The Experts below are selected from a list of 312 Experts worldwide ranked by ideXlab platform

Ken R Smith - One of the best experts on this subject based on the ideXlab platform.

  • parity progression ratios confirm higher Lifetime Fertility in women who bear twins
    Proceedings of The Royal Society B: Biological Sciences, 2012
    Co-Authors: Shannen L Robson, Ken R Smith
    Abstract:

    We appreciate the comments by Rickard et al. [[1][1]] of our recent paper which evaluated the effects of bearing twins on maternal reproduction and survival using a large sample of women in the Utah Population Database (UPDB) [[2][2]]. While they concur with our major finding showing improved post-

  • Twinning in humans: maternal heterogeneity in reproduction and survival
    Proceedings of The Royal Society B: Biological Sciences, 2011
    Co-Authors: Shannen L Robson, Ken R Smith
    Abstract:

    While humans usually give birth to singletons, dizygotic twinning occurs at low rates in all populations worldwide. We evaluate two hypotheses that have differing expectations about the effects of bearing twins on maternal Lifetime reproduction and survival. The maternal depletion hypothesis argues that mothers of twins will suffer negative outcomes owing to the higher physiological costs associated with bearing multiples. Alternatively, twinning, while costly, may indicate mothers with a greater capacity to bear that cost. Drawing from the vast natural Fertility data in the Utah Population Database, we compared the reproductive and survival events of 4603 mothers who bore twins and 54 183 who had not. These mothers were born between 1807 and 1899, lived at least to the age of 50 years and married once to men who were alive when their wives were 50. Results from proportional hazards and regression analyses are consistent with the second hypothesis. Mothers of twins exhibit lower postmenopausal mortality, shorter average inter-birth intervals, later ages at last birth and higher Lifetime Fertility than their singleton-only bearing counterparts. From the largest historical sample of twinning mothers yet published, we conclude that bearing twins is more likely for those with a robust phenotype and is a useful index of maternal heterogeneity.

Kermyt G. Anderson - One of the best experts on this subject based on the ideXlab platform.

  • Transitions: Modeling Multiple Currencies
    2020
    Co-Authors: Carl P. Simon, Kermyt G. Anderson
    Abstract:

    Life historytheorypostulates tradeoffs of current versus future reproduction; today women face evolutionarilynovel versions of these tradeoffs. Optimal age at first birth is the result of tradeoffs in Fertilityand mortality ; ceteris paribus, earlyreproduction is advantageous. Yet modern women in developed nations experience relativelylate first births; theyappear to be trading off socioeconomic status and the paths to raised SES, education and work, against earlyFertility . Here, (1) using delineating parameter values drawn from data in the literature, we model these tradeoffs to determine how much socioeconomic advantage will compensate for delayed first births and lower Lifetime Fertility; and (2) we examine the effects of work and education on women's Lifetime and age- specific Fertilityusing data from seven cohorts in the Panel Studyof Income Dynamics (PSID). Am. J. Hum. Biol. 14:149-167, 2002. � 2002 Wiley-Liss, Inc.

  • An evolutionary ecological perspective on demographic transitions: modeling multiple currencies.
    American Journal of Health Behavior, 2002
    Co-Authors: Carl P. Simon, Kermyt G. Anderson
    Abstract:

    Life history theory postulates tradeoffs of current versus future reproduction; today women face evolutionarily novel versions of these tradeoffs. Optimal age at first birth is the result of tradeoffs in Fertility and mortality; ceteris paribus, early reproduction is advantageous. Yet modern women in developed nations experience relatively late first births; they appear to be trading off socioeconomic status and the paths to raised SES, education and work, against early Fertility. Here, [1] using delineating parameter values drawn from data in the literature, we model these tradeoffs to determine how much socioeconomic advantage will compensate for delayed first births and lower Lifetime Fertility; and [2] we examine the effects of work and education on women's Lifetime and age-specific Fertility using data from seven cohorts in the Panel Study of Income Dynamics (PSID).

