A generation ago our society experienced a contentious reexamination of the concept of race and its relationship to equality in civil rights and benefits. We are now engaged in a similarly explosive reexamination of the concept of marriage—whether the civil rights and benefits that automatically accrue to heterosexual couples through marriage should be extended to bonded homosexual couples who wish to marry.

The issue incorporates complex biological, theological, cultural, and political elements. This month’s column will focus on the central issue of gender-related similarities and differences. Next month’s column will explore the fuzzy line that both unites and separates the concepts of male and female.

Gender has historically been defined as the separation of humans into male and female groups, with consequent cultural role and behavioral expectations.

Traditional gender perceptions and issues are now compounded by research technologies that can compare male and female body/brain structures and cognitive activity in ways not previously possible, and by the increasing public awareness of intersexuality—a condition affecting up to 2% of children who are born with an ambiguous sexual system that often creates gender identity and sexual orientation issues as they mature.

The traditional conventional wisdom that we consciously choose our sexual orientation has eroded as people thought more about their own personal experience, and about other biological predispositions (such as handedness and temperament) that they similarly didn’t consciously chose.

The roles culture and genetics play in gender behavior has similarly become problematic as parents observe developmental variations in children’s play patterns and adolescent friendship preferences.

It thus appears that individuals are either clearly male or female, or else exist (for whatever biological and/or cultural reason) somewhere along an androgynous continuum between the two pure gender strains. Gender isn’t the simple straightforward conscious phenomenon that most folks formerly believed, and that some folks continue to believe.

Some cultural gender differences seem to have little to do with biology, such as the constantly shifting clothing and hair styles, the division of household tasks, and the recent gender shifts in some vocations—such as that more women are becoming medical doctors and attorneys, and more men are becoming nurses and early childhood teachers.

Other differences are biological. It’s obvious that different reproductive roles require related differences in male/female bodies and brains. For example, although the hormones testosterone, estrogen, oxytocin, and vasopressin are present in everyone, females typically have more estrogen and oxytocin, and males more testosterone and vasopressin. Further, females have a monthly menstrual cycle, and males have both daily and yearly testosterone cycles (high morning and autumn, low evening and spring). The more complex question is whether other significant normative brain differences exist that aren’t as easily related to reproductive roles.

The average male brain is slightly larger than the average female brain, but the average female brain is slightly larger if we factor in body size differences. The corpus callosum that connects the two hemispheres is slightly larger in females, but the hypothalamic structure that seems to regulate sexual orientation is larger in males than females (although at least some homosexual men have a female size structure). Females tend to have a more dominant left hemisphere, and males a more dominant right hemisphere. The significance of these and other differences is problematic and controversial.

Further, our survival depends on our ability to understand how objects and systems function (systematizing capability), and to infer other people’s thoughts and intentions (empathizing capability). Although almost all males and females can do both adequately, males seem to have a slight edge in systematizing and females in empathizing. Memory involves recalling the general concept and also the factual knowledge that underlies the concept. Females seem to have an edge on factual recall and males on conceptual recall. Navigation strategies use geometric cues and the recall of landmarks. Males seem to depend more on geometric cues and females on landmarks. The typical male stress response is a fight/flight aggressive response, but in females it’s often a tend/befriend nurturing response.

These and other reported overlapping gender differences create interpretive dilemmas. What we do know is that: (1) Males and females are structurally and behaviorally much more similar than different; (2) differences don’t imply that one cognitive property or strategy is necessarily better than another; (3) measurable differences must be interpreted in light of the within/between factor in normative research studies that compare group scores on human properties, capabilities, and behaviors (such those listed above). The range of scores within each group is larger than the difference between the mean scores of the two groups. For example, consider height differences in large normally distributed male and female groups. The difference between the tallest and shortest person in each gender group will be greater than the difference between the average heights of the two groups of males and females. Thus, some females will be taller than some males in normative groups, even though the total population of males averages 7% taller than females.

Group differences thus only show group tendencies; they don’t predict for any single person in either group. So although it’s possible and appropriate to report general observations about male/female differences, it’s inappropriate to stereotype—to use a general observation about a group to predict the properties, capabilities, and behavior of any individual male or female within the group.

Last month’s column further suggested that it’s inappropriate to argue that only genetic or only cultural factors (and not a mix of the two) led to the difference.

Gender-related cultural phenomena such as marriage, sports teams, and clothing styles are currently in flux. We went through a contentious period a generation ago in which many were disturbed when men started to wear longer hair; and we’re now going through a period in which some female students want to join the wrestling team or become the football team’s place-kicker. Same-sex marriage is perhaps just another step on a path of gender redefinition we’ve already been traveling for some time. Is marriage thus a phenomenon that should only involve two separate and pure gender categories, or should marriage be redefined as a personal public bonding commitment between two people, irrespective of where each falls on the gender continuum?

So the issue comes down to how we should now define the concepts of male and female, considering recent biological thought and discovery on the issue. We’ll tackle that difficult issue next month.