When Young Men Are Scarce, They're More Likely To Play The Field Than To Propose
ScienceDaily (June 10, 2009) — In places where young women outnumber young men, research shows the hemlines rise but the marriage rates don't because the young men feel less pressure to settle down as more women compete for their affections.
But when those men reach their 30s, the reverse is true and proportionately more older men are married in areas where women outnumber men.
Daniel Kruger, a University of Michigan researcher who studies evolution and how it relates to contemporary behavior, looked at the 50 largest metropolitan areas in the United States to test his hypothesis on how the balance between women and men affects marital patterns. Results showed that men aged 20-24 are more likely to cruise than to commit if they live in an area with more women than men.
One would think that rationally, fewer young men than women would naturally lead to proportionately more young men getting married, but that's not the case.
"Marriage patterns aren't rational because men and women have somewhat different reproductive strategies," Kruger said. "Men have a greater reproductive benefit than women from having a greater quantity of relationships. If they can leverage their scarcity into attracting multiple short-term partners, they will not have as much of an incentive to settle down."
There are about nine unmarried men for every 10 unmarried women in Birmingham, Memphis, New Orleans, and Richmond-Petersburg, Virginia, Kruger says. Philadelphia, Washington, DC, Baltimore, and New York metropolitan areas are tied for the next region where women are relatively most plentiful. In these areas, about 84 percent of the men aged 20-24 are unmarried. In Las Vegas, San Diego, Salt Lake City, Austin, and Phoenix, there are about nine unmarried women for every 10 unmarried men. In these areas, about 77 percent of the men aged 20-24 are unmarried.
Once those young men hit their 30s, they tend to shift from seeking short-term relationships to entering into committed relationships. That's because when women evaluate partners for short-term relationships they value physical features signaling the kind of genes that would be passed on to potential offspring, which may be the only legacy of men who don't stick around for child rearing. These physical features decline as men age, making it more difficult to lure women into uncommitted relationships.
"You see a complete reversal in the pattern," Kruger said, and thus, proportionately more older men are married when women outnumber men.
So, does this mean that middle aged women in these cities get a break? Not really, Kruger says. The higher marital rates for older men likely benefit women who are substantially younger than their husbands, because older men still prefer partners with higher reproductive potential.
The ratio of men to women has other aspects, as well. For instance, studies have shown that when women outnumber men, hemlines actually rise, overall, as women to do more to physically attract men. Also, the rates of divorce and out-of-wedlock births are higher, and interests in women's rights increases. Surpluses of men tend to be associated with more conservative social norms and restricted roles for women.
Showing posts with label mate selection. Show all posts
Showing posts with label mate selection. Show all posts
Wednesday, July 8, 2009
Rating Attractiveness: Consensus Among Men, Not Women, Study Finds
http://www.sciencedaily.com/releases/2009/06/090626153511.htm
Rating Attractiveness: Consensus Among Men, Not Women, Study Finds
ScienceDaily (June 27, 2009) — Hot or not? Men agree on the answer. Women don't.
There is much more consensus among men about whom they find attractive than there is among women, according to a new study by Wake Forest University psychologist Dustin Wood.
The study, co-authored by Claudia Brumbaugh of Queens College, appears in the June issue of the Journal of Personality and Social Psychology.
"Men agree a lot more about who they find attractive and unattractive than women agree about who they find attractive and unattractive," says Wood, assistant professor of psychology. "This study shows we can quantify the extent to which men agree about which women are attractive and vice versa."
More than 4,000 participants in the study rated photographs of men and women (ages 18-25) for attractiveness on a 10-point scale ranging from "not at all" to "very." In exchange for their participation, raters were told what characteristics they found attractive compared with the average person. The raters ranged in age from 18 to more than 70.
Before the participants judged the photographs for attractiveness, the members of the research team rated the images for how seductive, confident, thin, sensitive, stylish, curvaceous (women), muscular (men), traditional, masculine/feminine, classy, well-groomed, or upbeat the people looked.
Breaking out these factors helped the researchers figure out what common characteristics appealed most to women and men.
Men's judgments of women's attractiveness were based primarily around physical features and they rated highly those who looked thin and seductive. Most of the men in the study also rated photographs of women who looked confident as more attractive.
As a group, the women rating men showed some preference for thin, muscular subjects, but disagreed on how attractive many men in the study were. Some women gave high attractiveness ratings to the men other women said were not attractive at all.
"As far as we know, this is the first study to investigate whether there are differences in the level of consensus male and female raters have in their attractiveness judgments," Wood says. "These differences have implications for the different experiences and strategies that could be expected for men and women in the dating marketplace."
For example, women may encounter less competition from other women for the men they find attractive, he says. Men may need to invest more time and energy in attracting and then guarding their mates from other potential suitors, given that the mates they judge attractive are likely to be found attractive by many other men.
Wood says the study results have implications for eating disorders and how expectations regarding attractiveness affect behavior.
"The study helps explain why women experience stronger norms than men to obtain or maintain certain physical characteristics," he says. "Women who are trying to impress men are likely to be found much more attractive if they meet certain physical standards, and much less if they don't. Although men are rated as more attractive by women when they meet these physical appearance standards too, their overall judged attractiveness isn't as tightly linked to their physical features."
The age of the participants also played a role in attractiveness ratings. Older participants were more likely to find people attractive if they were smiling.
Rating Attractiveness: Consensus Among Men, Not Women, Study Finds
ScienceDaily (June 27, 2009) — Hot or not? Men agree on the answer. Women don't.
There is much more consensus among men about whom they find attractive than there is among women, according to a new study by Wake Forest University psychologist Dustin Wood.
The study, co-authored by Claudia Brumbaugh of Queens College, appears in the June issue of the Journal of Personality and Social Psychology.
"Men agree a lot more about who they find attractive and unattractive than women agree about who they find attractive and unattractive," says Wood, assistant professor of psychology. "This study shows we can quantify the extent to which men agree about which women are attractive and vice versa."
More than 4,000 participants in the study rated photographs of men and women (ages 18-25) for attractiveness on a 10-point scale ranging from "not at all" to "very." In exchange for their participation, raters were told what characteristics they found attractive compared with the average person. The raters ranged in age from 18 to more than 70.
Before the participants judged the photographs for attractiveness, the members of the research team rated the images for how seductive, confident, thin, sensitive, stylish, curvaceous (women), muscular (men), traditional, masculine/feminine, classy, well-groomed, or upbeat the people looked.
Breaking out these factors helped the researchers figure out what common characteristics appealed most to women and men.
Men's judgments of women's attractiveness were based primarily around physical features and they rated highly those who looked thin and seductive. Most of the men in the study also rated photographs of women who looked confident as more attractive.
As a group, the women rating men showed some preference for thin, muscular subjects, but disagreed on how attractive many men in the study were. Some women gave high attractiveness ratings to the men other women said were not attractive at all.
"As far as we know, this is the first study to investigate whether there are differences in the level of consensus male and female raters have in their attractiveness judgments," Wood says. "These differences have implications for the different experiences and strategies that could be expected for men and women in the dating marketplace."
For example, women may encounter less competition from other women for the men they find attractive, he says. Men may need to invest more time and energy in attracting and then guarding their mates from other potential suitors, given that the mates they judge attractive are likely to be found attractive by many other men.
