The neuromodulator of exploration: A unifying theory of the role of dopamine in personality

The neuromodulator of exploration: A unifying theory of the role of dopamine in personality
Colin G DeYoung; 2013
http://www.frontiersin.org/Human_Neuroscience/10.3389/fnhum.2013.00762/full

->pdf version


Abstract

The neuromodulator dopamine is centrally involved in reward, approach behavior, exploration, and various aspects of cognition. Variations in dopaminergic function appear to be associated with variations in personality, but exactly which traits are influenced by dopamine remains an open question. This paper proposes a theory of the role of dopamine in personality that organizes and explains the diversity of findings, utilizing the division of the dopaminergic system into value coding and salience coding neurons (Bromberg-Martin et al., 2010). The value coding system is proposed to be related primarily to Extraversion and the salience coding system to Openness/Intellect. Global levels of dopamine influence the higher order personality factor, Plasticity, which comprises the shared variance of Extraversion and Openness/Intellect. All other traits related to dopamine are linked to Plasticity or its subtraits. The general function of dopamine is to promote exploration, by facilitating engagement with cues of specific reward (value) and cues of the reward value of information (salience). This theory constitutes an extension of the entropy model of uncertainty (EMU; Hirsh et al., 2012), enabling EMU to account for the fact that uncertainty is an innate incentive reward as well as an innate threat. The theory accounts for the association of dopamine with traits ranging from sensation and novelty seeking, to impulsivity and aggression, to achievement striving, creativity, and cognitive abilities, to the overinclusive thinking characteristic of schizotypy.

Distress about mating rivals

Distress about mating rivals
David M Buss et al.; 2000


Abstract

This research tested the evolutionary psychological hypothesis that men and women would be most distressed about threats from rivals who surpass them on sex-linked components of mate value. Six predictions were tested in samples from three cultures, the United States (N = 208), the Netherlands (N = 349), and Korea (N= 174). Five predictions were supported in all three cultures. Korean, Dutch, and American men, more than corresponding women, report greater distress when a rival surpasses them on financial prospects, job prospects, and physical strength. Korean, Dutch, and American women, in contrast, report greater distress when a rival surpasses them on facial and bodily attractiveness. The cultures differed on some variables. Korean women and men, for example, differed from Americans and Dutch in reporting more distress over rivals who had better financial prospects, better job prospects, and higher status and prestige. Americans exceeded Koreans in reporting distress when rivals had more attractive faces and bodies, whereas Dutch exceeded the other cultures in reporting more distress when rivals had a better sense of humor. Discussion focuses on possible proximate psychological mechanisms underlying distress over rivals and the theoretical importance of intrasexual competition.

Female's courtship threshold allows intruding males to mate with reduced effort (redback spider)

Female's courtship threshold allows intruding males to mate with reduced effort
J A Stolz and M C B Andrade; 2010
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2842684/?report=classic


Abstract

Female decision rules can influence the nature and intensity of sexual selection on males, but empirical demonstrations of rules underlying choice are rare. We hypothesized that female choice is largely based on a courtship duration threshold in the Australian redback spider (Latrodectus hasselti) because females kill males before copulation is complete (premature cannibalism) and reduce their paternity if courtship is brief. We used published data to infer that the female's threshold is approximately 100 min of courtship. We support this hypothesis by showing that premature cannibalism is common when the male's courtship duration is below this threshold, but is infrequent and unrelated to duration once courtship exceeds the threshold. We then ask whether females discriminate the source of courtship when rival males compete, as this will determine the effect of the threshold on male competitive tactics. We staged competitions where ‘resident’ males initially courted females in the absence of competition, exceeding the courtship threshold before ‘intruding’ males were introduced. Intruding males mated rapidly but were not prematurely cannibalized by females, in contrast to cases where competition starts before the threshold is surpassed. This suggests females do not distinguish which male satisfies the threshold, allowing intruders to parasitize the courtship efforts of residents. To our knowledge, such exploitation of mating efforts by rival males mediated by a female choice threshold has not been demonstrated elsewhere. Ironically, this female choice threshold and the attendant possibility of courtship parasitism may lead to selection for lower-quality males to recognize and seek out (rather than avoid) webs in which competitors are already present.

Low historical rates of cuckoldry in a Western European human population traced by Y-chromosome and genealogical data

Low historical rates of cuckoldry in a Western European human population traced by Y-chromosome and genealogical data
M.H.D. Larmuseau et al.; 2013
http://rspb.royalsocietypublishing.org/content/280/1772/20132400.full.pdf


Abstract

Recent evidence suggests that seeking out extra-pair paternity (EPP) can be a viable alternative reproductive strategy for both males and females in many pair-bonded species, including humans. Accurate data on EPP rates in humans, however, are scant and mostly restricted to extant populations. Here, we provide the first large-scale, unbiased genetic study of historical EPP rates in a Western European human population based on combining Y-chromosomal data to infer genetic patrilineages with genealogical and surname data, which reflect known historical presumed paternity. Using two independent methods, we estimate that over the last few centuries, EPP rates in Flanders (Belgium) were only around 1–2% per generation. This figure is substantially lower than the 8–30% per generation reported in some behavioural studies on historical EPP rates, but comparable with the rates reported by other genetic studies of contemporary Western European populations. These results suggest that human EPP rates have not changed substantially during the last 400 years in Flanders and imply that legal genealogies rarely differ from the biological ones. This result has significant implications for a diverse set of fields, including human population genetics, historical demography, forensic science and human sociobiology.

