Chapter 8. Hormones and Sex
Follow us on Facebook and Twitter, or subscribe to our mailing list, to receive news updates. Learn more.
By Brigid Schulte, Unlike the male pundits, politicians and even financiers who’ve opined freely recently about what they consider “natural” roles for mothers and fathers, with mom at home and dad at work, behavioral neuroscientist Kelly Lambert’s methodical approach has led her to a much more complicated conclusion. From her perch at Randolph-Macon College in rural Ashland, Va., Lambert has spent years designing elaborate experiments to test nurturing in both male and female rodents. She anesthetizes the animals, carefully removes their brains, firms the brains up with formalin, freezes them, then shaves them into slices thinner than a strand of human hair to study under a microscope. What Lambert’s rodent brain slices are revealing is nothing short of revolutionary, challenging the loud pundits and long-held cultural views that only mothers are wired for nurture. Lambert, one of a small but growing number of scientists who study the biology of father behavior, is finding that not just mothers experience surges of hormones associated with bonding and nurturing. The same hormones increase, though not to the same degree, in fathers. Rat mothers are not the only ones whose brains become sharper, making them more efficient foragers and more courageous and level-headed than females without offspring. Lambert has found that the same is true of fathers’ brains. Fatherhood makes the male California deer mouse smarter, too. © 1996-2013 The Washington Post
// by Jennifer Viegas It goes a little something like this: A young male zebra finch, whose father taught him a song, shared that song with a brother, with the two youngsters then creating new tunes based on dad’s signature sound. The musical bird family, described in the latest Biology Letters, strengthens evidence that imitation between siblings and similar-aged youngsters facilitates vocal learning. The theory could help to explain why families with multiple same sex siblings, such as the Bee Gees and the Jackson 5, often form such successful musical groups. Co-author Sébastien Derégnaucourt told Discovery News that, among humans, “infants have a visual preference for peers of the same age, which may facilitate imitation.” He added that it’s also “known that children can have an impact on each other’s language acquisition, such as in the case of the emergence of creole languages, whether spoken or signed, among children exposed to pidgin (a grammatically simplified form of a language).” Pidgin in this case is more like pigeon, since the study focused on birds. Derégnaucourt, an associate professor at University Paris West, collaborated with Manfred Gahr of the Max Planck Institute for Ornithology. The two researchers studied how the young male zebra finch from a bird colony in Germany learned from his avian dad. © 2013 Discovery Communications, LLC.
Helen Shen The case of the missing bird penis is a long-standing mystery in evolutionary biology. But the identification of a molecular mechanism that controls penis loss in birds goes some way to solving this conundrum. Roughly 97% of avian species sport little or nothing in the way of a phallus, despite reproducing by internal fertilization. A study published today in Current Biology1 shows that the development of chicken penises is cut short by signals that promote cell death. “This paper would be in Nature or Science if it were about people,” says Richard Prum, an evolutionary ornithologist at Yale University in New Haven, Connecticut. “The whole result is entirely novel.” Male chickens, which possess only a rudimentary phallic nub, pump their sperm into females using a 'cloacal kiss' — a move that presses together the male and female cloacas, openings used for waste excretion and copulation. By contrast, ducks boast large and elaborately coiled penises that can measure about half the length of their bodies2. To better understand the signals that control penis growth, researchers led by Martin Cohn, a developmental biologist at the University of Florida in Gainesville, looked for differences between developing duck and chicken embryos. © 2013 Nature Publishing Group
Keyword: Sexual Behavior
Link ID: 18246 - Posted: 06.08.2013
By Susan Milius Lyrebirds are famous for the mimicked sounds they sing, but they now have another claim to fame: They dance to their own songs. “Just as we waltz to waltz music but we salsa to salsa music, so lyrebirds perform different dance movements to different types of songs,” says Anastasia Dalziell of the Australian National University in Canberra. She and her colleagues scrutinized videos of male superb lyrebirds (Menura novaehollandiae) showing off in the wild for possible mates. The males’ combinations of hums, clicks, trills and other sexy syllables fell into four distinctive song types, the researchers say. At least the first three types are not mimicry but lyrebird originals, Dalziell says. In courtship, males sing the songs in a fairly predictable order and usually match each to its own mix of dance moves and postures. The birds side-step, turn and flare their outsized lyre-shaped tails. Matching a type of music with a style of gesture is not unique to humankind, the researchers report June 6 in Current Biology. Performing for females, a male lyrebird dances to the music he makes. And yes, the bird makes the noises heard in the video. © Society for Science & the Public 2000 - 2013
