Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases

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by Colin Barras Male marsupial mice just don't know when to stop. For Antechinus stuartii, their debut breeding season is so frenetic and stressful that they drop dead at the end of it from exhaustion or disease. It may be the females of the species that are driving this self-destructive behaviour. Suicidal breeding, known as semelparity, is seen in several marsupials. This is likely linked to short breeding seasons and the fact that the marsupial mice only breed once a year. It is not clear why this is, but it may be that females can only breed when the population of their insect prey reaches its peak. A year is a long and dangerous time for a small animal, so under these circumstances males might do best to pump all their resources into a single breeding season. To test this idea, Diana Fisher of the University of Queensland in St Lucia, Australia, and her colleagues tracked how insect abundance changed with the seasons in the marsupials' home forests. Sure enough, they found that the marsupials' breeding seasons were shortest where insect abundance followed a predictable annual pattern. But the insects are not the whole explanation. It turns out that females do sometimes survive the year and breed again. So why do the males always die? The key factor is that the females are highly promiscuous, says Fisher. Coupled with the short breeding season, this leads to intense competition between males. "Males that exert extreme effort in this short time are at an advantage." © Copyright Reed Business Information Ltd.

Keyword: Stress; Aggression
Link ID: 18758 - Posted: 10.08.2013

By Cat Bohannon Halos, auras, flashes of light, pins and needles running down your arms, the sudden scent of sulfur—many symptoms of a migraine have vaguely mystical qualities, and experts remain puzzled by the debilitating headaches' cause. Researchers at Harvard University, however, have come at least one step closer to figuring out why women are twice as likely to suffer from chronic migraines as men. The brain of a female migraineur looks so unlike the brain of a male migraineur, asserts Harvard scientist Nasim Maleki, that we should think of migraines in men and women as “different diseases altogether.” Maleki is known for looking at pain and motor regions in the brain, which are known to be unusually excitable in migraine sufferers. In one notable study published in the journal Brain last year, she and her colleagues exposed male and female migraineurs to painful heat on the backs of their hands while imaging their brains with functional MRI. She found that the women had a greater response in areas of the brain associated with emotional processing, such as the amygdala, than did the men. Furthermore, she found that in these women, the posterior insula and the precuneus—areas of the brain responsible for motor processing, pain perception and visuospatial imagery—were significantly thicker and more connected to each other than in male migraineurs or in those without migraines. In Maleki's most recent work, presented in June at the International Headache Congress, her team imaged the brains of migraineurs and healthy people between the ages of 20 and 65, and it made a discovery that she characterizes as “very, very weird.” In women with chronic migraines, the posterior insula does not seem to thin with age, as it does for everyone else, including male migraineurs and people who do not have migraines. The region starts thick and stays thick. © 2013 Scientific American

Keyword: Pain & Touch; Aggression
Link ID: 18757 - Posted: 10.08.2013

Alice Roberts It's the rutting season. From Richmond Park to the Isle of Rum, red deer hinds will be gathering, and the stags that have spent the past 10 months minding their own business in bachelor groups are back in town, with one thing on their minds. A mature male that has netted himself a harem is very dedicated. He practically stops eating, focusing instead on keeping his hinds near and his competitors at bay. If you're a red deer stag, one of the ways you make sure that your adversaries know you mean business – and that you're big – is roaring. And you don't let up. You can keep roaring all day, and through the night too, twice a minute, if necessary. While female red deer prefer the deeper roars of larger stags, roaring also appears to be part of how stags size one another up, before deciding whether or not to get engaged in a full-on physical fight. Most confrontations are settled without locking antlers. In male red and fallow deer, the voicebox or larynx is very low in the throat – and gets even lower when they roar. Strap-like muscles that attach to the larynx contract to drag it down towards the breastbone – lengthening the vocal tract and deepening the stag's roar. Deepening the voice exaggerates body size. Over generations, stags with deeper roars presumably had more reproductive success, so the position of the larynx moved lower and lower in the neck. When a red deer stag roars his larynx is pulled down so far that it contacts the front of his breastbone – it couldn't get any lower. In human evolution, much is made of the low position of the larynx in the neck. So much, in fact, that it has been considered to be a uniquely human trait, and intrinsically linked to that other uniquely human trait: spoken language. But if red and fallow deer also have low larynges, that means, first, that we're not as unusual as we like to think we are, and second, that there could be other reasons – that are nothing to do with speaking – for having a descended larynx. © 2013 Guardian News and Media Limited