Correlations in the population structure of music, genes and language

Correlations in the population structure of music, genes and language
Steven Brown et al.; 2014
http://rspb.royalsocietypublishing.org/content/281/1774/20132072.full


Abstract

We present, to our knowledge, the first quantitative evidence that music and genes may have coevolved by demonstrating significant correlations between traditional group-level folk songs and mitochondrial DNA variation among nine indigenous populations of Taiwan. These correlations were of comparable magnitude to those between language and genes for the same populations, although music and language were not significantly correlated with one another. An examination of population structure for genetics showed stronger parallels to music than to language. Overall, the results suggest that music might have a sufficient time-depth to retrace ancient population movements and, additionally, that it might be capturing different aspects of population history than language. Music may therefore have the potential to serve as a novel marker of human migrations to complement genes, language and other markers.

Mating strategies in Chinese culture: female risk avoiding vs. male risk taking

Mating strategies in Chinese culture: female risk avoiding vs. male risk taking
When Shan et al.; May 2012
Evolution and Human Behavior


Abstract

Previous evolutionary literature demonstrating risk taking as a male mating strategy ignored cultural influences and the function of risk avoiding for women. The present research is the first to support the hypothesis that risk taking and risk avoiding, respectively, reflect Chinese male and female mating strategies. In Study 1, when under the impression of being watched by the opposite sex, Chinese men took more risks and women took fewer risks than when watched by a same sex or alone. In Study 2, Chinese male risk taking and female risk avoiding were positively related to their mating-related evaluation of the opposite-sex observer, and these results were reinforced by behavioral findings in Study 3. The implications of the findings regarding Chinese traditional mate preference and the evolutionary mechanism behind it are discussed.

How Humans Cognitively Manage an Abundance of Mate Options

How Humans Cognitively Manage an Abundance of Mate Options
Alison P Lenton and Marco Francesconi; 2010


Abstract

To contribute to researchers’ understanding of how humans choose mates, we examined how the number of mate options influenced the dating decisions made by 1,868 women and 1,870 men across 84 speed-dating events. Multilevel modeling of these decisions revealed that when faced with abundant choice, choosers paid less attention to characteristics requiring more time to elicit and evaluate (e.g., occupational status and educational attainment) and more attention to characteristics that are quickly and easily assessed (e.g., height and weight). Human mate choice sits squarely within the domain of general cognition, as this study shows it to be constrained by bounds on cognitive resources.

[It seems that an abundance of mate options leads to a shallower mate choice and that shallow mate choosers are generally confronted with an abundance of mate options.]

Increased Prevalence of Myopia in the United States Between 1971-1972 and 1999-2004

Increased Prevalence of Myopia in the United States Between 1971-1972 and 1999-2004
Susan Vitale et al.; 2009


Objective:
To compare US population prevalence estimates for myopia in 1971-1972 and 1999-2004.

Methods:
The 1971-1972 National Health and Nutrition Examination Survey provided the earliest nationally representative estimates for US myopia prevalence; myopia was diagnosed by an algorithm using either lensometry, pinhole visual acuity, and presenting visual acuity (for presenting visual acuity >=20/40) or retinoscopy (for presenting visual acuity >=20/50). Using a similar method for diagnosing myopia, we examined data from the 1999-2004 National Health and Nutrition Examination Survey to determine whether myopia prevalence had changed during the 30 years between the 2 surveys.

Results:
Using the 1971-1972 method, the estimated prevalence of myopia in persons aged 12 to 54 years was significantly higher in 1999-2004 than in 1971-1972 (41.6% vs 25.0%, respectively; P <.001). Prevalence estimates were higher in 1999-2004 than in 1971-1972 for black individuals (33.5% vs 13.0%, respectively; P<.001) and white individuals (43.0% vs 26.3%, respectively; P<.001) and for all levels of myopia severity (>−2.0 diopters [D]: 17.5% vs 13.4%, respectively [P<.001]; <=−2.0 to >−7.9 D: 22.4% vs 11.4%, respectively [P < .001]; <=−7.9 D: 1.6% vs 0.2%, respectively [P <.001]).

Conclusions:
When using similar methods for each period, the prevalence of myopia in the United States appears to be substantially higher in 1999-2004 than 30 years earlier. Identifying modifiable risk factors for myopia could lead to the development of cost-effective interventional strategies.

The Handbook of Evolutionary Psychology

The Handbook of Evolutionary Psychology
Edited by D M Buss; 2005

The Evolution of Love

The Evolution of Love
D. M. Buss; 2006

Does a Long-Term Relationship Kill Romantic Love?

