This chapter reviews what can be gleaned about human sexuality from the evolutionary and ethnographic record. Ancestral human sexuality leaves neither fossil nor archaeological evidence, but inferences about how humans mated, consorted, parented, formed partnerships, and aggregated into families can be drawn from two large and growing bodies of work, both discussed in this chapter. The first are anatomical and biological indicators of ancestral mating patterns inferred from fossil evidence as well as observations from nonhuman primates. The second is ethnographic research across an array of contemporary human societies, which highlights variation in mating, marriage, and family structure. Together, biological indicators and cross-cultural patterns shed light on the legacy, constraints, and possibilities carried forward into the diverse and variable expression of human sexuality today. Humans have a deep ancestry in a social structure of males and females living in social groups together, although how humans organize themselves is structurally different from anything observed in our closest relatives. Not only do families form around long-term pairbonds in all societies, but there is also a great deal of flexibility in who constitutes the pairbond, the families that surround them, and in the prevalence of extra-pair relationships.

Among the diversity of perspectives for studying the nexus of evolution and human behavior, human behavioral ecology (HBE) emerged as the study of the adaptive nature of behavior as a function of socioecological context. This volume explores the history and diversification of HBE, a field which has grown considerably in the decades since its emergence in the 1970s. At its core, the principles of HBE have remained a clear and cogent way to derive predictions about the adaptive function of behavior, even as the questions and methods of the discipline have evolved to be more interdisciplinary and more synergistic with other fields in the evolutionary social sciences. This introductory chapter covers core concepts, including methodological individualism, conditional strategies, and optimization. The chapter then provides an overview of the state of the field, including a summary of current research topics, areas, and methods. The chapter concludes by emphasizing the integral role that human behavioral ecology continues to play in deepening scholarly understandings of human behavior.

Darwin’s Origin of Species [GK26][GK27](1859), despite its almost complete silence about human evolution, was the catalyst for widespread discussion and debate during the 1860s about the history and future of humanity; about slavery and the identity of the human ‘races’; and about competition and struggle in Victorian society. Three popular novels of the early 1860s – George Meredith’s Evan Harrington [GK28](1860), Charles Dickens’s Great Expectations [GK29](1860–61), and Charles Kingsley’s The Water-Babies [GK30](1862–63) – illustrate how quickly Darwin’s ideas were appropriated into fictions dealing with race and social class in the decade of the American Civil War, the Morant Bay Rebellion, and the Second Reform Bill. Although generally associated with literary realism, Darwin’s work may be better aligned with the new narrative form so popular in the 1860s: sensation fiction.

The chapter investigates the evolutionary origins of human moral cognition. It discusses the relation of moral and legal theory and evolutionary theory. It reconstructs different perspectives on the evolutionary process. Influential current approaches are evolutionary psychology, theories of ontogenetic development on the basis of joint intentions and what one may call "evolutionary pluralism." The latter approach underlines the importance of many factors beyond natural selection that determine the genesis of a certain species and the stochastic nature of evolution. The methodological and theoretical foundations of these competing approaches are discussed. The problem of finding evidence for the properties of early humans is investigated. That state of research in paleoanthropology is recapitulated and discussed in terms of what it teaches us (and leaves undecided) about the genesis of human cognition, in particular moral condition. Taking into account the evidence and the most plausible evolutionary theory, it is argued that there is no compelling reason to assume that the moral principles underlying human rights are irreconcilable with human psychology.

Our genus is characterized by a unique dependence on technology, which is first seen in the mid-Pleistocene and becomes more sophisticated through time. The trend towards increasing encephalization appears to accelerate once tools have been acquired, coincident with a focus on meat-eating. This chapter reviews later Pleistocene species, including the Neanderthals, with whom we share many behavioral adaptations. However, there appear to be several critical differences, especially in the potential for language and possibly figurative expression, that may have made the difference over millennia, so that by 25,000 years ago we were the only human species left on Earth.

This chapter provides a broad overview of primate diversity and evolution, as well as a relatively detailed accounting of early human evolution. It presents a summary of the major anatomical and behavioral differences between apes and humans and the adaptations involved. Humans diverged from the apes between 6 million and 8 million years ago and we have a reasonably good fossil record by 4 million years ago. We can readily track the major adaptive shifts in human evolution, as we became more bipedal and big brained, depending on stone tools by at least 2.5 million years ago. This chapter emphasizes the similarities between apes and humans, and the fact that, evolutionarily, we are apes. Importantly, although there are clear trends through time in hominins, human evolution is not unilineal, and there were as many as seven species and three genera of human existing across Africa at around 2 million years ago, and 27 human species are now known to have existed over the last 7 million years. We were an adaptively diverse group, and the modern idea of a single species of human is a result of a series of extinctions across the hominin order starting around 1 million years ago.

On November 24, 1859, the English naturalist Charles Robert Darwin published On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life . In that book (Darwin 1859), he argued that all organisms, living and dead, were produced by a long, slow, natural process, from a very few original organisms. He called the process “natural selection,” later giving it the alternative name of “the survival of the fittest.” This first chapter is devoted to presenting (without critical comment) the argument of the Origin, very much with an eye to the place and role of natural selection. As a preliminary, it should be noted that the Origin, for all it is one of the landmark works in the history of science, was written in a remarkably “user-friendly” manner. It is not technical, the arguments are straightforward, the illustrative examples are relevant and easy to grasp, the mathematics is at a minimum, meaning non-existent. Do not be deceived. The Origin is also a very carefully structured piece of work (Ruse 1979a). Darwin knew exactly what he was doing when he set pen to paper.

