had Gerald refused to support Victoria as his daughter, Carole could have gotten a court order establishing him as the father, compelling him to pay child support.  Its nineteenth century predecessor was unforgiving, and there was no grace period during which poor Gerald could contest the paternity presumption – even when it was known to be an absolutely incorrect determination. 

What is the reason for a rule that divests a biological father of his child, and then assigns the role and duty to support it to a completely unrelated man? To come up with answers to this question, and others like it that relate to family and matters of sexuality, we are going to use the tools of evolutionary theory and how they apply to human behavior.

The explanation for rules in general is straightforward.  Society would not be possible without a code of conduct that all its members agree to follow.  As Thomas Huxley in Evolution and Ethics observed, “wolves could not hunt in packs except for the real, though unexpressed, understanding that they should not attack one another during the chase.”  Rules facilitate cooperation and let people know how they are expected to behave.  Under the paternity rule at issue in Michael H, the husband expects that any child his wife bears will be presumed to be his own, and that he will have the duty to support it, irrespective of who is its biological father.  This may make him more vigilant and attentive to the needs of his wife. 

Paternity presumption is premised on institutionalized monogamy.  When males and females pin their reproductive success on a monogamous relationship, it becomes important to know that the offspring belong to them, and that this fact is insured by the law.  In primates, several different explanations have been given for the existence of monogamy, rather than promiscuity or polygamy.  One theory proposes that monogamy is favored when economic conditions prohibit a male from monopolizing more than one female.  A second theory states that, because of protracted infancy, two parent childcare is more effective than maternal care, alone.  A third explanation is that males in a monogamous relationship will protect their offspring from infanticide by unrelated males.  Thus, the adoption of monogamy has a clear advantage for reproductive success.

In humans, it has been argued that monogamy is the cultural epitome, evolving from other forms of reproductive relationships.  Led by Lewis H. Morgan – who had published a pioneering study of the matrilineal system of the Iroquois Indians in the Eastern United States – nineteenth century anthropologists believed that society had passed through certain states, beginning with a state of promiscuity, where men and women freely engaged in sex, and lived together in clans of related individuals.  This stage, the theory went, was succeeded by matriarchy.  In it, women were believed to have held the power in society, and kinship was determined exclusively by maternal descent.  For economic and other reasons, it was believed that matriarchy was replaced by the monogamous nuclear family, with a paternal head, and the female dominated by the male.

Frederick Engels, cofounder with Karl Marx of modern Communism.  In The Origin of the Family: Private Property and the State, Engels argued:  “Monogamy arose through the concentration of wealth in one hand – a man’s hand – and from the endeavor to bequeath this wealth to the children of this man to the exclusion of all others.”  The only way to establish the children as his own was to have monogamy.  The rule of paternity presumption, he wrote, was necessary to resolve the conflict between “irrepressible” acts of adultery and the father’s goal of establishing the certainty of paternal parentage.

In providing his explanation, Engel had assumed that a father was instinctually motivated to hand down his wealth to his children.  Is this a reasonable assumption to accept?  The first step in answering this question is to recognize that the family, like other social organizations and behaviors, is an adaptation that arose through natural selection.  The idea that human behavior and social structures are products of evolution is not new.   Ever since Darwin proposed his theory of evolution, scientists – including Darwin himself – have wondered about the relationship between genes, behavior, and natural selection.  Making the connection between natural selection and family organization means that rather than looking at it as an arbitrary lifestyle, the family can be viewed as intimately associated with biology, and massaged by natural forces of evolution and genetics.

The theory of evolution by natural selection was proposed by Charles Darwin to explain the diversity of life observed on earth.  In The Origin of the Species, first published in 1859, Darwin introduced the subject by discussing the process of animal husbandry and domestication.  He devoted its first chapters to establishing how variations in physical attributes, such as color and fur texture, that occurred spontaneously in domesticated animals had been selected by breeders to improve their utility for human purposes.  He described various examples where breeders had observed the appearance of desirable favorable traits in particular animals, and selected these animals for further breeding.  Over very few generations, human breeders had successfully modified the appearance of many animal and plant species to a considerable extent.  Pigeon breeding was a popular hobby in Darwin’s day.  Darwin recounted how by selective breeding fanciers had created wildly divergent birds, differing in color, feather appearance, fantail, and beak.  The same had been achieved in dogs, sheep, horses, and plants.  Whenever a trait that struck man’s fancy or use appeared, a breeder could select it, and by meticulous breeding, incorporate it into the breed.  Darwin reasoned that if humans could accomplish so much over a relatively short period of time, then nature ought to be able to achieve even more dramatic transformations over hundreds of thousands of generations.  Using this as starting point, Darwin laid out his theory of natural selection, the theory that nature selects for those traits that facilitate and enhance an organism’s ability to survive and reproduce in its environment. 

