Samuli Helle | University of Turku (original) (raw)
Papers by Samuli Helle
Human Reproduction, 2008
The article by Delbaere et al. 'Perinatal outcome of twin pregnancies in women of advanced a... more The article by Delbaere et al. 'Perinatal outcome of twin pregnancies in women of advanced age', in Hum Reprod (2008), showed that irrespective of reproductive techniques, socio-economic status and the zygosity of twins, perinatal outcome of twin pregnancies is more favourable ...
Archives of Sexual Behavior, 2009
Behavioral Ecology and Sociobiology, May 29, 2009
The ratio of second-to-fourth digit length (2D/4D) has been suggested to be a useful adult age ma... more The ratio of second-to-fourth digit length (2D/4D) has been suggested to be a useful adult age marker of intrauterine exposure to steroids because it should be sexually dimorphic and fixed already in utero. Numerous studies mainly on humans have supported this conclusion, but it is yet unclear how well this applies to other vertebrates. This information would be especially valuable to field biologists to whom measuring steroids in utero is often impossible. The non-human studies conducted so far have yielded inconsistent results, perhaps due to the variety of different methods employed in measuring 2D/4D. We examined the age and sex dependency and lateral asymmetry of 2D/4D in field voles (Microtus agrestis) and compared whether these effects differed between 2D/4D measurements taken from photographs and X-rays. Our results show that 2D/4D measurements from photos had a higher measurement error and gave consistently higher 2D/4D than those from X-rays. According to both measurement methods, the right paw showed higher 2D/4D values than the left paw (lateral asymmetry). Adult voles had a lower 2D/4D than juveniles when measured from X-rays, but not when measured from photographs. We found no evidence for a sex difference in 2D/4D using either of the measurement methods. Our findings thus suggest that X-rays, due to their greater accuracy, should be preferred over photographs for measuring digit ratios in rodents. Our results also indicate that in this species, 2D/4D is laterally asymmetric, but it may not be either fixed in utero or sexually dimorphic. In conclusion, 2D/4D appears to be a rather species-and method-specific measure and researchers should be careful when generalising its applicability to study early hormonal effects in vertebrates.
Ecology and evolution, 2015
For migratory birds, the earlier arrival of males to breeding grounds is often expected to have f... more For migratory birds, the earlier arrival of males to breeding grounds is often expected to have fitness benefits. However, the selection differential on male arrival time has rarely been decomposed into the direct effect of male arrival and potential indirect effects through female traits. We measured the directional selection differential on male arrival time in the pied flycatcher (Ficedula hypoleuca) using data from 6 years and annual number of fledglings as the fitness proxy. Using structural equation modeling, we were able to take into account the temporal structure of the breeding cycle and the hierarchy between the examined traits. We found directional selection differentials for earlier male arrival date and earlier female laying date, as well as strong selection differential for larger clutch size. These selection differentials were due to direct selection only as indirect selection for these traits was nonsignificant. When decomposing the direct selection for earlier male ...
Proceedings. Biological sciences / The Royal Society, Jan 7, 2014
A shift from nomadic foraging to sedentary agriculture was a major turning point in human evoluti... more A shift from nomadic foraging to sedentary agriculture was a major turning point in human evolutionary history, increasing our population size and eventually leading to the development of modern societies. We however lack understanding of the changes in life histories that contributed to the increased population growth rate of agriculturalists, because comparable individual-based reproductive records of sympatric populations of agriculturalists and foragers are rarely found. Here, we compared key life-history traits and population growth rate using comprehensive data from the seventieth to nineteenth century Northern Finland: indigenous Sami were nomadic hunter-fishers and reindeer herders, whereas sympatric agricultural Finns relied predominantly on animal husbandry. We found that agriculture-based families had higher lifetime fecundity, faster birth spacing and lower maternal mortality. Furthermore, agricultural Finns had 6.2% higher annual population growth rate than traditional ...