Wood says the study results have implications for eating disorders and how expectations regarding attractiveness affect behavior.
"The study helps explain why women experience stronger norms than men to obtain or maintain certain physical characteristics," he says. "Women who are trying to impress men are likely to be found much more attractive if they meet certain physical standards, and much less if they don't. Although men are rated as more attractive by women when they meet these physical appearance standards too, their overall judged attractiveness isn't as tightly linked to their physical features."
The age of the participants also played a role in attractiveness ratings. Older participants were more likely to find people attractive if they were smiling.
Friday, June 19, 2009
NO-FATHERS DAY: Remote Group Has No Dads, And Never Did
http://news.nationalgeographic.com/news/2009/06/090619-fathers-day-2009-no-fathers.html
NO-FATHERS DAY: Remote Group Has No Dads, And Never Did
Brian Handwerkfor National Geographic News
June 18, 2009
What would Father's Day—and every other day—be like without fathers? Maybe not so bad, according to experts on the Mosuo culture of the Chinese Himalaya.
The women of this matrilineal society shun marriage and raise their kids in homes with their entire extended families—but no dads.
By most accounts, children seem to do just fine under the arrangement.
"They are a society that we know hasn't had marriage for a thousand years, and they've been able to raise kids successfully," said Stephanie Coontz, family studies professor at the Evergreen State College in Olympia, Washington.
No Fathers: It Makes Genetic Sense?
Men of the Mosuo, who live around Lugu Lake on the border between Yunnan and Sichuan Provinces, do help to raise kids—just not their own, with whom the men typically have only limited relationships.
Instead the men help look after all the children born to their own sisters, aunts, and other women of the family.
Rather than "one father with a kid, it will be four or five uncles. That [father] role is shared among a number of people, and these are very large extended families," explained John Lombard, director of the Lugu Lake Mosuo Cultural Development Association.
The unusual parenting arrangement makes genetic sense, in terms of extending the family line—and many Mosuo men actually think of it that way, Lombard said.
"If you [father] a child with another woman, you can never be absolutely sure that the child really shares your genes," he said. "But if your sister has a child, you can be 100 percent sure that the kid shares some of your genes."
The women of the Mosuo's agricultural villages head the households, make business decisions, and own property, which they pass on to their matrilineal heirs.
In the unique Mosuo tradition called the walking marriage, women invite men to visit their rooms at night—and to leave in the morning.
Women may also change partners as often as they like, and promiscuity carries no social stigma. The practice has made the Mosuo famous, particularly to male Chinese tourists, many of whom see the walking marriages as evidence of sexual liberation and wanton lust, experts say. Though there are tourist-oriented brothels in Mosuo villages, most are staffed with non-Mosuo women and are considered shameful by the Mosuo, according to the the Lugu Lake Mosuo Cultural Development Association Web site.
"I think sometimes the media gets carried away with the possibility that the women can have all these husbands," said filmmaker Xiaoli Zhou, who produced and reported the 2006 documentary on the Mosuo, The Women's Kingdom.
In fact, most Mosuo women don't change walking-marriage partners very frequently. And they rarely carry on more than one romantic relationship at a time.
"Many of the women I interviewed had only had one or two relationships in their lives," Zhou said.
Family First
The lack of live-in fathers shouldn't be taken as evidence that the Mosuo don't value family life, said Lombard, of the Lugu Lake Mosuo Cultural Development Association.
In fact, they value it above all other relationships—particularly those founded on the sometimes fickle feelings of male-female amour, he said.
Extended families of siblings, uncles, aunts, and others are said to be extremely stable, Lombard added.
For example, there are no divorces to destablize the families. And even the death of a child's biological father has little effect on the family, given the father's distance from the family and the extensive support network in the household.
Brent Huffman, co-producer of The Women's Kingdom, said, "The society does kind of create this question: Are fathers really necessary?
"It's hard to think of in Western society, but there, it works."
NO-FATHERS DAY: Remote Group Has No Dads, And Never Did
Brian Handwerkfor National Geographic News
June 18, 2009
What would Father's Day—and every other day—be like without fathers? Maybe not so bad, according to experts on the Mosuo culture of the Chinese Himalaya.
The women of this matrilineal society shun marriage and raise their kids in homes with their entire extended families—but no dads.
By most accounts, children seem to do just fine under the arrangement.
"They are a society that we know hasn't had marriage for a thousand years, and they've been able to raise kids successfully," said Stephanie Coontz, family studies professor at the Evergreen State College in Olympia, Washington.
No Fathers: It Makes Genetic Sense?
Men of the Mosuo, who live around Lugu Lake on the border between Yunnan and Sichuan Provinces, do help to raise kids—just not their own, with whom the men typically have only limited relationships.
Instead the men help look after all the children born to their own sisters, aunts, and other women of the family.
Rather than "one father with a kid, it will be four or five uncles. That [father] role is shared among a number of people, and these are very large extended families," explained John Lombard, director of the Lugu Lake Mosuo Cultural Development Association.
The unusual parenting arrangement makes genetic sense, in terms of extending the family line—and many Mosuo men actually think of it that way, Lombard said.
"If you [father] a child with another woman, you can never be absolutely sure that the child really shares your genes," he said. "But if your sister has a child, you can be 100 percent sure that the kid shares some of your genes."
The women of the Mosuo's agricultural villages head the households, make business decisions, and own property, which they pass on to their matrilineal heirs.
In the unique Mosuo tradition called the walking marriage, women invite men to visit their rooms at night—and to leave in the morning.
Women may also change partners as often as they like, and promiscuity carries no social stigma. The practice has made the Mosuo famous, particularly to male Chinese tourists, many of whom see the walking marriages as evidence of sexual liberation and wanton lust, experts say. Though there are tourist-oriented brothels in Mosuo villages, most are staffed with non-Mosuo women and are considered shameful by the Mosuo, according to the the Lugu Lake Mosuo Cultural Development Association Web site.
"I think sometimes the media gets carried away with the possibility that the women can have all these husbands," said filmmaker Xiaoli Zhou, who produced and reported the 2006 documentary on the Mosuo, The Women's Kingdom.
In fact, most Mosuo women don't change walking-marriage partners very frequently. And they rarely carry on more than one romantic relationship at a time.
"Many of the women I interviewed had only had one or two relationships in their lives," Zhou said.
Family First
The lack of live-in fathers shouldn't be taken as evidence that the Mosuo don't value family life, said Lombard, of the Lugu Lake Mosuo Cultural Development Association.
In fact, they value it above all other relationships—particularly those founded on the sometimes fickle feelings of male-female amour, he said.
Extended families of siblings, uncles, aunts, and others are said to be extremely stable, Lombard added.
For example, there are no divorces to destablize the families. And even the death of a child's biological father has little effect on the family, given the father's distance from the family and the extensive support network in the household.
Brent Huffman, co-producer of The Women's Kingdom, said, "The society does kind of create this question: Are fathers really necessary?
"It's hard to think of in Western society, but there, it works."
