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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.


Related in: MedlinePlus

The number of years lived after the end of the potential reproductive period (age 55 years) related to the number of children born.Curves represent females (red) and males (blue) that reproduced and were born between 1820 and 1920. The raw data are grouped here for visual purposes only while analyses (see main text) are performed on ungrouped data and account for a number of fixed and random effects. Points with associated SE refer to grouped averages for all individuals of each sex at each parity. For ease of illustration, individuals are grouped at high parities into categories with 15–21 children and 22–65 children (only males, plotted at value 25 on the x-axis). Lines represent the best fit from third order polynomial regressions weighted by the sample size in each group (sample sizes range from 282 to 7264).
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f3: The number of years lived after the end of the potential reproductive period (age 55 years) related to the number of children born.Curves represent females (red) and males (blue) that reproduced and were born between 1820 and 1920. The raw data are grouped here for visual purposes only while analyses (see main text) are performed on ungrouped data and account for a number of fixed and random effects. Points with associated SE refer to grouped averages for all individuals of each sex at each parity. For ease of illustration, individuals are grouped at high parities into categories with 15–21 children and 22–65 children (only males, plotted at value 25 on the x-axis). Lines represent the best fit from third order polynomial regressions weighted by the sample size in each group (sample sizes range from 282 to 7264).

Mentions: We investigated the potential causes for the changed sexual dimorphism in adult lifespan over the study period by measuring changes in the relationship between reproduction and lifespan after the end of the potential reproductive period at age 55 (post-reproductive lifespan) of each sex across the time period. Figure 3 shows the relationship between reproductive effort and post-reproductive lifespan in the two sexes, based on grouped raw data of 118,911 individuals. We estimated the differences between the sexes in the linear slopes of the relationship between number of children born and post-reproductive lifespan in models that accounted for polygamy status, birth place, birth order, birth cohort and maternal identity. This showed that there was a trade-off between reproduction and post-reproductive lifespan in females, but not in males (posterior mode for the interaction between sex and number of children born: −1.12, Bayesian credibility interval (CI) = −1.23 to −0.99, pMCMC = <0.001). This pattern was consistent across the four birth cohorts (The posterior modes for the interaction between sex and number of children born in four separate models, one for each birth cohort, ranged from −0.38 to −0.77). Separate models in each sex revealed opposing directions of the effect on post-reproductive lifespan in males and females of children ever born, with increasing parity being associated with decreased post-reproductive lifespan in women but increased post-reproductive lifespan in men (Sex-specific slopes: females: quadratic slope: −0.12, CI = −0.19 to −0.047, linear slope: −0.37, CI = −0.47 to −0.29, males: quadratic slope: −0.076, CI = −0.11 to −0.037, linear slope: 0.33, CI = 0.23 to 0.44). An alternative analysis approach, using parametric survival models, found consistent results. Models showed a slight increase in lifespan for females with two to four children compared to females with one child and thereafter a progressive decline in female lifespan at higher parities. The acceleration factor indicates that females in the highest parity group with 15 children or more were predicted to live about 6 years shorter than females with one child (Table 2). In contrast, male lifespan was little affected by the level of reproductive effort with a predicted difference in mean lifespan of less than one year in the different parity groups (Table 2).


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)

The number of years lived after the end of the potential reproductive period (age 55 years) related to the number of children born.Curves represent females (red) and males (blue) that reproduced and were born between 1820 and 1920. The raw data are grouped here for visual purposes only while analyses (see main text) are performed on ungrouped data and account for a number of fixed and random effects. Points with associated SE refer to grouped averages for all individuals of each sex at each parity. For ease of illustration, individuals are grouped at high parities into categories with 15–21 children and 22–65 children (only males, plotted at value 25 on the x-axis). Lines represent the best fit from third order polynomial regressions weighted by the sample size in each group (sample sizes range from 282 to 7264).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: The number of years lived after the end of the potential reproductive period (age 55 years) related to the number of children born.Curves represent females (red) and males (blue) that reproduced and were born between 1820 and 1920. The raw data are grouped here for visual purposes only while analyses (see main text) are performed on ungrouped data and account for a number of fixed and random effects. Points with associated SE refer to grouped averages for all individuals of each sex at each parity. For ease of illustration, individuals are grouped at high parities into categories with 15–21 children and 22–65 children (only males, plotted at value 25 on the x-axis). Lines represent the best fit from third order polynomial regressions weighted by the sample size in each group (sample sizes range from 282 to 7264).
Mentions: We investigated the potential causes for the changed sexual dimorphism in adult lifespan over the study period by measuring changes in the relationship between reproduction and lifespan after the end of the potential reproductive period at age 55 (post-reproductive lifespan) of each sex across the time period. Figure 3 shows the relationship between reproductive effort and post-reproductive lifespan in the two sexes, based on grouped raw data of 118,911 individuals. We estimated the differences between the sexes in the linear slopes of the relationship between number of children born and post-reproductive lifespan in models that accounted for polygamy status, birth place, birth order, birth cohort and maternal identity. This showed that there was a trade-off between reproduction and post-reproductive lifespan in females, but not in males (posterior mode for the interaction between sex and number of children born: −1.12, Bayesian credibility interval (CI) = −1.23 to −0.99, pMCMC = <0.001). This pattern was consistent across the four birth cohorts (The posterior modes for the interaction between sex and number of children born in four separate models, one for each birth cohort, ranged from −0.38 to −0.77). Separate models in each sex revealed opposing directions of the effect on post-reproductive lifespan in males and females of children ever born, with increasing parity being associated with decreased post-reproductive lifespan in women but increased post-reproductive lifespan in men (Sex-specific slopes: females: quadratic slope: −0.12, CI = −0.19 to −0.047, linear slope: −0.37, CI = −0.47 to −0.29, males: quadratic slope: −0.076, CI = −0.11 to −0.037, linear slope: 0.33, CI = 0.23 to 0.44). An alternative analysis approach, using parametric survival models, found consistent results. Models showed a slight increase in lifespan for females with two to four children compared to females with one child and thereafter a progressive decline in female lifespan at higher parities. The acceleration factor indicates that females in the highest parity group with 15 children or more were predicted to live about 6 years shorter than females with one child (Table 2). In contrast, male lifespan was little affected by the level of reproductive effort with a predicted difference in mean lifespan of less than one year in the different parity groups (Table 2).

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.


Related in: MedlinePlus