Transcript 'Differential Mortality Between the Sexes: An Inevitable

Differential Mortality Between the Sexes:
Max Planck Institute for
Demographic Research
Anthropological Database
Syddansk University
An Inevitable Pattern in the Middle Ages?
Rostock
Germany
Odense
Denmark
Svenja Weise
Introduction:
Material and methods:
In Tirup, the lower survival probability for women compared to men is apparent for the ages from 20 to 38. After the childbearing
years, it remains nearly constant up to age 65, when it falls again. The Female:Male Mortality Ratio (F:M MR) in Fig. 5 shows
The burials in the parish cemetery S:t Jörgen cover a period lasting from around AD 1300, the establishment of the town, until
“Being male is now the single largest demographic risk factor for early mortality in developed countries”
(Kruger & Nesse, 2004)
the change to higher male mortality around age 38.
the dawn of the reformation in Malmö in the 1520s. It was a period of growth and well being for the city, mainly caused by the
Female survival probability in Malmö is only slightly lower than male in the years from age 20 to 35. Male survival lies in the
prosperous herring trade.
This is a new phenomenon in human history. In ancient samples, women from their early twenties until the end of their fertile
female 95% confidence intervals from age 30 upwards. The F:M MR indicates an even lower female than male mortality for the
period usually showed higher mortality rates than men. Around age 50, male mortality started to exceed female mortality.
The whole skeletal collection comprises 4182 individuals, of whom a sub-sample of 986 were chosen for this analysis. Their age
Since the middle of the 18th century – at the latest – higher life expectancy for females can be universally observed, and was
estimates were derived by Transition Analysis (Boldsen, 2002): a formal method of ageing skeletons by scoring multiple traits.
associated with lower female mortality for all age groups.
The scores are combined by Maximum Likelihood Estimation to derive Ages-at-death (MLA) with point estimates and 95%
ages 25 to 43 (Fig. 6). From 45 to 65 the mortality rates are very low which can exaggerate the relative risk.
The data for Sweden display a higher male mortality for all age groups (Fig. 7).
confidence intervals. Only individuals older then 16 and with known sex were included.
What shapes this excess female mortality in young adulthood is still a matter of debate. Three general factors seem to play a role:
Possible causes for the observed changes in mortality could be a changing lifestyle during young adulthood over time. Marriage
Comparative data were taken from the skeletal collection of the small rural village of Tirup, Denmark, (AD 1150-1350, N= 155;
•
Biology
“Dangerous fertile years”- higher mortality due to childbearing or maternal depletion
Boldsen, 2005) and period life tables for Sweden (1751-1759; Human Mortality Database).
•
Behaviour
Women’s role includes caring for the sick and cooking
For the two skeletal collections, the Mortality Rate Ratio was estimated based on 5 year groups for ages 20 to 75 years.
•
Resources
Unequal distribution of nutrition and health care between the sexes
newly established towns and were confronted with new diseases. It is possible that the higher number of men than women in
Urban (fully) market integrated agriculture
45
55
65
75
Figure 1. Age at death distribution for both sexes (years)
409
577
Women
Women
Men
Men
Figure 2. Age at death distribution by sex
Table 1. Number of deaths for different age groups
40
50
60
70
3.5
3.0
2.5
2.0
1.5
3.0
0.0
986
30
1.0
60
20
20
Total
F:M Mortality Ratio
284
0.5
28.8
0.0
167
2.5
117
2.0
40 +
85
1.5
490
1.0
49.7
F:M Mortality Ratio
298
0.5
192
0.0
20 - 40
2.5
212
2.0
21.5
1.5
112
1.0
100
F:M Mortality Ratio
16 - 20
0.5
Total
50
%
40
Male
30
Female
Sweden AD 1751-1759
3.5
Malmö S:t Jörgen
3.5
80
Tirup
3.0
35
Age (years)
Urban (partly) market integrated agriculture
towns resulted in an increase of male risk behaviour to compete for mates.
70
25
Age
Age (years)
20
15
10
5
0
Number of individuals
25
30
Malmö S:t Jörgen
15
Horticulture and foraging
occurred later in life and therefore led to fewer children and reduced risk of dying in childbirth. Young men immigrated to the
20
30
Age (years)
40
50
60
70
Age (years)
20
30
40
50
60
70
Age (years)
Figures 5 – 7. Ratio of female to male probability of dying by age (qx) for Tirup, Malmö and Sweden.
Results:
Conclusion:
development of a community might govern the mortality regimes of the individuals living in it. This can be examined for Malmö, a
Though nearly 50% of the deaths in Malmö occurred in the adult age group from 20 to 40 years (Table 1), there is no evidence
There is an epidemiological transition in young adult mortality patterns during the Middle Ages and Early History: from an
“boom town” in the Öresund region in Southern Scandinavia in the late Middle Ages. Skeletal data from a parish cemetery in
for excess female mortality during the childbearing years. The median of the distribution of ages-at-death is approximately
increased female mortality during the reproductive years through a period of nearly equal risk of dying for both sexes to a
Malmö, Sweden, is compared with skeletal data from Tirup, an early medieval rural village in Denmark, and with life table data
similar for both sexes (Fig. 2).
surplus mortality of young males.
for historical Sweden.
The survival curves of Tirup and Malmö show a clear difference in the mortality regimes in early adulthood (Fig. 3 + 4).
This transition runs parallel to important changes in the subsistence patterns between the analysed communities: from
Most likely, each of these reasons influences the different patterns of mortality. If so, the general level of economic and social
horticulture and foraging to an urban life and fully market integrated agriculture.
(Continued above right)
The data analysed here support the hypothesis that the level of social and economic development of a community influences
Hypothesis:
1.0
males
and
females
from
20
30
40
50
60
Survivaltime (years)
70
80
0.8
0.6
References:
Acknowledgement:
Boldsen, JL. 2005. Leprosy and mortality in the Medieval Danish village of Tirup. American Journal of
Physical Anthropology, vol. 126, pp. 159-168.
The author wishes to thank Prof. Jesper Lier Boldsen, who generously yielded the data of the
Tirup cemetery for this comparison. He and Ulla Freund (ADBOU) did a wonderful job in the
osteological analysis of the Malmö material. Thanks to Jim Oeppen (MPIDR) for his helpful
comments and a short brush-up on qx.
Boldsen, JL, Milner, GR, Konigsberg, LW, Wood, JW. 2002. Transition analysis: A new method for
estimating age from skeletons. In Paleodemography. Age distributions from skeletal samples, Hoppa,
RD,Vaupel, JW, eds, Cambridge, Cambridge University Press, pp. 73-106.
0.0
0.2
Tirup (left) and Malmö (right).
0.4
0.4
on survival to age 16 for
Survival probability
Survival curves conditioned
Males
Females
95% C.I. Females
0.2
1.0
0.6
Figures 3 + 4.
0.0
Survival probability
was a turning point between the different mortality regimes.
Males
Females
95% C.I. Females
0.8
The late medieval society with its newly established towns
the shape of sex-specific mortality.
Malmö S:t Jörgen
Tirup
20
30
40
50
60
Survivaltime (years)
70
80
Human Mortality Database. University of California, Berkeley (USA), and Max Planck Institute for
Demographic Research (Germany) (data downloaded on 3/20/2007).
Kruger & Nesse 2004. Sexual selection and the Male:Female Mortality Ratio. Evolutionary Psychology,
vol. 2, pp. 66-85.