Wednesday, June 17, 2009
Why Do We Choose Our Mates? Ask Charles Darwin, Prof Says
http://www.sciencedaily.com/releases/2009/06/090615185428.htm
ScienceDaily (June 17, 2009) — Charles Darwin wrote about it 150 years ago: animals don't pick their mates by pure chance – it's a process that is deliberate and involves numerous factors. After decades of examining his work, experts agree that he pretty much scored a scientific bullseye, but a very big question is, "What have we learned since then?" asks a Texas A&M University biologist who has studied Darwin's theories.
Adam Jones, an evolutional biologist who has studied Darwin's work for years, says that Darwin's beliefs about the choice of mates and sexual selection being beyond mere chance have been proven correct, as stated in Darwin's landmark book The Descent of Man, and Selection in Relation to Sex.
Bottom line: It's no accident that certain peahens submit to gloriously-colored male peacocks, that lions get the females of their choice or that humans spend hours primping to catch the perfect spouses – it's a condition that is ingrained into all creatures and a conscious "choice" is made between the two so the romantic fireworks can begin.
Jones says Darwin set the standard for original thinking about animal reproduction and was first scientist to propose plausible mechanisms of evolution, and from there he took it one step further – he confirmed that animals' mating choices can drive evolutionary change.
"He noticed that birds, especially, seemed to be a bit picky about who they mated with," Jones explains. "He discovered that birds – especially females – had preferences and that they did not just choose a mate randomly. He believed this is due to beauty of the plumage, that females usually selected the most colorful males.
"That was an important first step, and it's given us models to work from to try to answer other big questions."
Those include determining methods to find out the actual criteria used in choosing a mate, what methods work and which do not, and the passing of genes on to the next generation, a field of study Jones says gained popularity in the 1970s and 1980s.
"Another big recent advance was the development of molecular markers, which allow us to perform paternity testing," Jones adds.
"These markers can be applied to animal populations, and they give us a definitive record of who is mating with whom and what offspring resulted from the mating events. And also, what is the driving force behind sexual selection? We have an unprecedented ability to document mating patterns but we still don't completely understand why some populations experience strong sexual selection and others don't."
Jones notes that other key questions Darwin's work uncovered but has not yet answered include the role of population characteristics and the environment and how they work together to produce strong sexual selection, and also what determines whether or not female choice will evolve in a particular species.
And perhaps the biggest question of all: How does all of this pertain to humans?
"Darwin concluded that sexual selection existed in the animal world and that humans definitely followed a similar process," Jones confirms.
"But he realized he had to explain it first as it related to animals. Darwin thought that sexual selection was an important process in humans, both for males and females. But how much has sexual selection acted on males versus females in humans? Today, while we are celebrating the 200th year of the birth of Charles Darwin, we know sexual selection occurs and is very important but there are still many unanswered questions about precisely why and how it works, especially in humans."
Journal reference:
. Mate Choice and Sexual Selection: What Have We Learned Since Darwin? Proceedings of the National Academy of Sciences, June 16, 2009
Adapted from materials provided by Texas A&M University, via EurekAlert!, a service of AAAS.
ScienceDaily (June 17, 2009) — Charles Darwin wrote about it 150 years ago: animals don't pick their mates by pure chance – it's a process that is deliberate and involves numerous factors. After decades of examining his work, experts agree that he pretty much scored a scientific bullseye, but a very big question is, "What have we learned since then?" asks a Texas A&M University biologist who has studied Darwin's theories.
Adam Jones, an evolutional biologist who has studied Darwin's work for years, says that Darwin's beliefs about the choice of mates and sexual selection being beyond mere chance have been proven correct, as stated in Darwin's landmark book The Descent of Man, and Selection in Relation to Sex.
Bottom line: It's no accident that certain peahens submit to gloriously-colored male peacocks, that lions get the females of their choice or that humans spend hours primping to catch the perfect spouses – it's a condition that is ingrained into all creatures and a conscious "choice" is made between the two so the romantic fireworks can begin.
Jones says Darwin set the standard for original thinking about animal reproduction and was first scientist to propose plausible mechanisms of evolution, and from there he took it one step further – he confirmed that animals' mating choices can drive evolutionary change.
"He noticed that birds, especially, seemed to be a bit picky about who they mated with," Jones explains. "He discovered that birds – especially females – had preferences and that they did not just choose a mate randomly. He believed this is due to beauty of the plumage, that females usually selected the most colorful males.
"That was an important first step, and it's given us models to work from to try to answer other big questions."
Those include determining methods to find out the actual criteria used in choosing a mate, what methods work and which do not, and the passing of genes on to the next generation, a field of study Jones says gained popularity in the 1970s and 1980s.
"Another big recent advance was the development of molecular markers, which allow us to perform paternity testing," Jones adds.
"These markers can be applied to animal populations, and they give us a definitive record of who is mating with whom and what offspring resulted from the mating events. And also, what is the driving force behind sexual selection? We have an unprecedented ability to document mating patterns but we still don't completely understand why some populations experience strong sexual selection and others don't."
Jones notes that other key questions Darwin's work uncovered but has not yet answered include the role of population characteristics and the environment and how they work together to produce strong sexual selection, and also what determines whether or not female choice will evolve in a particular species.
And perhaps the biggest question of all: How does all of this pertain to humans?
"Darwin concluded that sexual selection existed in the animal world and that humans definitely followed a similar process," Jones confirms.
"But he realized he had to explain it first as it related to animals. Darwin thought that sexual selection was an important process in humans, both for males and females. But how much has sexual selection acted on males versus females in humans? Today, while we are celebrating the 200th year of the birth of Charles Darwin, we know sexual selection occurs and is very important but there are still many unanswered questions about precisely why and how it works, especially in humans."
Journal reference:
. Mate Choice and Sexual Selection: What Have We Learned Since Darwin? Proceedings of the National Academy of Sciences, June 16, 2009
Adapted from materials provided by Texas A&M University, via EurekAlert!, a service of AAAS.
Same-sex Behavior Seen In Nearly All Animals, Review Finds
http://www.sciencedaily.com/releases/2009/06/090616122106.htm
ScienceDaily (June 17, 2009) — Same-sex behavior is a nearly universal phenomenon in the animal kingdom, common across species, from worms to frogs to birds, concludes a new review of existing research.
"It's clear that same-sex sexual behavior extends far beyond the well-known examples that dominate both the scientific and popular literature: for example, bonobos, dolphins, penguins and fruit flies," said Nathan Bailey, the first author of the review paper and a postdoctoral researcher in the Department of Biology at UC Riverside.
There is a caveat, however. The review also reports that same-sex behaviors are not the same across species, and that researchers may be calling qualitatively different phenomena by the same name.
"For example, male fruit flies may court other males because they are lacking a gene that enables them to discriminate between the sexes," Bailey said. "But that is very different from male bottlenose dolphins, who engage in same-sex interactions to facilitate group bonding, or female Laysan Albatross that can remain pair-bonded for life and cooperatively rear young."
Published June 16 in the journal Trends in Ecology & Evolution, the review by Bailey and Marlene Zuk, a professor of biology at UCR, also finds that although many studies are performed in the context of understanding the evolutionary origins of same-sex sexual behavior, almost none have considered its evolutionary consequences.
"Same-sex behaviors—courtship, mounting or parenting—are traits that may have been shaped by natural selection, a basic mechanism of evolution that occurs over successive generations," Bailey said. "But our review of studies also suggests that these same-sex behaviors might act as selective forces in and of themselves."