Does a Long-Term Relationship Kill Romantic Love?

Bianca P Acevedo and Arthur Aron; 2009

Abstract

This article examines the possibility that romantic love (with intensity, engagement, and sexual interest) can exist in long-term relationships. A review of taxonomies, theory, and research suggests that romantic love, without the obsession component typical of early stage romantic love, can and does exist in long-term marriages, and is associated with marital satisfaction, well-being, and high self-esteem. Supporting the separate roles of romantic love and obsession in long-term relationships, an analysis of a moderately large data set of community couples identified independent latent factors for romantic love and obsession and a subsample of individuals reporting very high levels of romantic love (but not obsession) even after controlling for social desirability. Finally, a meta-analysis of 25 relevant studies found that in long- and short-term relationships, romantic love (without obsession) was strongly associated with relationship satisfaction; but obsession was negatively correlated with it in long-term and positively in short-term relationships.

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"We suggest that both a major reason for the assumption romantic love cannot exist in long-term relationships and confusion in the relevant literature is the mixing of romantic love with passionate love (defined based on new relationships) as including high obsession, uncertainty, and anxiety. By disentangling these constructs in a factor analysis, decades of research can be unraveled to suggest that romantic love—including intensity, interest, and sexuality—thrives in some enduring relationships, while obsession is much less common and unrelated to romantic love in long-term relationships."

“He Loves Me, He Loves Me Not . . . ”: Uncertainty Can Increase Romantic Attraction

“He Loves Me, He Loves Me Not . . . ”: Uncertainty Can Increase Romantic Attraction
Erin R Whitchurch et al.; 2011


Abstract

This research qualifies a social psychological truism: that people like others who like them (the reciprocity principle). College women viewed the Facebook profiles of four male students who had previously seen their profiles. They were told that the men (a) liked them a lot, (b) liked them only an average amount, or (c) liked them either a lot or an average amount (uncertain condition). Comparison of the first two conditions yielded results consistent with the reciprocity principle. Participants were more attracted to men who liked them a lot than to men who liked them an average amount. Results for the uncertain condition, however, were consistent with research on the pleasures of uncertainty. Participants in the uncertain condition were most attracted to the men—even more attracted than were participants who were told that the men liked them a lot. Uncertain participants reported thinking about the men the most, and this increased their attraction toward the men.

[Not a very useful study, but an interesting topic.]

Who dares, wins

Who dares, wins - Heroism versus altruism in women's mate choice
Susan Kelly and R I M Dunbar; June 2001
Human Nature


Abstract

Heroism is apparently nonadaptive in Darwinian terms, so why does it exist at all? Risk-taking and heroic behavior are predominantly male tendencies, and literature and legend reflect this. This study explores the possibility that heroism persists in many human cultures owing to a female preference for risk-prone rather than risk-averse males as sexual partners, and it suggests that such a preference may be exploited as a male mating strategy. It also attempts to quantify the relative influences of altruism and bravery in the evolution of heroism. Our study found that females do prefer risk-prone brave males to risk-averse non-brave males, and that men are aware of this preference. Bravery in a male was shown to be the stronger factor influencing female choice of short-term partners, long-term partners, and male friends, with altruism playing a lesser part in their choice. Altruism was deemed important in long-term relationships and friendships, but for short-term liaisons, non-altruists were preferred to altruists. Heroism may therefore have evolved owing to a female preference for brave, risk-prone males because risk-taking acts as an honest cue for "good genes." Altruism was judged to be a less influential factor in the evolution of heroism than bravery and a demonstrated willingness to take risks.

Do testosterone declines during the transition to marriage and fatherhood relate to men's sexual behavior? Evidence from the Philippines

Do testosterone declines during the transition to marriage and fatherhood relate to men's sexual behavior? Evidence from the Philippines
Lee T Gettler et al.; November 2013
Hormones and Behavior


Abstract

Testosterone (T) is thought to help facilitate trade-offs between mating and parenting in humans. Across diverse cultural settings married men and fathers have lower T than other men and couples' sexual activity often declines during the first years of marriage and after having children. It is unknown whether these behavioral and hormonal changes are related. Here we use longitudinal data from a large study in the Philippines (n = 433) to test this model. We show that among unmarried non-fathers at baseline (n = 153; age: 21.5 ± 0.3 years) who became newly married new fathers by follow-up (4.5 years later), those who experienced less pronounced longitudinal declines in T reported more frequent intercourse with their partners at follow-up (p < 0.01) compared to men with larger declines in T. Controlling for duration of marriage, findings were similar for men transitioning from unmarried to married (without children) (p < 0.05). Men who remained unmarried and childless throughout the study period did not show similar T-sexual activity outcomes. Among newly married new fathers, subjects who had frequent intercourse both before and after the transition to married fatherhood had more modest declines in T compared to peers who had less frequent sex (p < 0.001). Our findings are generally consistent with theoretical expectations and cross-species empirical observations regarding the role of T in male life history trade-offs, particularly in species with bi-parental care, and add to evidence that T and sexual activity have bidirectional relationships in human males.

