Is Mate Choice in Humans MHC-Dependent?

In several species, including rodents and fish, it has been shown that the Major Histocompatibility Complex (MHC) influences mating preferences and, in some cases, that this may be mediated by preferences based on body odour. In humans, the picture has been less clear. Several studies have reported a tendency for humans to prefer MHC-dissimilar mates, a sexual selection that would favour the production of MHC-heterozygous offspring, who would be more resistant to pathogens, but these results are unsupported by other studies. Here, we report analyses of genome-wide genotype data (from the HapMap II dataset) and HLA types in African and European American couples to test whether humans tend to choose MHC-dissimilar mates. In order to distinguish MHC-specific effects from genome-wide effects, the pattern of similarity in the MHC region is compared to the pattern in the rest of the genome. African spouses show no significant pattern of similarity/dissimilarity across the MHC region (relatedness coefficient, R = 0.015, p = 0.23), whereas across the genome, they are more similar than random pairs of individuals (genome-wide R = 0.00185, p<10(-3)). We discuss several explanations for these observations, including demographic effects. On the other hand, the sampled European American couples are significantly more MHC-dissimilar than random pairs of individuals (R = -0.043, p = 0.015), and this pattern of dissimilarity is extreme when compared to the rest of the genome, both globally (genome-wide R = -0.00016, p = 0.739) and when broken into windows having the same length and recombination rate as the MHC (only nine genomic regions exhibit a higher level of genetic dissimilarity between spouses than does the MHC). This study thus supports the hypothesis that the MHC influences mate choice in some human populations.     

Does Genetic Diversity Predict Health in Humans?

Genetic diversity, especially at genes important for immune functioning within the Major Histocompatibility Complex (MHC), has been associated with fitness-related traits, including disease resistance, in many species. Recently, genetic diversity has been associated with mate preferences in humans. Here we asked whether these preferences are adaptive in terms of obtaining healthier mates. We investigated whether genetic diversity (heterozygosity and standardized mean d²) at MHC and nonMHC microsatellite loci, predicted health in 153 individuals. Individuals with greater allelic diversity (d²) at nonMHC loci and at one MHC locus, linked to HLA-DRB1, reported fewer symptoms over a four-month period than individuals with lower d². In contrast, there were no associations between MHC or nonMHC heterozygosity and health. NonMHC-d² has previously been found to predict male preferences for female faces. Thus, the current findings suggest that nonMHC diversity may play a role in both natural and sexual selection acting on human populations.     

What Justifies a Future with Humans in It?

Antinatalist commentators recommend that humanity bring itself to a close, on the theory that pain and suffering override the value of any possible life. Other commentators do not require the voluntary extinction of human beings, but they defend that outcome if people were to choose against having children. Against such views, Richard Kraut has defended a general moral obligation to people the future with human beings until the workings of the universe render such efforts impossible. Kraut advances this view on the grounds that we are obliged to exercise beneficence toward others and on the grounds that the goods available in human lives are morally compelling. This account ultimately succeeds in making no more than a prima facie defense of human perpetuation because considerations of beneficence could override – in some cases probably should – override any duty to perpetuate human beings. While the goods of human life may be distinctive, they cannot serve as reason‐giving in regard to their own perpetuation. Ironically, the exercise of beneficence may authorize the extinction of human beings, if it becomes possible to enhance the goods available to human descendants in a way that moves them away from human nature as now given. The defense of a morally obligatory and strictly human future remains elusive, even as it becomes morally desirable to work against Fateful Catastrophes, those human‐caused events that threaten to extinguish existing lives already good and enriching for their bearers.     

Vitamin Deficiencies in Humans: Can Plant Science Help?

The term vitamin describes a small group of organic compounds that are absolutely required in the human diet. Although for the most part, dependency criteria are met in developed countries through balanced diets, this is not the case for the five billion people in developing countries who depend predominantly on a single staple crop for survival. Thus, providing a more balanced vitamin intake from high-quality food remains one of the grandest challenges for global human nutrition in the coming decade(s). Here, we describe the known importance of vitamins in human health and current knowledge on their metabolism in plants. Deficits in developing countries are a combined consequence of a paucity of specific vitamins in major food staple crops, losses during crop processing, and/or overreliance on a single species as a primary food source. We discuss the role that plant science can play in addressing this problem and review successful engineering of vitamin pathways. We conclude that while considerable advances have been made in understanding vitamin metabolic pathways in plants, more cross-disciplinary approaches must be adopted to provide adequate levels of all vitamins in the major staple crops to eradicate vitamin deficiencies from the global population.     

