of male and female reproductive behaviors and how they have helped to shape the biocultural trajectory of our species. In considering these theories, therefore, it is essential to gain an understanding of where their proponents stand on the fundamental issue of male and female reproductive strategies and their effect on human social life over time. This chapter will explore the basics of human anisogamy and discuss how its significance is perceived in both historic and contemporary schools of thought.
Size Matters
Anisogamy, simply defined, is sexual reproduction involving the fusion of gametes of different size or form. In humans, a large, slow-moving egg cell (ovum) is fertilized by a tiny, highly mobile sperm cell (spermatozoon). Egg cells, which are over eighty-five thousand times larger than sperm cells, contain DNA, mitochondria, nutrients, and the resources essential to support new life. Females are born with about 2 million egg cells, only four to five hundred of which will ripen (one each month) over a fertile lifespan, with the remainder degenerating over time. Sperm cells also contain DNA and mitochondria but no nutrients, and are instead optimized for mobility. Gamete production in males is continuous, with about 100 million sperm cells generated daily, or an estimated 2 trillion over a lifetime.
Anisogamy, by its very nature, creates disparate but complementary reproductive roles and strategies. Females produce a small number of nutrient-rich eggs that emit pheromones to attract male sperm for fertilization. Males, in contrast, produce huge numbers of sperm cells that must vie with one another in their typically ill-fated race to unite with an available egg. Since the demand for eggs is greater than the supply, ova enjoy much better odds of passing along their DNA to the next generation than do individual spermatozoa. The greater reproductive investments required of females by gestation and lactation also have the effect of delaying ovulation, thereby further restricting the supply of eggs potentially available to sperm for fertilization. These factors combine to make females the primary limiting resource in male reproductive success.
The traditional textbook version of how the fusion of ova and spermatozoa occurs typically begins with the egg being swept up into the fallopian tube and drifting toward the uterus. Sperm cells released in the vagina move through the female genital tract and race toward the large and essentially dormant egg. At the climax of this intense and somewhat perilous journey, the first among the thousands of sperm to arrive, successfully attack, and forcefully breach the egg’s zona or protective barrier wins, and fertilization occurs. This scenario thus paints female gametes as the passive recipients of male competition and penetration, and male gametes as active contestants and penetrators of the coveted target.
Perception of Conception
In 1991, Emily Martin (no relation) wrote an enlightened and entertaining article entitled “The Egg and the Sperm: How Science Has Constructed a Romance Based on Stereotypical Male-Female Roles.” Its focus is on how male and female behavioral stereotypes have become infused into the imagery of conception. How could the description of a relatively straightforward biological process be influenced by cultural bias? Martin’s paper calls attention to the findings of a Johns Hopkins University study that fundamentally revised the science on how fertilization actually occurs. Whereas it was formerly thought that sperm were the aggressors that burrowed through the egg’s zona by the force of their tails, the study discovered that eggs actually capture sperm cells, adhering to them firmly and forcing the head of the sperm to lie flat against the surface of the zona. Successful conception requires a unique and active partnership between the gametes:
The trapped sperm continues to wiggle ineffectually side to side. The mechanical force of its tail is so weak that a sperm cannot break even one chemical bond. This is where the digestive enzymes released by the sperm come in. If they start to soften the zona just at the tip of the sperm and the sides remain stuck, then the weak, flailing sperm can get oriented in the right direction and make it through the zona—provided that its bonds to the zona dissolve as it moves in. (Martin 1991: 493)
Martin’s point is that even in the seemingly objective context of reproductive physiology, biological facts can be construed in cultural terms. Thus, female gametes have been typically characterized as slow-moving, passive, dependent cells waiting to be “deflowered” and seeded with life, while male gametes are aggressive, active, and competitive cells bent on forceful penetration of the hapless egg. The fact that eggs play a very active and complementary role in facilitating fertilization by trapping sperm cells and preventing their escape—that eggs and sperm are mutually active partners in the business of conception—was an idea unexplored by biologists for decades. Instead, eggs and sperm in scientific discourse took on the idealized personalities of females and males in the larger society.1
Reproductive Roles and Social Origins Theory
Before the development of modern genetic science, theorists speculating on the evolution of early human sociality relied principally on observations of animal reproductive behavior, along with conclusions drawn from their own cultural experience (including sacred creation myths). The prevailing Victorian viewpoint was that perceived differences in male-female sexuality were linked to innate behavioral traits. Males were naturally sexual, aggressive, competitive, and cognitively superior. Females, in contrast, were both defined and limited by their maternal reproductive functions. As such, they were typically characterized as naturally asexual, passive, nurturing, noncompetitive, and also less capable of complex thought. Several nineteenth-century scholars proposed that these disparate male and female traits had consequences for the way that human society evolved. The abbreviated version of such theories is that, thanks to the alleged sexual restraint of women, early humans emerged from an original state of promiscuity to one of ancient matriarchy, in which society was organized around the obvious biological linkage between females and their offspring. This evolutionary stage was eventually overthrown by males, who established domestic units and enjoyed sociopolitical dominance from that point forward.2
Hindsight being 20/20, such notions about innate male and female aptitudes and universal evolutionary stages are now typically dismissed as examples of both gender stereotyping and immature science. But as with the story of the egg and the sperm, cultural bias continues to color our perception of human nature and societal origins. Although presented with a different veneer, behavioral stereotypes rooted in the perceived consequences of anisogamy have been amazingly persistent. International conferences and symposia held in the late 1950s and 1960s framed a model of ancient Paleolithic social life that equated the advent of hunting by males with the origin of human culture itself. As in Victorian times, males were portrayed as sexually dominant and competitive, but as presumably bridling this enthusiasm for the camaraderie of the hunt. This model assigned males active roles as family heads and providers to dependent consorts and offspring, and credited them with the defining achievements in human evolution, such as the invention of tool making.3 Females, in contrast, were cast in a largely peripheral role, serving as reproductive vessels and performing perfunctory domestic tasks of limited economic value. They were, in essence, silent partners in the evolutionary saga—dependents and nonproducers who traded sexual favors and reproductive functions for economic support.4
A subsequent spin-off of this model, the male-bonding hypothesis, gained some popularity in the early 1970s.5 Its basic thesis was that males are biologically predisposed toward cooperative activities, whereas females lack such built-in genetic codes. Proponents argued that this sexual divide originated from selective pressures that favored bonding among males, initially for group defense and eventually for the predation of the hunt. The model went further, linking such activities to cortical expansion in ancient humans—a consequence of subordinating male sexual competition to the interpersonal cooperation and emotional control necessitated by cooperative hunting. Opportunities for social and intellectual advancement provided by the hunt were allegedly unavailable to the other half of the species due to their reproductive responsibilities and assumed temperament. Females, allegedly burdened by serial pregnancies,
