Chimpanzees and children avoid mutual defection in a social dilemma

Cooperation often comes with the temptation to defect and benefit at the cost of others. This tension between cooperation and defection is best captured in social dilemmas like the Prisoner's Dilemma. Adult humans have specific strategies to maintain cooperation during Prisoner's Dilemma interactions. Yet, little is known about the ontogenetic and phylogenetic origins of human decision-making strategies in conflict scenarios. To shed light on this question, we compared the strategies used by chimpanzees and 5-year old children to overcome a social dilemma. In our task, waiting for the partner to act first produced the best results for the subject. Alternatively, they could mutually cooperate and divide the rewards. Our findings indicate that the two species differed substantially in their strategies to solve the task. Chimpanzees became more strategic across the study period by waiting longer to act in the social dilemma. Children developed a more efficient strategy of taking turns to reciprocate their rewards. Moreover, children used specific types of communication to coordinate with their partners. These results suggest that while both species behaved strategically to overcome a conflict situation, only children engaged in active cooperation to solve a social dilemma.     

Evolutionary games of cooperation: Insights through integration of theory and data

Cooperation is central to the regulation of many ecological processes and the persistence of ecosystems and their associated functions. However, the evolution of cooperation amongst non-kin appears paradoxical. Games such as the prisoner's dilemma, snowdrift and stag hunt have been borrowed from game theory and used extensively to investigate cooperation. Advances in this area have been numerous and have been provided by both empirical and theoretical studies. We outline some of the common games used and review some of the major findings and recent advancements made in this area. We show a clear link between data and theory, and how this link has been key to our understanding of cooperation.     

Coexistence of cooperation and defection in public goods games

The production of public goods by the contribution of individual volunteers is a social dilemma because an individual that does not volunteer can benefit from the public good produced by the contributions of others. Therefore it is generally believed that public goods can be produced only in the presence of repeated interactions (which allow reciprocation, reputation effects and punishment) or relatedness (kin selection). Cooperation, however, often occurs in the absence of iterations and relatedness. We show that when the production of a public good is a Volunteer's Dilemma, in which a fixed number of cooperators is necessary to produce the public good, cooperators and defectors persist in a mixed equilibrium, without iterations and without relatedness. This mixed equilibrium is absent in the N-person Prisoner's Dilemma, in which the public good is a linear function of the individual contributions. We also show that the Prisoner's Dilemma and the Volunteer's Dilemma are the two opposite extremes of a general public goods game, and that all intermediate cases can have a mixed equilibrium like the Volunteer's Dilemma. The coexistence of cooperators and defectors, therefore, is a typical outcome of most social dilemmas, which requires neither relatedness nor iterations.     

Shape matters: Lifecycle of cooperative patches promotes cooperation in bulky populations

Natural cooperative systems take many forms, ranging from one‐dimensional cyanobacteria arrays to fractal‐like biofilms. We use in silico experimental systems to study a previously overlooked factor in the evolution of cooperation, physical shape of the population. We compare the emergence and maintenance of cooperation in populations of digital organisms that inhabit bulky (100 × 100 cells) or slender (4 × 2500) toroidal grids. Although more isolated subpopulations of secretors in a slender population could be expected to favor cooperation, we find the opposite: secretion evolves to higher levels in bulky populations. We identify the mechanistic explanation for the shape effect by analyzing the lifecycle and dynamics of cooperator patches, from their emergence and growth, to invasion by noncooperators and extinction. Because they are constrained by the population shape, the cooperator patches expand less in slender than in bulky populations, leading to fewer cooperators, less public good secretion, and generally lower cooperation. The patch dynamics and mechanisms of shape effect are robust across several digital cooperation systems and independent of the underlying basis for cooperation (public good secretion or a cooperation game). Our results urge for a greater consideration of population shape in the study of the evolution of cooperation across experimental and modeling systems.     