Proceedings. Biological sciences / The Royal Society, Jan 7, 2010
The proximate physiological mechanisms producing the parental ability to vary offspring sex ratio... more The proximate physiological mechanisms producing the parental ability to vary offspring sex ratio in many vertebrates remain elusive. Recently, high concentrations of maternal testosterone and glucose and low concentrations of maternal corticosterone have been suggested to explain male bias in offspring sex ratio. We examined how these factors affect secondary offspring sex ratio in nondomesticated field voles, Microtus agrestis, while controlling for maternal age, testosterone level of the male and body condition of both the female and the male. We found that females with high preconception serum testosterone and glucose levels produced a male-biased litter, whereas there was no association between maternal corticosterone level and litter sex ratio. Older females produced a bias towards sons, but neither their body condition nor paternal testosterone level correlated with litter sex ratio. Finally, females mated with a high body-condition male tended to deliver a male-biased litter. Our results suggest that several physiological traits of the mother may simultaneously be related to offspring sex ratio in mammals.
PLoS ONE, 2012
Associations between fluctuating asymmetry (FA, a putative marker of developmental instability, D... more Associations between fluctuating asymmetry (FA, a putative marker of developmental instability, DI) and life history traits have received a great deal of attention in the non-human literature. However, the patterns found are very heterogeneous and generalizations are difficult to make. In humans, only a few studies have related FA to life histories and fitness. In this paper we study such relationships using hand FA and several key life history traits in 209 post-menopausal Finnish women born between 1946 and 1958. Asymmetry measurements were based on scans of the hands and the life histories of these women were collected using questionnaires. No significant associations were detected and trends were opposite to expectations. We did find evidence for directional asymmetry, as traits in the right hand were larger on average. This may be due to handedness, questioning the usefulness of hand FA as a measure of DI. We conclude that future studies in humans should carefully examine the usefulness of traits as measures of DI.
Although the Dark Triad of personality (i.e., Machiavellianism, narcissism, and psychopathy) has ... more Although the Dark Triad of personality (i.e., Machiavellianism, narcissism, and psychopathy) has been researched widely, few studies have looked at women’s preferences for men who are high and low in Dark Triad. Further, it is not clear what the relationships between the Dark Triad and facial masculinity are. We investigated female preference for computer manipulated Dark Triad male faces in two on-line studies (Study 1: n = 125; Study 2: n = 1633). We found that women rated the high psychopathy and narcissistic faces the most masculine (Study 1). We also found that women showed a low preference for the high morphs in both long and short term relationships, and that preference for masculinity was correlated with a preference for narcissism (Study 2). We discuss the results in terms of male and female mating strategies
Physiology & Behavior, 2010
Maternal corticosterone but not testosterone level is associated with the ratio of second-to-four... more Maternal corticosterone but not testosterone level is associated with the ratio of second-to-fourth digit length (2D:4D) in field vole offspring (Microtus agrestis)
In many mammal species with sexual dimorphism producing sons is energetically more demanding to t... more In many mammal species with sexual dimorphism producing sons is energetically more demanding to the mother than producing daughters. Although some studies in humans have suggested that offspring born after a brother have a smaller birth weight and adult height when compared with those born after a sister, little is known about this intergenerational cost of producing sons. We aimed to study whether the sex of preceding sibling is associated with anthropometrics of the subsequent child at birth and in young adulthood. This population-based study was carried out on two data sets derived from the Swedish registers. Information on birth weight and length was obtained for 752,723 children of both sexes. Adult weight, height and muscle strength were available for 506,326 men. Multiple linear regression analyses showed that boys and girls born after a brother were, respectively, 18 and 9 g lighter and 0.08 and 0.03 cm (P < 0.001) shorter at birth than those born after a sister. Adjustment for gestational age decreased the magnitude of the associations [10 g and 0.04 cm (P < 0.001) in men and nonsignificant estimates in women], suggesting that part of the lower mean birth weight and length of individuals born after a brother was due to a shorter gestation. In young adulthood, men with a preceding brother showed 0.16 kg more in weight, 0.3% higher body mass index (P < 0.001) and a trend towards reduced height and muscle strength. Our results suggest that even though the sex of the previous child is associated with the anthropometrics of the subsequent child, the effect sizes are very small questioning whether this mechanism has adaptive value in contemporary humans.
