Chief
Makwira and his wives, Malawi, 1903 (Wikicommons). Older men had first priority.
Younger men could gain access to women only through war or adultery.
In
my last column, I reviewed the findings of Butovskaya et al. (2015) on
testosterone and polygyny in two East African peoples:
-
Testosterone levels were higher in the polygynous Datoga than in the monogamous
Hadza. This difference is innate.
-
Datoga men were more aggressive than Hadza men on all measures used (physical
aggression, verbal aggression, anger, and hostility)
-
Datoga men were larger and more robust than Hadza men
-
All of these characteristics seem to be adaptive under conditions when men have
to compete against other men for access to women
Testosterone
levels were not only higher in the Datoga but also more variable. Alvergne et al. (2009) studied this variability in Senegalese men, finding that the monogamous
ones differed from the polygynous ones in the way testosterone levels changed
with age. The levels were higher in the polygynous men than in the monogamous
men between the ages of 15 and 30. After 45, this pattern reversed: the
monogamous men had the higher levels. At all ages, the polygynous men were more
extraverted than the monogamous ones, this quality being defined as
"pro-social behavior which reflects sociability, assertiveness, activity,
dominance and positive emotions." Extraversion may assist a reproductive
strategy of seducing women, rather than providing for them.
Thus,
when Africans gave up hunting and gathering for farming, there was selection
for a new package of male traits. Some of these traits are physiological
(higher testosterone levels), some anatomical (denser bones, greater arm and
leg girth; changes to muscle fiber properties, etc.), and some behavioral (polygyny,
aggressiveness, extraversion, etc.). But this selection didn't eliminate older
genotypes, at least not wholly. There seems to be a balanced polymorphism that
allows a minority of quieter, monogamous men to thrive in a high-polygyny
society like Senegal. When polygynous men become too numerous, they may spend
too much time looking for mating opportunities and not enough checking up on
their current wives to avoid being cuckolded. It might be better for some to live continuously
with one wife.
African Americans
versus Euro Americans
The
above differences within sub-Saharan Africa (Datoga vs. Hadza, polygynous
Senegalese vs. monogamous Senegalese) are also seen between African Americans
and Euro Americans. In all these cases, the differences are of degree and
proportion, rather than absolute and non-overlapping.
Testosterone
reaches high levels in young African American adults (Pettaway, 1999; Ross et al., 1986; Ross et al., 1992; Winters et al., 2001). African Americans are also
likelier to have alleles for high androgen-receptor activity (Kittles et al.,2001). Lifetime exposure to testosterone is reflected in development of
prostate cancer, with African American men having the world's highest
incidences (Brawley and Kramer, 1996). It was once thought that lower
incidences prevail among black West Indians and sub-Saharan Africans, but
underreporting is now thought to be responsible (Glover et al., 1998; Ogunbiyi and Shittu, 1999; Osegbe, 1997).
In
African Americans, blood testosterone levels peak during adolescence and early
adulthood, being higher than those of Euro Americans of the same age. Levels decline
after 24 years of age, and by the early 30s are similar to those of European
Americans (Gapstur et al., 2002; Nyborg, 1994, pp. 111-113; Ross et al., 1986;
Ross et al., 1992; Tsai et al., 2006; Winters et al., 2001). This is the same pattern
we saw in polygynous Senegalese men versus monogamous Senegalese men. In short,
polygyny seems associated with a more exaggerated pattern of variation with age.
The demographic
contradictions of a high-polygyny society
Testosterone
levels are normally higher in all young men, but why are they higher still when
polygyny is common? The reason seems to be the scarcity of available women.
High-polygyny societies generate a shortage of mateable women, and this
shortage is managed by giving priority to men who are at least ten years past
puberty. For instance, among the Nyakyusa: "[...] there is a difference of
ten years or more in the average marriage-age of girls and men, and it is this
differential marriage-age which makes polygyny possible" (Wilson, 1950, p.
112).
By
concentrating celibacy among young men, this age rule compels them to seek sex
through warfare or illicit means. According to Pierre van den Berghe (1979, pp.
50-51):
Typically,
the more men are polygynous in a given society, the greater the age difference
between husbands and wives. [...] The temporary celibacy of young men in
polygynous societies is rarely absolute, however. While it often postpones the
establishment of a stable pair-bond and the procreation of children, it often
does not preclude dalliance with unmarried girls, adultery with younger wives
of older men, or the rape or seduction of women conquered in warfare. Thus,
what sometimes looks like temporary celibacy is, in fact, temporary
promiscuity. These young men often devote themselves to warfare during their
unmarried years and sometimes homosexuality is tolerated during that period.
For
young men in a high-polygyny society, warfare—typically raids against
neighboring communities—is the main way to gain access to women. In a sense,
war becomes a means of resolving the demographic contradictions of a
high-polygyny society. Polygyny creates a wife shortage among young men, and
this contradiction is resolved by turning it outward. As warriors, young men
are encouraged to satisfy their sexual urges through raids against neighboring
peoples. Warfare thus becomes endemic.