Individual differences in women''s facial preferences as a function of digit ratio and mental rotation ability

The second-to-fourth digit ratio (2D:4D) and mental rotation (MR) ability are sexually dimorphic traits that appear early in development and have been correlated with exposure to prenatal androgens (Grimshaw, Sitarenios, & Finegan, 1995; Lutchmaya, Baron-Cohen, Raggatt, Knickmeyer, & Manning, 2004). The current study examined how 2D:4D and MR differences among women of European descent (N=41) were related to their (a) preferences for male faces: attractive (ATM), short-term (STM), and long-term mate (LTM), and (b) psychological femininity and masculinity, as measured by the Bem Sex-Role Inventory (BSRI) (Bem, 1981). To examine potential changes in facial preferences over their menstrual cycle, participants' preferences were measured during two experimental sessions separated by 2 weeks. The results indicated that (a) femininity scores decreased with decreasing 2D:4D, (b) masculinity scores increased with faster MR, (c) women preferred a more masculine male face for an STM than for an LTM, and (d) preference changes over the menstrual cycle varied systematically with 2D:4D. When compared with women with high 2D:4D ratios, low 2D:4D women (e) preferred a more masculine LTM, (f) recalled less parental bonding, (g) had shorter intimate relationships, and (h) reported more menstrual irregularity. The results are interpreted as support for an interactive hormonal theory of physical attraction.     

2D:4D ratios in the first 2 years of life: Stability and relation to testosterone exposure and sensitivity

The relative lengths of the 2nd and 4th digits (2D:4D) may provide an easily measurable and stable anthropometric index of prenatal androgen exposure, but no study has examined the development of 2D:4D in infancy and the potential impact of neonatal testosterone levels. We collected 2D:4D ratios from 364 children between 0 and 2 years of age. Saliva samples were collected from 236 of these children 3 months after birth and analyzed for testosterone. In addition, 259 children provided DNA samples which were genotyped for the CAG repeat polymorphism in the androgen receptor. There was substantial variability across age in 2D:4D. Sex differences were small compared to adults and did not consistently reach statistical significance. This suggests that 2D:4D may not function well as a proxy measure of prenatal testosterone exposure in infancy. In addition, the interaction of salivary T and CAG repeats predicted right hand digit ratio at 12 months and left hand digit ratio at 12 months and 24 months in males. The interaction of salivary testosterone and CAG repeat length also predicted change in left hand 2D:4D from 2 weeks to 12 months in males. This suggests that 2D:4D in adults may reflect, in part, neonatal testosterone exposure. No significant relationships were observed within females. No significant relationships were observed when salivary testosterone and CAG repeats were examined independent of each other. Results have important implications for the design and interpretation of studies which use 2D:4D as a proxy measure of prenatal testosterone exposure.     

A longitudinal study of digit ratio (2D:4D) and other finger ratios in Jamaican children

It has been hypothesised that the ratio between the length of the 2nd and 4th digits (2D:4D) is a correlate of prenatal sex steroids, and this relationship is strongest for the right hand. Furthermore, it has been suggested that 2D:4D is sexually dimorphic, the dimorphism is determined early, and 2D:4D among children is stable with growth. Here, we present the first longitudinal study of right and left hand 2D:4D. Our sample was 108 (54 males) Jamaican children. The first measurements were made in 1998 when mean age was 9.68 +/- 1.39 years, and a second set of measurements were made in 2002. We found that: (i) there was a small increase in 2D:4D with age which was lowest in the right hand; (ii) 2D:4D was sexually dimorphic, the means for males and females differed in the same direction in the 1998 and 2002 samples, and the sex difference was significant in the 1998 but not in the 2002 sample; (iii) the correlation between the 1998 and 2002 measurements of 2D:4D was high, indicating that rank order of the ratio was stable across year groups; and (iv) the rate of change in 2D:4D did not differ significantly across year groups. We conclude that 2D:4D increases slightly with age in children with the effect less marked for the right hand (i.e. the hand which is likely to show the strongest association with prenatal steroids), 2D:4D is sexually dimorphic from an early age, and the rank order of 2D:4D is stable in children. We discuss the implications of our findings for the status of 2D:4D as a correlate of prenatal sex steroids. The patterns of change in other finger ratios are also considered.     