Proceedings. Biological sciences / The Royal Society, Jan 22, 2015
Theoretical and empirical literature asserts that the sex ratio (i.e. M/F) at birth gauges the st... more Theoretical and empirical literature asserts that the sex ratio (i.e. M/F) at birth gauges the strength of selection in utero and cohort quality of males that survive to birth. We report the first individual-level test in humans, using detailed life-history data, of the 'culled cohort' hypothesis that males born to low annual sex ratio cohorts show lower than expected infant mortality and greater than expected lifetime reproductive success. We applied time-series and structural equation methods to a unique multigenerational dataset of a natural fertility population in nineteenth century Finland. We find that, consistent with culled cohorts, a 1 s.d. decline in the annual cohort sex ratio precedes an 8% decrease in the risk of male infant mortality. Males born to lower cohort sex ratios also successfully raised 4% more offspring to reproductive age than did males born to higher cohort sex ratios. The offspring result, however, falls just outside conventional levels of statist...
Twin Research and Human Genetics, 2013
The associations between height and reproductive success in humans have attracted long-time scien... more The associations between height and reproductive success in humans have attracted long-time scientific interest, but in addition to rather mixed previous results, little is still known about the background mechanisms of these associations. We analyzed the association of adult height with age at first birth and lifetime reproductive success using a twin study design that is able to optimally take into account family background and estimate the contributions of genetic and environmental factors. Information on live births as of June 2009 for 7,830 Finnish twins born 1950-1957 was extracted from the national population register. We found evidence for non-linear associations in men, as men in the third sex-specific height quintile had the highest probability of having one to two children, or three or more children at individual level analyses, and also to have any children when analyzing twin pairs discordant for height. Furthermore, the probability of having a spouse was highest in the third height category in men. Short stature was associated with earlier age at first birth in females, explained by correlated genetic factors, but not with lifetime number of children or having a spouse. Our results suggest that average stature may give some advantage for reproduction in males. In females, genetic factors explained the association between short stature and young age at first birth, which may suggest the role of hormonal factors.
Proceedings of the Royal Society B: Biological Sciences, 2005
Evolutionary theory of senescence emphasizes the importance of intense selection on early reprodu... more Evolutionary theory of senescence emphasizes the importance of intense selection on early reproduction owing to the declining force of natural selection with age that constrains lifespan. In humans, recent studies have, however, suggested that late-life mortality might be more closely related to late rather than early reproduction, although the role of late reproduction on fitness remains unclear. We examined the association between early and late reproduction with longevity in historical post-reproductive Sami women. We also estimated the strength of natural selection on early and late reproduction using path analysis, and the effect of reproductive timing on offspring survival to adulthood and maternal risk of dying at childbirth. We found that natural selection favoured both earlier start and later cessation of reproduction, and higher total fecundity. Maternal age at childbirth was not related to offspring or maternal survival. Interestingly, females who produced their last offspring at advanced age also lived longest, while age at first reproduction and total fecundity were unrelated to female longevity. Our results thus suggest that reproductive and somatic senescence may have been coupled in these human populations, and that selection could have favoured late reproduction. We discuss alternative hypotheses for the mechanisms which might have promoted the association between late reproduction and longevity.
Proceedings of the National Academy of Sciences, 2004
Life-history theory predicts a tradeoff between reproductive effort and lifespan. It has been sug... more Life-history theory predicts a tradeoff between reproductive effort and lifespan. It has been suggested that this tradeoff is a result of reproductive costs accelerating senescence of the immune system, leading to earlier death. Longevity costs of reproduction are suggested for some human populations, but whether high reproductive effort leads to impaired immune function is unknown. We examined how reproductive effort affected postreproductive survival and the probability of dying of an infectious disease in women born in preindustrial Finland between 1702 and 1859. We found that mothers delivering twins had reduced postreproductive survival after age 65. This effect arose because mothers of twins had a higher probability of succumbing to an infectious disease (mainly tuberculosis) than mothers delivering singletons. The risk among mothers of twins of dying of an infectious disease was further elevated if mothers had started reproducing early. In contrast, neither female postreproductive survival nor the risk of succumbing to an infectious disease was influenced by the total number of offspring produced. Our results provide evidence of a long-term survival cost of twinning in humans and indicate that the mechanism mediating this cost might have been accelerated immunosenescence.
