Hamilton's Law

<div> Natural selection favors genes that tend to increase copies of themselves in future generations. A signal accomplishment of William D. Hamilton was to establish a conceptual, and mathematical, framework for how this fundamental phenomenon affects such complex aspects of life as family relations, altruism, and selfishness. Hamilton’s Rule specifies that altruism tends to evolve when r × B &gt; C, where r represents genetic relatedness between an altruist and its relative, B the benefit conferred upon the relative, and C the cost to the altruist. Myriad biological evidence supports the predictions of Hamilton’s Rule, and its predictions regarding inclusive fitness. If Hamilton’s Rule works well to describe the behavior of organisms in general, might it also have explanatory power for human behavior embodied by complex institutions such as the law? The answer to this question appears to be “yes”. In fact, Hamilton’s Rule offers a powerful explanatory lens through which to view a number of otherwise quixotic legal rules. This chapter explores several examples of legal doctrines in which Hamilton’s Rule might be better named Hamilton’s Law. Examples are described from disparate doctrinal areas involving the law of contracts, child welfare, and wills. </div> <div> <br> </div> <div> A venerable principle of contract law makes it challenging for relatives to prove that formal agreements made between them should be considered legally enforceable. The closer the contracting relatives, the more challenging it is to enforce. Hamilton’s Rule suggests that close relatives tend to act more altruistically towards one another than would more distant relatives or nonrelatives, obviating the need for legal contracts conferring benefits. Here, the law appears to intuit that enforceable contracts are less necessary between close relatives. Child welfare law is often criticized for its obeisance to the doctrine that children should be returned to their genetic relatives even when the latter would not be ideal caregivers. Normally, this branch of law operates under the principle that decisions ought to be made in accordance with “the best interests of the child”. Returning a vulnerable child to a poor, badly educated, or low status parent would seem to run counter to this. However, Hamilton’s Rule suggests that close genetic relatedness tends to align strongly with the “best interests of the child”. A particularly stark case involves surrogate mothers who are genetic mothers of the babies they carry. Here, the law tends to allow genetic mothers to keep the surrogate babies they gestate regardless of what their surrogacy contract requires. </div> <div> <br> </div> <div> Under the law of wills and estates rules, there is a default legal doctrine that deals with inheritance in cases of intestacy. Often, there are many possible people whose actual relationships with a decedent suggest they be beneficiaries. These include close friends, caregivers, dependents, or others on whom the decedent may have bestowed gifts while alive. Nevertheless, when a person dies without a valid will, executors and courts tend to ignore these parties, instead ensuring that close genetic relatives benefit from the decedent’s estate more than distant relatives or unrelated parties. These and other legal doctrines reflect Hamilton’s Rule, tending to benefit survivors of a deceased person in proportion to their genetic relatedness to the decedent. In summary, this chapter suggests that Hamilton’s Rule can be a powerful predictive tool when trying to explain a number of odd or illogical seeming legal doctrines. </div>