Digit ratio (2D:4D) and handgrip strength in subjects of Han ethnicity: Impact of sex and age

The ratio of the length of the second finger to the fourth finger (2D:4D) is considered to be a putative proxy of prenatal exposure to testosterone, and has been increasingly used as a promising tool to evaluate the impact of prenatal androgenization in humans in such traits as physical performance. In this study, for the first time, we present 2D:4D data on adult participants of Han ethnicity. We consider the sexual dimorphism of 2D:4D and handgrip strength, and also report the relationship between 2D:4D and handgrip strength of males and females. The sample consisted of 54 males and 55 females recruited from a remote village in the Qinling Mountains, China. We found sexual dimorphism of both 2D:4D and handgrip strength, i.e., males had lower 2D:4D and right‐left 2D:4D than females and greater handgrip strength than females. There was a sex‐specific correlation between 2D:4D and handgrip strength, i.e., 2D:4D in the right hand was negatively correlated with handgrip strength in males but not in females. This relationship may be driven by sexual selection operating on fetal programming. Am J Phys Anthropol 149:266–271, 2012. © 2012 Wiley Periodicals, Inc.     

The relative lengths and weights of metacarpals and metatarsals in baboons (papio hamadryas)

The lengths and weights of metacarpals and metatarsals were measured in two collections of baboon skeletons-33 animals, all born and raised in the wild, and 60 animals, nearly all born and raised in captivity. For both length and weight, ratios were constructed for all possible pairings of the five bones in each individual hand and foot. The pattern of results was not identical for the two collections, but substantial sex differences existed in both collections for many of the ratios calculated. Nearly all of the large sex differences were in the direction of the length or weight ratio being smaller for males than for females. For the length ratios showing the largest sex differences, those differences were larger for the right hand than for the left, and larger for the left foot than for the right, but this pattern was less evident for the weight ratios. Some length ratios for human fingers show sex differences of the sort seen in the metacarpals and metatarsals of these baboons, and the human differences in relative length exist early in life. The implication is that the marked sex difference in androgen exposure during prenatal development may effect the relative size of the individual bones of the extremities in male and female humans and baboons. The relative sizes of the bones of the hand and foot may provide helpful supplemental information on the relations between species, thus making the study of hand and foot bones in other primates and mammals worthwhile.     

Digit ratio (2D:4D) and physical fitness in males and females: Evidence for effects of prenatal androgens on sexually selected traits

It has been suggested that male achievement in sports and athletics is correlated with a putative measure of prenatal testosterone the 2nd to 4th digit ratio (2D:4D). It is not known whether this association also extends to females, or whether the association results from an effect of testosterone on behavior (such as exercise frequency) or on physical fitness. Here, we report for the first time data from two studies which consider associations between 2D:4D and physical fitness in females in addition to males: Study I--in a sample of teenage boys (n = 114) and girls (n = 175), their 'physical education grade' was negatively associated with 2D:4D of the right hand (boys), and right and left hand (girls), and Study II-among a sample of young men (n = 102) and women (n = 77), a composite measure of physical fitness was negatively related to right hand 2D:4D in men and left hand 2D:4D in women. We conclude that 2D:4D is negatively related to physical fitness in both men and women. In Study II, there was evidence that the relationship between physical fitness and 2D:4D in men was mediated through an association with exercise frequency. Thus, 2D:4D in males may be a negative correlate of frequent exercise which then relates to achievement in sports and athletics.     