PLoS ONE, 2007
Life-history theory predicts that resource scarcity constrains individual optimal reproductive st... more Life-history theory predicts that resource scarcity constrains individual optimal reproductive strategies and shapes the evolution of life-history traits. In species where the inherited structure of social class may lead to consistent resource differences among family lines, between-class variation in resource availability should select for divergence in optimal reproductive strategies. Evaluating this prediction requires information on the phenotypic selection and quantitative genetics of life-history trait variation in relation to individual lifetime access to resources. Here, we show using path analysis how resource availability, measured as the wealth class of the family, affected the opportunity and intensity of phenotypic selection on the key life-history traits of women living in pre-industrial Finland during the 1800s and 1900s. We found the highest opportunity for total selection and the strongest selection on earlier age at first reproduction in women of the poorest wealth class, whereas selection favoured older age at reproductive cessation in mothers of the wealthier classes. We also found clear differences in female life-history traits across wealth classes: the poorest women had the lowest age-specific survival throughout their lives, they started reproduction later, delivered fewer offspring during their lifetime, ceased reproduction younger, had poorer offspring survival to adulthood and, hence, had lower fitness compared to the wealthier women. Our results show that the amount of wealth affected the selection pressure on female life-history in a pre-industrial human population.
Science (New York, N.Y.), Jan 10, 2002
In humans, sons are physiologically more demanding to produce than daughters, as indicated by the... more In humans, sons are physiologically more demanding to produce than daughters, as indicated by their faster intrauterine growth rate (1) and heavier birth weight (2) and the longer time it takes mothers producing sons to reproduce again (3). Large, and particularly strongly ...
PLoS ONE, 2011
Background: The fate of tropical forests is a global concern, yet many far-reaching decisions aff... more Background: The fate of tropical forests is a global concern, yet many far-reaching decisions affecting forest resources are made locally. We explore allocation of logging rights using a case study from Loreto, Peruvian Amazonia, where millions of hectares of tropical rainforest were offered for concession in a competitive tendering process that addressed issues related to locality.
Personality and Individual Differences, 2013
Although an indicator of prenatal testosterone (PT), 2D:4D ratio, has been extensively studied in... more Although an indicator of prenatal testosterone (PT), 2D:4D ratio, has been extensively studied in the domain of financial risk taking, other domains of risk have received less attention. It is thought that elevated levels of PT relate to more masculinised behaviours, including increased risk taking propensity. In this study, we report negative findings with regards to health (average weekly drinking and daily smoking) and sexual (lifetime number of sexual partners) risk in a sample of post-menopausal Finnish women (N = 146-262). Our results suggest that PT may not masculinise health and sexual risk taking in women, at least at an older age.
Human Reproduction, 2008
The article by Delbaere et al. 'Perinatal outcome of twin pregnancies in women of advanced a... more The article by Delbaere et al. 'Perinatal outcome of twin pregnancies in women of advanced age', in Hum Reprod (2008), showed that irrespective of reproductive techniques, socio-economic status and the zygosity of twins, perinatal outcome of twin pregnancies is more favourable ...
Archives of Sexual Behavior, 2009
Behavioral Ecology and Sociobiology, May 29, 2009
The ratio of second-to-fourth digit length (2D/4D) has been suggested to be a useful adult age ma... more The ratio of second-to-fourth digit length (2D/4D) has been suggested to be a useful adult age marker of intrauterine exposure to steroids because it should be sexually dimorphic and fixed already in utero. Numerous studies mainly on humans have supported this conclusion, but it is yet unclear how well this applies to other vertebrates. This information would be especially valuable to field biologists to whom measuring steroids in utero is often impossible. The non-human studies conducted so far have yielded inconsistent results, perhaps due to the variety of different methods employed in measuring 2D/4D. We examined the age and sex dependency and lateral asymmetry of 2D/4D in field voles (Microtus agrestis) and compared whether these effects differed between 2D/4D measurements taken from photographs and X-rays. Our results show that 2D/4D measurements from photos had a higher measurement error and gave consistently higher 2D/4D than those from X-rays. According to both measurement methods, the right paw showed higher 2D/4D values than the left paw (lateral asymmetry). Adult voles had a lower 2D/4D than juveniles when measured from X-rays, but not when measured from photographs. We found no evidence for a sex difference in 2D/4D using either of the measurement methods. Our findings thus suggest that X-rays, due to their greater accuracy, should be preferred over photographs for measuring digit ratios in rodents. Our results also indicate that in this species, 2D/4D is laterally asymmetric, but it may not be either fixed in utero or sexually dimorphic. In conclusion, 2D/4D appears to be a rather species-and method-specific measure and researchers should be careful when generalising its applicability to study early hormonal effects in vertebrates.
