Abstract: Paternal care in humans is facultative, with investment decisions responsive to socioecological context. In particular, paternity confidence is thought to have a significant impact on men's provisioning. However, various aspects of the relationship a man has with his partner can also influence the way he provides for his children. Previous papers have tended to focus either on these kinds of relationship dynamics or on the impact of paternity confidence. However, these categories are often intertwined and parsing their contributions can be conceptually and methodologically difficult. To better understand how paternity confidence and relationship dynamics impact men's investment decisions, we used a series of pictorial vignettes to assess the resource allocation strategies of Himba men. We focus on three traits: mate fidelity, partner type (marital or non-marital), and relationship status (current or former). Results suggest that men prioritize mate fidelity and current reproductive partners in investment decisions, but social obligations to past and current partners and the presence of other male investors also influence decisions. Himba men appear to be balancing social norms related to marriage and fatherhood with individually-driven incentives to invest in current and more faithful partners.
4. Discussion
Our
results show strong evidence for our primary predictions, which are
derived from life history theory, and which are fairly intuitive. Fig. 3
demonstrates this most clearly. All else equal, men favor more faithful
partners (rows 1, 10, 15), partners they have formal unions with (2, 7)
and, to a lesser extent, current partners (4, 9, 11, 14). Our secondary
predictions, which bring these factors together into a series of
potential strategies, show greatest support for the paternal investment
hypothesis, as partners with omoka children are consistently
short-changed in the allocations, and the social obligation hypothesis,
as wives are strongly favored over other types of partners (Fig. 1,
Panel D). The best fitting model included all three primary factors:
partner fidelity, relationship type and relationship status, providing
additional evidence that men are employing a mixed-strategy. These
experimental results emphasizing a mixed strategy are aligned with
behavioral data on Himba paternal investment (Prall and Scelza, 2016).
Measures of children's nutritional status, fosterage status and
livestock transfers show some titration of investment toward children
men believe to be omoka, but these occur largely when investments occur
in the more private household domain. When investments occur in more
public domains, social obligations to wives and marital offspring lead
men to treat biological and non-biological children more equally.
[Fig. 3.
Posterior predictions of differences between categories from the best
fit model predicting food allocation. Each distribution represents the
difference between the two types of women, so that distributions to the
right of zero indicate the first woman listed is predicted to receive
more food gifts.]
The best fitting model shows that overall girlfriends and ex-wives are treated relatively equally (Fig. 1, Panel D), but this finding masks some of the interesting variation that occurs in distributions to these two partner types (Fig. 3). In the two cases where omoka
status differs between girlfriends and ex-wives (rows 12 and 13), men
allocate substantially more to the partner with his biological child.
Paternal investment appears to be a greater motivator than either social
obligations or mating effort. Similarly, when the child is not omoka
in both cases, distributions to girlfriends and ex-wives are
indistinguishable (row 11). Where we see a breakdown is in the scenario
where both children are omoka. Here we see men favor girlfriends over ex-wives, suggesting some support for mating effort over social obligation (row 14).
The
second part of our study was designed to understand whether men are
titrating their allocations dependent on whether another partner (and
potential provider) is present. Men's allocations to girlfriends fit
this pattern, with substantially greater giving to girlfriends who are
unmarried than to those who are married. There are several explanations
that could account for these results, other than the need-based
explanation we are positing. Men could give less to women with other
partners as a form of punishment for their infidelity. Women without
other partners may also be more likely to father a man's next child, so
that giving more to her represents mating effort. Our data do not allow
us to test between these explanations. However, opportunistic quotes
recorded during the interview process invoking differential need were
frequent among our participants. In a typical iteration, one man stated,
“This woman has a husband. I will help this one because she doesn't
have a husband and needs support.” Therefore, we conclude that
need-based considerations are likely to be one important factor in men's
decision-making.
A slightly different pattern emerges
in Task 2B where men made allocations across wives. Those without
boyfriends still received more than those with boyfriends, but the
results were less consistent. Men were much more likely to distribute
resources evenly across wives than across girlfriends. In the two
categories where men were distributing an even number of items (for food
and clinic fees) they divided them equally between wives, 40% and 81%
of the time respectively, compared to only 19% and 42% of the time with
girlfriends. One man reported, “I think of them as my co-wives. You have
to treat them equally so that they don't get jealous and one doesn't
think that I don't like her.” In the third iteration of Task 2, men were
forced to make an unequal distribution. Unlike with girlfriends, where
this did not pose a problem, some men were very resistant to making a
choice between their wives, with one commenting “I would cut that goat
in half” rather than have to choose. This again speaks to the complex
interaction of factors affecting men's strategies. Social obligation may
dictate that men should treat their wives (relatively) equally, but men
may also be hedging their bets, keeping both wives happy may increase
their overall chance of paternity in future children.
We
also surmise that need was not driving men's choices in the wife
scenario to the same degree that it was with informal partners.
Opportunistic comments did not stress support from another partner in
the way they did in the girlfriend comparison. This may be due to the
difference in obligatory provisioning that exists between formal and
informal partners. While a man is obligated to provide for his wives,
giving to girlfriends is voluntary. Previously, our work showed that for
this reason, women had a stronger preference for generosity in
boyfriends, whereas in husbands, wealth mattered more (Scelza & Prall, 2018).
Here we see that men bias their giving to girlfriends based on need,
but factoring in the gifts of others to their wives seems secondary to
concerns about keeping the peace at home and treating wives equally.
4.1. Limitations and future directions
The
experimental approach used here provides some insight as to how Himba
men make decisions about allocating resources across partners of
different types. While the high rates of concurrency and nonpaternity in
this population mean that most men encounter these types of decisions
at some point in their lives, rarely would they encounter all of them at
once, highlighting an advantage of the vignette approach. However, as
with all studies that use hypothetical allocations, these data may not
reflect the ways that men divvy up real resources, but rather how they
view social expectations to allocate resources. In response to this,
many economic games use cash and follow through with distributions as
promised in the game; however, this approach was not feasible here.
Despite this limitation, we found that the men in our study understood
the complexity of the problem before them, as highlighted by
opportunistic comments made throughout the task.
In
addition while we thought it was important to address the ways in which
men's allocations could be altered by the presence of other providers,
this is neither the only nor necessarily the most important way that
need might influence giving patterns. Other factors we did not consider
in this study include the relative wealth or security of the woman
herself, the wealth of her parents, and her number of dependents.
Similarly, we did not look at how men's own wealth or security affect
his provisioning strategy. Finally, while we did not detect any effects
of age or marital status in our analyses (see Fig. S7), it is possible
this is due to small sample size. Future studies with larger numbers of
participants could address these shortcomings, using either behavioral
or experimental data.
Finally, this paper focuses
exclusively on men's provisioning decisions. The emphasis on men's care
as facultative in the literature drove the design of this study.
However, while certain aspects of maternal care are obligate in humans
(most significantly pregnancy), most care by mothers is quite variable.
Future work should consider how the factors studied here impact maternal
provisioning decisions.
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