By Breanna Draxler Is it a coincidence that the word vole is an anagram of love? Probably so, but since prairie voles mate for life, they have since been designated as the unofficial species used to study monogamy in lab animals. And a new study finds that their rare partnerships are cemented by chemical changes on their genes, called epigenetic changes, that result from their sexual encounters. When a prairie vole (Microtus ochrogaster) finds a mate, the two form a strong bond. Not only do they stay together for life and share child care duties, but the lovers will guard their mates aggressively against voles of the opposite sex. Scientists knew from previous studies that this bonding was regulated by neurotransmitters—chemical communicators in the brain such as oxytocin, which is linked to sex and reproduction, and vasopressin, associated with social recognition. However researchers were unsure what the biological basis was for such a sharp behavioral shift after mating. To find out, scientists at Florida State University paired up virgin male and female voles and gave the couples a cage together for a number of hours. Some couples were allowed to mate while others were prevented from doing so. The non-mating female voles instead received drug injections in the nucleus accumbens, a part of the brain’s pleasure center. The drugs affected the voles’ epigenetics by unwinding their DNA so that genes for vasopressin and oxytocin receptors were more highly transcribed.
A patient at the Kwong Wah and Queen Elizabeth Hospitals discovered he was also a woman when he came for treatment for a swelling abdomen. Photo: Nora Tam A 66-year-old apparently male patient made a stunning discovery when he sought treatment for swelling in his abdomen. The swelling was a cyst on his ovary and he was in fact a woman. The condition was caused by a very rare combination of two genetic disorders. One, Turner syndrome, causes women to lack some female features, including the ability to get pregnant. Sufferers usually look like women, but in this case the patient also had congenital adrenal hyperplasia (CAH), which boosted the male hormones and made the patient look like a man. The case was reported by doctors from Kwong Wah Hospital and Queen Elizabeth Hospital, who treated the patient. It was published in the Hong Kong Medical Journal yesterday. "The patient, by definition, is a woman who cannot get pregnant. But she also has CAH, which gave her the appearance of a man," Chinese University paediatrics professor Ellis Hon Kam-lun said. "It's an interesting and very rare case of having the two combinations. It probably won't be seen again in the near future." The 66-year-old Vietnam-born Chinese man is an orphan. He has a beard, small penis and no testes. Just 1.37 metres tall, he has decided to continue perceiving himself as a male and may receive male hormone treatment, the report said. © 2013 South China Morning Post Publishers Ltd
by Kim Krieger The song of the cicada has been romanticized in mariachi music, used to signify summer in Japanese cinematography, and cursed by many an American suburbanite wishing for peace and quiet. Despite the bugs' ubiquity, scientists haven't uncovered how they sing so loudly—some are as noisy as a jet engine—and why they don't expend much energy doing it. But researchers reported in Montreal yesterday at the 21st International Congress on Acoustics that they now have the answer. The detailed mechanism of the cicada's song is far from fully understood, says Paulo Fonseca, an animal acoustician at the University of Lisbon who was not involved in the project. The work by the researchers "is innovative and paves our way to a better understanding of this complex system allowing such small animals to produce such powerful sound." Cicadas aren't just a natural curiosity. Small devices that produce extremely loud noises while requiring very little power appeal to the U.S. Navy, which uses sonar for underwater exploration and communication. Derke Hughes, a research engineer at the Naval Undersea Warfare Center in Newport, Rhode Island, says that the loudest cicadas can make a noise 20 to 40 dB louder than the compact off-the-shelf RadioShack speaker in his office using the same amount of power. Intrigued, he and his colleagues used microcomputed tomography)—a kind of CT scan that picks up details as small as a micron in size—to image a cicada's tymbal, which helps the insect make its deafening chirp. © 2010 American Association for the Advancement of Science
