Be Fruitful and Multiply

Kevin Lewis

September 22, 2009

A must-read: A Life of Its Own: Where Will Synthetic Biology Lead Us? By Michael Specter, The New Yorker, September 28, 2009


The politics of ‘The Natural Family' in Israel: State policy and kinship ideologies

Daphna Birenbaum-Carmeli
Social Science & Medicine, October 2009, Pages 1018-1024

Israel is the only country in the world that provides nearly unlimited, universal state funding for fertility treatments. This exceptional policy has been widely understood as symbolising the state's pronatalism. In this paper I probe the policy and assess medical experts' practice to show how a specific modality of pronatalism — enhancing ‘the natural family' concept — is being construed through legislation and practice. Policy analysis discloses how the relatively efficient and safe technology of donor insemination has been devalued as a last resort solution to male infertility, to be applied only after all ‘natural' alternatives have failed. At the same time, in vitro fertilisation (IVF), despite its health risks and lower efficacy, is proactively encouraged through various policy measures including unrestricted public funding. Interviews with practitioners reveal that similar preferences are enhanced through the infusion of secrecy and shame into donor insemination, coupled with active support of IVF. To complete the picture, Israel's adoption law is outlined, showing tight restrictions on domestic adoption and complete lack of state support or subsidy for inter-country adoption. I suggest that both the marginalisation of non-genetic forms of kinning and the emphasis on IVF indicate a state interest in upgrading the ‘natural family' so as to nurture a geneticised notion of the local Jewish collectivity.


Pet Overpopulation: An Economic Analysis

Stephen Coate & Brian Knight
Cornell Working Paper, August 2009

"This paper presents a model of the market that captures some of its complexities and uses it to analyze market performance and the scope for beneficial government intervention. The equilibrium of the model qualitatively matches key features of the markets for dogs and cats in the U.S.. Old pets relinquished by their owners are euthanized, while pure breed puppies and kittens are sold for a positive price. Mixed breed puppies and kittens are available for free; some are adopted and some euthanized. The euthanization of pets makes the equilibrium inefficient and it is in this sense that the market creates pet overpopulation. The inefficiency stems from the assumption that consumers care about the animals they have owned. A common pool externality arises from the fixed number of "good homes" to which young or relinquished older pets can be allocated. When making their breeding or spaying decisions, owners do not take into account that their puppies or kittens crowd out homes for other needy pets. Restoring efficiency requires a combination of taxes on young pets and subsidies for spaying. A calibrated example is developed to illustrate the nature of the optimal corrective policies and to quantify the magnitude of potential welfare gains. The parameters of the model are chosen so the equilibrium quantitatively matches the market for dogs in the U.S.. The optimal taxes on young dogs are large, exceeding the prices currently paid for pure breed puppies. The aggregate welfare gains are also sizable, in the $16 to $21 billion range. These estimates suggest that the problem of pet overpopulation deserves serious policy consideration."


Falling Short of Highest Life Expectancy: How Many Americans Might Have Been Alive in the Twentieth Century?

Magdalena Muszyńska & Roland Rau
Population and Development Review, June 2009, Pages 585-603

Life expectancy at birth in the United States during the twentieth century was lower than in many other highly developed countries. We investigate how this mortality disadvantage in the last 100 years translates into the number of hypothetical lives lost and their sex and age structure. We estimate the hypothetical US population if it had experienced in each decade since 1900 the mortality level of the country with the then highest life expectancy and compare the results to the actual figures in 2000. By 2000, the number of additional people who could have been alive had the mortality levels in the United States been as low as those in countries with the highest life expectancy was 66 million. This number is distributed equally between males and females. Suboptimal mortality at reproductive ages is crucial for the cumulative effect of potential lives lost, resulting from premature deaths of women who could still become first-time mothers or bear additional children. Out of the 66 million additional persons who could have been alive in 2000, 45 million are attributable to those indirect deaths. Although the differences in the composition of the population by sex and age under the two mortality regimes are minor, the majority of people who might have been alive-54 million-were of working age or younger.


Good Semen Quality and Life Expectancy: A Cohort Study of 43,277 Men

Tina Kold Jensen, Rune Jacobsen, Kaare Christensen, Niels Christian Nielsen & Erik Bostofte
American Journal of Epidemiology, September 2009, Pages 559-565

Fertility status may predict later mortality, but no studies have examined the effect of semen quality on subsequent mortality. Men referred to the Copenhagen Sperm Analysis Laboratory by general practitioners and urologists from 1963 to 2001 were, through a unique personal identification number, linked to the Danish central registers that hold information on all cases of cancer, causes of death, and number of children in the Danish population. The men were followed until December 31, 2001, death, or censoring, whichever occurred first, and the total mortality and cause-specific mortality of the cohort were compared with those of all age-standardized Danish men or according to semen characteristics. Among 43,277 men without azospermia referred for infertility problems, mortality decreased as the sperm concentration increased up to a threshold of 40 million/mL. As the percentages of motile and morphologically normal spermatozoa and semen volume increased, mortality decreased in a dose-response manner (Ptrend < 0.05). The decrease in mortality among men with good semen quality was due to a decrease in a wide range of diseases and was found among men both with and without children; therefore, the decrease in mortality could not be attributed solely to lifestyle and/or social factors. Semen quality may therefore be a fundamental biomarker of overall male health.


