Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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By SINDYA N. BHANOO Mosquito sperm have a sense of smell, researchers are reporting, in a finding that could suggest ways to help control the spread of disease-carrying insects. The sperm carries a set of chemical sensors identical to the olfactory receptors on the mosquitoes’ antennas, according to a study in Proceedings of the National Academy of Sciences. Mosquitoes mate just once in their lifetime, and the female stores the male’s sperm in an organ called a spermatheca. Before the eggs mature, the female seeks out blood using the receptors on her antennas. Soon after, chemical signals cause the sperm tails to beat rapidly and start the fertilization process. “The sperm may need a chemical signal to become ready for fertilization,” said Jason Pitts, a researcher at Vanderbilt University and an author of the study, which was supported by the Gates Foundation as part of its efforts to improve global health. Another author, Laurence Zwiebel, also a Vanderbilt researcher, called the dual use of the olfactory receptors a clear and clever example of convergent evolution: The mosquitoes, he said, “found something that works and use it in multiple ways.” The scientists think olfactory receptors may exist on the sperm of many other insects, and they are developing chemical compounds that can be applied to breeding grounds to block the receptors. “You can effectively confuse the sperm or make them inactive,” Dr. Zwiebel said. © 2014 The New York Times Company
By JOHN LA PUMA SANTA BARBARA, Calif. — A FUNNY thing has happened in the United States over the last few decades. Men’s average testosterone levels have been dropping by at least 1 percent a year, according to a 2006 study in The Journal of Clinical Endocrinology and Metabolism. Testosterone appears to decline naturally with aging, but internal belly fat depresses the hormone further, especially in obese men. Drugs like steroids and opiates also lower testosterone, and it’s suspected that chemicals like bisphenol A (or BPA, commonly found in plastic food containers) and diseases like Type 2 diabetes play a role as well. Men feel the loss. Clinical testosterone deficiency, which is variously defined as lower than 220 to 350 nanograms of testosterone per deciliter of blood serum, can cause men to lose sex drive and fertility. Their bone density often declines, and they may feel tired and experience hot flashes and sweats. But “low T,” as the condition has been labeled, isn’t nearly as common as the drug ads for prescription testosterone would have you believe. Pharmaceutical companies have seized on the decline in testosterone levels as pathological and applicable to every man. They aim to convince men that common effects of aging like slowing down a bit and feeling less sexual actually constitute a new disease, and that they need a prescription to cure it. This is a seductive message for many men, who just want to feel better than they do, and want to give it a shot, literally. The problem is that prescription testosterone doesn’t just give your T level a boost: it may also increase your risk of heart attack. It can add huge numbers of red blood cells to your bloodstream and shrink your testes. In some men, it increases aggression and irritability. © 2014 The New York Times Company
Keyword: Hormones & Behavior
Link ID: 19238 - Posted: 02.11.2014
by Laura Sanders A new analysis of cows shows that mamas make more milk for daughters. Other studies have hinted that human moms produce different milk for sons than for daughters, so perhaps lactating women also boost production for daughters. I love eavesdropping on people’s overly detailed coffee orders. You, sir, with the temerity to order a skinny split quad shot latte no whip no foam, with a side of lemon? Your extreme customizing just made my day. Such personalization was running through my mind as I read a recent study on cows. It turns out that another beverage is also subject to the specific, exacting standards of its drinker: milk. And the customer’s bossy demands seem to start before he or she is born. Heifers produce more milk for daughters than sons, Katie Hinde and colleagues report February 3 in PLOS ONE. When a cow gives birth to her first female, she makes about 1.6 percent more milk than she would have for a son, Hinde and colleagues found by analyzing the dairy records from a million and a half cows. And because calves born at dairy farms are taken away from their mothers soon after birth, the female calves’ requests to “make me more milk” must have come during pregnancy. Another interesting finding: The first pregnancy had an outsized effect on the cow’s future milk production. Cows that had sons first saw a slight bump in production when they got pregnant with a daughter, but didn’t catch up to the cows that had a daughter followed by a son. The first born daughter set the mom’s milk-making machinery on high, and that’s where it stayed for subsequent pregnancies. © Society for Science & the Public 2000 - 2013