By Susan Milius After death, male guppies can keep on siring offspring because females store sperm for so long. As a result, a living male in a stream in Trinidad can end up competing with long-gone fish from his grandfather’s generation. At its most posthumously successful, stored ghost sperm sired about one in four of the offspring among wild guppies released into a stream, evolutionary biologist Andrés López-Sepulcre of École Normale Supérieure in Paris and his colleagues report June 5 in Proceedings of the Royal Society B. Biologists have long known that female Poecilia reticulata guppies store sperm. The cells clump in little pockets in a female’s ovarian cavity and feed on sugars released by ovarian tissue. Storage in itself isn’t unusual, López-Sepulcre says. Some crabs, turtles, lizards, bats and other creatures preserve sperm for later use. Posthumous reproduction by stored sperm also isn’t unheard of. “The fun part of our study,” López-Sepulcre says, “is that you have males who are alive and males who are dead competing with each other.” Researchers deployed guppies in several streams as part of a study on evolutionary change. Every month researchers catch, check and release as many fish as possible to track deaths and births. They also genetically analyze parenthood of the fish. Female guppies give live birth to broods of two to about 10 youngsters, with not all sired by the same male. Females live about 15 months; males about three. © Society for Science & the Public 2000 - 2013
By ANAHAD O'CONNOR The number of middle-aged men with prescriptions for testosterone is climbing rapidly, raising concerns that increasing numbers of men are abusing the powerful hormone to boost their libidos and feel younger, researchers reported on Monday. Testosterone replacement therapy is approved specifically for the treatment of abnormally low testosterone levels, a condition called hypogonadism. The hormone helps build muscle, reduce body fat and improve sex drive. But a study published in the journal JAMA Internal Medicine found that many men who get prescriptions for the hormone have no evidence of a deficiency at all. The new study is the largest of testosterone prescribing patterns to date, involving nearly 11 million men who were tracked through a large health insurer. The report showed that the number of older and middle-aged men prescribed the hormone has tripled since 2001. Men in their 40s represent the fastest-growing group of users. About half of men prescribed testosterone had a diagnosis of hypogonadism, and roughly 40 percent had erectile or sexual dysfunction. One third had a diagnosis of fatigue. The medical group that sets clinical guidelines for testosterone replacement therapy, the Endocrine Society, recommends treatment only in men who have unequivocally low testosterone levels. That finding requires a blood test. But the new report found that a quarter of men did not have their levels tested before they received the hormone. It was also unclear what proportion of men who did undergo testing actually had results showing a deficiency. Copyright 2013 The New York Times Company
Keyword: Hormones & Behavior
Link ID: 18228 - Posted: 06.04.2013
Zoe Cormier Love really does change your brain — at least, if you’re a prairie vole. Researchers have shown for the first time that the act of mating induces permanent chemical modifications in the chromosomes, affecting the expression of genes that regulate sexual and monogamous behaviour. The study is published today in Nature Neuroscience1. Prairie voles (Microtus ochrogaster) have long been of interest to neuroscientists and endocrinologists who study the social behaviour of animals, in part because this species forms monogamous pair bonds — essentially mating for life. The voles' pair bonding, sharing of parental roles and egalitarian nest building in couples makes them a good model for understanding the biology of monogamy and mating in humans. Previous studies have shown that the neurotransmitters oxytocin and vasopressin play a major part in inducing and regulating the formation of the pair bond. Monogamous prairie voles are known to have higher levels of receptors for these neurotransmitters than do voles who have yet to mate; and when otherwise promiscuous montane voles (M. montanus) are dosed with oxytocin and vasopressin, they adopt the monogamous behaviour of their prairie cousins. Because behaviour seemed to play an active part in changing the neurobiology of the animals, scientists suspected that epigenetic factors were involved. These are chemical modifications to the chromosomes that affect how genes are transcribed or suppressed, as opposed to changes in the gene sequences themselves. © 2013 Nature Publishing Group
by Paul Gabrielsen Take a whiff, men. A chemical component of other guys' sweat makes men more cooperative and generous, new research says. The study is the first to show that this pheromone, called androstadienone, influences other men's behavior and reinforces the developing finding that humans are susceptible and responsive to these chemical signals. Pheromones are everywhere in the animal world. Bugs in particular give off these chemicals to sound an alarm, identify a food source, or attract a mate. And smitten animals may indeed have "chemistry" together—pheromone signals are a subconscious part of their communication. Scientists didn't know if humans played that game as well. But in the last 30 years, they've identified both male and female putative pheromones that are linked to mood and reproductive cycles. Some fragrancemakers have even incorporated them into their products, hoping to add an extra emotional punch to colognes and perfumes. Real-life pheromones don't smell so nice, however: The specialized glands that produce these chemical compounds are located near the armpit, where they mix with sweat. Previous investigations focused on the chemicals as sexual attractants—studying a male pheromone's effect on female mood and behavior, for example. Turns out that women aren't the only ones susceptible to the power of male pheromones. Evolutionary biologist Markus Rantala of the University of Turku in Finland crafted an experiment in which 40 men in their mid-20s played a computer game in which two players decided how to share €10. One player offers a possible split, and the other decides whether to accept or reject it. Each participant took a turn making or deciding on offers. © 2010 American Association for the Advancement of Science