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Conclusion

In sum, we found that newly married new fathers who experienced greater declines in T also reported less frequent sexual intercourse with their partners at follow-up, 4.5 years later. We also showed that men who engaged in frequent sexual activity both before and after becoming married fathers experienced milder declines in T compared to less sexually active men, which suggests that sexual behavior could also have long-term implications for T production. This finding is consistent with the increasingly recognized observation that relationships between hormones and social behavior are likely reciprocal, rather than uni-directional. To our knowledge, these results are the first longitudinal evidence relating marriage/fatherhood-driven T decreases to men's sexual behavior.

The psychology of humor: an integrative approach

The psychology of humor: an integrative approach
Rod A Martin; 2007

(archive.org)

The Evolutionary Psychology of Envy

The Evolutionary Psychology of Envy
Sarah E Hill and David M Buss; 2008

Injustice, inequality and Evolutionary Psychology

Injustice, inequality and Evolutionary Psychology
Bruce G Charlton; 1997
http://www.hedweb.com/bgcharlton/evolpsych.html


Abstract

As biological knowledge of "human nature" continues to grow, political theory and public  policy will increasingly need to take account of Evolutionary Psychology in order effectively  to pursue its goals. This essay stands as an example. Socio-economic differentials are  perceived to be unjust, but the reason for this is not obvious given the ubiquity of  stratification. It is suggested that "the injustice of inequality" has an basis in social  instincts that evolved to promote co-operation in small-scale, egalitarian hunter-gatherer  societies with immediate-return economies. Modern Homo sapiens has been  "designed" by natural selection to live in such societies, and has "counter-dominance"  instincts that are gratified by equal sharing of resources and an equal distribution of  resources.  However, there are also phylogenetically older "dominance" social instincts  (status-seeking, nepotism, mutual reciprocity) deriving from pre-hominid ancestors, and  these tend to create inequality under "modern" conditions of economic surplus. Therefore  human instincts and gratifications are intrinsically in conflict under contemporary  conditions. The radical implications of this analysis are explored. These include support  for a Berlin-esque view of politics as an endemic negotiation of irreducibly plural values;  a clarification of the deficiencies of right- and left-wing political theory; and a rationale for  politics to concentrate primarily on the "micro-level" psychology of subjective gratification  of individuals in their local context, rather than the conventional emphasis upon macro-level policies based on abstract statistical analysis of aggregated population variables. 

Social Perception of Facial Resemblance in Humans

Social Perception of Facial Resemblance in Humans
Lisa M DeBruine et al.; 2007


Abstract

Two lines of reasoning predict that highly social species will have mechanisms to influence behavior toward individuals depending on their degree of relatedness. First, inclusive fitness theory leads to the prediction that organisms will preferentially help closely related kin over more distantly related individuals. Second, evaluation of the relative costs and potential benefits of inbreeding suggests that the degree of kinship should also be considered when choosing a mate. In order to behaviorally discriminate between individuals with different levels of relatedness, organisms must be able to discriminate cues of kinship. Facial resemblance is one such potential cue in humans. Computer-graphic manipulation of face images has made it possible to experimentally test hypotheses about human kin recognition by facial phenotype matching. We review recent experimental evidence that humans respond to facial resemblance in ways consistent with inclusive fitness theory and considerations of the costs of inbreeding, namely by increasing prosocial behavior and positive attributions toward self-resembling images and selectively tempering attributions of attractiveness to other-sex faces in the context of a sexual relationship.

Active Inbreeding in a Cichlid Fish and Its Adaptive Significance

Active Inbreeding in a Cichlid Fish and Its Adaptive Significance
Timo Thünken et al.; 2007
http://www.sciencedirect.com/science/article/pii/S0960982206025711


Abstract

Levels of inbreeding are highly variable in natural populations 1 and 2. Inbreeding can be due to random factors (like population size), limited dispersal, or active mate choice for relatives [3]. Because of inbreeding depression [4], mating with kin is often avoided [5], although sometimes intermediately related individuals are preferred (optimal outbreeding 6 and 7). However, theory predicts that the advantages of mating with close kin can override the effects of inbreeding depression 8, 9, 10, 11 and 12, but in the animal kingdom, empirical evidence for this is scarce. Here we show that both sexes of Pelvicachromis taeniatus, an African cichlid with biparental brood care, prefer mating with unfamiliar close kin over nonkin, suggesting inclusive fitness advantages for inbreeding individuals. Biparental care requires synchronous behavior among parents. Since parental care is costly [13], there is a conflict between parents over care 12 and 14, which can reduce offspring fitness [15]. Relatedness is expected to enhance cooperation among individuals [16]. The comparison of the parental behavior of in- and outbreeding pairs showed that related parents were more cooperative and invested more than unrelated parents. Since we found no evidence for inbreeding depression, our results suggest that in P. taeniatus, inbreeding is an advantageous strategy.