Keyword: Sexual Behavior
Link ID: 19237 - Posted: 02.11.2014
You probably saw dozens of people’s faces today, many more if you live in a city. You may not have been conscious of it, but you were subtly judging every one by its beauty. Your eyes are drawn to more attractive faces, and the almost inescapable result is that more attractive people have advantages in almost every aspect of life, from job interviews to prison sentencing. But what drives us to crave beauty? According to one theory, gazing upon beauty stimulates the brain’s μ-opioid receptors (MOR), thought to be a key part of our biochemical reward system. At least in rodents, stimulating or inhibiting MOR neurotransmission not only tweaks the animals’ appetite for sex or food, but also the strength of their preferences for particular foods or mates. Is our preference for pretty faces driven by the same biochemical reward circuit? To find out, researchers invited 30 heterosexual men to browse a series of female faces on a computer (one pictured). Each man received either a dose of the MOR-stimulating drug morphine, the opioid receptor–inhibiting drug naltrexone, or a placebo. The results, published today in Molecular Psychiatry, suggest that we seek out beautiful faces at least in part because our brains reward us. Not only did stimulating MOR neurotransmission cause men to linger longer on faces that they rated as more beautiful, but the beauty rating also became more extreme, with beautiful faces rated as even more attractive relative to the rest of the faces. Inhibiting MOR had the opposite effects. The findings are yet more evidence that our social interactions are strongly influenced by the invisible hand of evolution, pushing us to find attractive mates. But the question remains, how do we decide which face is attractive in the first place? © 2014 American Association for the Advancement of Science
Women have a poorer quality of life after a stroke than men, a study has found. The US research, published in Neurology, assessed the mental and physical health of 1,370 patients three months and a year after a stroke. Women had more depression and anxiety, pain and discomfort, and more restricted mobility. UK experts said women tended to have strokes later, and might therefore need more support. But the study did say more people survive a stroke now than 10 years ago because of improved treatment and prevention. The researchers at Wake Forest Baptist Medical Center, North Carolina, looked at patients who had had a stroke or transient ischaemic attack (TIA), also known as a mini-stroke. Quality of life is calculated using a formula that assesses mobility, self-care, everyday activities, depression/anxiety and pain. At three months, women were more likely than men to report problems with mobility, pain and discomfort, anxiety and depression, but the difference was greatest in those aged over 75. After a year, women still had lower quality-of-life scores overall than men but the difference between them was smaller. Support needs Prof Cheryl Bushnell, who led the study, said: "We found that women had a worse quality of life than men up to 12 months following a stroke." BBC © 2014
By Matt McGrath Environment correspondent, BBC News Successful professional cyclists are seen as more handsome than their struggling colleagues, according to new research. Women rated facial attractiveness among riders in the 2012 Tour de France, won by Britain's Sir Bradley Wiggins. The top 10% of performers were rated on average as 25% better looking than the laggards. The scientists conclude that humans have evolved to recognise athletic performance in faces. The research has been published in the Royal Society journal, Biology Letters. Some biologists argue that evolution has shaped women to select mates on the basis that they would either make good fathers or would pass on good genes. Healthy, physically fit men would on average be seen as more attractive by women. A number of other studies in recent years have suggested that women have a sophisticated radar for athletic performance, rating those with greater sporting skill as more attractive. This new work, though, set out to test if the same applied to more inherent physical qualities such as stamina and endurance. Cycle of life Dr Erik Postma, from the Institute of Evolutionary Biology at the University of Zurich, asked people to rate the attractiveness of 80 professional cyclists from the 2012 Tour de France. The cyclists were all of a similar physical stature, were tanned and around the same age. BBC © 2014
