Kinship, Sex, and Fitness in a Caribbean Communityweb.missouri.edu/~flinnm/pdf/QuinlanFlinn2005.pdfKinship, Sex, and Fitness 37 father, then two of three possible crew compositions

32 Human Nature / Spring 2005

Received March 30, 2004; accepted August 2, 2004; revised version received September 20, 2004.

Address all correspondence to Robert J. Quinlan, Anthropology Department, Ball State University,Muncie, IN 47306. Email: [email protected]

Human Nature, Spring 2005, Vol. 16, No. 1, pp. 32-57. 1045-6767/98/$6.00 = .15

Kinship, Sex, and Fitness ina Caribbean Community

Robert J. QuinlanBall State University

Mark V. FlinnUniversity of Missouri, Columbia

Patterns of human kinship commonly involve preferential treatment of relativesbased on lineal descent (lineages) rather than degree of genetic relatedness(kindreds), presenting a challenge for inclusive fitness theory. Here, we examineeffects of lineage and kindred characteristics on reproductive success (RS) andnumber of grandchildren for 130 men and 124 women in a horticultural communityon Dominica. Kindreds had little effect on fitness independently of lineage charac-teristics. Fitness increased with the number of lineal relatives residing in the com-munity but decreased beyond an apparently optimal lineage size, suggesting resourceenhancement and competition among kin. Female-biased patrilineage sex ratio waspositively associated with men’s fitness, while male-biased matrilineage sex ratiowas positively associated with women’s fitness. Number of brothers in the commu-nity was negatively associated with men’s, but not women’s, fitness. Parents andnumber of sisters had no effect on either male or female reproduction; however,women with younger sisters had higher RS, suggesting benefits of kin support forchildcare. In sum, imposed norms for lineage social organization may enhancelineal ancestors’ inclusive fitness at a cost to individual inclusive fitness.

KEY WORDS: Biocultural anthropology; Caribbean ethnography; Demography;Evolutionary ecology; Family; Kin selection; Reproduction; Sex differences

Kinship is a fundamental component of human sociality that affects eco-nomic, political, and reproductive behavior, especially in small-scale so-

cieties characteristic of our evolutionary history (Brown 1991). Although kin

03Quilan-Flinn.pmd 5/3/2005, 11:00 AM32

Kinship, Sex, and Fitness 33

networks are universally important cross-culturally, there are substantial varia-tions in network types, including complex maternal-paternal, affinal-consanguineal,1 and generational biases (Murdock 1949). Inclusive fitnesstheory predicts kin cooperation when relatedness (r) between individuals mul-tiplied by the benefit of receiving aid (b) exceeds the cost (c) of giving aid (br> c [Hamilton 1964]). Humans sometimes reckon kinship cognatically (throughall genetic/genealogical links; Figure 1a), conforming to patterns predicted bythe “r” in Hamilton’s rule. But humans often reckon kinship lineally (throughlinks that track Y-chromosome and mitochondrial inheritance; Figure 1b), ex-cluding half or more of our genetic/cognatic kin or “kindred.”2 Conflicts ofinterest regarding cognatic and lineal kinship may arise in multi-party interac-tions because ego-centric kindreds incompletely overlap, complicating pre-dictions from a model based on dyadic interactions (Alvard 2003; Jones 2000;Hughes 1988; van den Berghe 1979). Lineages may reflect compromises thatfacilitate kin-based coalitions.3 Most traditional societies have kinship rulesthat favor lineage members, excluding more closely related kindred members(e.g., Fortes 1969), though surreptitious “rule breaking” favoring nonlinealkin is commonplace (Chagnon 2000). Lineage membership, hence, may in-fluence fitness in ways not easily predicted by Hamilton’s rule. The costs andbenefits of interactions among kin may vary by lineage or other aspects ofsocial organization.

In a recent study Alvard (2003) demonstrated that lineages are more impor-tant than individual relatedness in téna (whale boat) organization in Indonesia.In this paper we build on Alvard’s findings by examining effects of kindredand lineage membership on current and long-term reproduction in a Carib-bean village. We use multiple linear regression models to examine the struc-ture of locally recognized patrilineages, informal matrilineages, and theirrelations with sex-specific fitness. We use ethnographic data to explore emicmodels of kinship and relations among sex, kin groups, and resource controlin this land-based economy.

Some kin-group characteristics may make the groups beneficial to theirmembers (Chagnon 1979) and may affect cooperation through residence andmating patterns (Murdock 1949). In some circumstances, kin of equal related-ness but different categories may have unequal abilities to translate nepotisminto fitness (see Alexander 1979:156–162). Categories of kin are based on afew, relatively simple principles (“primitives of social cognition”), such as“group membership,” “social rank,” and “genealogical distance” (Jones 2003,2004). Here we examine whether two aspects of group membership—sexand lineage—override genealogical distance as an apparent consideration fornepotism.

Sex differences in work and social behavior may have important implica-tions for the structure of kin groups and their benefits to members; hence, thesex ratio of kin groups may be important (Chagnon, Flinn, and Melancon



Figure 1. Kindred- and lineage-based investment strategies.

Circles are women, squares are men. * indicates ego. Kindred-based investment (A) includes ego’smother and 14 living patrilateral relatives in generations 2 through 5. Kin with r < .125 are assumed tobe too distant to include in the kindred. Matrilateral kin are excluded to simplify the diagram. Lineage-based investment (B) includes 16 relatives in generations 1 through 5. Average r to ego in generations2 through 5 is .31 for the kindred- and .21 for the lineage-based strategy. B excludes closely relatedrelatives in favor of distant lineal kin. Average r to ego’s great-grandfather in the kin group depicted inB is .20. If we extend ego’s kindred to include the same matrilateral kin depicted in diagram A, thenaverage r to ego’s paternal great-grandfather is .08. The pattern is opposite to ego’s average r to kin inA and B.



1979). If one sex is more helpful than the other, then a sex ratio biased towardthe more helpful sex may increase individual fitness. Alternatively, if one sexis less cooperative, then a sex ratio biased toward the less cooperative sex maybe associated with reduced fitness. Similarly, if people of one sex are impor-tant points of contact in social networks, then kin groups rich in the “nodal”sex may benefit from the flow of information, resources, and opportunities.The spatial distribution of households and inheritance pattern of residencesites may influence these sex-specific patterns of behavior. Household forma-tion and inheritance often depend on lineage characteristics (Murdock 1949).

Kin group size also may entail costs and benefits. Large groups may benefitindividuals through improved access to resources, but there may be a maxi-mum beyond which resources are strained. “Local competition” among kinalters the cost-benefit ratio of nepotism (Griffin, West, and Buckling 2004).Additionally, tensions between kindred and lineage relatedness may suggestan optimal lineage size beyond which coefficients of relatedness within a largelineage become too low to justify excluding kindred members. For example,Yanomamo village fissioning appears to restore balance in shabono (village)relatedness and may also improve access to land for hunting and gardeningand help resolve conflicts over mates (Chagnon 1979).