  • The life histories of American stepfathers in evolutionary perspective
    Human Nature, 2000
    Co-Authors: Kermyt G. Anderson
    Abstract:

    This paper presents an analysis of the characteristics of men who become stepfathers, and their subsequent Fertility patterns and Lifetime reproductive success. Because women who already have children are ranked lower in the marriage market than women without children, men who marry women with children (e.g., stepfathers) are likely to have lower rankings in the marriage market as well. Using retrospective Fertility and marital histories from the Panel Study of Income Dynamics (PSID), I show that men who become stepfathers have lower levels of education, less income, and are more likely to have been divorced before and to already have children, all characteristics that lower their rankings in the marriage market. Men with one or two stepchildren are just as likely to have children within a marriage as non-stepfathers, although men with three stepchildren show decreased Fertility. Among men age 45 and older, stepfathers have lower Lifetime Fertility than non-stepfathers, although the difference disappears when men’s age at first marriage is controlled for. Additionally, stepfathers have significantly higher Fertility than men who never marry. The results suggest that some men become stepfathers to procure mates and Fertility benefits that they would otherwise have been unlikely to obtain; for these men, raising other men’s children serves as a form of mating effort.

Pekka Martikainen - One of the best experts on this subject based on the ideXlab platform.

  • effect of family background on the educational gradient in Lifetime Fertility of finnish women born 1940 50
    Population Studies-a Journal of Demography, 2014
    Co-Authors: Jessica Nisen, Mikko Myrskyla, Karri Silventoinen, Pekka Martikainen
    Abstract:

    An inverse association between education and Fertility in women has been found in many societies but the causes of this association remain inadequately understood. We investigated whether observed and unobserved family-background characteristics explained educational differences in Lifetime Fertility among 35,212 Finnish women born in 1940-50. Poisson and logistic regression models, adjusted for measured socio-demographic family-background characteristics and for unobserved family characteristics shared by siblings, were used to analyse the relationship between education and the number of children, having any children, and Fertility beyond the first child. The woman's education and the socio-economic position of the family were negatively associated with Fertility. Observed family characteristics moderately (3-28 per cent) explained the association between education and Fertility, and results from models including unobserved characteristics supported this interpretation. The remaining association may represent a causal relationship between education and Fertility or joint preferences that form independently of our measures of background.

  • Effect of family background on the educational gradient in Lifetime Fertility of Finnish women born 1940–50
    Population Studies-a Journal of Demography, 2014
    Co-Authors: Jessica Nisen, Mikko Myrskyla, Karri Silventoinen, Pekka Martikainen
    Abstract:

    An inverse association between education and Fertility in women has been found in many societies but the causes of this association remain inadequately understood. We investigated whether observed and unobserved family-background characteristics explained educational differences in Lifetime Fertility among 35,212 Finnish women born in 1940-50. Poisson and logistic regression models, adjusted for measured socio-demographic family-background characteristics and for unobserved family characteristics shared by siblings, were used to analyse the relationship between education and the number of children, having any children, and Fertility beyond the first child. The woman's education and the socio-economic position of the family were negatively associated with Fertility. Observed family characteristics moderately (3-28 per cent) explained the association between education and Fertility, and results from models including unobserved characteristics supported this interpretation. The remaining association may represent a causal relationship between education and Fertility or joint preferences that form independently of our measures of background.

Brenda W Gillespie - One of the best experts on this subject based on the ideXlab platform.

  • life history theory Fertility and reproductive success in humans
    Proceedings of The Royal Society B: Biological Sciences, 2002
    Co-Authors: Beverly I Strassmann, Brenda W Gillespie
    Abstract:

    According to life-history theory, any organism that maximizes fitness will face a trade-off between female Fertility and offspring survivorship. This trade-off has been demonstrated in a variety of species, but explicit tests in humans have found a positive linear relationship between fitness and Fertility. The failure to demonstrate a maximum beyond which additional births cease to enhance fitness is potentially at odds with the view that human Fertility behaviour is currently adaptive. Here we report, to our knowledge, the first clear evidence for the predicted nonlinear relationship between female Fertility and reproductive success in a human population, the Dogon of Mali, West Africa. The predicted maximum reproductive success of 4.1+/-0.3 surviving offspring was attained at a Fertility of 10.5 births. Eighty-three per cent of the women achieved a Lifetime Fertility level (7-13 births) for which the predicted mean reproductive success was within the confidence limits (3.4 to 4.8) for reproductive success at the optimal Fertility level. Child mortality, rather than Fertility, was the primary determinant of fitness. Since the Dogon people are farmers, our results do not support the assumptions that: (i) contemporary foragers behave more adaptively than agriculturalists, and (ii) that adaptive Fertility behaviour ceased with the Neolithic revolution some 9000 years ago. We also present a new method that avoids common biases in measures of reproductive success.

