Unlike extensive research conducted on courtship, foreplay, and intercourse, what happens after ejaculation is one of the most neglected dimensions of human sexual behavior. As described in this chapter, postejaculatory adaptations have important and diverse implications for such things as penis hypersensitivity, the refractory period, female infidelity, sperm competition, semen displacement, self-semen displacement, spousal rape, the risk of transmitting sexually transmitted diseases for uncircumcised men, and the incidence of nonpaternity. This chapter also outlines ways to test the Bruce effect in human females and provides a novel explanation for the absence of the Coolidge effect in women.

Introduction

Our interest in the psychological properties of semen arose as a byproduct of an initial interest in menstrual synchrony. In reviewing that literature we discovered several articles (Trevathan, Burleson, & Gregory, 1993; Weller & Weller, 1998) reporting that lesbians who live together fail to show menstrual synchrony. Since the evidence suggests that menstrual synchrony is mediated by the exchange of subtle olfactory cues among cohabitating women (Preti et al., 1986, Stern & McClintock, 1998) this struck us as peculiar, because lesbians would be expected to be in closer, more intimate contact with one another on a daily basis than other females who live together. What is it about heterosexual females that promotes menstrual synchrony, or conversely what is it about lesbians that prevents menstrual synchrony? It occurred to us that one feature that distinguishes heterosexual women from lesbians is the presence or absence of semen in the female reproductive tract. Lesbians have semen-free sex.

Human semen is a very complicated mixture of many different ingredients. If you extract the sperm from semen, what is left is called seminal plasma. We speculated that there may be chemicals in seminal plasma that, through vaginal absorption, affect female biology and triggers the release of pheromones that function to entrain menstrual cycles among cohabitating women. Some of the components in semen pass through vaginal epithelial tissue, and within an hour or two after intercourse heightened levels of certain seminal chemicals can be detected in the female bloodstream (Benziger & Edelson, 1983).

Introduction

Among sexually reproducing species, the penis evolved as an internal fertilization device. But across different species, penises exist in a bewildering array of shapes and sizes (see Eberhard, 1985). Among primates, the human penis is distinctive by virtue of both its size and its enlarged glans and protruding coronal ridge (see Gallup & Burch, 2004). There has been some speculation that the human penis evolved not only as an internal fertilization device, but also as a mechanism for displacing semen left by rival males in the female reproductive tract (e.g. Baker & Bellis, 1995).

In a series of studies designed to simulate sexual intercourse under laboratory conditions using artificial genitals, we found that when latex vaginas contained simulated semen, phalluses that approximated the configuration of the human penis displaced 80% or more of the semen by drawing it away from the cervical end of the vagina (Gallup et al., 2003). Through a series of experimental manipulations, we determined that the coronal ridge may be an important feature of the penis in mediating semen displacement. Thus, as a mechanical means of affecting sperm competition, the human penis may enable successive males to displace foreign semen from the female reproductive tract and substitute their semen for those of their rivals.

Preeclampsia

Preeclampsia is a leading cause of prenatal infant mortality (Mac Gillivray, 1983; Robillard, Dekker, & Hulsey, 2002). Preeclampsia occurs as a consequence of abnormal invasion by the trophoblast in the uterine spiral arteries and endothelial cell dysfunction (Friedman, 1993), and as a consequence the fetus may not receive adequate nutrition resulting in growth retardation. Whereas all mammalian embryos undergo implantation shortly after conception, humans are the only mammalian species known to undergo a second phase of deep trophoblastic implantation at the end of the first trimester (Robillard et al., 2003). In normal development, this second stage of implantation provides for the modification of spiral arteries that result in an increase in the blood flow to the placenta. Preeclampsia is believed to be the result of a failure to achieve or to complete this second implantation phase (Robillard et al., 2003). It is clinically diagnosed by maternal hypertension and proteinuria. The hypertension results from cytotrophic factors that are released by the fetus and serve to increase the amount of blood flowing to the placenta (Haig, 1993).