A fundamental tenet of Darwin’s theory is the existence of variations in phenotype among individuals of the same species.  Nature acts by scrutinizing and choosing from among the natural differences between individuals those which confer the most benefit in the individual’s effort to survive and reproduce.  In turn, these traits are passed on to their progeny, and in time, become firmly fixed in the species, leading to gradual changes in the species’ physical characteristics – its phenotype.  Reiterative cycles of variation, selection, and reproduction, explain the gradual evolution of one species into another.  Speciation, and the associated observed diversity in animal and plant life, is a response to pressures in the environment – the conditions and organisms that are encountered in day to day living.  This includes others of one’s own species, as well as predators, parasites, food sources, and each and every organism encountered during one’s life.

Darwin did not understand the genetics of hereditary, but he recognized that, for evolution to be move forward, favorable characteristics had to be passed on from parent to offspring.  At the time Darwin was formulating his theory of evolution, another giant in the field of biology – Gregor Mendel – was carrying out experiments that would establish the foundation of modern genetics.  In the classic experiments on peas performed by Mendel from 1857 to 1863, he found that each physical trait of the plant was controlled independently by its own unique pair of factors that he called “elementen.”  These elementen are now known as genes.  Each parent packages half of its genes into its gamete – the egg and sperm.  Upon fertilization and conception, the embryo offspring inherits equal parts of its mother’s and father’s genes.  The importance of Mendel’s work went completely unrecognized during his lifetime.  It wasn’t until the early twentieth century when a new generation of scientists began to unravel the mechanism of heredity that the buried genius of his work was discovered. 

The relationship between genes and behavior broke new ground in the 1970’s, when biologists working with the simple fruit fly, first identified genes that affected basic behaviors, such as learning and courtship.  With names like dunce and rutabaga to signal their inability to learn, genetic strains of flies were isolated that permitted scientists for the first time to identify the genes underlying seeming complex behaviors.  As more sophisticated technologies were developed, this work was extended to mammals.  Using combinations of genetic technology and careful tracing of family histories, a collection of genes have now been identified which influence behavior in animals, including humans.  In most cases, especially in humans and other mammals, it is known that a particular gene has an effect on a behavior, but its precise mechanism has not been worked out.

In the animal kingdom, there are many examples of communities with complex social organizations that appear to be entirely a product of genetic factors evolved during the process of natural selection.  Social insects are highly cooperative societies in which members are organized into distinct castes, each caste performing a defined role necessary to promote the community’s success.  One or more queens are the fertile individuals bearing primary responsibility for procreation.  Worker and soldier castes are infertile, carrying out the business of the group – harvesting food, taking care of the larvae, and defending the group against invaders.  A gene has been identified in the social insect, fire ants, that appears to regulate whether a colony will have single or multiple queens.  When individuals have one form (“allele”) of the gene, the colony is ruled by a single queen, but when they have another form of it, several cooperative queens are found reigning in the nest.  Krieger and Ross, Science, 295:328, 2002.  Thus, social structure is a very simple animal society is determined directly by a single gene carried by the community members.

Natural selection works the same way on behavioral characteristics that it operates on physical traits. To put it in evolutionary terms, behaviors that lead individuals to succeed in the struggle to survive and reproduce are inherited by their progeny, and through many generations of reproductive success, disseminate throughout the population. 

But how does this help us understand family law?  First, we need to recognize that laws are utilized by a society to influence and shape the individual’s behavior to achieve certain goals and priorities set by the policy makers.  Rules that make parties responsible for their conduct act as a deterrent, discouraging the kinds of behavior that society considers harmful.  By imposing a penalty on bad behaviors, the law’s goal is to change human conduct.  Tort law provides an obvious example of a legal construct that regulates behavior.  To encourage behaviors that minimize accidents, liability is placed on the party who is in the best position to avoid, or reduce, injury.  This encourages individuals to take necessary precautions to prevent accidents from happening in the future.  Contract law follows the same principles.  The goal of each party to a contract is to maximize his wealth.  For everyone to be better off, we want to encourage parties to keep their contractual promises, and breach only when it is economically efficient.  As a consequence, individuals who break their promises are held liable for the economic damages that flow from their bad conduct. In each case, the law’s purpose is to maximize resources that society considers valuable.  It achieves it by formulating rules that encourage resource maximizing behaviors. 

Behavior forms the bridge between the legal system and natural selection.  The legal system – the laws, statutes, and judicial decisions that comprise it – is aimed squarely at human behavior, and human behavior is a consequence of evolution. Appreciating this connection is the small part of the story.  The bigger issue is how to define the character of the relationship between the two.  It is evident that the human legal system is not directly determined by single genes in the same way that a fire ant society is dependent upon which gene allele is possessed by community members.  But how do the two fit together?  Behavior in humans and in animals is a complicated business driven by the interaction of many different genes that operate in the depths of the brain.  Behaviors, and the genes which underlie them, are more likely act more as guiding principles that either restrain or promote the likelihood of certain rule-making.