Why did the first farmers toil? Human metabolism and the origins of agriculture

Jacob Weisdorf
European Review of Economic History, August 2009, Pages 157-172

Time-budget studies done among contemporary primitive people suggest that the first farmers worked harder to attain subsistence than their foraging predecessors. This makes the adoption of agriculture in the Stone Age one of the major curiosities in human cultural history. Theories offered by economists and economic historians largely fail to capture work-intensification among early farmers. Attributing a key role to human metabolism, this study provides a simple framework for analysing the adoption of agriculture. It demonstrates how the additional output that farming offered could have lured people into agriculture, but that subsequent population increase would eventually have swallowed up its benefits, forcing early farmers into an irreversible trap, where they had to do more work to attain subsistence compared to their foraging ancestors. The framework draws attention to the fact that, if agriculture arose out of need, as some scholars have suggested, then this was because prehistoric foragers turned down agriculture in the first place. Estimates of population growth before and after farming, however, in the light of the present framework seem to suggest that hunters were pulled rather than pushed into agriculture.


Understanding the link between the economy and teenage sexual behavior and fertility outcomes

Jeremy Arkes & Jacob Alex Klerman
Journal of Population Economics, July 2009, Pages 517-536

We use individual-level data from the 1997 National Longitudinal Survey of Youth and state unemployment rates to examine how the economy affects fertility and its proximate determinants for several groups based on gender, age (15-17 and 18-20 groups), and race/ethnicity. We find that, for 15- to 17-year-old females, several behaviors leading to pregnancies and pregnancies themselves are higher when the unemployment rate is higher, which is consistent with the counter-cyclical fertility patterns for this group. For 18- to 20-year-old males, the results suggested counter-cyclical patterns of fertility behaviors/outcomes for whites, but pro-cyclical patterns for blacks.


Birthweight and paternal involvement predict early reproduction in British women: Evidence from the National Child Development Study

Daniel Nettle, David Coall & Thomas Dickins
American Journal of Human Biology, forthcoming

There is considerable interest in the mechanisms maintaining early reproduction in the most socioeconomically disadvantaged groups in developed countries. Previous research has suggested that differential exposure to early-life factors such as low birthweight and lack of paternal involvement during childhood may be relevant. Here, we used longitudinal data on the female cohort members from the UK National Child Development Study (n = 3,014-4,482 depending upon variables analyzed) to investigate predictors of early reproduction. Our main outcome measures were having a child by age 20, and stating at age 16 an intended age of reproduction of 20 years or lower. Low paternal involvement during childhood was associated with increased likelihood of early reproduction (O.R. 1.79-2.25) and increased likelihood of early intended reproduction (O.R. 1.38-2.50). Low birthweight for gestational age also increased the odds of early reproduction (O.R. for each additional s.d. 0.88) and early intended reproduction (O.R. for each additional s.d. 0.81). Intended early reproduction strongly predicted actual early reproduction (O.R. 5.39, 95% CI 3.71-7.83). The results suggest that early-life factors such as low birthweight for gestational age, and low paternal involvement during childhood, may affect women's reproductive development, leading to earlier target and achieved ages for reproduction. Differential exposure to these factors may be part of the reason that early fertility persists in socioeconomically disadvantaged groups. We discuss our results with respect to the kinds of interventions likely to affect the rate of teen pregnancy.


Sociosexually Unrestricted Parents Have More Sons: A Further Application of the Generalized Trivers-Willard Hypothesis (gTWH)

Satoshi Kanazawa & Péter Apari
Annals of Human Biology, May 2009, Pages 320-330

Background: The generalized Trivers-Willard hypothesis (gTWH) proposes that parents who possess any heritable trait which increases male reproductive success at a greater rate than female reproductive success in a given environment will have a higher-than-expected offspring sex ratio, and parents who possess any heritable trait which increases the female reproductive success at a greater rate than male reproductive success in a given environment will have a lower-than-expected offspring sex ratio.

Aim: One heritable trait which increases the reproductive success of sons much more than that of daughters is unrestricted sociosexual orientation. We therefore predict that parents with unrestricted sociosexual orientation (measured by the number of sexual partners, frequency of sex, and attitudes toward relationship commitment and sexual exclusivity) have a higher-than-expected offspring sex ratio (more sons).

Subjects and method: We analyse the US General Social Surveys and the National Longitudinal Study of Adolescent Health (Add Health), both with large nationally representative samples.

Results: Our analyses support the prediction from the gTWH.