Using Ultrasonography to Define Fetal�CMaternal Relationships: Moving from Humans to Mice

Ultrasound scanning is a noninvasive, accurate, and cost-effective method to create images of the female reproductive tract clinically and in research. Ultrasonography is particularly valuable for studying the dynamic relationships among mother, placenta, and fetus during pregnancy because this modality does not disturb the ongoing course of gestation. Importantly, the complex vascular changes in the mother induced by pregnancy and the vascular system generated to support placental function can be assessed quantitatively and functionally by ultrasonography. Many mouse models are available that address aspects of human placental function and dysfunction, but high-quality microultrasound technology suitable for use in pregnant mice has become widely available only recently. This technical advance now enables real-time recording of maternal–fetal interactions in pregnant rodents. The ability to perform microultrasonic analyses of parameters such as uterine arterial remodeling, hemodynamic changes, placental development, and fetal growth in mice now permits research that uses the same imaging platform as that for human patients. This capability will enhance the translation of information derived from rodent studies to the clinic.Abbreviations: gd, gestation day; IUGR, intrauterine growth restrictionHuman pregnancy is a complex, dynamic progress accompanied by both inspiring and amazing events. Clinically, disorders of pregnancy are among the least understood areas in health science because of ethical and cultural challenges and the involvement of 2 (or more) subjects (mother and fetus) rather than 1. Because continuation and successful conclusion of pregnancy typically are desired, advances in clinical and research investigations of human pregnancy are highly dependent upon technological advances in noninvasive imaging. The most common human gestational complications are preeclampsia (acute onset of hypertension during the second half of pregnancy), intrauterine growth restriction (IUGR), and diabetes. These pathologies are thought to share many risk factors, particularly an inadequate response of the maternal vasculature to the state of pregnancy.⁵⁹ In all mammals, maternal vascular adaptation is essential to meet the requirements of blastocyst implantation and placental and fetal development to ensure a successful pregnancy. In species with hemochorial placentation (including human, rat, and mouse), endometrial decidualization is associated with maternal vascular remodeling at implantation sites, and the remodeling process has become a diagnostic and therapeutic target.^39,47Ultrasonography was introduced in 1958 and has become the diagnostic tool of choice to study human gestational health,¹⁸ not only because this modality is noninvasive with very low risk but also because it provides real-time images with positional information.²⁴ Ultrasonography is relatively inexpensive and portable, compared with other modalities such as MRI and computed tomography. Modern clinical ultrasonography usually is performed by using a pulse–echo approach with a brightness-mode (B-mode) output that can be augmented by using advanced functions such as color Doppler mapping, 3D or 4D imaging, and spectral measurements. Application of these ultrasound techniques has enabled exploration and understanding of human maternal–fetal relationships that previously had been virtually inaccessible. Most studies of the physiology and pathology of pregnancy in animal models still rely on postmortem approaches rather than serial examinations, which would decrease experimental animal numbers. A key advance for studies of pregnancy in mice has been the development of microultrasonography. This technology now provides in vivo morphometric quantification of embryonic and placental growth for mice.^21,33 Here we review the application of microultrasonography to hemodynamic monitoring, vascular assessment, and placental development in mice and address its limitations briefly.     

Fecal Transplants: What Is Being Transferred?

Fecal transplants are increasingly utilized for treatment of recurrent infections (i.e., Clostridium difficile) in the human gut and as a general research tool for gain-of-function experiments (i.e., gavage of fecal pellets) in animal models. Changes observed in the recipient''s biology are routinely attributed to bacterial cells in the donor feces (~10¹¹ per gram of human wet stool). Here, we examine the literature and summarize findings on the composition of fecal matter in order to raise cautiously the profile of its multipart nature. In addition to viable bacteria, which may make up a small fraction of total fecal matter, other components in unprocessed human feces include colonocytes (~10⁷ per gram of wet stool), archaea (~10⁸ per gram of wet stool), viruses (~10⁸ per gram of wet stool), fungi (~10⁶ per gram of wet stool), protists, and metabolites. Thus, while speculative at this point and contingent on the transplant procedure and study system, nonbacterial matter could contribute to changes in the recipient''s biology. There is a cautious need for continued reductionism to separate out the effects and interactions of each component.     

Do Humans Optimally Exploit Redundancy to Control Step Variability in Walking?