Here we examine effects of kindred, matrilineage and patrilineage size, andsex ratio on the reproductive success and long-term fitness (number of grand-children) of men and women in a horticultural village in the Commonwealthof Dominica. Additionally, we compare fitness effects of emically recognized(named) patrilineages with those of informal (unnamed) matrilineages. Wealso examine whether kin group effects are mediated by siblings and parents.The objective is to simultaneously assess effects of each category of kin onindividual fitness. Basic inclusive fitness theory predicts that kindred compo-sition should have stronger effects on individual fitness than does lineagecomposition.

A CLASSIC KINSHIP QUESTION FOR EVOLUTIONARY ECOLOGY

Why lineages? Without consanguineous marriage, lineages deny resourcesto half of one’s kindred, the members of which may have equal or highercoefficients of relatedness to ego than do lineage members. Why don’t hu-mans typically use a more “genetically efficient” social mechanism for nepo-tism? Why not ego-centric kindreds?

Lineages may allow kin-based cooperation on a larger scale than does kin-dred membership (Alvard 2003; van den Berghe 1979) and also may offerpredictable social norms that are important in cooperation (Alvard 2003).Additionally, lineages may regulate collective action where resources (land,knowledge, tools, etc.) can be transferred to younger kin. Lineages avoid prob-lems of asymmetry of relatedness and nonoverlapping membership among a



cluster of ego-centric kindreds. Indeed, a lineage may represent a core ele-ment of a cluster of ego-centric kindreds; hence, it becomes a kind of compro-mise “kindred” for collective action and resource pooling through time.

Some anthropologists suggest that a lineage is a cultural construct that isadaptively suboptimal because one could choose to cooperate with ego-centric kindred members, resulting in higher individual inclusive fitness (re-viewed in Alvard 2003). Lineages may be a convenient tradeoff, ensuring atleast minimal kindred overlap among collective action parties where coopera-tion is enhanced by kinship (van den Berghe 1979). But much human collectiveaction involves groups including unrelated members, and high levels of coopera-tion can be achieved in non-kin groups. In fact, groups composed of lineagemembers and non-kin may have substantially lower coefficients of relatednessthan do groups composed of incompletely overlapping ego-centric kindreds.There may be, then, additional adaptive explanations for lineal affiliation.

Among humans, focused inheritance of durable resources may be a majoradvantage of lineage membership (Fortes 1969; Murdock 1949:37–39). Ineconomies where “capital” can be accumulated over time, lineages can in-crease long-term benefits of individual effort by preventing loss of resourcesat the margins of incompletely overlapping kindreds. Hence, lineages may bea feature of human sociality that enhances multigenerational (grandparental,etc.) fitness at a cost to other avenues for nepotism among collateral kin. Lin-eages offer a forward-looking kin investment strategy by promoting coopera-tion in the future, when the composition of ego-centric kindreds is unpredictable.The benefit, then, is the predictable transfer of resources across generations. Inland-based economies, lineages may ensure that individual pioneering andconquest effort benefits grandchildren, great-grandchildren, etc. Likewise,“expensive” knowledge or alliances between lineages forged by individualsmay persist in subsequent generations. Durable alliances, resources, and knowl-edge, hence, benefit ancestors through multigenerational inclusive fitness. Incontrast, a cognatic system may allow effort to be siphoned off at the marginsof nonoverlapping kindreds over several generations. In sum, lineages mayreduce the risk that non-kin benefit from kin-directed altruism.

Where resources/effort are inherited, kindred cooperation would be at oddswith grandparental inclusive fitness. Imagine a rule for fishing boat organiza-tion requiring the boat owner to crew his boat with two first cousins. From theowner’s standpoint, cooperation results in equal inclusive fitness irrespectiveof which cousins he chooses. If he chooses one matrilateral and one patrilateralcousin, cooperation may be hampered because the two crew members areunrelated. If productivity is not sensitive to symmetry of relatedness amongthe crew (e.g., when tasks are largely parallel—i.e., mechanical solidarity—orwhere reciprocity can override kinship), then there is no fitness problem. Fur-ther, if the owner chooses either two matrilateral or two patrilateral cousins,symmetry is achieved. However, if the man inherited the boat from his grand-



father, then two of three possible crew compositions reduce grandpaternal in-clusive fitness. Now imagine a rule requiring a man to crew his boat withpatrilineal kin only. If only one first cousin is available, then the owner choosesa patrilineal second cousin (FBSS),4 and his inclusive fitness is reduced com-pared with a crew that included matrilineal and patrilineal first cousins, but hispatrilineal grandfather’s inclusive fitness is preserved at a cost to ego’s fitness.Note also that if the patrilineal first and second cousins are not father and son,then average relatedness among the crew is the same regardless of whether theowner chooses one matrilineal and one patrilineal first cousin or one first andone second patrilineal cousin, though symmetry of relatedness is lower in theformer. Where resources are inherited, leaving future kin affiliations up todescendants can reduce the multigenerational efficiency of kin investment.Hence, lineages may be not just a culturally convenient way of organizingcollective action around kinship; rather, they could enhance fitness of ances-tors whose effort may benefit descendants. Lineage-based social organizationmay reflect imposed social norms (Jones 2000) that benefit ancestors’ fitnessat a cost to individuals. In sum, lineages may enhance cooperation throughsymmetry of relatedness in large groups and they may improve ancestral in-clusive fitness. Lineage-based strategies, however, may also entail costs toindividual inclusive fitness.

ETHNOGRAPHIC SETTING

The Commonwealth of Dominica is a small, rural island nation located be-tween the French departments of Guadeloupe to the north and Martinique tothe south (15°N, 61°W). The island is mountainous and relatively undevel-oped. Dominica’s population of about 65,000 is of mixed African, European,and Island-Carib descent. Most Dominicans are bilingual in English and French-Patois.

Bwa Mawego is one of the least developed villages on the remote, wind-ward side of the island. The village is located about a half-hour drive from amain road at the end of a narrow, mountainous road. There are approximately700 full- and part-time residents. Average annual income in Bwa Mawego isapproximately $5,000 E.C. ($1,850 U.S.). Economic opportunities are lim-ited, and many villagers have emigrated either temporarily or permanently inthe past three decades. The people of Bwa Mawego live in small (150–600ft2), mostly one- to three-room houses of wood or cinderblock. Many houseshave electricity, but only a few have rudimentary plumbing.

Economic activities are few. They include subsistence gardening, commer-cial agriculture, fishing, and, for a few villagers, wage labor. Cash crops are animport source of income for many families. Bananas and bay leaf are the twomain crops. Most families have for the past several decades cultivated at leastsome bay and banana trees. Other economic activities include driving a van or



truck, working in town, running a shop, teaching school, and part-time tradessuch as electrician and carpenter.