The genetic interpretation of inbreeding depression and outbreeding depression

The genetic interpretation of inbreeding depression and outbreeding depression
Michael Lynch; 1991

Simultaneous inbreeding and outbreeding depression in reintroduced Arabian oryx

Simultaneous inbreeding and outbreeding depression in reintroduced Arabian oryx
T C Marshall and J A Spalton; August 2000
Animal Conservation


Abstract

In most species the offspring of closely related parents have reduced fitness compared with the offspring of unrelated parents, a phenomenon known as inbreeding depression. However if parents are very distantly related, their offspring may also have reduced fitness. This pattern, outbreeding depression, has been most commonly observed in plants and only rarely in animals. Here we examine the consequences of inbreeding and outbreeding on juvenile survival of reintroduced Arabian oryx (Oryx leucoryx) in Oman, a population with a small number of founders drawn from a number of sources. Using microsatellite-based measures of inbreeding and outbreeding, there was no apparent relationship between inbreeding or outbreeding and survival when inbreeding and outbreeding were tested in separate statistical models. However when inbreeding and outbreeding were tested in the same statistical model, we found simultaneous inbreeding depression and outbreeding depression acting on juvenile survival. Outbreeding depression may be more common in vertebrates than previously supposed, and conservation strategies that seek to maximize the genetic diversity of managed populations may risk mixing lineages that are sufficiently differentiated to cause outbreeding depression among descendants.

Modeling Factors Affecting the Severity of Outbreeding Depression

Modeling Factors Affecting the Severity of Outbreeding Depression
Suzanne Edmands and Charles C Tmmerman; June 2003
Conservation Biology


Abstract

Hybridization between populations may cause either increased fitness ( “hybrid vigor” ) or decreased fitness ( “outbreeding depression” ). Translocation between populations may therefore in some cases be a successful means of combating genetic erosion and preserving evolutionary potential, whereas in other cases it may make the situation worse by inducing outbreeding depression. Because genetic distance alone is a poor predictor of the success or failure of hybridization, we developed a computer model ( ELAB ) to explore other factors affecting the consequences of hybridization. Our model simulates diploid, unisexual populations following Mendelian rules, and in this study we used it to test the effect of a variety of parameters on both the magnitude and duration of outbreeding depression. We focused our simulations on the effects of ( 1 ) divergence between populations, ( 2 ) the genetic basis of outbreeding depression ( disruption of local adaptation vs. intrinsic coadaptation ), ( 3 ) population parameters such as mutation rate and recombination rate, and ( 4 ) alternative management schemes ( 50:50 mixture vs. one migrant per generation ). The magnitude of outbreeding depression increased linearly with genetic distance, whereas the duration of outbreeding depression showed a more complex curvilinear relationship. With genetic distance held constant, magnitude increased with larger population size, lower mutation rate, cross-fertilization, and higher recombination rate, whereas duration increased with larger population size and partial self-fertilization. Fitness problems caused by disruption of local adaptation were stronger but more transient than those caused by a disruption of intrinsic coadaptation. Finally, simulations showed that, depending on the genetic basis of outcrossing problems, recurrent transfer of only one migrant per generation into a population of 100 individuals could cause as much or more damage as a one-time 50:50 mixture.

Inbreeding and outbreeding depression in Caenorhabditis Nematodes

Inbreeding and outbreeding depression in Caenorhabditis Nematodes
Elie S Dolgin et al.; 2007


Abstract

The nematode Caenorhabditis elegans reproduces primarily by self-fertilization of hermaphrodites, yet males are present at low frequencies in natural populations (androdioecy). The ancestral state of C. elegans was probably gonochorism (separate males and females), as in its relative C. remanei. Males may be maintained in C. elegans because outcrossed individuals escape inbreeding depression. The level of inbreeding depression is, however, expected to be low in such a highly selfing species, compared with an outcrosser like C. remanei. To investigate these issues, we measured life-history traits in the progeny of inbred versus outcrossed C. elegans and C. remanei individuals derived from recently isolated natural populations. In addition, we maintained inbred lines of C. remanei through 13 generations of full-sibling mating. Highly inbred C. remanei showed dramatic reductions in brood size and relative fitness compared to outcrossed individuals, with evidence of both direct genetic and maternal-effect inbreeding depression. This decline in fitness accumulated over time, causing extinction of nearly 90% of inbred lines, with no evidence of purging of deleterious mutations from the remaining lines. In contrast, pure strains of C. elegans performed better than crosses between strains, indicating outbreeding depression. The results are discussed in relation to the evolution of androdioecy and the effect of mating system on the level of inbreeding depression.