A selective force, which is a sudden or gradual stress placed on a population, affects the reproductive success of individuals in the population.
"When we think of selective forces, we tend to think of things like weather, temperature, or geographic features, but we can think of the social circumstances in a population of animals as a selective force, too," Bailey said. "Same-sex behavior radically changes those social circumstances, for example, by removing some individuals from the pool of animals available for mating."
Bailey, who works in Zuk's lab, noted that researchers in the field have made significant strides in the past two and a half decades studying the genetic and neural mechanisms that produce same-sex behaviors in individuals, and the ultimate reasons for their existence in populations.
"But like any other behavior that doesn't lead directly to reproduction—such as aggression or altruism—same-sex behavior can have evolutionary consequences that are just now beginning to be considered," he said. "For example, male-male copulations in locusts can be costly for the mounted male, and this cost may in turn increase selection pressure for males' tendency to release a chemical called panacetylnitrile, which dissuades other males from mounting them."
The review paper:
Examines work done to test hypotheses about the origins of same-sex behavior in animals.
Provides a framework for categorizing same-sex behavior, for example, is it adaptive, not adaptive, occurs often, infrequently?
Discusses what has been discovered about the genetics of same-sex behavior, especially in the model organism, the fruit fly Drosophila, and in human beings.
Examines connections between human sexual orientation research, and research on non-human animals, and highlights promising avenues of research in non-human systems.
The reviewers expected the research papers they read for their article would give them a better understanding of the degree to which same-sex behaviors are heritable in animals.
"How important are genes to the expression of these behaviors, compared to environmental factors?" Bailey said. "This is still unknown. Knowing this information would help us better understand how the behaviors evolve, and how they affect the evolution of other traits. It could also help us understand whether they are something that all individuals of a species are capable of, but only some actually express."
Bailey recommends that fellow evolutionary biologists studying same-sex behavior in animals adopt some of the research approaches that have been successful in human studies.
"We have estimates, for example, of the heritability of sexual orientation in humans, but none that I know of in other animals," he said. "Scientists have also targeted locations on the human genome that may contribute to sexual orientation, but aside from the fruit fly, we have no such detailed knowledge of the genetic architecture of same-sex behavior in other animals."
Next in their research, Bailey and Zuk plan to begin experimentally addressing some of the many issues raised in their review.
Said Bailey, "We want to get at this question: what are the evolutionary consequences of these behaviors? Are they important in the evolution of mating behavior, or do they just add extra 'background noise'? We are pursuing work on the Laysan Albatross, in which females form same-sex pairs and rear young together. Same-sex behavior in this species may not be aberrant, but instead can arise as an alternative reproductive strategy."
The UCR Academic Senate funded the one-year study.
ScienceDaily (June 17, 2009) — Same-sex behavior is a nearly universal phenomenon in the animal kingdom, common across species, from worms to frogs to birds, concludes a new review of existing research.
"It's clear that same-sex sexual behavior extends far beyond the well-known examples that dominate both the scientific and popular literature: for example, bonobos, dolphins, penguins and fruit flies," said Nathan Bailey, the first author of the review paper and a postdoctoral researcher in the Department of Biology at UC Riverside.
There is a caveat, however. The review also reports that same-sex behaviors are not the same across species, and that researchers may be calling qualitatively different phenomena by the same name.
"For example, male fruit flies may court other males because they are lacking a gene that enables them to discriminate between the sexes," Bailey said. "But that is very different from male bottlenose dolphins, who engage in same-sex interactions to facilitate group bonding, or female Laysan Albatross that can remain pair-bonded for life and cooperatively rear young."
Published June 16 in the journal Trends in Ecology & Evolution, the review by Bailey and Marlene Zuk, a professor of biology at UCR, also finds that although many studies are performed in the context of understanding the evolutionary origins of same-sex sexual behavior, almost none have considered its evolutionary consequences.
"Same-sex behaviors—courtship, mounting or parenting—are traits that may have been shaped by natural selection, a basic mechanism of evolution that occurs over successive generations," Bailey said. "But our review of studies also suggests that these same-sex behaviors might act as selective forces in and of themselves."
A selective force, which is a sudden or gradual stress placed on a population, affects the reproductive success of individuals in the population.
"When we think of selective forces, we tend to think of things like weather, temperature, or geographic features, but we can think of the social circumstances in a population of animals as a selective force, too," Bailey said. "Same-sex behavior radically changes those social circumstances, for example, by removing some individuals from the pool of animals available for mating."
Bailey, who works in Zuk's lab, noted that researchers in the field have made significant strides in the past two and a half decades studying the genetic and neural mechanisms that produce same-sex behaviors in individuals, and the ultimate reasons for their existence in populations.
"But like any other behavior that doesn't lead directly to reproduction—such as aggression or altruism—same-sex behavior can have evolutionary consequences that are just now beginning to be considered," he said. "For example, male-male copulations in locusts can be costly for the mounted male, and this cost may in turn increase selection pressure for males' tendency to release a chemical called panacetylnitrile, which dissuades other males from mounting them."
The review paper:
Examines work done to test hypotheses about the origins of same-sex behavior in animals.
Provides a framework for categorizing same-sex behavior, for example, is it adaptive, not adaptive, occurs often, infrequently?
Discusses what has been discovered about the genetics of same-sex behavior, especially in the model organism, the fruit fly Drosophila, and in human beings.
Examines connections between human sexual orientation research, and research on non-human animals, and highlights promising avenues of research in non-human systems.
The reviewers expected the research papers they read for their article would give them a better understanding of the degree to which same-sex behaviors are heritable in animals.
"How important are genes to the expression of these behaviors, compared to environmental factors?" Bailey said. "This is still unknown. Knowing this information would help us better understand how the behaviors evolve, and how they affect the evolution of other traits. It could also help us understand whether they are something that all individuals of a species are capable of, but only some actually express."
Bailey recommends that fellow evolutionary biologists studying same-sex behavior in animals adopt some of the research approaches that have been successful in human studies.
"We have estimates, for example, of the heritability of sexual orientation in humans, but none that I know of in other animals," he said. "Scientists have also targeted locations on the human genome that may contribute to sexual orientation, but aside from the fruit fly, we have no such detailed knowledge of the genetic architecture of same-sex behavior in other animals."
Next in their research, Bailey and Zuk plan to begin experimentally addressing some of the many issues raised in their review.
Said Bailey, "We want to get at this question: what are the evolutionary consequences of these behaviors? Are they important in the evolution of mating behavior, or do they just add extra 'background noise'? We are pursuing work on the Laysan Albatross, in which females form same-sex pairs and rear young together. Same-sex behavior in this species may not be aberrant, but instead can arise as an alternative reproductive strategy."
The UCR Academic Senate funded the one-year study.