“Which way do you swing?” It’s such a simple, but loaded question. Social-economic issues aside, even the biological basis of sexual preference is hotly debated. Homosexual behavior isn’t limited to humans; it’s evolutionarily conserved in species as diverse as the lowly fruit fly to the mighty lion. Some argue that genes are involved, but so far the hunt for “gay genes” have only led to dead ends (and a lot of controversy!). Sex hormones are the next suspect, but they seem to only change sex drive, not so much preference. Now this study suggests that the answer may be as simple as one SINGLE neurotransmitter: serotonin. First off, why serotonin? We know that serotonin is involved in sexual behaviour. SSRI antidepressants, like Celexa and Zoloft, work by increasing the amount of serotonin in the synapses. This relieves depressive symptoms, but has the unfortunate side effect of lowering libido. Many other studies converge to support the same simple conclusion: more serotonin=less sexual behaviour, less serotonin= more sexual behaviour. But what about PREFERENCE? The same group published a highly controversial study a few years ago, in which they argued that abolishing serotonin in male mice wiped out their preference for females. These mice showed sexual interest in both males and females, and mounted both sexes equally when given the chance. It caused quite a stir back then, with many pointing out that their conclusions were premature. One major problem is that serotonin-lacking mice are much more likely to engage in sexual behavior. Hence, they might have just been so horny that they didn’t care to pick-and-choose, mounting everything within sight regardless of gender.
By DANIEL BERGNER Linneah sat at a desk at the Center for Sexual Medicine at Sheppard Pratt in the suburbs of Baltimore and filled out a questionnaire. She read briskly, making swift checks beside her selected answers, and when she was finished, she handed the pages across the desk to Martina Miller, who gave her a round of pills. The pills were either a placebo or a new drug called Lybrido, created to stoke sexual desire in women. Checking her computer, Miller pointed out gently that Linneah hadn’t been doing her duty as a study participant. Over the past eight weeks, she took the tablets before she planned to have sex, and for every time she put a pill on her tongue, she was supposed to make an entry in her online diary about her level of lust. “I know, I know,” Linneah said. She is a 44-year-old part-time elementary-school teacher, and that day she wore red pants and a canary yellow scarf. (She asked that only a nickname be used to protect her privacy.) “It’s a mess. I keep forgetting.” Miller, a study coordinator, began a short interview, typing Linneah’s replies into a database that the medication’s Dutch inventor, Adriaan Tuiten, will present to the Food and Drug Administration this summer or fall as part of his campaign to win the agency’s approval and begin marketing what might become the first female-desire drug in America. “Thinking about your desire now,” Miller said, “would you say it is absent, very low, low, reasonable or present?” “Low.” This was no different from Linneah’s reply at the trial’s outset two months before. © 2013 The New York Times Company
By Sandra G. Boodman, ‘Oh my God,” Leigh Partridge remembers thinking, her mind reeling as she tried to contemplate the unimaginable. “This cannot be happening again.” Doctors in the emergency room of Children’s Hospital of Philadelphia (CHOP) had just told Partridge that a mass in the abdomen of her 16-year-old daughter might be cancer. Further testing would be required. To Partridge, who had lost her husband two years earlier when brain cancer killed him in a matter of months, the possibility that their middle daughter might have a malignancy was terrifying. “I didn’t even know who to call to come sit with me,” Partridge recalled. “The person who was supposed to be with me wasn’t there” anymore. Allison Partridge, then a high school junior, had found the fist-size tumor in her abdomen the previous evening while lying in bed at home. For months, Allie had suffered from severe and worsening pain in her lower abdomen and tailbone, which she usually tried to minimize or deny to protect herself and her mother. But now the pain and the giant lump were too obvious to downplay. “My mom was definitely freaking out a lot more than I was,” Allie recalled. Her hospitalization in April 2011 was both traumatic and a turning point, revealing the unusual cause of her problem as well as the essential clue — unknown to her mother — that was overlooked by doctors. © 1996-2013 The Washington Po