This
relationship between polygyny and war has often been noted in studies of
African societies:
Dorjahn
(1959) says African warfare emphasized taking captives, rather than killing the
enemy. Kelly's discussion of Nuer warfare provides an interesting perspective
on this phenomenon. In Nuer warfare the main casualties were younger men and
older women, with male and female mortality being almost equal. Younger women
and children were captured. Female captives were valued because they could be
used to generate bridewealth when they were married to other Nuer, whereas
captive boys were adopted into the lineage of their captor and would require
bridewealth payment when they married. Consequently, few males were taken captive
(Kelly 1985:56-57). (White and Burton, 1988)
In
their cross-cultural study of the causes of polygyny, White and Burton (1988)
conclude that "polygyny is associated with warfare for plunder and/or
female captives":
[...]
polygyny is seen as associated with the expansion of male-oriented kin groups
through favorable environments, facilitated by capture of women or bridewealth
via warfare. Following this analysis, it is difficult to see polygyny as having
benign effects upon the lives of all women. Rather, polygyny produces benefits
for senior wives, who have sons and can mobilize the labor of junior wives and
children (Hartung 1982); it has negative effects on women who become slaves,
captives, or junior wives, or who do not have sons.
We
now come to a leading cause of the African slave trade. Polygyny led to
warfare, which led to a surplus of unwanted male captives. These captives could
be sold as slaves, but local markets would soon be saturated. The excess supply
had to be sold farther away, with the result that slave trading networks began
to reach the Middle East as early as the time of Christ (Frost, 2008).
While
outsiders from the Middle East and Europe would later get more and more
involved, becoming not only traders but also captors, it was Africans
themselves who initially controlled the supply chain. In its early stages, and
even later, this trade was driven by factors internal to Africa.
Contrary evidence
Whenever
I discuss this subject, some people will counter that certain studies have shown
an absence of racial/ethnic differences in testosterone levels. Let me discuss
these studies at some length.
This
meta-analysis concluded: "After adjustment for age, black men have a
modestly but significantly 2.5 to 4.9% higher free testosterone level than
white men." Here, “adjustment for age” means comparing black and white men
of the same age. The conclusion isn't surprising, since African American men
have a testosterone advantage only from puberty to their early 30s. At other
ages, their testosterone levels are either equal to or less than those of Euro
American men.
This
meta-analysis has two other flaws. First, it included only studies on "men,"
thus excluding studies on teenagers, among whom the race difference is greatest.
Second,
it included Rohrmann et al. (2007). This study suffers from serious
methodological problems, as I will now explain.
This
study concluded that "contrary to the postulated racial difference,
testosterone concentrations did not differ notably between black and white
men."
This
study also found that 45-69 year old black men have higher testosterone levels
(5.62 ng/ml) than do 20-44 year old black men (5.35 ng/ml). Such a finding is
paradoxical and indicates a faulty dataset. The authors used serum samples from
the National Center for Health Statistics that had been earlier collected for
its Third National Health and Nutrition Examination Survey (NHANES III). The
authors state they used 1,479 samples that remained out of an initial total of
1,998. Over 25% of the original samples were missing. The authors state that
some samples were missing because they were being used for another study.
The
same serum bank had in fact been used for research on a sexually transmitted
disease. This was the study by Fleming et al. (1997), who reported that more
than 25% of adults between 30 and 39 years of age were positive for HSV-2
(Herpes Simplex virus type 2). Those samples may have been set aside either for
further testing or for legal reasons. The serum bank would have thus lost some
of its most polygynous donors.
This
study measured salivary testosterone in young men (15-30 years) from the United
States, Congo, Nepal, and Paraguay. Americans had the highest levels (335
pmol/l), followed by Congolese (286 pmol/l), Nepalese (251 pmol/l), and
Paraguayans (197 pmol/l).
Who
were these Americans? They are simply identified as ... young Americans—a
demographic that is now less than 60% of European descent. In Boston, where the
study was conducted, public schools in 2005 were 46% black and 31% Latino
(mainly Puerto Ricans and Dominicans). The authors also state that "the
USA participants were recruited by public advertisement." The pool of
participants may have therefore resembled that of people who give blood in
exchange for payment, i.e., it may have been disproportionately poor and
non-white. In any event, the results are unusable without any information on racial
background.
The
Congolese participants were likewise unrepresentative of Congolese in general.
They were Lese who inhabit the Ituri forest in proximity to the Efe pygmies.
Many Lese are, in fact, partly of pygmy ancestry. As such, their testosterone
levels would be closer to that of hunter-gatherers with lowers levels of
polygyny and less male-male competition for mates.
This
study concluded that testosterone levels did not differ between African
American and Euro American boys between the ages of 6 and 18. Such a finding is
to be expected for the first few years of this age range, when no difference
should exist between the two groups. The main flaw, however, is that the participants
were compared not by age but by Tanner stage. Since African Americans enter
puberty earlier, this study compared younger African American boys with older
Euro American boys.
Testosterone
levels may differ between the two groups because of earlier maturation by
African American boys. But why would this difference persist beyond adolescence
and into the mid-twenties? This question remains unresolved because none of the
participants were older than 18.
Various African studies
Several
studies have found lower testosterone levels in African populations than in
North Americans. This difference might be partly due to the effects of
malnutrition or infectious diseases, notably among the Zimbabwean subjects
studied by Lukas et al. (2004). The main reason, however, is that these studies
mostly had middle-aged or even elderly participants. Lukas et al. (2004) report
a mean age of 42.18. The scatter plot (Fig. 2) suggests a logarithmic decline
in testosterone with age, but there were too few participants below 25 for
analysis of that age group. The same criticism applies to Campbell et al. (2003), a study of testosterone levels in Ariaal pastoralists from northern
Kenya. The mean age was 46.8.
In
addition, some of these studies concern hunter-gatherers, like the !Kung of
Namibia and the Ituri Forest pygmies of the Congo, who have low polygyny rates
and weak male-male competition for mates (e.g., Winkler and Christiansen, 1993). Their low testosterone levels are thus to be expected.
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