Ecology and evolution, 2015
For migratory birds, the earlier arrival of males to breeding grounds is often expected to have f... more For migratory birds, the earlier arrival of males to breeding grounds is often expected to have fitness benefits. However, the selection differential on male arrival time has rarely been decomposed into the direct effect of male arrival and potential indirect effects through female traits. We measured the directional selection differential on male arrival time in the pied flycatcher (Ficedula hypoleuca) using data from 6 years and annual number of fledglings as the fitness proxy. Using structural equation modeling, we were able to take into account the temporal structure of the breeding cycle and the hierarchy between the examined traits. We found directional selection differentials for earlier male arrival date and earlier female laying date, as well as strong selection differential for larger clutch size. These selection differentials were due to direct selection only as indirect selection for these traits was nonsignificant. When decomposing the direct selection for earlier male ...
Proceedings. Biological sciences / The Royal Society, Jan 7, 2014
A shift from nomadic foraging to sedentary agriculture was a major turning point in human evoluti... more A shift from nomadic foraging to sedentary agriculture was a major turning point in human evolutionary history, increasing our population size and eventually leading to the development of modern societies. We however lack understanding of the changes in life histories that contributed to the increased population growth rate of agriculturalists, because comparable individual-based reproductive records of sympatric populations of agriculturalists and foragers are rarely found. Here, we compared key life-history traits and population growth rate using comprehensive data from the seventieth to nineteenth century Northern Finland: indigenous Sami were nomadic hunter-fishers and reindeer herders, whereas sympatric agricultural Finns relied predominantly on animal husbandry. We found that agriculture-based families had higher lifetime fecundity, faster birth spacing and lower maternal mortality. Furthermore, agricultural Finns had 6.2% higher annual population growth rate than traditional ...
Proceedings. Biological sciences / The Royal Society, Jan 7, 2010
The proximate physiological mechanisms producing the parental ability to vary offspring sex ratio... more The proximate physiological mechanisms producing the parental ability to vary offspring sex ratio in many vertebrates remain elusive. Recently, high concentrations of maternal testosterone and glucose and low concentrations of maternal corticosterone have been suggested to explain male bias in offspring sex ratio. We examined how these factors affect secondary offspring sex ratio in nondomesticated field voles, Microtus agrestis, while controlling for maternal age, testosterone level of the male and body condition of both the female and the male. We found that females with high preconception serum testosterone and glucose levels produced a male-biased litter, whereas there was no association between maternal corticosterone level and litter sex ratio. Older females produced a bias towards sons, but neither their body condition nor paternal testosterone level correlated with litter sex ratio. Finally, females mated with a high body-condition male tended to deliver a male-biased litter. Our results suggest that several physiological traits of the mother may simultaneously be related to offspring sex ratio in mammals.
PLoS ONE, 2012
Associations between fluctuating asymmetry (FA, a putative marker of developmental instability, D... more Associations between fluctuating asymmetry (FA, a putative marker of developmental instability, DI) and life history traits have received a great deal of attention in the non-human literature. However, the patterns found are very heterogeneous and generalizations are difficult to make. In humans, only a few studies have related FA to life histories and fitness. In this paper we study such relationships using hand FA and several key life history traits in 209 post-menopausal Finnish women born between 1946 and 1958. Asymmetry measurements were based on scans of the hands and the life histories of these women were collected using questionnaires. No significant associations were detected and trends were opposite to expectations. We did find evidence for directional asymmetry, as traits in the right hand were larger on average. This may be due to handedness, questioning the usefulness of hand FA as a measure of DI. We conclude that future studies in humans should carefully examine the usefulness of traits as measures of DI.
