This chapter identifies ten lessons for international relations that emerge from the book.

This chapter presents latent nuclear deterrence theory. It explains how it is possible to gain international leverage from a nuclear program if countries do not have nuclear weapons.

This chapter addresses when nuclear latency leads to nuclear weapons proliferation and arms races. It shows that under certain conditions, nuclear latency can deter rivals from arming. In other situations, however, nuclear latency can foment nuclear weapons proliferation. It includes six case studies of nuclear proliferation: Argentina, Brazil, France, India, Pakistan, and South Africa.

Chapter 4 considers the rising nuclear threat and how individuals can help forestall it.

Despite significant reductions in nuclear arsenals after the Cold War, the world’s nuclear nations still are pointing thousands of warheads at each other, using systems that are vulnerable to human error, miscalculation, or cyberwarfare. Over the past decades, humankind has come hair-raisingly close in several well-documented instances to unleashing full-scale nuclear war. The logic of arms races makes it very hard for nations to resist the temptation of modernizing and building up their arsenals. On the other hand, new designs for nuclear reactors – whether for fission or fusion processes – hold out the tantalizing possibility of safe, cheap, and abundant electricity. Nuclear-generated electricity does not release greenhouse gases, and therefore could play a key role in creating a sustainable energy system over the coming century.

Sexual conflict arises from differences in the fitness interests of males and females. A trait that is beneficial for the reproductive success of one sex reduces the fitness of the other sex, resulting in opposing selection pressures on the two sexes. The two sexes need each other for reproduction, but their dependence is asymmetric. Males benefit from a higher mating rate than females, as their reproductive success is usually constrained by the number of receptive mates, while female reproductive success is limited by egg production. Sexual conflict can occur at any stage of reproductive interactions – before or during copulation, or after insemination – and over almost any aspect of reproduction, from the decision to mate to the investment into parental care. The conflict results in a perpetual tug of war between the sexes. Each sex attempts to maximize its fitness at a cost to the other sex, which results in sexually antagonistic selection. This can cause the rapid evolution of sexual traits, and ultimately results in the diversification of traits, and possibly even in speciation. Sexual conflict can manifest in two ways, intra- and interlocus sexual conflict. Intralocus sexual conflict occurs when a trait expressed in both sexes (determined by alleles in the same locus in the two sexes) has opposite effects on male and female fitness. Interlocus sexual conflict occurs when the conflicting traits are determined by alleles in different loci in the two sexes and the optimal outcome of male–female interactions differs between the two sexes. Intralocus sexual conflict generates a genetic tug of war between the sexes over the optimal trait expression, while interlocus sexual conflict can lead to open-ended cycles of sexually antagonistic coevolution. Sexual conflict before mating has resulted in a diversity of tactics and strategies that males use to overcome female unwillingness to mate, from forced copulations and sneaky fertilization to the emission of love darts. Sexual conflict after mating has favored the evolution of male traits that increase success in sperm competition, such as postcopulatory mate guarding, toxic seminal substances that destroy the sperm of other males, mating plugs that prevent other males from mating with the female, and morphological and physiological traits that harm females, such as spines on the intromittent organ that pierce the reproductive tract of the female. Females have evolved cryptic choice of sperm to influence which males fertilize her ova. Whether the sexual conflict between males and females can be resolved depends on the type of conflict. Several mechanisms may reduce the strength of intralocus conflict, such as sex-limited expression of traits, but the interests of males and females are unlikely to become aligned when it comes to interlocus conflict. The relative influence of sexual conflict on the fitness of organisms, and the degree to which it can be resolved, are open questions.

This chapter summarises the science behind nuclear weapons and describes their development first by the United States and then by the Soviets with a narrative of the nuclear arms race between the two superpowers during the Cold War. Also described are the nuclear weapons programmes of the United Kingdom, France, China, Israel, India, South Africa, Pakistan, and North Korea. Of these, only South Africa has eliminated its programmes and the associated weapons.

The adoption of the Treaty on the Prohibition of Nuclear Weapons (TPNW) at the United Nations General Assembly and its movement toward ratification raises both hopes amongst some and fears amongst others regarding the development of customary practice under international law. Although the TPNW purports to strive for universality, significant questions remain regarding the Treaty’s aims and achieving legal unity within the international legal order. The purpose of this chapter is to explore these and other issues regarding the TPNW’s prospects of achieving universality under customary international law and opinio juris.