The neural and cognitive correlates of aimed throwing in chimpanzees: a magnetic resonance image and behavioural study on a unique form of social tool use

It has been hypothesized that neurological adaptations associated with evolutionary selection for throwing may have served as a precursor for the emergence of language and speech in early hominins. Although there are reports of individual differences in aimed throwing in wild and captive apes, to date there has not been a single study that has examined the potential neuroanatomical correlates of this very unique tool-use behaviour in non-human primates. In this study, we examined whether differences in the ratio of white (WM) to grey matter (GM) were evident in the homologue to Broca's area as well as the motor-hand area of the precentral gyrus (termed the KNOB) in chimpanzees that reliably throw compared with those that do not. We found that the proportion of WM in Broca's homologue and the KNOB was significantly higher in subjects that reliably throw compared with those that do not. We further found that asymmetries in WM within both brain regions were larger in the hemisphere contralateral to the chimpanzee's preferred throwing hand. We also found that chimpanzees that reliably throw show significantly better communication abilities than chimpanzees that do not. These results suggest that chimpanzees that have learned to throw have developed greater cortical connectivity between primary motor cortex and the Broca's area homologue. It is suggested that during hominin evolution, after the split between the lines leading to chimpanzees and humans, there was intense selection on increased motor skills associated with throwing and that this potentially formed the foundation for left hemisphere specialization associated with language and speech found in modern humans.     

The relationships between otoacoustic emissions and relative lengths of fingers and toes in humans

Both otoacoustic emissions (OAEs) and the relative length of the index and ring fingers (the 2D:4D ratio) exhibit large sex differences, and both exhibit masculinization effects in female homosexuals and bisexuals. Because these sex differences exist in young children, the implication is that both types of measure are affected by prenatal androgen exposure, but it has been unknown to what degree these two types of measure are related. Accordingly, OAEs and the relative lengths of the fingers and the toes were measured in 59 heterosexual females, 55 heterosexual males, 29 homosexual females, and 33 homosexual males. The correlations between the two types of measure were unexpectedly quite low in both the heterosexual and nonheterosexual groups. For example, the correlation between number of spontaneous OAEs per ear and 2D:4D was less than 0.25, for both sexes and both sexual orientations. One interpretation of these results is that the prenatal hormonal mechanisms producing the sex differences in OAEs differ in quality, degree, or timing from those producing the sex differences in relative finger length. That is, OAEs and 2D:4D may be windows onto slightly different prenatal processes or times during prenatal development. Measures of mental-rotation ability also were obtained on these participants, and those correlations with relative finger length also were small.     

Testosterone enhancement during pregnancy influences the 2D:4D ratio and open field motor activity of rat siblings in adulthood

In humans, the relationship between the prenatal testosterone exposure and the ratio of the second and the fourth digits (2D:4D) has been extensively studied. Surprisingly, data on this relationship have thus far been lacking in experimental animals such as rats. We studied the effect of maternal testosterone enhancement during pregnancy on the digit ratio and open field activity of adult progeny in Wistar rats. Elevated levels of maternal testosterone resulted in lower 2D:4D ratios and an elongated 4D on the left and right forepaws in both males and females. We found no sex difference in 2D:4D in control animals. In the open field test, control females were more active than control males and testosterone females, while the activity of testosterone females did not differ from that of control males. We found a positive correlation between motor activity and the right forepaw 2D:4D ratio of control males and females. Prenatal exposure to testosterone resulted in the disappearance of this correlation in both males and females. Our results show that elevated levels of testosterone during the prenatal period can influence forepaw 4D length, 2D:4D ratio, and open field motor activity of rats, and that these variables are positively correlated. Thus, this approach represents a noninvasive and robust method for evaluating the effects of prenatal testosterone enhancement on anatomical and physiological parameters.     