Although the Dark Triad of personality (i.e., Machiavellianism, narcissism, and psychopathy) has ... more Although the Dark Triad of personality (i.e., Machiavellianism, narcissism, and psychopathy) has been researched widely, few studies have looked at women’s preferences for men who are high and low in Dark Triad. Further, it is not clear what the relationships between the Dark Triad and facial masculinity are. We investigated female preference for computer manipulated Dark Triad male faces in two on-line studies (Study 1: n = 125; Study 2: n = 1633). We found that women rated the high psychopathy and narcissistic faces the most masculine (Study 1). We also found that women showed a low preference for the high morphs in both long and short term relationships, and that preference for masculinity was correlated with a preference for narcissism (Study 2). We discuss the results in terms of male and female mating strategies
Physiology & Behavior, 2010
Maternal corticosterone but not testosterone level is associated with the ratio of second-to-four... more Maternal corticosterone but not testosterone level is associated with the ratio of second-to-fourth digit length (2D:4D) in field vole offspring (Microtus agrestis)
In many mammal species with sexual dimorphism producing sons is energetically more demanding to t... more In many mammal species with sexual dimorphism producing sons is energetically more demanding to the mother than producing daughters. Although some studies in humans have suggested that offspring born after a brother have a smaller birth weight and adult height when compared with those born after a sister, little is known about this intergenerational cost of producing sons. We aimed to study whether the sex of preceding sibling is associated with anthropometrics of the subsequent child at birth and in young adulthood. This population-based study was carried out on two data sets derived from the Swedish registers. Information on birth weight and length was obtained for 752,723 children of both sexes. Adult weight, height and muscle strength were available for 506,326 men. Multiple linear regression analyses showed that boys and girls born after a brother were, respectively, 18 and 9 g lighter and 0.08 and 0.03 cm (P < 0.001) shorter at birth than those born after a sister. Adjustment for gestational age decreased the magnitude of the associations [10 g and 0.04 cm (P < 0.001) in men and nonsignificant estimates in women], suggesting that part of the lower mean birth weight and length of individuals born after a brother was due to a shorter gestation. In young adulthood, men with a preceding brother showed 0.16 kg more in weight, 0.3% higher body mass index (P < 0.001) and a trend towards reduced height and muscle strength. Our results suggest that even though the sex of the previous child is associated with the anthropometrics of the subsequent child, the effect sizes are very small questioning whether this mechanism has adaptive value in contemporary humans.
Proceedings. Biological sciences / The Royal Society, Jan 22, 2015
Theoretical and empirical literature asserts that the sex ratio (i.e. M/F) at birth gauges the st... more Theoretical and empirical literature asserts that the sex ratio (i.e. M/F) at birth gauges the strength of selection in utero and cohort quality of males that survive to birth. We report the first individual-level test in humans, using detailed life-history data, of the 'culled cohort' hypothesis that males born to low annual sex ratio cohorts show lower than expected infant mortality and greater than expected lifetime reproductive success. We applied time-series and structural equation methods to a unique multigenerational dataset of a natural fertility population in nineteenth century Finland. We find that, consistent with culled cohorts, a 1 s.d. decline in the annual cohort sex ratio precedes an 8% decrease in the risk of male infant mortality. Males born to lower cohort sex ratios also successfully raised 4% more offspring to reproductive age than did males born to higher cohort sex ratios. The offspring result, however, falls just outside conventional levels of statist...
Twin Research and Human Genetics, 2013
The associations between height and reproductive success in humans have attracted long-time scien... more The associations between height and reproductive success in humans have attracted long-time scientific interest, but in addition to rather mixed previous results, little is still known about the background mechanisms of these associations. We analyzed the association of adult height with age at first birth and lifetime reproductive success using a twin study design that is able to optimally take into account family background and estimate the contributions of genetic and environmental factors. Information on live births as of June 2009 for 7,830 Finnish twins born 1950-1957 was extracted from the national population register. We found evidence for non-linear associations in men, as men in the third sex-specific height quintile had the highest probability of having one to two children, or three or more children at individual level analyses, and also to have any children when analyzing twin pairs discordant for height. Furthermore, the probability of having a spouse was highest in the third height category in men. Short stature was associated with earlier age at first birth in females, explained by correlated genetic factors, but not with lifetime number of children or having a spouse. Our results suggest that average stature may give some advantage for reproduction in males. In females, genetic factors explained the association between short stature and young age at first birth, which may suggest the role of hormonal factors.
Proceedings of the Royal Society B: Biological Sciences, 2005
Evolutionary theory of senescence emphasizes the importance of intense selection on early reprodu... more Evolutionary theory of senescence emphasizes the importance of intense selection on early reproduction owing to the declining force of natural selection with age that constrains lifespan. In humans, recent studies have, however, suggested that late-life mortality might be more closely related to late rather than early reproduction, although the role of late reproduction on fitness remains unclear. We examined the association between early and late reproduction with longevity in historical post-reproductive Sami women. We also estimated the strength of natural selection on early and late reproduction using path analysis, and the effect of reproductive timing on offspring survival to adulthood and maternal risk of dying at childbirth. We found that natural selection favoured both earlier start and later cessation of reproduction, and higher total fecundity. Maternal age at childbirth was not related to offspring or maternal survival. Interestingly, females who produced their last offspring at advanced age also lived longest, while age at first reproduction and total fecundity were unrelated to female longevity. Our results thus suggest that reproductive and somatic senescence may have been coupled in these human populations, and that selection could have favoured late reproduction. We discuss alternative hypotheses for the mechanisms which might have promoted the association between late reproduction and longevity.