By Scicurious Aging happens. As you get older, your body slows down, eventually your brain slows down, too. Some things go gradually, and some go suddenly. To many people, this might seem like a pretty random process. We used to think of aging this way, as just…well cells get old, which means we get old, too. DNA replication after a while starts making errors in repair, the errors build up, and on the whole body scale the whole thing just kind of goes downhill. It seems random. But in fact, it’s not. There are specific proteins which can help control this process. And one of these, NF-kB, in one particular brain region, may have a very important role indeed. NF-kB (which stands for nuclear factor kappa-light-chain-enhancer of activated B cells, which is why we use NF-kB) is a protein complex that has a lot of roles to play. It’s an important starting player in the immune system, where it helps to stimulate antibodies. It’s important in memory and stress responses. NF-kB is something called a transcription factor, which helps to control what DNA is transcribed to RNA, and therefore what proteins will eventually be produced. Transcription factors, as you can see, can have a very large number of functions. But in the hypothalamus, NF-kB may have the added function of helping to control aging. The hypothalamus is an area of many small nuclei (further sub areas of neurons) located at the base of the brain. It’s been coming more and more into vogue lately among neuroscientists. In the past, we were interested in the hypothalamus mostly for its role in controlling hormone release from the dangling pituitary gland before it, but now we are learning that the hypothalamus can play roles in fear, mood, food intake, reproduction, and now…aging. © 2013 Scientific American
By Melanie Tannenbaum Imagine that you’re an infant monkey, and you’ve just been thrown into a cage after several hours in isolation. You’ve been deprived of food, so you’re starving. Facing you are two adult-looking (fake) monkeys, designed to look like each one could potentially be your mother. On the left is a “wire mother,” equipped with a bottle and feeding tube so you can cling to her and fill your belly with milk. On the right is a “cloth mother,” with no bottle, but with a fuzzy terrycloth exterior that will allow for hours of soft, warm snuggles. You can only run to one of the monkeys. Which one will you choose? Six or seven decades ago, many psychologists would have claimed that any affection that we experience towards our parental figures is a purely behaviorist response. After many instances of conditioning a sense of “positive affect” after receiving life-sustaining food from mothers, children associate that positive emotion with these caregivers, an association that serves as the sole explanation for why people “love” their mothers. But that’s not what Harry Harlow thought. Harlow, a psychologist working at the University of Wisconsin – Madison during the 1960s, believed that there was something more important underlying our affection for Mom and Dad than our primal need to eat and survive. He believed that there was an additional factor: Comfort. What Harlow did to test this hypothesis was arguably ingenious, though inarguably cruel.1 Harlow deprived monkeys of food, making them desperately hungry, and then stuck them into a cage where they had a choice of two “mother figures” to run towards. On the left was a wire mother – cold and uncomfortable, yet equipped with a bottle that would feed the baby with life-sustaining nutrients. On the right was a cloth mother – warm, soft, and comfortable, yet unable to provide the infant with any food. If the only reason why we “love” our mothers (and fathers) is based on a conditioned response to our need for food, then the infant monkeys should run to the wire mothers who can feed them every time. © 2013 Scientific American
Researchers at the National Institutes of Health have uncovered firm evidence for what many mothers have long suspected: women’s brains appear to be hard-wired to respond to the cries of a hungry infant. Researchers asked men and women to let their minds wander, then played a recording of white noise interspersed with the sounds of an infant crying. Brain scans showed that, in the women, patterns of brain activity abruptly switched to an attentive mode when they heard the infant cries, whereas the men’s brains remained in the resting state. “Previous studies have shown that, on an emotional level, men and women respond differently to the sound of an infant crying,” said study co-author Marc H. Bornstein, Ph.D., head of the Child and Family Research Section of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), the institute that conducted the study. “Our findings indicate that men and women show marked differences in terms of attention as well.” The earlier studies showed that women are more likely than men to feel sympathy when they hear an infant cry, and are more likely to want to care for the infant. Their findings appear in NeuroReport. Previous studies have shown differences in patterns of brain activity between when an individual’s attention is focused and when the mind wanders. The pattern of unfocused activity is referred to as default mode, Dr. Bornstein explained. When individuals focus on something in particular, their brains disengage from the default mode and activate other brain networks.