By RONI CARYN RABIN Nearly a decade ago, researchers in Boston decided to see whether older men who were not in very good shape could benefit from daily doses of testosterone. The scientists recruited several hundred volunteers and gave them the hormone or a placebo. Those taking testosterone got stronger, compared with those taking the placebo, and they could carry a load up stairs faster. But they also had nearly five times the number of cardiovascular problems, including heart attacks and strokes, and safety monitors ended the trial early. Since those findings were published in 2010, studies of testosterone treatment have produced mixed results. A 2012 study of veterans aged 40 and over with low testosterone found that those treated with the hormone were less likely to die, but more recent reports, including one published last week, have documented an increase in cardiovascular risk in men over age 65 taking testosterone, as well as in younger men with a history of heart disease. Officials at the Food and Drug Administration said on Friday that they were reassessing the safety of testosterone products in light of the recent studies, and will investigate rates of stroke, heart attack and death in men using the drugs. In recent years, testosterone has been heavily promoted as a cure-all for low energy, low libido, depression and other ills among middle-aged men. “Low T” is a ubiquitous diagnosis, heard in television commercials and locker rooms. Between 2001 and 2011, hormone use by men 40 and over nearly quadrupled. By the end of that period, nearly one in 25 men in their 60s was taking testosterone. Though the drug is indicated for men with abnormally low testosterone levels, a condition called hypogonadism, doctors have been prescribing it to many men with normal levels. © 2014 The New York Times Company
Controversy delights Dick Swaab; brains delight him; complexity delights him, though I don't know if you'd get that from reading his book, We Are Our Brains, in which causal links are made quite casually, like a man doing a crossword with a pencil. The Dutch neurologist is, after a 50-year career, a giant in the field. He is a professor of neurobiology at the University of Amsterdam. His directorship of the Dutch Institute for Brain Research yielded material that has been sent to 500 other research groups in 25 countries. He has propounded groundbreaking theories in his specialist area: the impact on brain development in the womb. Nonetheless, his book, despite directing itself squarely to the layperson, has been miles more successful than he thought, selling 100,000 copies ("the publishers say they knew it would be a hit. But at the start, they only printed 3,000 copies. So I know that is not true."). There are a number of lines you might file under, "Well, there's a curiosity" (for instance: "In professional violinists, the part of the cerebral cortex that directs the fingers of the left hand is five times as large as it is in people who don't play a stringed instrument"). And yet the real fireworks of the book are both more predictable and more profound: Swaab says hormones and chemical substances in utero affect the development of our sexual orientation or, put more simply, you have a gay brain by the time you are born. Male and female brains have "hundreds of differences", which explain all the ways in which men and women are different; "phobia, impulsiveness, ADHD and depression later in life" can be traced back to a mother's fearfulness during pregnancy, which activates her baby's "fear axis". © 2014 Guardian News
Keyword: Sexual Behavior
Link ID: 19189 - Posted: 01.30.2014
Parasites don’t just cause nasty infections; they can also take over the minds of their hosts. The Ophiocordyceps fungus, for example, forces ants to climb up the stems of plants, where they die and release the fungus’s spores into the air to infect more ants. Likewise, it would make sense for sexually transmitted parasites to force their hosts to have sex more. But biologists have found very few examples of this in nature. A new study may explain why. To figure out why there isn’t more “sexual mind control” in nature, theoretical ecologist Ludek Berec, of the Biology Centre of the Academy of Sciences of the Czech Republic, and biological mathematician Daniel Maxin, of Valparaiso University in Indiana, turned to mathematical modeling. They created two strains of a hypothetical parasite species: an “ancestor” that did not make its hosts have sex more, and a mutant that did. Then they turned the two strains loose in a hypothetical host population and watched the parasites compete until the mutant strain either died out or replaced its ancestor. If the mutant strain replaced its ancestor, the researchers introduced a new mutant that had even more power over its host’s sex life. They then watched the two strains compete again, introduced yet another, stronger mutant when the old one outcompeted its predecessor, and so on. In this way, the species as a whole could “evolve” to exert more or less sexual mind control over its host. © 2014 American Association for the Advancement of Science.