Many villagers are involved in some subsistence agriculture. Root cropsmake up the bulk of the rural Dominican diet. Family gardens primarily con-sist of one or more of several varieties of taro. Bitter manioc and yams are alsoimportant root crops. Gardens are usually cleared from the secondary forest atthe periphery of the village. Larger gardens are sometimes cleared farther out inthe bush. Plots can be cultivated almost indefinitely because small-scale farmershave easy access to herbicide and fertilizer. New economic opportunities andherbicide may have reduced land pressure in the community in recent times.

Bay oil, from bay leaf or bwa den, is the most important source of cash formost people in Bwa Mawego. Bay oil production is a labor-intensive, multiphaseprocess and is often an extended family affair in which the family owns thebay leaf and still (or “factory”) and provides the majority of the labor.

Land tenure in the village is complicated and sometimes contentious, andland ownership has a pattern similar to that of other Caribbean populations(e.g., Clarke 1957). Rights to use family land in Bwa Mawego are transferredthrough generations to many descendants. As the village founders died, eachof their children had rights to cultivate a portion of their land. Current partrilinealdescendants also have a right to use family land. Family land several genera-tions removed from the grantee is referred to by the original owner’s surname(e.g., L’Homme land).

This custom of naming family land reflects a general patrilineal bias in cal-culating genealogical relationships. For example, an individual with uncon-tested paternity calls both his father’s and mother’s families “my people.” Butin cases where ego’s parents had a stable conjugal union following a neolocalor patrilocal residence pattern, then matrilineal kin may be relatively unimpor-tant beyond second-degree relatives. Hence, offspring of stable conjugal unionswith parents from stable conjugal unions have a different model of kinshipthan do offspring of single mothers: One model of kinship is lineal while theother is cognatic (see Murdock 1968). These different models of kinship some-times play a role in land disputes (Quinlan 2000:87–90).

Kinship and family are the foundation of economic, social, and reproduc-tive behavior in Bwa Mawego. Almost everyone in the village is related throughconsanguineal or affinal links.5 Kin ties provide a map for navigating sociallife, and they offer avenues for the flow of goods and services. Family mem-bers cooperate for their mutual benefit. Husbands, wives, and children sharegardening chores. Male kinsmen work together on family construction projectsand garden clearing. Related women share childcare duties. This does notmean that friendships are not important, but the axiom of amity (Fortes 1969)has priority in Bwa Mawego.

Formal marriage in Bwa Mawego is an institution in decline, but many vil-lagers still forge durable conjugal unions. In Bwa Mawego, as elsewhere in the



Caribbean, a couple commonly has a child together before deciding to estab-lish a conjugal household. Once established, conjugal households are oftenstable. Currently about 30% of mothers are in long-term unions. This com-pares with about 21% for rural Jamaica and 41% for the Grenadines (M. Smith1962:231–232). Consanguineous unions are rare in Bwa Mawego.

Household composition varies in ways that may influence fitness. Conjugalhouseholds, male-headed extended family households, single-mother house-holds, and various permutations are common. Here “household” is defined asa group of people, primarily kin, who live in contiguous dwellings and whointeract regularly for economic, childcare, and recreational purposes. Figure 2shows common household configurations in Bwa Mawego. Matrilocality isrelatively rare as a long-term living arrangement. The general pattern is forconjugal families to occupy a house in the man’s extended family compoundor to take up neolocal residence. Households with at least one conjugal unionare associated with higher fertility, and adult males tend to increase householdwealth (Quinlan 2000).

The nature of cooperation among kin depends in large part on the structureof households and their relation to other households. For example, a womanwho moves into her husband’s extended family compound may receive littledirect assistance from affinal kinswomen, but her children receive care andsupport from paternal relatives. Coresident adult sisters, in contrast, assist eachother with childcare and daily chores. Women often motivate and organizefamily work parties. For example, bay leaf processing has many steps involv-ing multiple people over the course of several weeks. It is often an extendedfamily affair organized by a mature kinswoman. In general, male contribu-tions to household well-being are economic. For example, households with anadult male (including fathers, brothers, and husbands) have an average oftwice as many luxury items and three times the house value of householdswithout males (t = 3.1, one-tailed p = .002 for luxury items, t = 3.6, one-tailedp = .005 for house value).

Beyond households, larger kin groups are important. There are several largepatrilineages and many more small lineages. One “lineage,” in fact, techni-cally qualifies as a “clan” or “sib,” with two lineages sharing an unknowncommon ancestor. Generally, only patrilineal surnames are inherited, but whenthe father is completely uninvolved, a child may take her mother’s surname.Patrilineal descent provides individuals with access to ancestral family lands.This can be an advantage to individuals whose immediate family does notown land. In addition, distant kin generally look out for each other’s interestsin situations where non-kin would mind their own business. For example, aman might escort a drunken distant cousin home when non-kin would mostlikely ignore him. Reckoning distant relationships in Bwa Mawego depends,largely, on surnames that track patrilineal links.



Figure 2. Common household structures in Bwa Mawego.

Black circles and squares indicate nonresident kin. 1 = Conjugal neolocal; 2 = Conjugal extended; 3 =Patrilocal; 4 and 4' = Matrifocal extended; 5 = Single mother. 2' and 3' are combinations of conjugalextended and patrilocal.

METHODS

Field Techniques

Biocultural ethnography benefits from an interactive approach to qualita-tive and quantitative data wherein insights from each suggest analytical refine-ments and new questions (Aunger 1995). Kinship analysis is necessarily aniterative and dialectical process with a series of qualitative and quantitativesteps (Chagnon 1974; Chagnon and Bryant 1984): Understanding multigen-erational kin patterns requires ethnographic interviews, preliminary analysis,new interviews, quantitative analysis, and ethnographic interpretation, leadingto a new round of qualitative and quantitative inquiry. Data and analyses pre-sented here mark a point in time in a longitudinal study of multigenerationalfitness.

Genealogical data were used to examine relations between kin group mem-bership and fitness in Bwa Mawego. Data were collected and cross-checkedthrough a series of interviews. Multiple key informants provided the names ofeach ego’s mother and father for a list of all village residents obtained through



annual census updates (1987–2004). After the initial interviews the genealogi-cal database was analyzed for errors and missing data using the DIAGNOSEroutine of the KINDEMCOM software package (Chagnon and Bryant 1984).5

Once errors and missing data were identified a second round of interviews andcross-checks was conducted. The updated genealogical database was analyzedagain using the DIAGNOSE routine, and a third round of interviews filled innewly identified gaps in the data, including missing siblings. The process ofinterviewing and analysis was repeated four more times, after which the ge-nealogical memory of our informants was more or less exhausted. The result-ing database contains genealogical information for 1,826 individuals bornbetween 1835 and 2004.

Sample and Analysis

A sample of 130 males and 124 females born between 1900 and 1955 wasused to examine the sex-specific effect of kinship on number of offspring andgrandoffspring. Individuals who have emigrated or whose parents are notknown were excluded from the analyses.