  • Life–history theory, Fertility and reproductive success in humans
    Proceedings of The Royal Society B: Biological Sciences, 2002
    Co-Authors: Beverly I Strassmann, Brenda W Gillespie
    Abstract:

    According to life-history theory, any organism that maximizes fitness will face a trade-off between female Fertility and offspring survivorship. This trade-off has been demonstrated in a variety of species, but explicit tests in humans have found a positive linear relationship between fitness and Fertility. The failure to demonstrate a maximum beyond which additional births cease to enhance fitness is potentially at odds with the view that human Fertility behaviour is currently adaptive. Here we report, to our knowledge, the first clear evidence for the predicted nonlinear relationship between female Fertility and reproductive success in a human population, the Dogon of Mali, West Africa. The predicted maximum reproductive success of 4.1+/-0.3 surviving offspring was attained at a Fertility of 10.5 births. Eighty-three per cent of the women achieved a Lifetime Fertility level (7-13 births) for which the predicted mean reproductive success was within the confidence limits (3.4 to 4.8) for reproductive success at the optimal Fertility level. Child mortality, rather than Fertility, was the primary determinant of fitness. Since the Dogon people are farmers, our results do not support the assumptions that: (i) contemporary foragers behave more adaptively than agriculturalists, and (ii) that adaptive Fertility behaviour ceased with the Neolithic revolution some 9000 years ago. We also present a new method that avoids common biases in measures of reproductive success.

Virpi Lummaa - One of the best experts on this subject based on the ideXlab platform.

  • An evolutionary approach to change of status–Fertility relationship in human Fertility transition
    Behavioral Ecology, 2013
    Co-Authors: Virpi Lummaa
    Abstract:

    The change in benefits of high socioeconomic status to Fertility in humans during the demographic transition from high to low Fertility has interested both demographers and evolutionary biologists. Evolutionary analyses add to demographic analyses by considering also males and status-related differential in male mating success, but they have been limited to time cross-sections and have not linked this differential to differentials in other determinants of male Fertility. We use life-history records of males (n = 3791) entering marriage market before (1810s–1880s) and during (1890s–1960s) the Finnish Fertility transition to investigate associations between socioeconomic status and chance and timing of marriage, choice for spouse, and Lifetime Fertility. Low status invariantly brought a lower marriage chance throughout these 160 years, which partly explained why ever-married high-status men lost advantage at early marriage when the system of achieving a high status shifted from inheritance to self-effort. The loss, coupled with assortative mating by age, promoted disappearance of differential in wife’s age at marriage and thus, disappearance of differential in Fertility between ever-married high- and low-status men in the Finnish Fertility transition. Consequently, among all men (married and unmarried), status-related differential in Lifetime Fertility—not selection coefficient—declined over the transition. This study is among the first to show the interrelated dynamics of status-related differentials in male mating and reproductive traits; by doing so, it contributes to an evolutionary understanding of change of status–Fertility relationship in human Fertility transition and confirms continuing phenotypic selection on male status/wealth in modern societies.

  • why is Lifetime Fertility higher in twinning women
    Proceedings of The Royal Society B: Biological Sciences, 2012
    Co-Authors: Ian J Rickard, Alexandre Courtiol, Virpi Lummaa
    Abstract:

    In a recent paper published in Proceedings of the Royal Society B , Robson & Smith (RS) presented an analysis of a database comprising the life histories of more than 50 000 women born in the nineteenth century UT, USA. They addressed the question of whether a woman's likelihood of producing twins