Keyword: Sexual Behavior
Link ID: 19180 - Posted: 01.29.2014
By SINDYA N. BHANOO In pursuit of a mate, male fruit flies often engage in combat, battling one another with their front legs. But when the flies are brothers, they are more likely to cooperate, researchers are reporting. In a new study in the journal Nature, Tommaso Pizzari, a zoologist at the University of Oxford, and colleagues write that brother flies live longer as a result. And there are clear benefits for females who live among brothers: They have a longer reproductive life span, a faster rate of egg production and a greater chance of laying eggs that mature to adulthood. The researchers exposed female flies in a laboratory to several different sets of males — three brothers; two brothers and an unrelated male; and three unrelated males. The most peaceful groups were the ones with three brothers, perhaps because supporting one’s kin is an alternative way to pass on common genes. “You can improve your reproductive success yourself or help individuals who also share your genes,” Dr. Pizzari said. Although fruit flies have been extensively studied in labs, the structure of their natural societies remain a bit of a mystery. © 2014 The New York Times Compan
by Erika Engelhaupt Twerking is so 50 million years ago. In fact, it’s probably much older than that. Today, the provocative, butt-shaking dance move is enough of a social phenomenon to merit a word in the dictionary (with twerking defined about as tastefully as possible here by actor Morgan Freeman), but animals have been shaking their hindquarters for ages, for a variety of purposes (more on that below). Black widow spiders are the latest documented twerkers. In their case, it’s the males that shake their rears. Black widow females are aggressive predators and will immediately kill any prey detected in their webs. This presents a problem for males approaching a female to mate; in this case a literal misstep means becoming the female’s dinner. To figure out how the males avoid being eaten (at least before mating), researchers at Simon Fraser University in Canada measured vibrations created by males and by prey in webs of western black widows (Latrodectus hesperus). They compared the vibrations, and the females’ responses, to those of the hobo spider (Tegenaria agrestis), a species in which females rarely attack courting males. To capture the details of small vibrations, they used a fun tool called a laser Doppler vibrometer, which measures small changes in a laser beam aimed at a surface. Sure enough, black widow males appeared to have a death-avoidance strategy. They produced vibrations different from thrashing prey by means of “lengthy andrepeated bouts of abdominal tremulations” averaging 43 wiggles per second, the researchers report January 17 in Frontiers in Zoology. You can see a male's moves in this video: © Society for Science & the Public 2000 - 2014
|By Stephanie Pappas and LiveScience Even water tastes sweeter when you're in love, new research finds. But not every emotion heightens the senses. Jealousy fails to bring out bitter or sour tastes, despite metaphors that suggest it might, researchers report in the December 2013 issue of the journal Emotion. That love alters one's sensory perceptions and jealousy does not is important to psychologists who study what are called "embodied" metaphors, or linguistic flourishes people quite literally feel in their bones. For example, studies have shown that people induced to feel lonely rate the temperature of the room as colder than do their unprimed counterparts. And the idea that important things have heft plays out physically, too: When someone believes a book is important, it feels heavier. But "just because there is a metaphor does not necessarily imply that we will get these kind of sensations and perception effects," said study researcher Kai Qin Chan, a doctoral candidate at Radboud University Nijmegen in the Netherlands. After seeing previous research on emotional metaphors, like the studies linking loneliness to coldness and heaviness to importance, Chan and his colleagues wanted to expand the question. "We always say, 'love is sweet,' 'honey baby,' this kind of thing," Chan told LiveScience. "We thought, let's see whether this applies to love." © 2014 Scientific American
By CARL ZIMMER The term “X chromosome” has an air of mystery to it, and rightly so. It got its name in 1891 from a baffled biologist named Hermann Henking. To investigate the nature of chromosomes, Henking examined cells under a simple microscope. All the chromosomes in the cells came in pairs. All except one. Henking labeled this outlier chromosome the “X element.” No one knows for sure what he meant by the letter. Maybe he saw it as an extra chromosome. Or perhaps he thought it was an ex-chromosome. Maybe he used X the way mathematicians do, to refer to something unknown. Today, scientists know the X chromosome much better. It’s part of the system that determines whether we become male or female. If an egg inherits an X chromosome from both parents, it becomes female. If it gets an X from its mother and a Y from its father, it becomes male. But the X chromosome remains mysterious. For one thing, females shut down an X chromosome in every cell, leaving only one active. That’s a drastic step to take, given that the X chromosome has more than 1,000 genes. In some cells, the father’s goes dormant, and in others, the mother’s does. While scientists have known about this so-called X-chromosome inactivation for more than five decades, they still know little about the rules it follows, or even how it evolved. In the journal Neuron, a team of scientists has unveiled an unprecedented view of X-chromosome inactivation in the body. They found a remarkable complexity to the pattern in which the chromosomes were switched on and off. © 2014 The New York Times Company