Variables were extracted from the genealogical database using Descent soft-ware (Hagen n.d.). Current and long-term fitness are measured by numbers ofsurviving offspring and grandoffspring residing in and out of the village. Lin-eage variables include sex ratio of matri- and patrilineages and the number ofmatrilineal and patrilineal kin residing in the village. (See Table 1 for descrip-tive statistics.) Sex ratio is the number of lineage males resident in the villagedivided by the total number of resident lineage members. Sex ratio was usedrather than numbers of males and females in the kin group because the lattercaused substantial multicolinearity (number of males in the lineage is highly cor-related with number of females). Kindred variables include sex ratio of the kin-dred and total number of nonlineal relatives residing in the community. Numberof nonlineal relatives was used instead of total number of relatives because thelatter variable caused substantial multicolinearity when included in models withmatri- and patrilineage sizes. Mother, father, and number of brothers and sistersresiding in the community were entered in the models to test whether kindred andlineage effects are mediated by characteristics of the immediate family.

Multiple linear regression modeled effects of kindred, lineage, and immedi-ate family characteristics on number of surviving offspring (reproductive suc-cess or RS) and number of grandchildren (long-term reproduction or LR). Theanalysis is in four steps: Year of birth was entered on the first step to control forsecular trends in fertility. The second step examines the effect of kindred vari-ables. The third step includes matri- and patrilineage variables. And the fourthstep includes mother, father, and number of brothers and sisters. At each stepquadratic terms were entered for each predictor and significant terms (p < .10)were retained in the models.



Tabl

e 1.

Des

crip

tive

Sta

tist

ics

N =

254

(12

4 W

omen

and

130

Men

)

*Inc

lude

s re

lati

ves

livi

ng o

utsi

de th

e vi

llag

e

**R

elat

ives

resi

ding

in th

e vi

llag

e

Var

iabl

e

M

ean

Med

ian

s

.d.

M

in.

Max

. Y

ear

of b

irth

19

27.7

1929

17

.0

1900

1955

N

of

chil

dren

(R

S)*

4.

75

3.5

012

N

of

sons

* 2.

22

1.9

08

N o

f da

ught

ers*

2.

52

2.2

010

G

rand

child

ren

(LR

)*

6.6

3 9.

1 0

52

Kin

dred

sex

rat

io**

0.

560.

56

0.1

01

Pat

rilin

eage

sex

rat

io**

0.

560.

52

0.2

01

Mat

rilin

eage

sex

rat

io**

0.

470.

47

0.1

00.

88

Mat

rilin

eage

siz

e**

22.0

17

17.0

1

54

Pat

rilin

eage

siz

e**

26.3

15

26.9

1

81

N o

f no

nlin

eal r

elat

ives

**

13.4

10

14.3

0

59

N o

f br

othe

rs**

1.

41

1.4

06

N o

f si

ster

s**

1.2

1 1.

2 0

6



RESULTS

Year of birth was not significantly associated with reproductive success formen (rp = –.05, p =.55) or women (rp =.11, p =.23) and was negatively associ-ated with number of grandchildren for both (rp = –.48, p <.001; rp = –.35, p<.001). A quadratic function did not increase the proportion of variance ex-plained by year of birth.

There were small, statistically insignificant differences in male and femalefitness. Mean surviving offspring is 4.4 for men (95%CI: 3.8–5.1) and 5.0 forwomen (95%CI: 4.4–5.6), suggesting low fertility but a growing population.Mean age-adjusted number of grandoffspring is 6.2 for men (95%CI: 4.7–7.6)and 6.9 for women (95%CI: 5.5–8.4). Proportion of males and numbers ofsons and daughters in the completed fertility sample indicate a balanced popu-lation sex ratio (Table 1).

Kindred and Lineage Effects on Fitness

Lineage characteristics were more strongly associated with fitness than werekindred characteristics, and sex differences in kinship effects are apparent.Initially only matrilineage characteristics showed significant effects on malereproductive success (RS), with female-biased sex ratio and moderate-sizematrilineage tending to increase male RS (Table 2, model 3). However, the sexratio effect was mediated by number of brothers. In the final model, RS was aquadratic function of matri- and patrilineage size: A matrilineage with about32 members and a patrilineage with about 73 members in the village tended tomaximize male RS, which decreased in larger lineages. Number of brothers inthe community was negatively associated with men’s RS, suggesting competi-tion for resources among males over the life course. Number of sisters andpresence of mother and father in the village were not significant predictors ofmen’s RS. When immediate family variables were included in the model, male-biased kindred sex ratio is positively associated with RS, but the effect wasonly marginally significant (P = .092). Together these results indicate substan-tially higher fitness among men from moderately large matrilineages, and largepatrilineages, who have few brothers.

For women, matrilineage sex ratio and patrilineage size were associatedwith reproductive success, but patrilineage sex ratio and matrilineage size werenot (Table 3). Initially, women’s reproduction was associated with kindred sizeand sex ratio, but the relations were mediated when lineage variables enteredthe model (Table 3, models 2 and 3). Women’s RS was positively associatedwith male-biased matrilineage sex ratio, and it was a quadratic function ofpatrilineage size. A patrilineage with about 63 members residing in Bwa Mawegotended to maximize women’s RS. Number of siblings and presence of parentswere not associated with women’s RS.


Tabl

e 2.

Mul

tipl

e L

inea

r R

egre

ssio

n S

how

ing

Eff

ect o

f K

indr

ed, L

inea

ge, a

nd I

mm

edia

te F

amil

y on

Men

’s R

S

Mod

el 1

M

odel

2

Mod

el 3

Mod

el 4

V

aria

bles

B

β

P

B

β P

B

β

P

B

β P

(C

onst

ant)

25

.191

—

0.

466

39.1

74

—

0.27

7 57

.753

—

0.

161

40.4

71

—

0.35

4 Y

ear

of b

irth

–0

.011

–0

.053

0.

548

–0.0

19

–0.0

92

0.32

1 –0

.028

–0

.137

0.

194

–0.0

21

–0.1

02

0.35

6 K

indr

ed s

ex r

atio

1.46

6 0.

053

0.55

4 5.

469

0.19

6 0.

091

6.11

0 0.

219

0.09

2 N

of

nonl

inea

l rel

ativ

es

0.

031

0.11

8 0.

204

–0.0

01

–0.0

05

0.95

4 –0

.009

–0

.034

0.

.727

M

atri

line

age

sex

ratio

–6

.522

–0

.253

0.

023

–2.4

81

–0.0

96

0.47

1 M

atri

line

age

size

0.

168

—

0.03

3 0.

192

—

0.02

4 (M

atri

linea

ge s

ize)

2

–0

.003

—

0.

046

–0.0

03

—

0.02

9 P

atri

line

age

sex

ratio

–3

.504

–0

.140

0.

