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Reduced costs of reproduction in females mediate a shift from a male-biased to a female-biased lifespan in humans.

Bolund E, Lummaa V, Smith KR, Hanson HA, Maklakov AA - Sci Rep (2016)

Bottom Line: Life-history theory suggests that reduced reproduction should benefit female lifespan when females pay higher costs of reproduction than males.Only women paid a cost of reproduction in terms of shortened post-reproductive lifespan at high parities.Further, our results have important implications for demographic forecasts in human populations and advance our understanding of lifespan evolution.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, Uppsala SE-752 36, Sweden.

ABSTRACT
The causes underlying sex differences in lifespan are strongly debated. While females commonly outlive males in humans, this is generally less pronounced in societies before the demographic transition to low mortality and fertility rates. Life-history theory suggests that reduced reproduction should benefit female lifespan when females pay higher costs of reproduction than males. Using unique longitudinal demographic records on 140,600 reproducing individuals from the Utah Population Database, we demonstrate a shift from male-biased to female-biased adult lifespans in individuals born before versus during the demographic transition. Only women paid a cost of reproduction in terms of shortened post-reproductive lifespan at high parities. Therefore, as fertility decreased over time, female lifespan increased, while male lifespan remained largely stable, supporting the theory that differential costs of reproduction in the two sexes result in the shifting patterns of sex differences in lifespan across human populations. Further, our results have important implications for demographic forecasts in human populations and advance our understanding of lifespan evolution.

No MeSH data available.


Change in adult survival over four 25-year birth cohorts.Survival curves represent females (a) and males (b) that reproduced and had full known reproductive history. Colours indicate the birth years contained in each cohort. For sample sizes, see Fig. 2.
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f2: Change in adult survival over four 25-year birth cohorts.Survival curves represent females (a) and males (b) that reproduced and had full known reproductive history. Colours indicate the birth years contained in each cohort. For sample sizes, see Fig. 2.

Mentions: We found clear evidence that sexual dimorphism in adult lifespan changed across the transition of the population from high to low mortality and fertility rates. Over the study period, which included individuals born between 1820 and 1919, average reproduction was halved from 8.5 to 4.2 children born per female and average adult lifespan increased by 12% in females and 2% in males (Fig. 1, Supplementary Table 1). Figure 1 shows the Kaplan-Meier survival curves and associated log-rank and Wilcoxon tests separately for the two sexes over four 25-year birth cohorts covering the demographic transition in Utah. The population changed from a significant male-biased adult survival in the earliest cohort to a progressively more female-biased adult survival in the later three cohorts. Parametric survival models that accounted for polygamy status, birth place, birth order and maternal identity showed a significant difference in the adult lifespan of the two sexes in all four cohorts (Table 1). The acceleration factor indicates the estimated mean survival time for females in relation to males in each cohort. Thus, males were predicted by the model to outlive females during adulthood by almost one year in the first cohort (birth years 1820–1844), the sexes had nearly identical predicted adult lifespans in the second cohort (1845–1869), and in the third (1870–1894) and fourth (1895–1919) cohorts, females were predicted to outlive males by about two and four years, respectively. Figure 2 illustrates the clear increase in female lifespan over time (2a) while male lifespan increased only marginally (2b, Supplementary Table 1).


Reduced costs of reproduction in females mediate a shift from a male-biased to a female-biased lifespan in humans.

Bolund E, Lummaa V, Smith KR, Hanson HA, Maklakov AA - Sci Rep (2016)

Change in adult survival over four 25-year birth cohorts.Survival curves represent females (a) and males (b) that reproduced and had full known reproductive history. Colours indicate the birth years contained in each cohort. For sample sizes, see Fig. 2.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4834564&req=5

f2: Change in adult survival over four 25-year birth cohorts.Survival curves represent females (a) and males (b) that reproduced and had full known reproductive history. Colours indicate the birth years contained in each cohort. For sample sizes, see Fig. 2.
Mentions: We found clear evidence that sexual dimorphism in adult lifespan changed across the transition of the population from high to low mortality and fertility rates. Over the study period, which included individuals born between 1820 and 1919, average reproduction was halved from 8.5 to 4.2 children born per female and average adult lifespan increased by 12% in females and 2% in males (Fig. 1, Supplementary Table 1). Figure 1 shows the Kaplan-Meier survival curves and associated log-rank and Wilcoxon tests separately for the two sexes over four 25-year birth cohorts covering the demographic transition in Utah. The population changed from a significant male-biased adult survival in the earliest cohort to a progressively more female-biased adult survival in the later three cohorts. Parametric survival models that accounted for polygamy status, birth place, birth order and maternal identity showed a significant difference in the adult lifespan of the two sexes in all four cohorts (Table 1). The acceleration factor indicates the estimated mean survival time for females in relation to males in each cohort. Thus, males were predicted by the model to outlive females during adulthood by almost one year in the first cohort (birth years 1820–1844), the sexes had nearly identical predicted adult lifespans in the second cohort (1845–1869), and in the third (1870–1894) and fourth (1895–1919) cohorts, females were predicted to outlive males by about two and four years, respectively. Figure 2 illustrates the clear increase in female lifespan over time (2a) while male lifespan increased only marginally (2b, Supplementary Table 1).

Bottom Line: Life-history theory suggests that reduced reproduction should benefit female lifespan when females pay higher costs of reproduction than males.Only women paid a cost of reproduction in terms of shortened post-reproductive lifespan at high parities.Further, our results have important implications for demographic forecasts in human populations and advance our understanding of lifespan evolution.

View Article: PubMed Central - PubMed

Affiliation: Department of Ecology and Genetics, Evolutionary Biology Centre, Uppsala University, Uppsala SE-752 36, Sweden.

ABSTRACT
The causes underlying sex differences in lifespan are strongly debated. While females commonly outlive males in humans, this is generally less pronounced in societies before the demographic transition to low mortality and fertility rates. Life-history theory suggests that reduced reproduction should benefit female lifespan when females pay higher costs of reproduction than males. Using unique longitudinal demographic records on 140,600 reproducing individuals from the Utah Population Database, we demonstrate a shift from male-biased to female-biased adult lifespans in individuals born before versus during the demographic transition. Only women paid a cost of reproduction in terms of shortened post-reproductive lifespan at high parities. Therefore, as fertility decreased over time, female lifespan increased, while male lifespan remained largely stable, supporting the theory that differential costs of reproduction in the two sexes result in the shifting patterns of sex differences in lifespan across human populations. Further, our results have important implications for demographic forecasts in human populations and advance our understanding of lifespan evolution.

No MeSH data available.