By Scicurious In the great novel The Great Gatsby, Daisy, one of the love interests of the book, has a beautiful voice. She’s described otherwise, but you don’t really remember what she looked like, you remember how she sounded. Fitzgerald describes her voice as musical, running up and down and the scales when she talks. And you know what he’s talking about. You hear that voice in your head: light, breathy, utterly charming. You don’t really know what she looks like, but from imagining her voice, you know she is beautiful. What is it about this, or any voice, that makes it attractive? Is it the pitch? The tone? The firmness or breathiness of voice? And what is it about that voice, or any voice, that makes you know that someone is beautiful, handsome, masculine, feminine? The authors of this study wanted to see what makes a voice a VOICE. What acoustic factors make it most attractive to women and to men? To do this, they first took 10 young men, and had them rate the attractiveness of a female voice saying “good luck on your exams”. The voice actor said the phrase without any emotion using three different sound qualities: normal, breathy, and pressed (more of a hard tone). They then took the recording of this voice and modified it up and down, to create the phrase in several different pitches and formats. Specifically, they modified it upward toward what they hypothesized to mean “small body size and happiness” or downward toward what they hypothesized to mean “large body size and anger”. They showed that while increasing the pitch (higher) did not increase the attractiveness of the voice, lowering it decreased the attractiveness. And increasing the breathiness of the sentence increased attractiveness. The authors believe that this means that lowering the voice, and presumably indicating a larger body size (larger body size in general means the normal voice will be lower), reduced how attractive the men found the voice. © 2013 Scientific American
Symmetry study deemed a fraud Eugenie Samuel Reich Few researchers have tried harder than Robert Trivers to retract one of their own papers. In 2005, Trivers, an evolutionary biologist at Rutgers University in New Brunswick, New Jersey, published an attention-grabbing finding: Jamaican teenagers with a high degree of body symmetry were more likely to be rated ‘good dancers’ by their peers than were those with less symmetrical bodies. The study, which suggested that dancing is a signal for sexual selection in humans, was featured on the cover of this journal (W. M. Brown et al. Nature 438, 1148–1150; 2005). But two years later, Trivers began to suspect that the study data had been faked by one of his co-authors, William Brown, a postdoctoral researcher at the time. In seeking a retraction, Trivers self-published The Anatomy of a Fraud, a small book detailing what he saw as evidence of data fabrication. Later, Trivers had a verbal altercation over the matter with a close colleague and was temporarily banned from campus. An investigation of the case, completed by Rutgers and released publicly last month, now seems to validate Trivers’ allegations. Brown disputes the university’s finding, but it could help to clear the controversy that has clouded Trivers’ reputation as the author of several pioneering papers in the 1970s. For example, Trivers advanced an influential theory of ‘reciprocal altruism’, in which people behave unselfishly and hope that they will later be rewarded for their good deeds. He also analysed human sexuality in terms of the investments that mothers and fathers each make in child-rearing. © 2013 Nature Publishing Group
By Breanna Draxler The ruse is common in spy movies—an attractive female saunters in at a critical moment and seduces the otherwise infallible protagonist, duping him into giving up the goods. It works in Hollywood and it works in real life, too. Men tend to say yes to attractive women without really scrutinizing whether or not they are trustworthy. But scientists have shown, for the first time, that a drug may be able to overcome this “honey trap,” and help men make more rational decisions. Nearly 100 men participated in the study; half were given minocycline, an antibiotic normally used to treat acne, and half were given a placebo. After four days of this drug regimen, participants played a computerized one-on-one trust game with eight different women, based only on pictures of the female players. In each round, the male player was given $13 and shown a picture of one of the female players. The male player would choose how much money he wanted to keep and how much he wanted to give to the female player. The amount given away was then tripled, and the female player would decide whether to split the money with the man or keep it all for herself. Unbeknownst to the men, however, the women kept the money every time. The researchers also asked the men to evaluate the photos of the females to determine how trustworthy and attractive they appeared, on a scale of 0 to 10.