Thursday, June 4, 2009
Males, females swap sex-role stereotypes
http://www.sciencenews.org/view/generic/id/43212/title/Males%2C_females_swap_sex-role_stereotypes
Analysis finds that mating strategies are not universal
By Bruce Bower
May 23rd, 2009; Vol.175 #11 (p. 5)
SEX ROLES IN SOCIETIES A new cross-cultural study finds that men and women in monogamous societies, such as Pitcairn Islanders (left), and some polygynous societies, including the Aka in the Central African Republic (right), have overlapping ranges of number of offspring. Luis Marden/National Geographic/Getty; Barry Hewlett
Chuck that nonsense about “men are from Mars, women are from Venus.” Here on Earth, the sexes play the mating game with a flexible set of rules. A new study suggests that scientists should abandon the idea that males evolved to be promiscuous and females to be selective. Combined data from 18 modern and traditional societies show greater overall variation in reproductive success for men than for women — with some men producing lots of children with multiple partners and other men conceiving few or no children, say psychologist Gillian Brown of the University of St. Andrews in Fife, Scotland, and her colleagues. Women tend to have a handful of children.
In the past, researchers have treated this pattern as a sign of universal mating tendencies, with women limiting how many children they bear and men conceiving as many children as possible.
Yet the same pattern of distinctive male and female sex roles doesn’t appear when many of these same 18 societies are examined individually, Brown’s group reports in the June Trends in Ecology & Evolution. In monogamous societies and even in some polygynous ones, where men can have more than one wife or mate, men and women can have similar variation in the number of children they produce, the scientists find.
Monogamous societies in the new study included Pitcairn Islanders in the South Pacific, Dobe !Kung hunter-gatherers in southern Africa and 19th century Swedes. Polygynous societies displaying comparable or only slightly unequal patterns of reproductive success for men and women included Aka hunter-gatherers in central Africa, Hadza hunter-gatherers in southern Africa and nomadic Yomut Turkmen in Iran.
Looking at the data all together, patterns of reproductive success were skewed by data from a few polygynous societies in which small numbers of men conceived the bulk of the offspring, the researchers contend. Examples of this pattern came from the Dogon and Kipsigis, both in Africa.
“Half of the populations we studied had similar variations in male and female reproductive success, which is inconsistent with universal stereotypes of passive, discriminating females and promiscuous males,” Brown says.
These scientific generalizations originated with fruit fly studies conducted by English geneticist Angus Bateman in 1948. He reported that male flies exhibited greater variation than females in numbers of sexual partners and offspring. Females mating with several males showed less of an increase in the number of offspring than males mating with many females.
Bateman concluded that it was more costly for females to produce a single egg than for males to produce a single sperm, leading to “discriminating passivity” among female flies and “undiscriminating eagerness” among male flies.
But in the past decade or so, studies of fruit flies and other animals have documented considerable variation in numbers of sexual partners and offspring for both sexes. Situational factors shape animals’ mating decisions, Brown asserts. Investigations suggest that females often get choosy when outnumbered by males or required to raise offspring alone. Males become picky when outnumbered by females or when required to help raise offspring. In small, spread out populations with roughly equal numbers of males and females, both sexes tend to mate indiscriminately.
Brown and her colleagues provide initial evidence that the “astonishing flexibility” of mating strategies also applies to people, remarks behavioral ecologist Stephen Emlen of Cornell University.
“A lot of nonhuman animals that are thought of as innately controlled robots actually perform sophisticated cost-benefit analyses of different choices and adjust their behavior based on flexible rules of thumb,” asserts Emlen, who studies mating decisions in birds. Emlen says it would be surprising if people didn’t have even more variable mating strategies than other animals.
Anthropologist Lee Cronk of Rutgers University in New Brunswick, N.J., says that he hopes the study “will have a major impact on future evolutionary work on human mating patterns.”
Cronk still thinks that universal mating strategies exist for men and women and were genetically ingrained during the Stone Age. But these strategies can play out in a variety of ways depending on the cultural, social and demographic features of modern societies.
Brown sees the situation differently. Disparities in learned mating strategies and cultural beliefs that have developed among groups over the past 50,000 years or so have also led to genetic differences among those populations, not to universal mating tendencies, she suspects.
Brown’s group analyzed information on reproduction and mating in hunter-gatherer, farming and industrialized societies from already published studies. Although these studies depended on women’s reports of who fathered their children, Brown regards the reliability of such evidence as comparable between monogamous and polygynous societies.
Scientists must now try to estimate and compare numbers of sexual partners, as well as offspring, for individuals in different societies, she says. Doing so will be challenging, since attempts to establish the numbers of sexual partners for men and women have relied on self-reports that are unreliable, Brown asserts.
She and her colleagues remain cautious about assuming that men always have more sexual partners than women in polygynous societies. In about half of polygynous societies, most men still take no more than one wife, they note. In others, women as well as men conceive children with two or more partners.
Thorough cross-cultural studies would likely reveal a great variety of mating strategies that respond to local conditions, predicts behavioral ecologist Mhairi Gibson of the University of Bristol in England. “Unfortunately, few anthropologists continue to collect such quantitative data on human behavior,” she says.
Source: Adapted from Brown et al.
Analysis finds that mating strategies are not universal
By Bruce Bower
May 23rd, 2009; Vol.175 #11 (p. 5)
SEX ROLES IN SOCIETIES A new cross-cultural study finds that men and women in monogamous societies, such as Pitcairn Islanders (left), and some polygynous societies, including the Aka in the Central African Republic (right), have overlapping ranges of number of offspring. Luis Marden/National Geographic/Getty; Barry Hewlett
Chuck that nonsense about “men are from Mars, women are from Venus.” Here on Earth, the sexes play the mating game with a flexible set of rules. A new study suggests that scientists should abandon the idea that males evolved to be promiscuous and females to be selective. Combined data from 18 modern and traditional societies show greater overall variation in reproductive success for men than for women — with some men producing lots of children with multiple partners and other men conceiving few or no children, say psychologist Gillian Brown of the University of St. Andrews in Fife, Scotland, and her colleagues. Women tend to have a handful of children.
In the past, researchers have treated this pattern as a sign of universal mating tendencies, with women limiting how many children they bear and men conceiving as many children as possible.
Yet the same pattern of distinctive male and female sex roles doesn’t appear when many of these same 18 societies are examined individually, Brown’s group reports in the June Trends in Ecology & Evolution. In monogamous societies and even in some polygynous ones, where men can have more than one wife or mate, men and women can have similar variation in the number of children they produce, the scientists find.
Monogamous societies in the new study included Pitcairn Islanders in the South Pacific, Dobe !Kung hunter-gatherers in southern Africa and 19th century Swedes. Polygynous societies displaying comparable or only slightly unequal patterns of reproductive success for men and women included Aka hunter-gatherers in central Africa, Hadza hunter-gatherers in southern Africa and nomadic Yomut Turkmen in Iran.
Looking at the data all together, patterns of reproductive success were skewed by data from a few polygynous societies in which small numbers of men conceived the bulk of the offspring, the researchers contend. Examples of this pattern came from the Dogon and Kipsigis, both in Africa.
“Half of the populations we studied had similar variations in male and female reproductive success, which is inconsistent with universal stereotypes of passive, discriminating females and promiscuous males,” Brown says.
These scientific generalizations originated with fruit fly studies conducted by English geneticist Angus Bateman in 1948. He reported that male flies exhibited greater variation than females in numbers of sexual partners and offspring. Females mating with several males showed less of an increase in the number of offspring than males mating with many females.