Conclusion: One standard deviation increase in unrestrictedness of sociosexual orientation increases the odds of having a son by 12-19% in the representative American samples.


Prevalence of Consanguineous Marriages in Syria

Hasan Othman & Mostafa Saadat
Journal of Biosocial Science, September 2009, Pages 685-692

Consanguineous marriage is the union of individuals having at least one common ancestor. The present cross-sectional study was done in order to illustrate the prevalence and types of consanguineous marriages in the Syrian Arab Republic. Data on consanguineous marriages were collected using a simple questionnaire. The total number of couples in this study was 67,958 (urban areas: 36,574 couples; rural areas: 31,384 couples) from the following provinces: Damascus, Hamah, Tartous, Latakia, Al Raqa, Homs, Edlep and Aleppo. In each province urban and rural areas were surveyed. Consanguineous marriage was classified by the degree of relationship between couples: double first cousins (F=1/8), first cousins (F=1/16), second cousins (F=1/64) and beyond second cousins (F<1/64). The coefficient of inbreeding (F) was calculated for each couple and the mean coefficient of inbreeding (α) estimated for the population of each province, stratified by rural and urban areas. The results showed that the overall frequency of consanguinity was 30.3% in urban and 39.8% in rural areas. Total rate of consanguinity was found to be 35.4%. The equivalent mean inbreeding coefficient (α) was 0.0203 and 0.0265 in urban and rural areas, respectively. The mean proportion of consanguineous marriages ranged from 67.5% in Al Raqa province to 22.1% in Latakia province. The α-value ranged from 0.0358 to 0.0127 in these two provinces, respectively. The western and north-western provinces (including Tartous, Lattakia and Edlep) recorded lower levels of inbreeding than the central, northern and southern provinces. The overall α-value was estimated to be about 0.0236 for the studied populations. First cousin marriages (with 20.9%) were the most common type of consanguineous marriages, followed by double first cousin (with 7.8%) and second cousin marriages (with 3.3%), and beyond second cousin was the least common type.


Proximate Sources of Population Sex Imbalance in India

Emily Oster
Demography, May 2009, Pages 325-339

There is a population sex imbalance in India. Despite a consensus that this imbalance is due to excess female mortality, the specific source of this excess mortality remains poorly understood. I use microdata on child survival in India to analyze the proximate sources of the sex imbalance. I address two questions: when in life does the sex imbalance arise, and what health or nutritional investments are specifically responsible for its appearance? I present a new methodology that uses microdata on child survival. This methodology explicitly takes into account both the possibility of naturally occurring sex differences in survival and possible differences between investments in their importance for survival. Consistent with existing literature, I find significant excess female mortality in childhood, particularly between the ages of 1 and 5, and argue that the sex imbalance that exists by age 5 is large enough to explain virtually the entire imbalance in the population. Within this age group, sex differences in vaccinations explain between 20% and 30% of excess female mortality, malnutrition explains an additional 20%, and differences in treatment for illness play a smaller role. Together, these investments account for approximately 50% of the sex imbalance in mortality in India.


Foreign Aid, Fertility and Human Capital Accumulation

Leonid Azarnert
Economica, November 2008, Pages 766-781

This paper analyses the effect of foreign aid on population growth and human capital accumulation. Consistent with empirical evidence from sub-Saharan Africa, the model shows that foreign aid can work against its stated goal of alleviating poverty and promoting growth. Humanitarian aid fosters population growth and adversely affects the recipients' incentive to invest in human capital. The analysis suggests that foreign aid may lock a recipient economy in a low-equilibrium trap.


When Stress Predicts a Shrinking Gene Pool, Trading Early Reproduction for Longevity Can Increase Fitness, Even with Lower Fecundity

William Ratcliff, Peter Hawthorne, Michael Travisano & Ford Denison
PLoS ONE, 25 June 2009

Background: Stresses like dietary restriction or various toxins increase lifespan in taxa as diverse as yeast, Caenorhabditis elegans, Drosophila and rats, by triggering physiological responses that also tend to delay reproduction. Food odors can reverse the effects of dietary restriction, showing that key mechanisms respond to information, not just resources. Such environmental cues can predict population trends, not just individual prospects for survival and reproduction. When population size is increasing, each offspring produced earlier makes a larger proportional contribution to the gene pool, but the reverse is true when population size is declining.

Principal Findings: We show mathematically that natural selection can favor facultative delay in reproduction when environmental cues predict a decrease in total population size, even if lifetime fecundity decreases with delay. We also show that increased reproduction from waiting for better conditions does not increase fitness (proportional representation) when the whole population benefits similarly.

Conclusions: We conclude that the beneficial effects of stress on longevity (hormesis) in diverse taxa are a side-effect of delaying reproduction in response to environmental cues that population size is likely to decrease. The reversal by food odors of the effects of dietary restriction can be explained as a response to information that population size is less likely to decrease, reducing the chance that delaying reproduction will increase fitness.

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