200

–1.9

79

–0.0

79

0.48

9 P

atri

line

age

size

0.

084

0.62

7 0.

202

0.13

5 —

0.

071

(Pat

rili

neag

e si

ze)2

–0.0

01

–0.5

31

0.24

2 –0

.001

—

0.

093

N o

f B

roth

ers

–0

.636

–0

.281

0.

034

N o

f S

iste

rs

0.

265

0.08

2 0.

763

Mot

her

–1

.088

–0

.084

0.

479

Fat

her

1.

081

0.10

2 0.

356

∆

R2 =

.003

∆P

= .5

48

∆R2 =

.015

∆P

= .3

75

∆R

2 = .1

32

∆P =

.007

∆R2 =

.051

∆P

= .1

23

Cri

teri

on V

aria

ble:

RS

N =

130

Men

Mod

el 4

R2 =

0.2

02

B =

uns

tand

ardi

zed

coef

fici

ent,

β =

sta

ndar

dize

d co

effi

cien

t, P

= s

igni

fica

nce,

∆R

2 is c

hang

e in

R2 , ∆

P is

sig

nifi

canc

e fo

r ∆R

2

N N N


Tabl

e 3.

M

ulti

ple

Lin

ear

Reg

ress

ion

Sho

win

g E

ffec

t of

Kin

dred

, Lin

eage

, and

Im

med

iate

Fam

ily

on W

omen

’s R

S

B =

uns

tand

ardi

zed

coef

fici

ent,

β =

sta

ndar

dize

d co

effi

cien

t, P

= s

igni

fica

nce,

∆R

2 is c

hang

e in

R2 , ∆

P is

sig

nifi

canc

e fo

r ∆R

2

M

odel

1

M

odel

2

M

odel

3

M

odel

4

Var

iabl

es

B

β P

B

β

P

B

β P

B

β

P

(Con

stan

t)

–38.

494

—

0.28

2 –2

6.43

8 —

0.

472

–40.

061

—

0.28

7 –3

7.63

0 —

0.

355

Yea

r of

bir

th

0.02

3 0.

110

0.22

5 0.

014

0.07

1 0.

452

0.02

1 0.

101

0.29

0 0.

019

0.09

3 0.

363

Kin

dred

sex

rat

io

5.

248

0.18

2 0.

042

2.73

3 0.

095

0.35

4 2.

713

0.09

4 0.

358

N o

f no

nlin

eal r

elat

ives

0.14

9 —

0.

021

0.02

9 —

0.

697

0.03

9 —

0.

596

(N o

f no

nlin

eal r

elat

ives

)2

–0.0

04

—

0.00

8 –0

.002

—

0.

318

–0.0

02

—

0.26

5 M

atri

linea

ge s

ex r

atio

5.

573

0.24

5 0.

012

6.37

0 0.

280

0.00

6 M

atri

linea

ge s

ize

0.01

6 0.

081

0.40

9 0.

015

0.07

9 0.

480

Pat

rilin

eage

sex

rat

io

–0.7

14

–0.0

33

0.74

7 0.

534

0.02

5 0.

827

Pat

rilin

eage

siz

e

0.

117

—

0.03

5 0.

132

—

0.02

1 (P

atri

linea

ge s

ize)

2

–0

.001

—

0.

046

–0.0

01

—

0.03

1 N

of

Bro

ther

s

–0.3

36

–0.1

19

0.25

8 N

of

Sis

ters

–0.1

97

–0.0

75

0.46

6 M

othe

r

1.36

4 0.

137

0.17

2 F

athe

r

–1.2

47

–0.1

26

0.23

7

∆R

2 = .0

12

∆P =

.225

∆R

2 = .0

91

∆P =

.009

∆

R2 =

.104

∆P

= .0

14

∆R

2 = .0

30

∆P =

.372

C

rite

rion

Var

iabl

e: R

S

N =

124

Wom

en

Mod

el 4

R2 =

.238



For men, kindred characteristics were not associated with long-term repro-duction (LR, or number of grandchildren) (Table 4). LR was negatively asso-ciated with male-biased patrilineage sex ratio and was a quadratic function ofmatrilineage size (Table 4, model 3). A matrilineage with about 33 membersresiding in the village tended to maximize men’s LR. Patrilineage size andmatrilineage sex ratio were not significant predictors of LR. Again, number ofbrothers was negatively associated with male LR, but it did not mediate effectsof patrilineage sex ratio or matrilineage size (Table 4, model 4). Other immedi-ate family members had insignificant effects on LR.

For women, long-term fitness was relatively insensitive to kinship effects.Again women’s LR initially was associated with kindred size, but the relationwas mediated when lineage variables entered the model (Table 5, models 2and 3). Women’s long-term fitness was a quadratic function of matrilineagesize: LR decreased in matrilineages with greater than 36 members in the vil-lage. Other variables were not significantly associated with women’s numberof grandchildren.

Analysis of Residuals

Cumulative probability plots of the residuals indicated approximately nor-mally distributed errors. Cumulative probability and ordered residuals werehighly correlated for all models: rp ranged between .91 and .99.

These linear models had substantial unexplained variance (R2 = .23 to .39).Inspection of the raw data for “poor fit cases” among men suggested thatalcoholism is a potentially important variable. About 38% of men over 30years of age in Bwa Mawego were regularly intoxicated (Quinlan, unpub-lished data). However, among men with lower than predicted RS (Observed –Expected RS ≤ –4, n = 16), about 69% were regularly intoxicated, while only24% of men with higher than expected RS (Observed – Expected RS ≥ 4,n = 21) were regularly intoxicated. When added to model 4 in Table 2, adichotomous “alcoholism” variable was negatively associated with male RS(B = –1.66, β = –.23, P = .02), but it did not “dislodge” the other associations.

Wealth differences may also account for poor model fit. Relatively poorermen, whom multiple key informants categorized as “below normal” for wealth(Quinlan, unpublished data), were less likely to have higher than predicted RS(OR = .28, likelihood ratio = 3.62, one-tailed P = .03). Similarly, wealthier menwere less likely to have lower than predicted RS (OR = .86, likelihood ratio =3.91, one-tailed P = .03). However, neither the dichotomous wealth variablenor a three-level ordinal wealth variable were significantly associated withmale RS when added to the regression model. Lack of significance may bedue to imperfect reliability of this crude measure of wealth.

Finally, five sets of brothers have at least one brother in the high and one inthe low residual groups. In other words, in five cases a man with higher than



Tabl

e 4.

M

ulti

ple

Lin

ear

Reg

ress

ion

Sho

win

g E

ffec

t of

Kin

dred

, Lin

eage

, and

Im

med

iate

Fam

ily

on M

en’s

LR

B =

uns

tand

ardi

zed

coef

fici

ent,

β =

sta

ndar

dize

d co

effi

cien

t, P

= s

igni

fica

nce,

∆R

2 is c

hang

e in

R2 , ∆

P is

sig

nifi

canc

e fo

r ∆R

2

M

odel

1

M

odel

2

M

odel

3

M

odel

4

Var

iabl

es

B

β P

B

β

P

B

β P

B

β

P

(Con

stan

t)

493.