by Susan Milius For springtails, sex can be an Easter egg hunt. Many males of the tiny soil organisms sustain their species by leaving drops of sperm glistening here and there in the landscape in case a female chooses to pick one up. “The male never meets the female,” says Zaira Valentina Zizzari of VU University Amsterdam, who studies a species of these extreme loners called Orchesella cincta. Just about every degree of mating intimacy, from unseen sperm donors to elaborate courtship and internal insemination, shows up in springtails. That makes the ancient group — which may not belong to the insects but to another set of six-legged arthropods on its own evolutionary trajectory — a treasure trove for biologists studying sex. In O. cincta, little brown-and-white males roam the leaf litter making no apparent effort to find a female. Instead, males pause here and there for a few seconds to leave behind white stalks topped by a shiny-coated globes, each holding more than 1,000 sperm. Sperm on a stalk is still viable after sitting two days in the lab. Outdoors it may not last so long. “You have a lot of rivals searching for sperm just to destroy it,” Zizzari says. Males eat rivals’ sperm. Given the rivalry, it wouldn’t be surprising if males engaged in an arms race to produce more sperm stalks than their competitors. But Zizzari was surprised to discover that male O. cincta make fewer sperm packages when a competitor is sperm-dotting the neighborhood. Maybe he’s enhancing the few he makes with extra sex appeal, Zizzari mused. To test the idea, she offered lab females a choice of globes from males with rivals or those made by an uncrowded guy. © Society for Science & the Public 2000 - 2014
Keyword: Sexual Behavior
Link ID: 19152 - Posted: 01.20.2014
Dan Hurley Forget mindfulness meditation, computerized working-memory training, and learning a musical instrument; all methods recently shown by scientists to increase intelligence. There could be an easier answer. It turns out that sex might actually make you smarter. Researchers in Maryland and South Korea recently found that sexual activity in mice and rats improves mental performance and increases neurogenesis (the production of new neurons) in the hippocampus, where long-term memories are formed. In April, a team from the University of Maryland reported that middle-aged rats permitted to engage in sex showed signs of improved cognitive function and hippocampal function. In November, a group from Konkuk University in Seoul concluded that sexual activity counteracts the memory-robbing effects of chronic stress in mice. “Sexual interaction could be helpful,” they wrote, “for buffering adult hippocampal neurogenesis and recognition memory function against the suppressive actions of chronic stress.” So growing brain cells through sex does appear to have some basis in scientific fact. But there’s some debate over whether fake sex—pornography—could be harmful. Neuroscientists from the University of Texas recently argued that excessive porn viewing, like other addictions, can result in permanent “anatomical and pathological” changes to the brain. That view, however, was quickly challenged in a rebuttal from researchers at the University of California, Los Angeles, who said that the Texans "offered little, if any, convincing evidence to support their perspectives. Instead, excessive liberties and misleading interpretations of neuroscience research are used to assert that excessive pornography consumption causes brain damage." © 2014 by The Atlantic Monthly Group
By Felicity Muth Whether there exist differences between boys and girls is passionately debated (for example, see this debate about gender disparity between Stephen Pinker and Elizabeth Spelke). Some studies have found that girls are more sociable than boys, but prefer to play with just one other person, while boys prefer a larger group to play with. However, it is very difficult to say whether differences that we see in boys’ and girls’ behaviour has a biological basis, as boys and girls are also treated differently. Even before a baby is born, parents have often painted its room pink or blue, and bought gender-differentiated toys. A mother is more likely to under-estimate her female baby’s crawling abilities, and over-estimate her male baby’s (he’s a boy, of course he’s going to be stronger and better at crawling?!). Perceptions on the personality and abilities of a baby also differ depending on whether the adult is told that the child is male or female. Given these differences in how people treat male and female children, it can be difficult to say whether the behaviours we see are have a biological basis or not. However, we can look for certain clues to biological differences in child behaviour from our ‘cousins’ the chimpanzees. Chimpanzees live in communities of 20 to 180 individuals, with sub-groups within this. One recent study looked at the behaviour of eight female and twelve male chimpanzee infants to see if their behaviour differed from each other. They found that the young males were more sociable than the young females. © 2014 Scientific American