The starting place for an analysis of the relationship between evolution and the law is to consider what kinds of behaviors would be expected to be favorably selected by evolution, and then to explore how the law treats these behaviors.  Reproductive behavior is an obvious place to begin the inquiry since reproduction is so essential to the evolutionary process.  Without reproductive success, favorable traits would not be carried forward, and an individual would lose the ability to contribute to the species’ evolving look.  Given this significance, it is logical that reproduction is a target of the law, and that the family – as the basic unit of reproduction in the American legal system – is a central pawn in the regulatory scheme. 

The conflict between the sexes

One of Darwin’s key observations was that individuals are in struggle to survive – against individuals of the same species, of different species, and against the physical environment, itself.  Conflict is therefore a basic element of evolutionary theory.  Included in it, is the reproductive struggle between species members.  We compete with each other for reproductive partners. Characteristics that facilitate reproductive competition and success – good looks, fertility, and the ability to provide for a family – are passed on to progeny, gradually accumulating over time, displacing less beneficial traits in the population.  The key point to ponder is how these evolutionary principles are applied in the law.  For this reason, we need to spend some time on understanding their basic workings.

Conflicts between the sexes begin with the differences in the investments they make in their quest for progeny.  Female investment in a single reproductive event is, for the most part, much higher than the male’s.  The key jewel is the female’s egg.  In oviparous organisms that lay eggs – like birds and reptiles – she is responsible for manufacturing, and depositing into a fully formed egg, the entire energy source necessary for the embryo to develop from a single cell into the multi-cellular offspring that eventually hatches from it.  Viviparous organisms – including humans and other mammals – have as difficult a task.  They produce live offspring directly, and the mother must continuously provide nutrients to her child until it is ready to emerge into the world. 

The father, in stark contrast, usually gives his embryonic child only a small package of genetic material – a spark to initiate embryogenesis – but no nutritive resources.  Even the cellular machine to make energy – the mitochondria – comes from the mother.  Instead of expending the considerable energy that his partner does on providing for the embryogenesis of the nascent child, the male strategy is to father as many children as possible with the hope that at least a few make it to adulthood.  With this strategy, a male has a lot less to lose when he makes a bad choice of a particular mother for his child.  If he has played his cards right, he has placed his bets on a number of fertile women willing to provide food for his developing baby.  Failure of one or two would not terminate his reproductive output for that season.

A female, whether she is oviparous or viviparous, must sock away valuable resources and time in carrying out the reproductive process to its successful completion.  Her reproductive output is limited by how many eggs she is capable of producing.  She doesn’t produce the swarm of gametes that a man does, instead concentrating on a few good eggs.  If she errs in choosing a father for her child, she looses far more than the male because it can mean starting all over again.   Females who acquire adaptations that guide them in “good” mate choice – fathers whose genetic material enhance the babies own survival and reproductive success – are ultimately more successful, passing these mate preference adaptations on to future generations.

The disparity between male and female investment is good reason for battles between the sexes.  To increase their reproductive output, all males have to do is chase and impregnate as many females as possible.  The number of females they can find limits their reproductive output. As a result, characteristics that enhance their appeal to females become important vehicles to success.  This is the basis for what has become known as “sexual selection.”  A female’s taste in males ends up being reproduced in her male offspring because he is the kind of mate she chooses to father her children, and as a consequence, his appealing qualities end up immortalized genetically in any progeny they co-produce.  The females’ selection of male traits eventually shapes the appearance and behavior of the male population.

How does a female choose a father for her child?  Potentially, she can discriminate between males based on their possession of economic or genetic resources.  In many species of birds, males compete with each other to establish territories that are rich with the resources to provide to their progeny.  Success in acquiring territory translates into reproductive success because it increases the likelihood of being chosen to father a fertile female’s brood.

While recognizing whether a male is economically well off may be relatively easy, how does a female chose a male for his good genes?  In a study of European starlings, it was discovered that male birds who sang the loudest and longest also had the strongest immune systems.  Duffy and Ball, Royal Soc. Lond B, 2002.  Females selecting the premium crooners from the crowd were also picking the males with the greatest resistance to disease and infection.  Bird song was therefore a proxy for the male’s good health, and presumably for the good genes responsible for it.  The same explanation has been offered for the observation that females in several bird species prefer males with elaborate ornaments.  Krebs and Davies, An Introduction to Behavioural Ecology, Third Edition, Blackwell Science, 1993, Pages 188-197.  Male peacocks, birds of paradise, and pheasants, to name a few, have evolved extravagant feather displays that are used to attract reproductive partners.  According to one theory, ornament exhibition by males is a method by which they show off their genetic resistance to disease and disability.  Males who are able to bear the physiological costs of elaborate body ornaments are more likely to be healthy individuals possessing good genes. 