396

—

0.00

0 52

0.50

2 —

0.

000

578.

959

—

0.00

0 51

7.23

4 —

0.

000

Yea

r of

bir

th

–0.2

53

–0.4

84

0.00

0 –0

.266

–0

.510

0.

000

–0.2

95

–0.5

65

0.00

0 –0

.270

–0

.518

0.

000

Kin

dred

sex

rat

io

–3

.342

–0

.046

0.

551

4.36

1 0.

061

0.53

4 11

.869

0.

165

0.11

7 N

of

nonl

inea

l rel

ativ

es

0.

074

0.10

9 0.

180

0.01

4 0.

021

0.80

0 –0

.015

–0

.022

0.

784

Mat

rili

neag

e se

x ra

tio

–7.6

71

–0.1

15

0.22

9 7.

663

0.11

5 0.

317

Mat

rili

neag

e si

ze

0.37

9 —

0.

033

0.48

3 —

0.

011

Mat

rili

neag

e si

ze2

–0.0

06

—

0.06

3 –0

.007

—

0.

023

Pat

rili

neag

e se

x ra

tio

–12.

076

–0.1

86

0.03

2 –1

3.44

2 –0

.208

0.

017

Pat

rili

neag

e si

ze

0.02

7 0.

079

0.38

1 0.

039

0.11

2 0.

234

N o

f B

roth

ers

–2

.164

–0

.371

0.

001

N o

f S

iste

rs

0.

665

0.08

0 0.

389

Mot

her

5.

384

0.16

2 0.

110

Fat

her

–0

.780

–0

.028

0.

761

∆R

2 = .2

34

∆P =

.000

∆

R2 =

.013

∆P

= .3

40

∆R

2 = .0

96

∆ P

= .0

05

∆

R2 =

.060

∆

P =

.0

23

Cri

teri

on V

aria

ble:

LR

N

= 1

30 M

en

Mod

el 4

R2 =

0.3

94

.023



Tabl

e 5.

Mul

tipl

e L

inea

r R

egre

ssio

n S

how

ing

Eff

ect o

f K

indr

ed, L

inea

ge, a

nd I

mm

edia

te F

amil

y on

Wom

en’s

LR

B =

uns

tand

ardi

zed

coef

fici

ent,

β =

sta

ndar

dize

d co

effi

cien

t, P

= s

igni

fica

nce,

∆R

2 is c

hang

e in

R2 , ∆

P is

sig

nifi

canc

e fo

r ∆R

2

M

odel

1

M

odel

2

M

odel

3

M

odel

4

Var

iabl

es

B

β P

B

β

P

B

β P

B

β

P

(Con

stan

t)

390.

456

—

0.00

0 43

4.72

4 —

0.

000

461.

905

—

0.00

0 49

5.23

1 —

0.

000

Yea

r of

bir

th

–0.1

99

–0.3

63

0.00

0 –0

.226

–0

.412

0.

000

–0.2

42

–0.4

42

0.00

0 –0

.259

–0

.473

0.

000

Kin

dred

sex

rat

io

10

.255

0.

133

0.11

1 5.

688

0.07

4 0.

437

5.17

0 0.

067

0.48

2 N

of

nonl

inea

l rel

ativ

es

0.

456

—

0.00

5 0.

253

—

0.16

2 0.

291

—

0.11

2 (N

of

nonl

inea

l rel

ativ

es)2

–0

.011

—

0.

003

–0.0

08

—

0.04

8 –0

.009

—

0.

036

Mat

rilin

eage

sex

rat

io

2.81

9 0.

046

0.61

2 2.

883

0.04

8 0.

618

Mat

rilin

eage

siz

e

0.

567

—

0.00

6 0.

652

—

0.00

2 (M

atri

line

age

size

)2

–0

.007

—

0.

035

–0.0

08

—

0.02

1 P

atri

linea

ge s

ex r

atio

1.

761

0.03

1 0.

734

2.05

1 0.

036

0.72

6 P

atri

linea

ge s

ize

–0.0

20

–0.0

61

0.49

9 –0

.008

–0

.023

0.

815

N o

f B

roth

ers

–0

.560

–0

.075

0.

442

N o

f S

iste

rs

–1

.048

–0

.150

0.

122

Mot

her

–0

.028

–0

.001

0.

991

Fat

her

–0

.527

–0

.020

0.

840

∆

R2 =

.132

∆

P =

.000

∆

R2 =

.079

∆

P =

.009

∆

R2 =

.111

∆

P =

.004

∆

R2 =

.020

∆

P =

.501

C

rite

rion

Var

iabl

e: L

R

N =

124

Wom

en

Mod

el 4

R2 =

0.3

42



predicted RS had at least one brother with lower than predicted RS. This pat-tern may be related to the negative association between number of brothers inthe community and men’s RS and LR. It may be that some men gain fitness atthe expense of a less able brother. In each case it appears to us that the morecognitively skilled brothers end up with higher than expected RS.

Poor model fit among women is more difficult to interpret. Twenty womenhad higher than predicted RS (Observed – Expected RS ≥ 4) and 11 had lowerthan expected RS (Observed – Expected RS ≤ –4). Inspection of the raw datarevealed no obvious patterns; however, women with “above normal” wealthtended to have greater than expected RS (OR = 2.79, likelihood ratio = 2.60,one-tailed P = .05). Wealth was not associated with lower than expected RS,nor was wealth significantly associated with female RS when entered into theregression models in Table 3.

Prevalence of “alcoholism” is considerably lower among women (15%)compared with men. Among women, alcoholism was not associated with higheror lower than expected RS, nor was it a significant predictor of women’s RSwhen included in the multiple regression models.

There are also four pairs of sisters for which one sister had higher thanexpected RS and another had lower than expected RS. In each case the oldersister had higher than expected RS. It may be that older sisters are more likelyto reproduce first and their younger sisters delay reproduction to aid them withchildcare (Quinlan 2001). “Firstborn” status was positively associated withwomen’s RS when included as a dummy variable (1 = firstborn, 0 = later born)in the linear regression in Table 3, model 4; however, the effect was marginallysignificant (B = 1.08, β = .15, P < .10).

DISCUSSION

Results indicate that kindred variables had less effect on fitness than didlineage variables. In each model kindred characteristics either accounted forinsignificant variance in fitness or were fully mediated by lineage characteris-tics. Furthermore, immediate family variables did not fully mediate lineage ef-fects, indicating that associations between lineage and fitness are not solely due tohousehold composition. These findings suggest that norms for lineage organiza-tion have reproductive effects. These “socially imposed” norms for group nepo-tism (Jones 2000) may be part of a “descendant-leaving strategy” (Palmer andSteadman 1997). We propose that norms promoting lineage solidarity increasegrandparental (and great-grandparental, etc.) long-term fitness at a cost to otheravenues for inclusive fitness enhancement among descendants. Individualsmay willingly redirect nepotism toward lineage mates when lineally inheritedresources (including social reciprocity) offset costs of excluding closer kin.