Increased Infectious Disease Susceptibility Resulting from Outbreeding Depression

Increased Infectious Disease Susceptibility Resulting from Outbreeding Depression
Tony L Goldberg et al.; April 2005
Conservation Biology


Abstract

The mechanisms by which outbreeding depression leads to reduced fitness are poorly understood. We considered the hypothesis that outbreeding can depress fitness by increasing the susceptibility of hybrid individuals and populations to infectious disease. Competitive breeding trials in experimental ponds indicated that outbred largemouth bass ( Micropterus salmoides) crossed from two geographically and genetically distinct populations suffered a reduction in fitness of approximately 14% relative to parental stocks. We measured the comparative susceptibility of these same outbred stocks to a novel viral pathogen, largemouth bass virus. Following experimental inoculation, F2 generation hybrids suffered mortality at a rate 3.6 times higher than either F1 generation hybrids or wild-type parental fish. Analysis of viral loads indicated that viral replication was more rapid in F2 fish than in F1 hybrids or wild-type parental fish. We attribute these results to the disruption of coadapted gene complexes in the immune systems of outbred fish in the F2 generation. Increased susceptibility to infectious disease may be an important but underappreciated mechanism by which outbreeding reduces the fitness of individuals and populations and by which novel infectious diseases emerge in populations of hybrid organisms.

Hybridization rapidly reduces fitness of a native trout in the wild

Hybridization rapidly reduces fitness of a native trout in the wild
Clint C Muhlfeld et al.; 2009
http://rsbl.royalsocietypublishing.org/content/5/3/328.full


Abstract

Human-mediated hybridization is a leading cause of biodiversity loss worldwide. How hybridization affects fitness and what level of hybridization is permissible pose difficult conservation questions with little empirical information to guide policy and management decisions. This is particularly true for salmonids, where widespread introgression among non-native and native taxa has often created hybrid swarms over extensive geographical areas resulting in genomic extinction. Here, we used parentage analysis with multilocus microsatellite markers to measure how varying levels of genetic introgression with non-native rainbow trout (Oncorhynchus mykiss) affect reproductive success (number of offspring per adult) of native westslope cutthroat trout (Oncorhynchus clarkii lewisi) in the wild. Small amounts of hybridization markedly reduced fitness of male and female trout, with reproductive success sharply declining by approximately 50 per cent, with only 20 per cent admixture. Despite apparent fitness costs, our data suggest that hybridization may spread due to relatively high reproductive success of first-generation hybrids and high reproductive success of a few males with high levels of admixture. This outbreeding depression suggests that even low levels of admixture may have negative effects on fitness in the wild and that policies protecting hybridized populations may need reconsideration.

Outbreeding depression, but no inbreeding depression in haplodiploid ambrosia beetles with regular sibling mating

Outbreeding depression, but no inbreeding depression in haplodiploid ambrosia beetles with regular sibling mating
Katharina Peer and Michael Taborsky; 2005


Abstract

In sexual reproduction the genetic similarity or dissimilarity between mates strongly affects offspring fitness. When mating partners are too closely related, increased homozygosity generally causes inbreeding depression, whereas crossing between too distantly related individuals may disrupt local adaptations or coadaptations within the genome and result in outbreeding depression. The optimal degree of inbreeding or outbreeding depends on population structure. A long history of inbreeding is expected to reduce inbreeding depression due to purging of deleterious alleles, and to promote outbreeding depression because of increased genetic variation between lineages. Ambrosia beetles (Xy-leborini) are bark beetles with haplodiploid sex determination, strong local mate competition due to regular sibling mating within the natal chamber, and heavily biased sex ratios. We experimentally mated females of Xylosandrus germanus to brothers and unrelated males and measured offspring fitness. Inbred matings did not produce offspring with reduced fitness in any of the examined life-history traits. In contrast, outcrossed offspring suffered from reduced hatching rates. Reduction in inbreeding depression is usually attributed to purging of deleterious alleles, and the absence of inbreeding depression in X. germanus may represent the highest degree of purging of all examined species so far. Outbreeding depression within the same population has previously only been reported from plants. The causes and consequences of our findings are discussed with respect to mating strategies, sex ratios, and speciation in this unusual system.

Predicting the Probability of Outbreeding Depression

Predicting the Probability of Outbreeding Depression
Richard Frankham et al.; 2011


Abstract

Fragmentation of animal and plant populations typically leads to genetic erosion and increased probability of extirpation. Although these effects can usually be reversed by re-establishing gene flow between population fragments, managers sometimes fail to do so due to fears of outbreeding depression (OD). Rapid development of OD is due primarily to adaptive differentiation from selection or fixation of chromosomal variants. Fixed chromosomal variants can be detected empirically. We used an extended form of the breeders’ equation to predict the probability of OD due to adaptive differentiation between recently isolated population fragments as a function of intensity of selection, genetic diversity, effective population sizes, and generations of isolation. Empirical data indicated that populations in similar environments had not developed OD even after thousands of generations of isolation. To predict the probability of OD, we developed a decision tree that was based on the four variables from the breeders’ equation, taxonomic status, and gene flow within the last 500 years. The predicted probability of OD in crosses between two populations is elevated when the populations have at least one of the following characteristics: are distinct species, have fixed chromosomal differences, exchanged no genes in the last 500 years, or inhabit different environments.  Conversely, the predicted probability of OD in crosses between two populations of the same species is low for populations with the same karyotype, isolated for <500 years, and that occupy similar environments. In the former case, we recommend crossing be avoided or tried on a limited, experimental basis. In the latter case, crossing can be carried out with low probability of OD. We used crosses with known results to test the decision tree and found that it correctly identified cases where OD occurred. Current concerns about OD in recently fragmented populations are almost certainly excessive.

