In 1871 in The Descent of Man and Selection in Relation to Sex, Darwin introduced the notion of sexual selection. Sexual selection leads to features that help individuals gain access to mates and takes two forms – intrasexual and intersexual selection. Intrasexual selection involves competition between members of one sex for access to the opposite sex, while intersexual selection involves members of one sex attempting to attract members of the opposite sex. In nature these forces are believed to lead to elevated levels of aggression, greater body strength and the development of attractive features in males. For females sexual selection leads to choosiness over mates. Sexual selection theory and the notion of female choice have recently become important concepts for the understanding of behaviour. There is now clear evidence from a number of species that female choice has been a driving force in the evolution of male adornment and aggressive behaviour.

Chapter 11 deals with the timescale of history and human evolution. It offers a complexity approach to the evolution of art that attempts to move beyond simplistic theories of the survival function of art, including the much-debated issue of the function of art in the context of sexual selection. After discussing the basic principles of evolution from a complex systems approach, the chapter outlines different evolutionary scenarios: the survival-enhancing function, on the one hand, and the view of art as an evolutionary by-product, on the other. By showing how both evolution and human activity are entangled, interaction-dominated dynamics, the chapter provides an alternative to simplistic gene-for-art assumptions.

The first chapter traces the notion of “art for art’s sake” to the evolutionary theories of Charles Darwin and Herbert Spencer, who first engaged with questions of aesthetics in the early 1850s. In their attempts to account for the evolution of the sense of beauty – an adaptation with no obvious survival value – both writers exempted a wide swath of aesthetic activities from the natural laws of scarcity and struggle that governed other areas of biological life. This chapter argues that their evolutionary explanations for beauty (the theories of sexual selection and “play," respectively) thus laid the scientific groundwork for later conceptions of aesthetic experience as escapist, salutary, and therefore beneficial for the species. The chapter concludes with an analysis of selected literary works by Algernon Charles Swinburne, Thomas Hardy, and George Meredith, whose respective corpuses illustrate the diffuse impact of these ideas on literary evocations of the beautiful.

Remarkably, literature was the field where Darwinian thinking was immediately and warmly received. Charles Dickens’s weekly magazine, All the Year Round, at once published articles that gave detailed, sympathetic accounts of the theory of the Origin, and these were followed by writers using Darwinian themes in their fiction and poetry, Dickens himself using sexual selection to structure a key relationship in Our Mutual Friend. This continues to the present, when leading novelists like Ian McEwan and Marilynne Robinson use very different reactions to Darwin to mold their narratives.

Sex differences in lifespan have been labelled as one of the most robust features in biology. In human populations, women live consistently longer than men, a pattern that encompasses most mammalian species. However, when expanding both the taxonomic scope beyond mammals and the range of mortality metrics the female survival advantage over males is no longer the rule. Moreover, current evidence suggests that sex differences in actuarial ageing parameters (i.e. age at the onset of ageing and rate of ageing) are far from consistent across the tree of life. This chapter first reviews current knowledge of sex differences in mortality patterns across animals and appraises how these diverse patterns can be explained by the current evolutionary framework. It then emphasizes the relevance of going beyond the differences in mortality patterns by exploring how natural and sexual selection have shaped age- and sex-specific changes in reproductive performance and body mass across the tree of life, and by identifying some possible biological pathways modulating ageing in a sex-specific way. Finally, it highlights how evolutionary theories can be relevant to understand the widespread differences in causes of death between sexes, offering a complementary approach to gain a comprehensive understanding of the evolution of sex differences in health and ageing, with likely biomedical implications.

Threespine sticklebacks, numerous species of disease-causing bacteria, and Darwin’s finches have all shown rapid evolutionary change in response to changing environments. Evolutionary ecologists use a variety of genetic and molecular approaches to study evolutionary change in these and other species. Gene flow, genetic drift, mutation, and natural selection can cause evolutionary change within a population, but natural selection is the only evolutionary process that can lead to adaptation. The benefits and costs of adaptations are environment-dependent and reflect evolutionary tradeoffs, so a trait may be beneficial in one environmental context and costly in a second. Natural selection may lead to speciation when genetic divergence is maintained either by physical barriers to gene flow, or by assortative mating of similar genotypes within a population. Evolutionary ecologists compare morphological, behavioral, and, most commonly, molecular characters in related groups of organisms, and use similarities in these characters to create phylogenetic trees that reflect evolutionary relationships.

This chapter will focus on debunking the myth that sexual selection was Darwin’s afterthought to natural selection by more fully situating sexual reproduction and sex differentiation in Darwin’s intellectual trajectory, dating to the 1830s. This long-standing myth results, in part, from the scientific communities’ discomfort with sexual selection theory and, more to the point, the social radicals who embraced it in the late 19th and early 20th centuries. To unpack the gendered reception of the Descent, this chapter also analyzes the related myth that sexual selection theory naturalized female inferiority by highlighting the nuanced and varied reception of sexual selection theory within and, importantly, beyond the scientific community especially among socialists and feminists.

Darwin’s theory, in its uniformitarianism, its materialism, and its elimination of all metaphysical explanations and any element of intelligent agency from the world’s biological phenomena has been taken as an important influence in the growth of the idea that all living creatures are automata – more or less “conscious machines.” Darwin himself, in a least four different aspects of his writing, belies this inference from his theories: the metaphorical work done by his dominant idea – natural selection; his anthropomorphism; his views on instinct; and his theory of sexual selection.