The roles of amino acid residues at positions 43 and 45 in microsomal contents and enzymatic functions of rat CYP2D1 and CYP2D2

The effects of the substitution of amino acid residues at positions 43 and 45 of rat CYP2D1 and CYP2D2 on their microsomal contents and enzymatic functions were examined. The substitution of Val-45 of CYP2D1 by glycine decreased the microsomal content, whereas the substitution of Gly-45 of CYP2D2 by valine increased. The substitution of Leu-43 of CYP2D2 by tryptophan also increased the microsomal protein content. In reduced CO-difference spectra, CYP2D2 showed a P420 peak as well as a P450 peak, whereas CYP2D1 gave only a P450 peak. The substitution of Leu-43 and Gly-45 of CYP2D2 by valine and tryptophan, respectively, markedly decreased the P420 peak in parallel with an increase in P450 content. These substitutions did not cause remarkable changes in drug oxidation capacities (bufuralol 1'-hydroxylation and debrisoquine 4-hydroxylation) of the recombinant enzymes in terms of nmol/min/nmol CYP. The results indicate that amino acid residues at positions 43 and 45 are important for anchoring of the rat CYP2D proteins and their stabilities in the endoplasmic reticulum membrane.     

Anionic effects on the formation of tridentate 4′-chloro-2,2′:6′,2″-terpyridine copper(II) complexes having 1:1 or 1:2 ratio of metal and ligand and their crystal symmetry

A facile synthetic procedure has been used to prepare one five-coordinate and four six-coordinate copper(II) complexes of 4′-chloro-2,2′:6′,2″-terpyridine (tpyCl) ligand with different counterions (, , , , and ) in high yields. They are formulated as [Cu(tpyCl-κ³N,N′,N′′)(SO₄-κO)(H₂O-κO)] · 2H₂O (1), trans-[Cu(tpyCl-κ³N,N′,N″)(NO₃-κO)₂(H₂O-κO)] (2), [Cu(tpyCl-κ³N,N′,N″)₂](BF₄)₂ (3), [Cu(tpyCl-κ³N,N′,N″)₂](PF₆)₂ (4) and [Cu(tpyCl-κ³N,N′,N″)₂](ClO₄)₂ (5) and versatile interactions in supramolecular level including coordinative bonding, O-H?O, O-H?Cl, C-H?F, and C-H?Cl hydrogen bonding, π-π stacking play essential roles in forming different frameworks of 1-5. It is concluded that the difference of coordination abilities of the counterions used and the experimental conditions codominate the resulting complexes with 1:1 or 1:2 ratio of metal and ligand.     

The difference between generalist and specialist: the effects of wide fluctuations in main food abundance on numbers and reproduction of two co-existing predators

Specialist individuals within animal populations have shown to be more efficient foragers and/or to have higher reproductive success than generalist individuals, but interspecific reproductive consequences of the degree of diet specialisation in vertebrate predators have remained unstudied. Eurasian pygmy owls (hereafter POs) have less vole-specialised diets than Tengmalm's owls (TOs), both of which mainly subsist on temporally fluctuating food resources (voles). To test whether the specialist TO is more limited by the main prey abundance than the generalist PO, we studied breeding densities and reproductive traits of co-existing POs and TOs in central-western Finland during 2002–2019. Breeding densities of POs increased with augmenting densities of voles in the previous autumn, whereas breeding densities of TOs increased with higher vole densities in both the previous autumn and the current spring. In years of vole scarcity, PO females started egg-laying earlier than TOs, whereas in years of vole abundance TO females laid eggs substantially earlier than PO females. The yearly mean clutch size and number of fledglings produced of both POs and TOs increased with abundance of voles in the current spring. POs laid large clutches and produced large broods in years of both high and low vole abundance, whereas TOs were able to do so only in years of high vole abundance. POs were able to raise on average 73% of the eggs to fledglings whereas TOs only 44%. The generalist foraging strategy of POs including flexible switching from main prey to alternative prey (small birds) appeared to be more productive than the strictly vole-specialized foraging strategy of TOs. In contrast to earlier studies at the individual-level, specialist predators at the species level (in this case TOs) appear to be less effective than generalists (POs), but diet specialisation was particularly costly under conditions when scarcity of main foods limited offspring production.     