It has been theorized that the origins of preeclampsia in humans are linked to the increase in cranial capacity associated with the genus Homo (Robillard et al., 2003). The greater nutritional needs of the developing brain in the human fetus, compared to the more modest needs of developing brains in species with lower cranial capacities, has been hypothesized to explain the second wave of implantation characteristic of humans.

Abstract

The purpose of this chapter is to review the evidence concerning mirror self-recognition as a measure of self-awareness and examine its applicability to schizophrenia. The evidence suggests that the ability to identify yourself correctly in a mirror is not only related to the capacity to conceive of yourself, but may also be related to your ability to take into account what other individuals may know, want or intend to do. This ability to make accurate inferences about mental states in others (known as mental state attribution, theory of mind or social intelligence) begins to emerge during childhood at the same point in time as mirror self-recognition. Species that fail to recognize themselves in mirrors fail to show any evidence that they can infer mental states in one another. Also consistent with the proposition that these phenomena go hand in hand, recent neuropsychological evidence shows that self-awareness and mental state attribution in humans appear to be a byproduct of brain activity that is related to the frontal cortex. As detailed here and elsewhere in this volume, there is growing evidence that both self-awareness and mental state attribution is impaired in schizophrenic patients and that schizophrenia may be related to frontal lobe dysfunction.

Mirror self-recognition

Mirrors have a number of unique psychological properties. In principle, mirrors represent a means of seeing yourself as you are seen by others. In front of a mirror you are literally an audience to your own behaviour.

Experimental background

The first experimental test of self-recognition in animals was conducted on a group of preadolescent chimpanzees and several species of monkeys (Gallup, 1970). Initially all of the animals acted as if they were seeing other animals when they looked at themselves in the mirror. After a couple of days, however, the chimpanzees (but not the monkeys) began to respond as if they had come to appreciate the dualism implicit in mirrors and now realized that their behavior was the source of the behavior being depicted in the reflection. That is, rather than responding to the mirror as such with species-typical patterns of social behavior, they began to show self-directed responding by using the mirror to respond to themselves (e.g., to investigate parts of their bodies that they had not seen before). In an attempt to validate my impressions of what had transpired, I devised a more rigorous, unobtrusive test of selfrecognition. After the 10th day of mirror exposure the chimpanzees were placed under anesthesia and removed from their cage. While the animals were unconscious, I applied a bright red, odorless, alcohol-soluble dye (rhodamine-B base) to the uppermost portion of an eyebrow ridge and the top half of the opposite ear. The subjects were then returned to their cages in the absence of the mirror and allowed to recover from anesthetization.

To date, the only species to show compelling evidence of self-recognition are humans, chimpanzees, and orangutans. (Only one gorilla, Koko, has displayed self-recognition; see Patterson & Cohn, SAAH17). An important question is whether self-awareness is a uniquely primate (great ape–human) ability or a potential outcome of any sufficiently intelligent system. In order to address this question we can compare tests of self-awareness in primates with another taxonomic group that has diverged extensively from them yet displays a comparable level of neurobehavioral complexity, namely, the Cetacea. Comparisons of primates and cetaceans, therefore, form the basis for a test of convergent cognitive evolution and could set the stage for subsequent tests of the generality of Gallup's (1982) model of self-awareness.

Dolphins are provocative candidates for self-awareness for a number of reasons. They share those neurological, cognitive, and social characteristics with great apes and humans that are generally regarded as having been important for the development of self-awareness in primates. Humans, great apes, and dolphins show similarities across several measures of encephalization, including a high brain-weight / body-weight ratio (Glezer, Jacobs, & Morgane, 1988; Jerison, 1982), extensive cortical surface area (Jerison, 1982), and a high neocortical-volume / total-cortical-volume ratio (Glezer et al., 1988). The bottlenose dolphin is capable of high levels of performance on a variety of auditory learning, artificial language comprehension, and memory tasks comparable to those mastered by chimpanzees (for a review of this literature see Herman, 1986).