Sexual selection theory has undergone both a theoretical and an empirical revolution over the last few decades. New understandings of female choice, partnership dynamics and the impact of sociodemographic factors on mating strategies have led to a flourishing of studies within human behavioral ecology and related evolutionary social sciences. Drawing from this literature, this chapter outlines how mating markets operate and the particular traits that are thought to be most important in human mate choice. Following this overview, the chapter examines how temporal and contextual facets of human partnerships affect mating decisions. Finally, the chapter shifts the focus to debates about the dual roles of fidelity and paternity and how these affect mating strategies. Throughout, the chapter focuses on data from non-WEIRD societies in order to highlight aspects of mating where universals are evident and where cross-cultural variation is important. In addition, the chapter highlights how studies of human mating by human behavioral ecologists offer a distinct and valuable perspective which cannot be found in other subfields of the evolutionary social sciences.

For most people, the most obvious thought or image that sexual reproduction brings to mind is that of sexual intercourse, a mating between two individuals of opposite sexes, which will result in the birth of their common offspring. While biparental reproduction is certainly the most common mode of sexual reproduction among all eukaryotes, it is not the only one, and the way it is carried out can depart substantially, in many different ways, from the ‘canonical’ description above. What is common to all these modes is that two distinct sexually compatible individuals (parents) undertake a sexual exchange that leads to the generation of new individuals with a genetic constitution obtained from the association and/or the reassortment of those parents’ genomes. The key event in this mode of reproduction, technically called amphigony, is the fusion of two gametes or two nuclei functioning as gametes (syngamy), each produced by one parent, to form a zygote. While in species with anisogamy (i.e. with distinct male and female gametes; Chapter 4), only gametes of opposite sex are compatible, the two individuals that produce them are not necessarily a male and a female.

We are all familiar with the changes in an organism during development, followed by its reproduction, which are repeated generation after generation. Biologists describe this development–reproduction sequence as the life cycle: the series of transformations and reproductive events that, from a given stage of life of an organism, leads to the corresponding stage in a subsequent generation. We can describe a biological cycle as going from zygote to zygote, but also from adult to adult, or from embryo to embryo: in a cyclical process, the choice of the ‘initial phase’ is arbitrary or conventional, as the notorious ‘the chicken or the egg’ dilemma beautifully illustrates.

In the course of their lives, organisms spend time and energy on a number of activities and functions, of which reproduction is only one – think of growth, defence against predators and pests, and others. How many resources are used for reproduction, how much time is devoted to it and how this time is distributed over the course of life are all elements that characterize the different reproductive strategies. From an even wider perspective, in those organisms that at certain times in their lives can opt for one or another reproductive mode (e.g. sexual or asexual reproduction, as in many plants and many marine invertebrates), a reproductive strategy includes also this reproductive policy.

On February 1997 the birth was announced of a sheep named Dolly, the first mammal to be cloned from an adult cell of a mother individual. The event attracted enormous media attention. Dolly, born on 5 July 1996, actually had three ‘mothers’: one provided the egg (whose nucleus was removed), another the nucleus with the DNA picked out from a somatic cell (i.e. a cell of the body not specialized for reproduction), while the third mother carried the cloned embryo in her womb until parturition.

Ever since living beings arose from non-living organic compounds on a primordial planet, more than 3.5 billion years ago, a multitude of organisms has unceasingly flourished by means of the reproduction of pre-existing organisms. Through reproduction, living beings generate other material systems that to some extent are of the same kind as themselves. The succession of generations through reproduction is an essential element of the continuity of life. Not surprisingly, the ability to reproduce is acknowledged as one of the most important properties to characterize living systems. But let’s step back and put reproduction in a wider context, the endurance of material systems.

Acquiring the traits specific to a given sex, during early development or at another point during the life of an organism, is usually a complex process. Although the sex condition of an individual is conventionally defined based on the type of gametes it is able to produce (Chapter 4), the sex-specific phenotype is generally not limited to the organs of reproduction. Each of these characters can maintain a certain degree of independence from other sexual traits in the same organism, be subject to different developmental control, and show different degrees of sensitivity to the environment. Therefore, sexual differentiation extends to the development of the secondary sexual characters, which can be morphological, physiological, behavioural, or combinations of these. An exploration of this fascinating subject requires some preliminary clarification about systems and mechanisms of sex determination and sex differentiation.

In Chapter 1 we defined sexual reproduction as a form of reproduction that generates new individuals carrying a genome obtained by the association and/or the reassortment of genetic material from more than one source. In the most familiar form of sexual reproduction, the new genome is formed by the union of (partial) copies of the genomes of two parents through the fusion of two special cells produced for that purpose, the gametes, into a single cell, the zygote. This is the way most multicellular eukaryotes, ourselves included, reproduce sexually.

A zygote does not necessarily derive from the fusion of gametes or gametic nuclei produced by different individuals. Both egg and sperm may instead be produced by the same individual, a sufficient simultaneous hermaphrodite (Chapter 4). In this case, the offspring has only one parent. However, the gametes that merge are the products of independent processes of meiosis undergone by different germ cells, although in the same individual: this distinguishes self-fertilization (or selfing) from some forms of parthenogenesis where there is the fusion of two of the four nuclei deriving from the same meiosis, as we will see in the next sections (Figure 6.1).