The law favors reproductive success

The law recapitulates the conflicts between and among the sexes that evolutionary theory predicts.  After all, the law is about regulating behavior.  Just as tort law encourages people to take proper precautions to avoid accidents, we might expect that family law promotes reproductive success.  In disputes that involve families, and other relations between women, men, and, their children, the aim – from the Darwinian perspective – is to find an outcome that favors reproductive efficiency.  This leads to the question of whose reproductive capability does the law protect.  In the paternity presumption rule raised in the Michael H. case, it’s the mother’s interest which appeared to be favored.  Michael lost his bid for fatherhood.  Gerald was stuck supporting a kid who wasn’t his own.  But Carole won out because she got to choose who would contribute the genes to her child, and who would be the best provider for it.  Michael also got away like bandit.  He successfully procreated, but at little cost to himself.  Gerald may have ended up with the worst deal since he was left responsible for Michael’s child, but, of course, he did get Carole, and continued reproductive opportunity with a woman who had proven herself fertile.  Considering that the law shaping this strange deal was made exclusively made by men, it’s intriguing that it’s Carole who gets the best end of the bargain.  But more on this later.

In explaining the origin of the paternity presumption rule, Engels stated that men sought to bequeath their wealth to their biological children.  From an evolutionary viewpoint, this seems like a reasonable proposition.  Consider the case where there are two kinds of males – males who prefer to share their money with their biological children, and males who don’t care, and give it away indiscriminately.  Assume that this behavior is somehow genetically coded, making it an inheritable trait.  Kids who get the wealth are better off, and more successful reproductively than those who don’t get it.  Under these conditions, the kids with dads who keep the money in the family will end up with more children of their own, than the kids whose fathers don‘t care.  Not only will the kids with generous dads do better, but they and their own progeny will exhibit the same favorable trait, having inherited it from their father.  After many generations, this behavior would predominate in the population, becoming the behavioral rule.  

The same logic that resulted in the selection of men who passed wealth on to their own natural children would apply similarly to women.  But there’s even another factor that is as interesting.  Let’s say that females are more likely to select a mate who has the quality of willing his wealth to his children, rather than a man who gives it up arbitrarily.  This would make sense when money is advantage.  The female’s choice becomes an additional and potent selection factor, further enhancing the reproductive potential of the man who shares his wealth only with his family.  Since she only chooses men who practice nepotism toward their children, men who don’t tend to be fruitless.  This facilitates the spread of the “nepotic” genes, while impeding those of the arbitrary man.  The behavioral trait becomes fixed in the population, as Engels had argued.  Engels blamed the man entirely for the emergence of monogamy, but this analysis predicts that the woman has equal culpability.

According to this theory, men – by hard-wired inheritable instinct – would tend to give resources away to their biological children.  If this behavioral rule is embedded in the man’s psyche, what kind of legal code should we expect to be erected around it?  One approach is to enact laws that effectuate choices that a person would have made had he the opportunity, but who is deceased or otherwise incapacitated.  In this case, the solution is quite clear.  Our evolutionarily-tuned rule maker codifies his instinct by adopting a law that vests a decedent’s wealth in his kids.  As predicted, most states codify the practice.  When a father dies without a will, his children are automatic potential beneficiaries.  We will return to this topic later on.

There is no single reflection of evolution in the law.  One class of rules are those that codify practices which are in the best interest of a person’s reproductive goals.  The point of this kind of rule is to protect the individual’s interest from intrusion by the state.  An example of this is illustrated in Skinner v. Oklahoma described in Chapter 2.  In another reflection, the law executes choices for a person who is dead, incompetent, or otherwise incapacitated.  The laws of estate succession are a good example.  A third category comprises rules which codify behaviors contrary to those which have been evolutionarily selected.  An example of this arises in circumstances where there is a conflict between the male and female reproductive interests, and the law favors one sex.  As discussed later, abortion laws fall into this group.

In the selection of cases presented here, principles of evolutionary biology are applied to legal conflicts that arise in the context of human sexuality in disputes over procreation rights, paternity, parenthood, ownership of sperm, and sexual orientation. Evolutionary theory fits into evolutionary jurisprudence by providing a foundation to frame questions about the impact of laws on reproductive behaviors, and to ask whether a particular law is consistent with the reproductive interests of the players involved.  In reading the cases which follow, consider whether the law has been crafted to support an individual in his drive to reproduce and express his sexuality.