Bateman concluded that it was more costly for females to produce a single egg than for males to produce a single sperm, leading to “discriminating passivity” among female flies and “undiscriminating eagerness” among male flies.
But in the past decade or so, studies of fruit flies and other animals have documented considerable variation in numbers of sexual partners and offspring for both sexes. Situational factors shape animals’ mating decisions, Brown asserts. Investigations suggest that females often get choosy when outnumbered by males or required to raise offspring alone. Males become picky when outnumbered by females or when required to help raise offspring. In small, spread out populations with roughly equal numbers of males and females, both sexes tend to mate indiscriminately.
Brown and her colleagues provide initial evidence that the “astonishing flexibility” of mating strategies also applies to people, remarks behavioral ecologist Stephen Emlen of Cornell University.
“A lot of nonhuman animals that are thought of as innately controlled robots actually perform sophisticated cost-benefit analyses of different choices and adjust their behavior based on flexible rules of thumb,” asserts Emlen, who studies mating decisions in birds. Emlen says it would be surprising if people didn’t have even more variable mating strategies than other animals.
Anthropologist Lee Cronk of Rutgers University in New Brunswick, N.J., says that he hopes the study “will have a major impact on future evolutionary work on human mating patterns.”
Cronk still thinks that universal mating strategies exist for men and women and were genetically ingrained during the Stone Age. But these strategies can play out in a variety of ways depending on the cultural, social and demographic features of modern societies.
Brown sees the situation differently. Disparities in learned mating strategies and cultural beliefs that have developed among groups over the past 50,000 years or so have also led to genetic differences among those populations, not to universal mating tendencies, she suspects.
Brown’s group analyzed information on reproduction and mating in hunter-gatherer, farming and industrialized societies from already published studies. Although these studies depended on women’s reports of who fathered their children, Brown regards the reliability of such evidence as comparable between monogamous and polygynous societies.
Scientists must now try to estimate and compare numbers of sexual partners, as well as offspring, for individuals in different societies, she says. Doing so will be challenging, since attempts to establish the numbers of sexual partners for men and women have relied on self-reports that are unreliable, Brown asserts.
She and her colleagues remain cautious about assuming that men always have more sexual partners than women in polygynous societies. In about half of polygynous societies, most men still take no more than one wife, they note. In others, women as well as men conceive children with two or more partners.
Thorough cross-cultural studies would likely reveal a great variety of mating strategies that respond to local conditions, predicts behavioral ecologist Mhairi Gibson of the University of Bristol in England. “Unfortunately, few anthropologists continue to collect such quantitative data on human behavior,” she says.
Source: Adapted from Brown et al.
Wednesday, June 3, 2009
Women May Not Be So Picky After All About Choosing A Mate
http://www.sciencedaily.com/releases/2009/06/090603101406.htm
ScienceDaily (June 2, 2009) — Men and women may not be from two different planets after all when it comes to choosiness in mate selection, according to new research from Northwestern University.
When women were assigned to the traditionally male role of approaching potential romantic partners, they were not any pickier than men in choosing that special someone to date, according to the speed dating study.
That finding, of course, is contrary to well established evolutionary explanations about mate selection. An abundance of such research suggests that women are influenced by higher reproductive costs (bearing and raising children) than men and thus are much choosier when it comes to love interests.
The new study is the latest research of two Northwestern psychologists whose well-reported work on speed dating offers unparalleled opportunities for studying romantic attraction in action.
Deviating from standard speed-dating experiments – and from the typical conventions at professional speed-dating events -- women in the study were required to go from man to man during their four-minute speed dates half the time, rather than always staying put. In most speed-dating events, the women stay in one place as the men circulate.
"The mere act of physically approaching a potential partner, versus being approached, seemed to increase desire for that partner," said Eli Finkel, associate professor of psychology in the Weinberg College of Arts and Sciences at Northwestern and co-investigator of the study.
Regardless of gender, those who rotated experienced greater romantic desire for their partners, compared to those who sat throughout the event. The rotators, compared to the sitters, tended to have a greater interest in seeing their speed-dating partners again.
"Given that men generally are expected -- and sometimes required – to approach a potential love interest, the implications are intriguing," Finkel said.
"Let's face it, even today, there is a huge difference in terms of who is expected to walk across the bar to say 'hi,'" added Northwestern's Paul Eastwick, the study's other co-investigator.
Three hundred fifty undergraduates were recruited for the study's speed-dating events. In half of the events, the men rotated while the women sat. In the remaining events, the women rotated. Following each four-minute "date," the participants indicated their romantic desire in that partner and how self-confident they felt. Following the event, the students indicated on a Website whether they would or would not be interested in seeing each partner again.
When the men rotated, the results supported the long-held notion of men being less selective. When the women rotated, this robust sex difference disappeared.
The study draws upon embodiment research that suggests that physical actions alter perception. In one such study, for example, participants who were told to pull an unrelated object toward themselves while evaluating Chinese ideographs rated them as prettier than participants who pushed an unrelated object away from themselves while viewing the symbols.
"The embodiment research shows that our physical activity and psychological processes interface in ways that are outside our conscious awareness," Finkel said. "In conjunction with this previous embodiment research, our speed-dating results strongly suggest that the mere act of approaching a potential love interest can boost desire."
The researchers suggest that confidence also may have affected the results. Approaching a potential date increases confidence, which in turn makes the approacher less selective.
The study presents a clear example of how inconspicuous gender norms (having men rotate and women sit) can not only affect the outcome of a study, but also skew the chances of a speed dater walking away with a potential match.
"Our society is structured in gendered ways that can be subtle but very powerful," Eastwick concluded. The study has implications both for companies that capitalize on the business of dating and for researchers concerned with how social norms may affect research.
ScienceDaily (June 2, 2009) — Men and women may not be from two different planets after all when it comes to choosiness in mate selection, according to new research from Northwestern University.
When women were assigned to the traditionally male role of approaching potential romantic partners, they were not any pickier than men in choosing that special someone to date, according to the speed dating study.
That finding, of course, is contrary to well established evolutionary explanations about mate selection. An abundance of such research suggests that women are influenced by higher reproductive costs (bearing and raising children) than men and thus are much choosier when it comes to love interests.
The new study is the latest research of two Northwestern psychologists whose well-reported work on speed dating offers unparalleled opportunities for studying romantic attraction in action.
Deviating from standard speed-dating experiments – and from the typical conventions at professional speed-dating events -- women in the study were required to go from man to man during their four-minute speed dates half the time, rather than always staying put. In most speed-dating events, the women stay in one place as the men circulate.
"The mere act of physically approaching a potential partner, versus being approached, seemed to increase desire for that partner," said Eli Finkel, associate professor of psychology in the Weinberg College of Arts and Sciences at Northwestern and co-investigator of the study.
Regardless of gender, those who rotated experienced greater romantic desire for their partners, compared to those who sat throughout the event. The rotators, compared to the sitters, tended to have a greater interest in seeing their speed-dating partners again.
"Given that men generally are expected -- and sometimes required – to approach a potential love interest, the implications are intriguing," Finkel said.
"Let's face it, even today, there is a huge difference in terms of who is expected to walk across the bar to say 'hi,'" added Northwestern's Paul Eastwick, the study's other co-investigator.