Brittany Fallon In today’s focal party, the main characters are Nambi, the Alpha female who engages in regular sexual relations with young males; Nick, the former Alpha male, replaced by Nambi’s son Musa; and Zefa, Nick’s former Beta male, who is forming new alliances to overthrow Musa. It’s hard not to pretend I’m witnessing the real world version of Game of Thrones – except it’s not humans I’m observing, but chimpanzees. There’s no Iron Throne involved in this power struggle – just the race for reproductive success. Dominant individuals enjoy a number of benefits that improve their chance of passing on genes, including richer access to sexual partners. But how does this influence their tactics for attracting mates? Perhaps no effort is needed, the chimpanzee equivalent to the philandering Robert, with potential sex partners who line up in hopes of birthing the next possible heir. Or is it that, like promiscuous Cersei, they’ve learned a number of coy and successful pick up lines (“Tears aren’t a woman’s only weapon.”)? Elaborate metaphors aside, this is exactly the sort of question that I attempt to answer for my PhD on sexual displays in the Sonso chimpanzee community of the Budongo Forest Reserve in Uganda. Chimpanzees, like a variety of animals, produce ‘courtship displays’ to attract mates. Displays are largely comprised of gestures, which can be broadly defined as distinct bodily movements that do not physically manipulate the receiver toward the goal of the signaller. Both males and females, ranging in age from 2 to 52 years old in my community, can produce these solicitations. Displays can be elaborate, many signals strung together, or they can be simple, a single shaking of a branch followed immediately by copulation. What’s particularly amazing about chimpanzee solicitations is that they seem to be intentionally communicative: following a display, signallers will visibly wait for a response from their target by gaze-checking, and, if met with failure, will persist in gesturing. © 2014 Scientific American
By Alexandra Sifferlin It’s always been conventional wisdom that girls reach maturity more quickly than boys, but now scientists have provided some proof. In new research published in the journal Cerebral Cortex, an international group of researchers led by a team from Newcastle University in England found that girls’ brains march through the reorganization and pruning typical of normal brain development earlier than boys’ brains. In the study, in which 121 people between ages 4 to 40 were scanned using MRIs, the scientists documented the ebb and flow of new neural connections, and found that some brain fibers that bridged far-flung regions of the brain tended to remain stable, while shorter connections, many of which were redundant, were edited away. And the entire reorganization seemed to occur sooner in girls’ brains than in boys’ brains. Females also tended to have more connections across the two hemispheres of the brain. The researchers believe that the earlier reorganization in girls makes the brain work more efficiently, and therefore reach a more mature state for processing the environment. What drives the gender-based difference in timing isn’t clear from the current study, but the results suggest that may be a question worth investigating. © 2013 Time Inc.
// by Megan Gannon, Live Science News Editor Bonobos have a reputation among the great apes as "hippie chimps," and new research hints that high levels of a key thyroid hormone may play a role in keeping the animals' aggression in check. Found in the lowland forests of the Democratic Republic of the Congo, bonobos (Pan troglodytes) are closely related to chimpanzees (Pan troglodytes) but the two diverge in behavior. Bonobos seem to diffuse social tension with an impressive repertoire of sex acts rather than physical fights. Males in particular show low levels of aggression — they even maintain platonic friendships with females and stick by their mothers into adulthood. The life of male chimpanzees, meanwhile, revolves around climbing the social ladder (or at least hanging onto their current rung), and navigating cooperative and aggressive relationships with other males. [8 Humanlike Behaviors of Primates] Scientists recently found another big difference between the two Pan species: A key thyroid hormone decreases at a much later age in bonobos compared with chimps. For their study, scientists took urine samples from about 100 chimpanzees and 96 bonobos living in zoos. The researchers specifically looked at the apes' levels of triiodothyronine (T3), a hormone in the thyroid gland that is crucial for development in all vertebrates (animals with backbones). © 2013 Discovery Communications, LLC
by Chelsea Whyte For chameleons, war paint isn't just an accessory, it is a battle flag. The brightness of the colours these lizards display and how rapidly they change are good indicators of which animal will win in a fight. Chameleons are famous for changing colour to hide from predators by blending into their surroundings, but they also use colour for social communication. One of the most diversely coloured species is the veiled chameleon (Chamaeleo calyptratus), which lives in parts of Saudi Arabia and Yemen. "At their brightest, they have vertical yellow stripes, blue-green bellies, black speckles that provide contrast and make their stripes stand out, and orange around the corner of their mouths," says Russell Ligon, a behavioural ecologist at Arizona State University in Tempe. To see if individual variations in these colours and patterns influenced the outcome of a fight, Ligon and his colleague Kevin McGraw staged a round-robin tournament in which 10 male veiled chameleons were pitted against each other. Using a high-speed camera, they were able to capture the brightness and colour changes from 28 points on each animal, taking into account how the colours would look to a chameleon's eye – which sees both visible and ultraviolet light. They found that males with the brightest side stripes were more likely to instigate a fight, whereas those with brighter heads that changed colour most rapidly were more likely to win. This suggests that different colours and patterns may signal different aspects of competitive behaviour – how motivated the chameleon is versus its strength. © Copyright Reed Business Information Ltd.