It is particularly interesting that emically recognized patrilineages and un-recognized, informal matrilineages both showed effects on fitness. Matrilineal



effects are intriguing because, without benefit of surnames, it is difficult forvillagers to reckon matrilineal relations beyond several generations in BwaMawego. This finding suggests that matrilineal variables tap into matrifocal house-hold composition effects (see Figure 2). It is difficult, unfortunately, to extractlifetime household data from genealogies. Additional analyses reconstructinghousehold composition (see Quinlan and Flinn 2003) may be informative.

It is also possible that kin create informal matrilineages through points ofcontact in a social network. Matrilineal relations in Bwa Mawego may havesome priority even in the absence of emically identified lineages. The smaller“optimal” size of matrilineages (with about 35 members) relative to patrilineages(with about 65 members) may suggest that, without surnames, matrilineagesbecome fragmented beyond a relatively small optimal size. If people give cer-tain relationships priority—through propinquity or encouragement from kin—even in the absence of specific emic models, then it may suggest a process bywhich kinship patterns develop through the ranking of “primitives for socialcognition” that ultimately generates kin terminologies (see Jones 2003, 2004).In other words, local conditions may favor contact among matrilineal kin be-cause they efficiently translate nepotism into fitness, which eventually maylead to recognized matrilineages. One problem is that kin terminologies, andperhaps explicitly expressed norms for kin group organization, are rather con-servative (Murdock 1949). Ideologies for kinship behavior may be poorlyarticulated or formalized even when patterns of kinship have important mate-rial and social consequences. Such incongruity may be particularly prominentin populations whose history includes the disruptive effects of globalization.We propose then that the study of kinship can benefit from detailed demo-graphic analysis of patterns “on the ground” as well as by more traditionalcultural, cognitive, and linguistic analyses.

Interpreting Kinship Effects on Fitness in Bwa Mawego

Kin appeared to have stronger influence on men’s reproductive successthan on women’s, with kinship accounting for 18% of variance in male RS and13% in female RS. It may be that women are more sensitive to householdcharacteristics than to broader patterns of kinship. Much of the daily coopera-tion in work and childcare is organized at the household level, and householdcomposition is associated with fitness traits among women in Bwa Mawego(Quinlan 2001). The structure of households is associated with women’s ageat first birth, number of mates, and RS. Costs of kinship may be reflected insuppressed fertility when alloparental care is an option: Female reproductionis suppressed when nieces and nephews live in the household (Quinlan 2001;see also Flinn 1989).

The size of lineages has apparent benefits and costs. Patrilineage size waspositively associated with RS up to a maximum of between 63 and 73 lineage



members, at which point fitness decreased in larger lineages. Matrilineage sizealso was positively associated with fitness to a maximum of between 32 and36 members, and fitness again decreased in larger lineages. It is unclear whethercosts in larger lineages come through competition for resources or throughcosts of kin altruism. It is possible that larger lineages become fragmented andoperate as nominally related smaller lineages, analogous to settlement fission-ing among the Yanomamo (see Chagnon 1979). The different optimal sizesfor matrilineages and patrilineages suggest that emic recognition of the latterallows them to operate effectively with almost twice as many members asmatrilineages. In sum, reduced RS in larger lineages, at least, suggests a tradeoffbetween reproduction and indirect fitness, which appears to be influenced bycultural norms for lineage organization.

Lineage sex ratio also had significant effects on male and female fitness,which may reflect competition for lineage resources. For men, male-biasedpatrilineage sex ratio was negatively associated with long-term fitness, and forwomen, male-biased matrilineage sex ratio was positively associated with re-productive success. It is possible that these findings reflect cross-sex resourceenhancement (male kin help women and female kin help men). The effect,however, was on men in patrilineages and women in matrilineages, whichmay suggest that costs of same-sex competition may be more important thanbenefits of cross-sex cooperation. Same-sex kin may compete over lineageresources and mates, and women may incur alloparental care costs. Similarly,lineage resources may be focused on rare males in patrilineages or rare fe-males in matrilineages, creating an effect comparable to primogeniture (seeHrdy and Judge 1993). In sum, unraveling effects of same-sex competitionfrom cross-sex cooperation requires additional research.

Immediate family characteristics appeared to have greater effect on men’sthan on women’s fitness in Bwa Mawego, a pattern similar to that found amongthe Kipsigis (Borgerhoff Mulder 1998). Number of brothers in the communitywas negatively associated with men’s RS and LR. The inverse relation mayindicate resource competition. Competition among male kin may arise overaccess to family land (Flinn 1992). Similar associations between number ofbrothers and male fitness have been demonstrated among the Kipsigis andGabbra pastoralists (Borgerhoff Mulder 1998; Mace 1996), and a negativeassociation between number of brothers and female fertility was found inGambia (Sear, Mace, and McGregor 2003). Parents and number of sisters werenot associated with either male or female fitness in Bwa Mawego. Again, thisnull result is consistent with similar studies: In rural Gambia parents and sistersdid not have significant effects on female fertility (Sear et al. 2003); however,maternal grandmothers had a positive effect on child survival (Sear et al. 2002).

Finally, analysis of residuals suggests at least two important sex-specificvariables: Among men, alcoholism is negatively associated with RS. Amongwomen, having younger sisters in the village may be positively associated



with RS, which may reflect benefits of alloparental care. Wealth and individualdifferences in ability may also account for some variance in fitness, though wepresently lack sufficiently reliable measures of wealth for definitive tests.

Limitations of the Study

Among humans, heritability of fertility is drastically different in differentenvironments and historical periods (Kohler, Rodgers, and Christensen 1999).Human fitness, hence, is a moving target for natural selection, embedded inecological context and attained by evolved psychological mechanisms. It maybe exceedingly difficult to predict fitness because multiple proximate mecha-nisms track, create, and react to social micro-niches that are crucial for humanreproduction. This study leaves substantial unexplained variance, which is notsurprising given a mind evolved to generate a personalized fit between imme-diate environmental exigencies and life history. Life history includes the tim-ing of one’s own reproduction and possibly the developmental stage of one’sfamily or lineage. Complex historically, demographically, and genealogicallysituated, time/development-dependent, and stochastic factors remain unex-plored. Longitudinal research combined with ethnography and complex mod-eling of censored data may advance our understanding of the social ecologyof human fitness. This study offers a probe into relations among sex, fitness,and kin structure of a horticultural Caribbean population.