Maximum for partial reproductive compatibility:

Crustaceans: 9.6 my
Insects:         9.8 my
Amphibians: 56 my
Birds:            60 my
Mammals:       8 my


[Source: Does parental divergence predict reproductive compatibility?; 2002]

Between a rock and a hard place: evaluating the relative risks of inbreeding and outbreeding for conservation and management

Between a rock and a hard place: evaluating the relative risks of inbreeding and outbreeding for conservation and management
Suzanne Edmands; 2007
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-294X.2006.03148.x/full


Abstract

As populations become increasingly fragmented, managers are often faced with the dilemma that intentional hybridization might save a population from inbreeding depression but it might also induce outbreeding depression. While empirical evidence for inbreeding depression is vastly greater than that for outbreeding depression, the available data suggest that risks of outbreeding, particularly in the second generation, are on par with the risks of inbreeding. Predicting the relative risks in any particular situation is complicated by variation among taxa, characters being measured, level of divergence between hybridizing populations, mating history, environmental conditions and the potential for inbreeding and outbreeding effects to be occurring simultaneously. Further work on consequences of interpopulation hybridization is sorely needed with particular emphasis on the taxonomic scope, the duration of fitness problems and the joint effects of inbreeding and outbreeding. Meanwhile, managers can minimize the risks of both inbreeding and outbreeding by using intentional hybridization only for populations clearly suffering from inbreeding depression, maximizing the genetic and adaptive similarity between populations, and testing the effects of hybridization for at least two generations whenever possible.


["Hybridization between divergent populations or species can result in increased fitness in some cases, but it is generally expected to result in reduced fitness."]

Reliance on head versus eyes in the gaze following of great apes and human infants: the cooperative eye hypothesis

Reliance on head versus eyes in the gaze following of great apes and human infants: the cooperative eye hypothesis
M Tomasello et al.; 2006


Abstract

As compared with other primates, humans have especially visible eyes (e.g., white sclera). One hypothesis is that this feature of human eyes evolved to make it easier for conspecifics to follow an individual’s gaze direction in close-range joint attentional and communicative interactions, which would seem to imply especially cooperative (mututalistic) conspecifics. In the current study, we tested one aspect of this cooperative eye hypothesis by comparing the gaze following behavior of great apes to that of human infants. A human experimenter ‘‘looked’’ to the ceiling either with his eyes only, head only (eyes closed), both head and eyes, or neither. Great apes followed gaze to the ceiling based mainly on the human’s head direction (although eye direction played some role as well). In contrast, human infants relied almost exclusively on eye direction in these same situations. These results demonstrate that humans are especially reliant on eyes in gaze following situations, and thus, suggest that eyes evolved a new social function in human evolution, most likely to support cooperative (mututalistic) social interactions.

Unique morphology of the human eye and its adaptive meaning: comparative studies on external morphology of the primate eye

Unique morphology of the human eye and its adaptive meaning: comparative studies on external morphology of the primate eye
Hiromi Kobayashi & Shiro Kohshima; 2001


Abstract

In order to clarify the morphological uniqueness of the human eye and to obtain cues to understanding its adaptive significance, we compared the external morphology of the primate eye by measuring nearly half of all extant primate species. The results clearly showed exceptional features of the human eye: (1) the exposed white sclera is void of any pigmentation, (2) humans possess the largest ratio of exposed sclera in the eye outline, and (3) the eye outline is extraordinarily elongated in the horizontal direction. The close correlation of the parameters reflecting (2) and (3) with habitat type or body size of the species examined suggested that these two features are adaptations for extending the visual field by eyeball movement, especially in the horizontal direction. Comparison of eye coloration and facial coloration around the eye suggested that the dark coloration of exposed sclera of nonhuman primates is an adaptation to camouflage the gaze direction against other individuals and/or predators, and that the white sclera of the human eye is an adaptation to enhance the gaze signal. The uniqueness of human eye morphology among primates illustrates the remarkable difference between human and other primates in the ability to communicate using gaze signals.

Staying alive: Evolution, culture, and women’s intrasexual aggression

Staying alive: Evolution, culture, and women’s intrasexual aggression
Anne Campbell; 1999


Abstract

Females’ tendency to place a high value on protecting their own lives enhanced their reproductive success in the environment of evolutionary adaptation because infant survival depended more upon maternal than on paternal care and defence. The evolved mechanism by which the costs of aggression (and other forms of risk taking) are weighted more heavily for females may be a lower threshold for fear in situations which pose a direct threat of bodily injury. Females’ concern with personal survival also has implications for sex differences in dominance hierarchies because the risks associated with hierarchy formation in nonbonded exogamous females are not offset by increased reproductive success. Hence among females, disputes do not carry implications for status with them as they do among males, but are chiefly connected with the acquisition and defence of scarce resources. Consequently, female competition is more likely to take the form of indirect aggression or low-level direct combat than among males. Under patriarchy, men have held the power to prop- agate images and attributions which are favourable to the continuance of their control. Women’s aggression has been viewed as a gender-incongruent aberration or dismissed as evidence of irrationality. These cultural interpretations have “enhanced” evolutionarily based sex differences by a process of imposition which stigmatises the expression of aggression by females and causes women to offer exculpatory (rather than justificatory) accounts of their own aggression.