Proceedings of the National Academy of Sciences, 2004
Life-history theory predicts a tradeoff between reproductive effort and lifespan. It has been sug... more Life-history theory predicts a tradeoff between reproductive effort and lifespan. It has been suggested that this tradeoff is a result of reproductive costs accelerating senescence of the immune system, leading to earlier death. Longevity costs of reproduction are suggested for some human populations, but whether high reproductive effort leads to impaired immune function is unknown. We examined how reproductive effort affected postreproductive survival and the probability of dying of an infectious disease in women born in preindustrial Finland between 1702 and 1859. We found that mothers delivering twins had reduced postreproductive survival after age 65. This effect arose because mothers of twins had a higher probability of succumbing to an infectious disease (mainly tuberculosis) than mothers delivering singletons. The risk among mothers of twins of dying of an infectious disease was further elevated if mothers had started reproducing early. In contrast, neither female postreproductive survival nor the risk of succumbing to an infectious disease was influenced by the total number of offspring produced. Our results provide evidence of a long-term survival cost of twinning in humans and indicate that the mechanism mediating this cost might have been accelerated immunosenescence.
PLoS ONE, 2007
Life-history theory predicts that resource scarcity constrains individual optimal reproductive st... more Life-history theory predicts that resource scarcity constrains individual optimal reproductive strategies and shapes the evolution of life-history traits. In species where the inherited structure of social class may lead to consistent resource differences among family lines, between-class variation in resource availability should select for divergence in optimal reproductive strategies. Evaluating this prediction requires information on the phenotypic selection and quantitative genetics of life-history trait variation in relation to individual lifetime access to resources. Here, we show using path analysis how resource availability, measured as the wealth class of the family, affected the opportunity and intensity of phenotypic selection on the key life-history traits of women living in pre-industrial Finland during the 1800s and 1900s. We found the highest opportunity for total selection and the strongest selection on earlier age at first reproduction in women of the poorest wealth class, whereas selection favoured older age at reproductive cessation in mothers of the wealthier classes. We also found clear differences in female life-history traits across wealth classes: the poorest women had the lowest age-specific survival throughout their lives, they started reproduction later, delivered fewer offspring during their lifetime, ceased reproduction younger, had poorer offspring survival to adulthood and, hence, had lower fitness compared to the wealthier women. Our results show that the amount of wealth affected the selection pressure on female life-history in a pre-industrial human population.
Science (New York, N.Y.), Jan 10, 2002
In humans, sons are physiologically more demanding to produce than daughters, as indicated by the... more In humans, sons are physiologically more demanding to produce than daughters, as indicated by their faster intrauterine growth rate (1) and heavier birth weight (2) and the longer time it takes mothers producing sons to reproduce again (3). Large, and particularly strongly ...
PLoS ONE, 2011
Background: The fate of tropical forests is a global concern, yet many far-reaching decisions aff... more Background: The fate of tropical forests is a global concern, yet many far-reaching decisions affecting forest resources are made locally. We explore allocation of logging rights using a case study from Loreto, Peruvian Amazonia, where millions of hectares of tropical rainforest were offered for concession in a competitive tendering process that addressed issues related to locality.
Personality and Individual Differences, 2013
Although an indicator of prenatal testosterone (PT), 2D:4D ratio, has been extensively studied in... more Although an indicator of prenatal testosterone (PT), 2D:4D ratio, has been extensively studied in the domain of financial risk taking, other domains of risk have received less attention. It is thought that elevated levels of PT relate to more masculinised behaviours, including increased risk taking propensity. In this study, we report negative findings with regards to health (average weekly drinking and daily smoking) and sexual (lifetime number of sexual partners) risk in a sample of post-menopausal Finnish women (N = 146-262). Our results suggest that PT may not masculinise health and sexual risk taking in women, at least at an older age.