Three hundred fifty undergraduates were recruited for the study's speed-dating events. In half of the events, the men rotated while the women sat. In the remaining events, the women rotated. Following each four-minute "date," the participants indicated their romantic desire in that partner and how self-confident they felt. Following the event, the students indicated on a Website whether they would or would not be interested in seeing each partner again.
When the men rotated, the results supported the long-held notion of men being less selective. When the women rotated, this robust sex difference disappeared.
The study draws upon embodiment research that suggests that physical actions alter perception. In one such study, for example, participants who were told to pull an unrelated object toward themselves while evaluating Chinese ideographs rated them as prettier than participants who pushed an unrelated object away from themselves while viewing the symbols.
"The embodiment research shows that our physical activity and psychological processes interface in ways that are outside our conscious awareness," Finkel said. "In conjunction with this previous embodiment research, our speed-dating results strongly suggest that the mere act of approaching a potential love interest can boost desire."
The researchers suggest that confidence also may have affected the results. Approaching a potential date increases confidence, which in turn makes the approacher less selective.
The study presents a clear example of how inconspicuous gender norms (having men rotate and women sit) can not only affect the outcome of a study, but also skew the chances of a speed dater walking away with a potential match.
"Our society is structured in gendered ways that can be subtle but very powerful," Eastwick concluded. The study has implications both for companies that capitalize on the business of dating and for researchers concerned with how social norms may affect research.
Myth About 'Dirty Old Men' Supported By Science
http://www.sciencedaily.com/releases/2008/12/081204074654.htm
ScienceDaily (Dec. 4, 2008) — Middle-aged men want younger women, often touting their intelligence and their high income. This is shown in research at Gothenburg University and Oxford University that studied 400 lonely hearts ads to see how men and women choose partners.
Research in the theory of evolution includes a number of accepted theories about how men and women choose their partners. Among the more established ones is that men place more emphasis on attractive appearance, whereas resources and social status are more important to women.
By examining lonely hearts advertisements, researchers at the University of Gothenburg and the University of Oxford have now tested how valid these presumed preferences are when modern individuals choose partners.
In the study, published in the journal Evolutionary Psychology, the researchers looked at 400 lonely hearts ads in the Swedish newspapers Göteborgs-Posten and Aftonbladet and on the Websites Spraydate and match.com.
To some extent, the findings support established theories:
Women, more than men, look for solid resources and social status. As a result men also offer this in their ads, through formulations like ‘large house’ and ‘economically independent.’
Men in all categories prefer younger partners. Of a total of 97 men who mentioned age in their ads, only three were looking for an older partner – among men aged 40 to 59, only one out of 67.
Younger women, on the other hand, prefer older men: fully 14 of 16 women aged 20-39 were looking for an older partner. Among women over 60, however, the majority were looking for a younger man.
Another point of departure for the study was that men are more fixated on appearance than women are. This turned out not to be the case.
“When it comes to physical characteristics, it turned out that men and women were the same. Both used words like, ‘athletic,’ ‘beautiful,’ ‘pretty,’ ‘tall,’ ‘handsome,’ and ‘trim’ to the same extent, and this goes both for their descriptions of themselves and for the characteristics they were looking for in a partner,” says Jörgen Johnsson at the Department of Zoology, University of Gothenburg, one of the researchers behind the study.
“This might indicate that men have learned to respond to women’s interest in looks, therefore stressing to the same extent their attractiveness in the ads. The fact that both sexes focus on looks may also be influenced by our times, with the great fixation on appearance in the media.”
The study is an elaboration of an undergraduate paper at the Department of Zoology, written by Linda Gustavsson. The associate at the University of Oxford is Tobias Uller.
ScienceDaily (Dec. 4, 2008) — Middle-aged men want younger women, often touting their intelligence and their high income. This is shown in research at Gothenburg University and Oxford University that studied 400 lonely hearts ads to see how men and women choose partners.
Research in the theory of evolution includes a number of accepted theories about how men and women choose their partners. Among the more established ones is that men place more emphasis on attractive appearance, whereas resources and social status are more important to women.
By examining lonely hearts advertisements, researchers at the University of Gothenburg and the University of Oxford have now tested how valid these presumed preferences are when modern individuals choose partners.
In the study, published in the journal Evolutionary Psychology, the researchers looked at 400 lonely hearts ads in the Swedish newspapers Göteborgs-Posten and Aftonbladet and on the Websites Spraydate and match.com.
To some extent, the findings support established theories:
Women, more than men, look for solid resources and social status. As a result men also offer this in their ads, through formulations like ‘large house’ and ‘economically independent.’
Men in all categories prefer younger partners. Of a total of 97 men who mentioned age in their ads, only three were looking for an older partner – among men aged 40 to 59, only one out of 67.
Younger women, on the other hand, prefer older men: fully 14 of 16 women aged 20-39 were looking for an older partner. Among women over 60, however, the majority were looking for a younger man.
Another point of departure for the study was that men are more fixated on appearance than women are. This turned out not to be the case.
“When it comes to physical characteristics, it turned out that men and women were the same. Both used words like, ‘athletic,’ ‘beautiful,’ ‘pretty,’ ‘tall,’ ‘handsome,’ and ‘trim’ to the same extent, and this goes both for their descriptions of themselves and for the characteristics they were looking for in a partner,” says Jörgen Johnsson at the Department of Zoology, University of Gothenburg, one of the researchers behind the study.
“This might indicate that men have learned to respond to women’s interest in looks, therefore stressing to the same extent their attractiveness in the ads. The fact that both sexes focus on looks may also be influenced by our times, with the great fixation on appearance in the media.”
The study is an elaboration of an undergraduate paper at the Department of Zoology, written by Linda Gustavsson. The associate at the University of Oxford is Tobias Uller.
Sexual Partner Status Affects A Woman's, But Not A Man's, Interest In The Opposite Sex
http://www.sciencedaily.com/releases/2009/05/090528120657.htm ScienceDaily (June 3, 2009) — A study by Indiana University neuroscientist Heather Rupp found that a woman's partner status influenced her interest in the opposite sex. In the study, women both with and without sexual partners showed little difference in their subjective ratings of photos of men when considering such measures as masculinity and attractiveness. However, the women who did not have sexual partners spent more time evaluating photos of men, demonstrating a greater interest in the photos.
No such difference was found between men who had sexual partners and those who did not. "These findings may reflect sex differences in reproductive strategies that may act early in the cognitive processing of potential partners and contribute to sex differences in sexual attraction and behavior," said Rupp, assistant scientist at The Kinsey Institute for Research in Sex, Gender and Reproduction.
For the study, 59 men and 56 women rated 510 photos of opposite-sex faces for realism, masculinity/femininity, attractiveness, or affect. Participants were instructed to give their "gut" reaction and to rate the pictures as quickly as possible. The men and women ranged in age from 17 to 26, were heterosexual, from a variety of ethnic backgrounds and were not using hormonal contraception. Of the women, 21 reported they had a current sexual partner; 25 of the men reported having a sexual partner. This is the first study to report whether having a current sexual partner influences interest in the opposite sex. Other studies have demonstrated that hormones, relationship goals and social context influence such interest.