Where are kin recognition signals in the human face?

Where are kin recognition signals in the human face?
MF Dal Martello and LT Maloney; 2006
http://www.journalofvision.org/content/6/12/2.long


Abstract

We report two experiments that aimed to determine where in the face the cues that signal kinship fall. In both experiments, participants were shown 30 pairs of photographs of children's faces. Half of the pairs portrayed siblings and half did not. The 220 participants were asked to judge whether each pair of photographs portrayed siblings. We measured the effect on kin recognition performance of masks that covered the upper half or the lower half of the face (Experiment 1) and the eye region or the mouth region (Experiment 2). In Experiment 1, we found that the signal detection estimate of performance d' decreased only 5.3% (ns) when the lower face was masked but by more than 65% when the upper face was masked. We tested whether the combination of kinship information from the two halves of the face can be treated as optimal combination of independent cues and found that it could be. In Experiment 2, we found that masking the eye region led to only a 20% reduction (ns) in performance whereas masking the mouth region led to a nonsignificant increase in performance. We also found that the eye region contains only slightly more information about kinship than the upper half of the face outside of the eye region.

Human Beings as Evolved Nepotists - Exceptions to the Rule and Effects of Cost of Help

Human Beings as Evolved Nepotists - Exceptions to the Rule and Effects of Cost of Help
Steve Stewart-Williams; 2008


Abstract

Inclusive fitness theory provides a compelling explanation for the evolution of altruism among kin. However, a completely satisfactory account of non-kin altruism is still lacking. The present study compared the level of altruism found among siblings with that found among friends and mates and sought to reconcile the findings with an evolutionary explanation for human altruism. Participants (163 males and 156 females) completed a questionnaire about help given to a sibling, friend, or mate. Overall, participants gave friends and mates as much or more help than they gave siblings. However, as the cost of help increased, siblings received a progressively larger share of the help, whereas friends and mates received a progressively smaller share, despite the fact that participants were closer emotionally to friends and mates than they were to siblings. These findings help to explain the relative standing of friends and mates as recipients of altruistic aid.

Estimating ethnic genetic interests: Is it adaptive to resist replacement migration?

Estimating ethnic genetic interests: Is it adaptive to resist replacement migration?
Frank K Salter; 2002


Abstract

Analyses of the costs and benefits of immigration have not considered the dependence of an ethny’s reproductive fitness on its monopoly of a demarcated territory. Global assays of human genetic variation allow estimation of the genetic losses incurred by a member of a population when random fellow ethnics are replaced by immigrants from different ethnies. This potential loss defines an individual’s ethnic genetic interest as a quantity that varies with the genetic distance of potential immigrants. W. D. Hamilton showed that self-sacrificial altruism is adaptive when it preserves the genetic interests of a population of genetically similar individuals. Ethnic genetic interest can be so large that altruism on behalf of one’s ethny—‘ethnic nepotism’—can be adaptive when it prevents replacement. It follows that ethnies usually have an interest in securing and maintaining a monopoly over a demarcated territory, an idea consonant with the universal nationalism of Bismarck and Woodrow Wilson.


[See also: http://www.humanbiologicaldiversity.com/]

Intelligence tests with higher g-loadings show higher correlations with body symmetry

Intelligence tests with higher g-loadings show higher correlations with body symmetry: Evidence for a general fitness factor mediated by developmental stability
Mark D Prokosch, Ronald A Yeo and Geoffrey F Miller; 2005


Abstract

Just as body symmetry reveals developmental stability at the morphological level, general intelligence may reveal developmental stability at the level of brain development and cognitive functioning. These two forms of developmental stability may overlap by tapping into a bgeneral fitness factor.Q If so, then intellectual tests with higher g-loadings should show higher correlations with a composite measure of body symmetry. We tested this prediction in 78 young males by measuring their left–right symmetry at 10 body points, and by administering five cognitive tests with diverse g-loadings. As predicted, we found a significant (z=3.64, p<0.003) relationship between each test’s rank order g-loading and its body symmetry association. We also found a substantial correlation (r=0.39, p<0.01) between body symmetry and our most highly g-loaded test (Ravens Advanced Progressive Matrices). General intelligence is apparently a valid indicator of general developmental stability and heritable fitness, which may partly explain its social and sexual attractiveness.

Life history traits of humans compared with chimpanzees:

(full size: click at the image)














Source:
Patterns and processes of human life history evolution. MP Muehlenbein & MV Flinn; 2011