Genealogical data have significant limitations, not least of which is personalexperience with a necessarily limited set of informants. We used genealogicaldata and multiple regression analysis to explore the rough edges of kinshipand fitness in Bwa Mawego. Migration is a potential source of error and bias.About 48% of people born in the village since 1955 have emigrated, andyounger people and women are more likely to emigrate (year of birth OddsRatio = 1.04, P = .004; women Odds Ratio = 1.68, P = .008) (Quinlan, unpub-lished data). Some individuals who have left the village and children of villag-ers born abroad may be lost to the genealogical method. Census updates,multiple informants, and iterative genealogical interviewing reduce error causedby “lost” individuals. We assume that the likelihood of being lost is greateramong older individuals, and hence, year of birth partially controls for short-comings of the genealogical method. Lineage variables also include some“noise” resulting from temporal variation. We lack data on precise dates ofemigration and death that are sufficient to determine kin group composition ata single point in time. Furthermore, we lack information on childhood andpostmarital residence, and simple land data for more than half of our sampleborn between 1900 and 1955—particularly older individuals. As our firsthandknowledge of longitudinal household composition increases through contin-ued monitoring, and as we develop better retrospective methods, more robustanalyses will be possible.



The empirical situation is further complicated because even the simplestissues are complex in horticultural societies where success is guarded (Edgerton1971; Wolf 1966). Villagers actively negotiate and defend land rights, hidematerial resources from each other (and researchers), and use gossip to adjuststatus and alliances. Kinship plays a significant role in these interactions, butmuch of that role is difficult to observe as villagers surreptitiously navigateand manipulate relationships and resources for their particular interests. Nowonder, then, that human fitness should be such a difficult target for selection,competitors, and social scientists: Perhaps explaining 20% of the variance is areasonable beginning.

CONCLUSION

In sum, a vertically integrated approach (Barkow 1989) suggests interac-tion and correlation among different levels of social organization. Householdcomposition appears to influence proximate correlates of fitness among chil-dren in Bwa Mawego. Particular household residents show kin effects onchildren’s growth and developmental stability (Flinn, Leone, and Quinlan 1999),glucocorticoid stress response (Flinn et al. 1996), age at weaning (Quinlan,Quinlan, and Flinn 2003), time allocation (Quinlan and Flinn 2003), andmother’s reproduction (Quinlan 2001). Ethnography and results here suggestrelations among residence and extended kin relationships: The structure ofhouseholds may promote different lineage-based strategies.

From an evolutionary perspective, conflict between norms for lineage orga-nization and individual inclusive fitness are particularly interesting. “Second-ary values” (see Durham 1991) for lineage solidarity might break down underacutely stressful circumstances. For example, Chagnon and Bugos (1979) foundthat relatedness rather than lineage membership predicted sides in an ax fightamong the Yanomamo. Other conflicts between lineage membership and dy-adic relatedness should be predictable, and we expect a degree of “rule break-ing” and manipulation in certain situations.

Many other kinship questions wait for answers: Do norms for lineage soli-darity protect multigenerational “embodied capital” (Kaplan 1996; Kaplan andLancaster 2000; Bock 2002) and influence investment efficiency within lin-eages? When should we expect people to organize themselves through con-sanguineous marriage (resulting in convergence of ego-centric kindreds andlineages) rather than through lineage organization (see Murdock 1968)? Towhat extent does the social organization of work influence and depend onkinship? How does reliance on matri- or patrilineages affect patterns of sex-biased parental investment? These are only a few possibilities.

Kinship was once a vibrant topic at the core of anthropology, but formalkinship analysis was largely abandoned late in the twentieth century—with avery few notable exceptions (e.g., Alexander 1979; Chagnon and Irons 1979;



Flinn 1981; Riviere 1988; van den Berghe 1979; Hughes 1988; Schweizer andWhite 1996). This unfortunate hiatus may have been due to theoretical andanalytical limitations of the times. New developments in evolutionary ap-proaches to human kinship (e.g., Alvard 2003; Borgerhoff Mulder et al. 2001;Holden, Sear, and Mace 2003; Jones 2000, 2003; Rao 1996; and this specialissue of Human Nature) may herald a renaissance. We hope that other behav-ioral scientists will take up the challenge to tease apart the intricacies of auniversal but widely variable aspect of human social behavior.

We thank the people of Bwa Mawego for their good-natured tolerance of our presence intheir community. Drs. D. Shillingford, R. Nasiiro, P. Rickets, Sister D. James, and the DominicaMinistry of Health provided valuable assistance. Research was supported by grants fromthe National Science Foundation (BNS 8920569 and SBR 9205373); the Universityof Missouri Research Board to MVF; the Earthwatch Center for Field Research toMVF, Marsha B. Quinlan, and RJQ; and the B.S.U. Center for International Programsand Office of Academic Research and Sponsored Programs to RJQ. Marsha Quinlanand Napoleon Chagnon provided valuable advice on earlier drafts. Ed Hagen gavegenerous help with Descent software for kinship analysis. Many friends, teachers, andconsultants in Bwa Mawego contributed generously to this study: the Durand clan—Juranie, Jonah, Elford, Induria, Margelia, Eugenia, Lillia, Elquimedo, Zexia, Delfine,Wilford, Nathalie, and Sarah; the Warringtons—Martina, Amatus, Onia, Belltina,Zabius, Sarah-Gene, and Heckery; the Laudats—Eddie, Benedict, and Dellie; theLaurents—Aron and Tito; the Lewises—Eddie, Melanie, Eulina, Spliffy, Ganjala, Julina,Jalina, and Marietta; Franklin Vigilante; Lawrence Prosper; Edmund Sanderson; Alex andTita Alie; and especially Mistress Didi and Mr. McField Coipel.

Rob Quinlan is Assistant Professor of Anthropology at Ball State University. His maininterests include human evolutionary ecology, reproductive development, parentalcare, kinship, and medical anthropology. He has conducted fieldwork in Dominicasince 1993.

Mark Flinn is Associate Professor of Anthropology and Psychological Sciences at theUniversity of Missouri-Columbia. His main interests include evolutionary theory, child-hood stress, family relationships, and health. He has conducted fieldwork in Dominicaevery year since 1987.

NOTES

1. Affines are kin by marriage. Consanguineal kin are related genetically.2. Ego-centric kindred is defined as all individuals genetically or genealogically related to ego. It

includes lineal and non-lineal kin.3. Lineage includes all kin related to ego either through males or females and tracks Y chromosome

and mitochondrial inheritance.4. Following anthropological convention, M = mother, F = father, Z = sister, B = brother, S = son, and

D = daughter.5. In this case “affinal” refers to linkages through mating rather than marriage.6. Hagen’s “Descent” software includes diagnostic features similar to KINDEMCOM and is much

more versatile and user-friendly. <http://itb.biologie.hu-berlin.de/~hagen/Descent/>



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Documents

Kinship, Sex, and Fitness in a Caribbean Communityweb.missouri.edu/~flinnm/pdf/QuinlanFlinn2005.pdfKinship, Sex, and Fitness 37 father, then two of three possible crew compositions