It is widely accepted that humans and animals minimize energetic cost while walking. While such principles predict average behavior, they do not explain the variability observed in walking. For robust performance, walking movements must adapt at each step, not just on average. Here, we propose an analytical framework that reconciles issues of optimality, redundancy, and stochasticity. For human treadmill walking, we defined a goal function to formulate a precise mathematical definition of one possible control strategy: maintain constant speed at each stride. We recorded stride times and stride lengths from healthy subjects walking at five speeds. The specified goal function yielded a decomposition of stride-to-stride variations into new gait variables explicitly related to achieving the hypothesized strategy. Subjects exhibited greatly decreased variability for goal-relevant gait fluctuations directly related to achieving this strategy, but far greater variability for goal-irrelevant fluctuations. More importantly, humans immediately corrected goal-relevant deviations at each successive stride, while allowing goal-irrelevant deviations to persist across multiple strides. To demonstrate that this was not the only strategy people could have used to successfully accomplish the task, we created three surrogate data sets. Each tested a specific alternative hypothesis that subjects used a different strategy that made no reference to the hypothesized goal function. Humans did not adopt any of these viable alternative strategies. Finally, we developed a sequence of stochastic control models of stride-to-stride variability for walking, based on the Minimum Intervention Principle. We demonstrate that healthy humans are not precisely “optimal,” but instead consistently slightly over-correct small deviations in walking speed at each stride. Our results reveal a new governing principle for regulating stride-to-stride fluctuations in human walking that acts independently of, but in parallel with, minimizing energetic cost. Thus, humans exploit task redundancies to achieve robust control while minimizing effort and allowing potentially beneficial motor variability.     

Fetal genes in mother's blood: A novel mechanism for telegony?

Telegony is a discredited genetic phenomenon that a previous male may influence the characteristics of offspring subsequently borne by the same female to another male. Although its reality was acknowledged by such authorities as Charles Darwin and Herbert Spencer, it has been met with skepticism because of a lack of understanding of the theoretical basis for telegony. With the discovery of fetal genes in mother's blood, the penetration of somatic cells by sperm, and the ability of RNA to program genome rearrangement, mechanisms might exist for telegony.     

Have We Neglected the Role of Fetal Endothelium in Transplacental Transport?

Maternal‐to‐fetal transfer of nutrient and other substances occurs across the placental barrier (PB) which is made up of endothelial cells (EC) on the fetal side and the syncytiotrophoblast (STB) on the maternal side. Numerous studies were conducted to explore the transport characteristics across the STB layer, which is also considered as the major resistance for maternal‐to‐fetal exchange of materials. In contrast the layer of EC has received very little attention if at all. A recently developed viable co‐culture model of the PB revealed significant resistance of the EC layer for maternal‐to‐fetal transfer of glucose. This argues for a major contribution of the EC to overall transplacental transfer of nutrients. Accordingly, it is recommended to fill the void of knowledge and expand our understanding on the role of the feto‐placental endothelium for transplacental transport characteristics.     

Fetal DNA in maternal serum: does it persist after pregnancy?

Fetal DNA and cells present in maternal blood have previously been used for non-invasive prenatal diagnosis. However, some fetal cells can persist in maternal blood after a previous pregnancy. Fetal rhesus status and sex determination have been performed by using amplification by real-time polymerase chain reaction (PCR) of fetal DNA sequences present in maternal circulation; no false-positive results related to persistent fetal DNA from a previous pregnancy have been reported. This idea has recently been challenged. An SRY real-time PCR assay was performed on the serum of 67 pregnant women carrying a female fetus but having previously given birth to at least one boy and on the serum of 30 healthy non-pregnant women with a past male pregnancy. In all cases, serum was negative for the SRY gene. These data suggest that fetal DNA from a previous pregnancy cannot be detected in maternal serum, even by using a highly sensitive technique. Therefore, non-invasive prenatal diagnosis by fetal sex determination for women at risk of producing children with X-linked disorders, and fetal RHD genotyping is reliable and secure as previously demonstrated.     

May Organically Farmed Animals Pose a Risk for Campylobacter Infections in Humans?

Organic farming of meat producing poultry like broilers, means that the animals should be kept outdoors as much as possible. This pose a risk that they get infected with Campylobacter. At slaughter, carcasses may be contaminated with campylobacter. If cross contamination occurs in the kitchen or if the meat is undercooked people may ingest the bacteria and suffer from enteritis. It seems possible that close to 100 percent of organically farmed flocks may be infected with campylobacter while under Swedish conditions only 10 percent of conventionally reared flocks are infected.