Now we come to the elephant in the room. Darwin’s theory was incomplete. When the theory was completed, would natural selection prove to be that effective? Although he threw in a lot of assorted, presumed-relevant facts, no one, starting with Darwin, had much idea about the nature of variation – how it comes, what form it takes, how regular it is. And, without this knowledge, given that natural selection supposedly works on this variation, it is hard to make definite judgments about its effectiveness; especially since Darwin stressed that, although variation has causes, it is random in the sense of not appearing according to need. When he was not pushing the Lamarckian alternative, he was adamant that it is selection alone that is responsible for adaptation.

Turn now to those who think natural selection is vastly overrated as a cause of evolutionary change. It is at best a clean-up process after the real creative work has been done. It is little surprise that these critics come from within the organismic model, implicitly or explicitly. At the scientific level, we have encountered already the most (and properly) distinguished of them all, the American population geneticist Sewall Wright. Remember his “shifting balance theory,” where the key lay in genetic drift, as gene levels fluctuated randomly in small subpopulations, and then, when new adaptive features appeared, the subpopulations rejoined the larger group (probably the species), and through a form of group selection the new feature spread through the whole group. This is highly Spencerian – infused with a solid dose of Bergsonian vitalism – as equilibrium is disturbed and then regained at a higher level, part of an overall progressive process, presumably ending in humankind.

A little arbitrarily, but not entirely without reason, let us take 1959, the 100th anniversary of the Origin, as the date when the Darwinian paradigm finally came into its own. Natural selection and Mendelian genetics, now rapidly becoming molecular genetics, gave the explanation of the tree of life. If we continue to think in Kuhnian terms, what now of normal science? We should expect to see the subbranches of the consilience come into their own, as practitioners moved forward, theoretically, experimentally, and in nature, raising and solving their problems. And in major respects we do see exactly this.

In 1866, Thomas Hardy, raised a sincere member of the Church of England, wrote his sonnet “Hap.” It expressed the anxiety about – “fear of” is not too strong a term – the world into which natural selection has pitched us. No longer can we rely on a Good God to care for us, to suffer for us, to make possible eternal life. In the non-progressive world of Darwinian evolution, all is meaningless.

Among the many books authored by Peter Bowler, the eminent historian of evolutionary biology, three stand out: The Eclipse of Darwinism (1983); The Non-Darwinian Revolution: Reinterpreting a Historical Myth (1988); and Darwin Deleted: Imagining a World without Darwin (2013). Bluntly, he says: “there is now a substantial body of literature to convince anyone that the part of Darwin’s theory now recognized as important by biologists had comparatively little impact on late nineteenth century thought” (Bowler 1988, ix). I cannot say Bowler is entirely wrong. Indeed, in The Darwinian Revolution: Science Red in Tooth and Claw (1979), I contributed to this “body of literature,” and my book was quite openly a synthesis of the state of Darwinian play in the second half of the nineteenth century. But is this the end of the story, and if it is, why is it the end of the story? Today, as Bowler also recognizes, we accept the finding of natural selection as a major scientific achievement, up there with relativity theory. Let us pick up on this paradox.

Natural selection. I am an evolutionist, which means that, to understand the present, we must dig into the past. That holds for culture as much as for biology. So, taking my own advice, where do we end up? Or, more precisely, where do we start off? As always, when dealing with Western culture, we begin with the Greeks, Plato and Aristotle. Neither of them was an evolutionist. Indeed, rather like the Buddhists, they believed that the (physical) world is eternal: no beginning, no end. But they did have much to say of great interest to our inquiry.

Time to pull back and get a little more conceptual. We need to ask some penetrating questions about the nature, the scope, the truth-value of natural selection. Finding answers, the quest begins in the past. Charles Darwin was a graduate of the University of Cambridge. The greatest British scientist of them all, Isaac Newton, was also a graduate of the University of Cambridge, and his spirit, his achievements, his reputation, infused every discussion about science, including about the life sciences. In his Principia, Newton started with his three laws of motion, together with his law of gravitational attraction, and then went on to infer, deductively, the pertinent terrestrial laws, those of Galileo, and the pertinent celestial laws, those of Copernicus affirming the heliocentric nature of the Universe and those of later thinkers, especially Kepler on planetary motion. It was a given that the ambitious young Charles Darwin would want to show Kant dead wrong. There could be a Newton of the blade of grass, and that Newton was going to be Charles Darwin.

When a new cause is introduced into science, as often as not it is accepted without trouble. Few, if any, had worries about the Watson–Crick double helix and the subsequent working out of the genetic code. Genetics was put on a molecular causal basis. However, it is not uncommon for there to be opposition. Huygens’ wave theory of light was an outsider for nearly two centuries. Sometimes worries are ongoing. One doubts that, as long as there are those interested in mental health, Freud’s Oedipus Complex is going to be happily accepted by all. There have been, continue to be, and probably always will be disputes, often bitter, about its causal status. As we have seen, natural selection did not have an altogether easy birth. But as time went by, things seem to have improved. Newton and Leibniz all over again.