The role of superoxide and hydroxyl radicals in the degradation of hyaluronic acid induced by metal ions and by ascorbic acid

Purified commercial hyaluronic acid contains significant amounts of iron. Addition of Fe2+ to solutions of it causes depolymerization, which is inhibited by catalase and scavengers of the hydroxyl radical (. OH) but not by superoxide dismutase. Fe3+ is ineffective. Ascorbic acid also depolymerizes hyaluronic acid, apparently because it can reduce Fe3+ in the reaction mixtures to Fe2+. Ascorbate-induced depolymerization is inhibited by the specific iron chelator desferrioxamine, by catalase, and by scavengers of the hydroxyl radical. The relevance of these observations to rheumatoid arthritis and inflammatory joint diseases is discussed.     

The influence of local environment on the aging and mortality ofAedes aegypti (L.): Case study in Fortaleza‐CE,Brazil

It is generally assumed that the daily probability of survival of mosquitoes is independent of age. To test this assumption we have conducted a three‐year experimental fieldwork study (2005–2007) at Fortaleza‐CE in Brazil, determining daily survival rates of the dengue vector Aedes aegypti (L.). Survival rates of adult Ae. aegypti may be age‐dependent and the statistical analysis is a sensitive approach for comparing patterns of mosquito survival. The mosquito survival data were better fit by a Weibull survival function than by the more traditionally used Gompertz or logistic survival functions. Gompertz, Weibull, or logistic survival functions often fit the survival, and the tails of the survival curves usually appear to fall between the values predicted by the three functions. We corroborate that the mortality of Ae. aegypti in semi‐natural conditions may no more be considered as a constant phenomenon during the life of adult mosquitoes but varies according to the age and environmental conditions under a tropical climate. This study estimates the variability in the survival rate of Ae. aegypti and environmental factors that are related to such variability. The statistical analysis shows that the fitting ability, concerning the hazard function, was in decreasing order: Seasonal Cox, the three‐parameter Gompertz, and the three‐parameter Weibull, that was similar to the three‐parameter logistic. The advantage of using the Cox model is that it is convenient for exploring the relationship between survival and several explanatory variables. The Cox model has the advantage of preserving the variable in its original quantitative form and of using a maximum of information. The survival analyses indicate that mosquito mortality is both age‐ and environment‐dependent.     

The influence of serum components on the growth and mutation of Chinese hamster cells in medium containing 8-azaguanine

Low concentrations (?20 μg/ml) of 8-azaguanine are 1000 fold more toxic to V79 Chinese hamster cells in medium containing 10% dialyzed fetal calf serum than in medium containing 10% undialyzed serum. Serum enzyme activity that converts AG to nontoxic 8-azaxanthine degrades AG at the same rate, whether or not the serum is dialyzed. However, cytotoxicity results similar to those obtained with US were produced in medium containing DS and 2.5 μg of hypoxanthine (HX)/ml (DSH). Therefore, serum HX is considered to be responsible for the relatively low cytotoxicity of AG in medium containing US. Colonies that arose in medium containing AG were isolated and characterized. Those that remained resistant to AG (40 μg/ml) and sensitive to aminopterin in the presence of HX and thymidine (HAT) were considered mutants; nonmutants were sensitive to AG and resistant to HAT. Colonies isolated from medium containing DSH of US and low concentrations of AG were not mutants, but those from medium containing high concentrations (? μg/l) of AG were mutants. Spontaneous and N-methyl-N′-nitrosoguanidine induced mutants were detectable in medium containing DSH without replating the cells prior to adding AG (?30 μg/ml), but in order to detect MNNG induced mutations in medium containing DS replating was essential. In DS, the mutation frequency increased as an exponential function of the toxicity of MNNG, but remained two orders of magnitude lower than the induced mutation frequencies that occurred in DSH, HX, in DSH or US, produced profound effects, other than interference with AG toxicity, that distort the results of mutagenesis assays. To study mutation using AG resistance as the endpoint, it is essential to use dialyzed serum.