"That there were no detectable effects of sexual partner status on women's subjective ratings of male faces, but there were on response times, which emphasizes the subtlety of this effect and introduces the possibility that sexual partner status impacts women's cognitive processing of novel male faces but not necessarily their conscious subjective appraisal," the authors wrote in the journal article. The researchers also note that influence of partner status in women could reflect that women, on average, are relatively committed in their romantic relationships, "which possibly suppresses their attention to and appraisal of alternative partners."
No such difference was found between men who had sexual partners and those who did not. "These findings may reflect sex differences in reproductive strategies that may act early in the cognitive processing of potential partners and contribute to sex differences in sexual attraction and behavior," said Rupp, assistant scientist at The Kinsey Institute for Research in Sex, Gender and Reproduction.
For the study, 59 men and 56 women rated 510 photos of opposite-sex faces for realism, masculinity/femininity, attractiveness, or affect. Participants were instructed to give their "gut" reaction and to rate the pictures as quickly as possible. The men and women ranged in age from 17 to 26, were heterosexual, from a variety of ethnic backgrounds and were not using hormonal contraception. Of the women, 21 reported they had a current sexual partner; 25 of the men reported having a sexual partner. This is the first study to report whether having a current sexual partner influences interest in the opposite sex. Other studies have demonstrated that hormones, relationship goals and social context influence such interest.
"That there were no detectable effects of sexual partner status on women's subjective ratings of male faces, but there were on response times, which emphasizes the subtlety of this effect and introduces the possibility that sexual partner status impacts women's cognitive processing of novel male faces but not necessarily their conscious subjective appraisal," the authors wrote in the journal article. The researchers also note that influence of partner status in women could reflect that women, on average, are relatively committed in their romantic relationships, "which possibly suppresses their attention to and appraisal of alternative partners."
Thursday, May 28, 2009
Opposites Attract: How Genetics Influences Humans To Choose Their Mates
http://www.sciencedaily.com/releases/2009/05/090525105435.htm
ScienceDaily (May 25, 2009) — New light has been thrown on how humans choose their partners, according to new findings presented May 25 at the annual conference of the European Society of Human Genetics.
Professor Maria da Graça Bicalho, head of the Immunogenetics and Histocompatibility Laboratory at the University of Parana, Brazil, says that her research had shown that people with diverse major histocompatibility complexes (MHCs) were more likely to choose each other as mates than those whose MHCs were similar, and that this was likely to be an evolutionary strategy to ensure healthy reproduction.
The MHC is a large genetic region situated on chromosome 6, and found in most vertebrates. It plays an important role in the immune system and also in reproductive success. Apart from being a large region, it is also an extraordinarily diverse one.
Females' preference for MHC dissimilar mates has been shown in many vertebrate species, including humans, and it is also known that MHC influences mating selection by preferences for particular body odours. The Brazilian team has been working in this field since 1998, and decided to investigate mate selection in the Brazilian population, while trying to uncover the biological significance of MHC diversity.
The scientists studied MHC data from 90 married couples, and compared them with 152 randomly-generated control couples. They counted the number of MHC dissimilarities among those who were real couples, and compared them with those in the randomly-generated 'virtual couples'. "If MHC genes did not influence mate selection", says Professor Bicalho, "we would have expected to see similar results from both sets of couples. But we found that the real partners had significantly more MHC dissimilarities than we could have expected to find simply by chance."
Within MHC-dissimilar couples the partners will be genetically different, and such a pattern of mate choice decreases the danger of endogamy (mating among relatives) and increases the genetic variability of offspring. Genetic variability is known to be an advantage for offspring, and the MHC effect could be an evolutionary strategy underlying incest avoidance in humans and also improving the efficiency of the immune system, the scientists say.
"Although it may be tempting to think that humans choose their partners because of their similarities", says Professor Bicalho, "our research has shown clearly that it is differences that make for successful reproduction, and that the subconscious drive to have healthy children is important when choosing a mate."
The scientists believe that their findings will help understanding of conception, fertility, and gestational failures. Research has already shown that couples with similar MHC genes had longer intervals between births, which could imply early, unperceived miscarriages. "We intend to follow up this work by looking at social and cultural influences as well as biological ones in mate choice, and relating these to the genetic diversity of the extended MHC region", says Professor Bicalho.
"We expect to find that cultural aspects play an important role in mate choice, and certainly do not subscribe to the theory that if a person bears a particular genetic variant it will determine his or her behaviour. But we also think that the unconscious evolutionary aspect of partner choice should not be overlooked. We believe our research shows that this has an important role to play in ensuring healthy reproduction, by helping to ensure that children are born with a strong immune system better able to cope with infection."
ScienceDaily (May 25, 2009) — New light has been thrown on how humans choose their partners, according to new findings presented May 25 at the annual conference of the European Society of Human Genetics.
Professor Maria da Graça Bicalho, head of the Immunogenetics and Histocompatibility Laboratory at the University of Parana, Brazil, says that her research had shown that people with diverse major histocompatibility complexes (MHCs) were more likely to choose each other as mates than those whose MHCs were similar, and that this was likely to be an evolutionary strategy to ensure healthy reproduction.
The MHC is a large genetic region situated on chromosome 6, and found in most vertebrates. It plays an important role in the immune system and also in reproductive success. Apart from being a large region, it is also an extraordinarily diverse one.
Females' preference for MHC dissimilar mates has been shown in many vertebrate species, including humans, and it is also known that MHC influences mating selection by preferences for particular body odours. The Brazilian team has been working in this field since 1998, and decided to investigate mate selection in the Brazilian population, while trying to uncover the biological significance of MHC diversity.
The scientists studied MHC data from 90 married couples, and compared them with 152 randomly-generated control couples. They counted the number of MHC dissimilarities among those who were real couples, and compared them with those in the randomly-generated 'virtual couples'. "If MHC genes did not influence mate selection", says Professor Bicalho, "we would have expected to see similar results from both sets of couples. But we found that the real partners had significantly more MHC dissimilarities than we could have expected to find simply by chance."
Within MHC-dissimilar couples the partners will be genetically different, and such a pattern of mate choice decreases the danger of endogamy (mating among relatives) and increases the genetic variability of offspring. Genetic variability is known to be an advantage for offspring, and the MHC effect could be an evolutionary strategy underlying incest avoidance in humans and also improving the efficiency of the immune system, the scientists say.
"Although it may be tempting to think that humans choose their partners because of their similarities", says Professor Bicalho, "our research has shown clearly that it is differences that make for successful reproduction, and that the subconscious drive to have healthy children is important when choosing a mate."
The scientists believe that their findings will help understanding of conception, fertility, and gestational failures. Research has already shown that couples with similar MHC genes had longer intervals between births, which could imply early, unperceived miscarriages. "We intend to follow up this work by looking at social and cultural influences as well as biological ones in mate choice, and relating these to the genetic diversity of the extended MHC region", says Professor Bicalho.
"We expect to find that cultural aspects play an important role in mate choice, and certainly do not subscribe to the theory that if a person bears a particular genetic variant it will determine his or her behaviour. But we also think that the unconscious evolutionary aspect of partner choice should not be overlooked. We believe our research shows that this has an important role to play in ensuring healthy reproduction, by helping to ensure that children are born with a strong immune system better able to cope with infection."
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