Keyword: Sexual Behavior; Aggression
Link ID: 18751 - Posted: 10.07.2013

By EILEEN POLLACK Last summer, researchers at Yale published a study proving that physicists, chemists and biologists are likely to view a young male scientist more favorably than a woman with the same qualifications. Presented with identical summaries of the accomplishments of two imaginary applicants, professors at six major research institutions were significantly more willing to offer the man a job. If they did hire the woman, they set her salary, on average, nearly $4,000 lower than the man’s. Surprisingly, female scientists were as biased as their male counterparts. The new study goes a long way toward providing hard evidence of a continuing bias against women in the sciences. Only one-fifth of physics Ph.D.’s in this country are awarded to women, and only about half of those women are American; of all the physics professors in the United States, only 14 percent are women. The numbers of black and Hispanic scientists are even lower; in a typical year, 13 African-Americans and 20 Latinos of either sex receive Ph.D.’s in physics. The reasons for those shortages are hardly mysterious — many minority students attend secondary schools that leave them too far behind to catch up in science, and the effects of prejudice at every stage of their education are well documented. But what could still be keeping women out of the STEM fields (“STEM” being the current shorthand for “science, technology, engineering and mathematics”), which offer so much in the way of job prospects, prestige, intellectual stimulation and income? As one of the first two women to earn a bachelor of science degree in physics from Yale — I graduated in 1978 — this question concerns me deeply. I attended a rural public school whose few accelerated courses in physics and calculus I wasn’t allowed to take because, as my principal put it, “girls never go on in science and math.” Angry and bored, I began reading about space and time and teaching myself calculus from a book. When I arrived at Yale, I was woefully unprepared. The boys in my introductory physics class, who had taken far more rigorous math and science classes in high school, yawned as our professor sped through the material, while I grew panicked at how little I understood. The only woman in the room, I debated whether to raise my hand and expose myself to ridicule, thereby losing track of the lecture and falling further behind. © 2013 The New York Times Company

Keyword: Sexual Behavior
Link ID: 18749 - Posted: 10.05.2013

by Laura Sanders When I started to get out and about with Baby V, I occasionally experienced a strange phenomenon. Women would approach and coo some pleasant little noises. After an appropriate amount of time had passed, these strangers would lean in close and ask to smell my baby. I’m the first to admit that this sounds creepy. Truth be told, it is a little creepy. But now I completely get it. The joy from a single whiff of newborn far outweighs any trifling social conventions about personal space and body odors. So when women approach looking for a little hit of eau de bebe, I get sharey. By all means, ladies, lean in and smell away. Tiny babies smell very, very good. So good that I’m getting a little high from just thinking about how good babies smell. So good that people attempt to bottle and sell this scent (like this baby-head-scented spray— pleasant, but pales in comparison). So good that scientists really want to know why some women find this smell irresistible. Scientists recently studied the brains of women as they sniffed new baby scent. Two-day-old babies delivered the good stuff by wearing the same pajamas for two nights. Women then sniffed the odor extracted from the outfit while brain scans assessed neural activity. Overall, the 30 women in the study (who weren’t told what they were sniffing, by the way) rated the scent as mildly pleasant. As the intoxicating scent of newborn wafted into their brains, neural activity increased in areas of the brain linked to good feelings, called neostriate areas. In the brains of the 15 women who also happened to be mothers, the brain activity seemed stronger. (No word yet on what new baby smell does to dads’ brains.) © Society for Science & the Public 2000 - 2013.

Keyword: Chemical Senses (Smell & Taste); Aggression
Link ID: 18746 - Posted: 10.05.2013

Sarah C. P. Williams A person might be caught off-guard without an umbrella in a sudden downpour, but rain doesn’t catch insects by surprise. Moths, beetles, and aphids predict storms by sensing changes in air pressure and then alter their behavior, researchers have discovered. In particular, the new study finds that insects change their mating behaviors when the air pressure drops, which often precedes rain, or when the air pressure rises, which can signal strong winds. “People have observed before that birds, bats, and even fish respond to changes in [air] pressure,” says entomologist Maria Fernanda Peñaflor of the University of São Paulo in Brazil, a co-author of the new study. “This is the first time such behavior has been studied in insects.” Peñaflor and her colleagues knew that insect behavior was mediated by temperature, wind, and rainfall and wondered whether air pressure played a role as well. They first correlated air pressure data from a local meteorology station with the behavior of male cucurbit beetles (Diabrotica speciosa), green and yellow beetles about 6 millimeters long that feed on cucurbit vegetables, such as cucumbers, pumpkins, and squashes, in South America. They discovered that on days when the pressure was falling—indicating impending rain—the male beetles were less likely to walk in the direction of female pheromones, which they normally follow to pursue mates. To find out more, Peñaflor’s group collaborated with researchers at the University of Western Ontario in Canada who had a controlled pressure chamber in which they could perform experiments. © 2013 American Association for the Advancement of Science.

Keyword: Sexual Behavior
Link ID: 18738 - Posted: 10.03.2013

By WILLIAM J. BROAD SCIENCE has looked into some strange things over the centuries — reports of gargantuan sea monsters, purported images of Jesus, sightings of alien spaceships and so on. When I first heard of spontaneous orgasm, while researching a book on yoga, including its libidinal cousin, tantra, I figured it was more allegory than reality and in any event would prove beyond the reach of even the boldest investigators. Well, I was wrong. It turns out science has tiptoed around the subject for more than a century and of late has made considerable progress in determining not only the neurophysiological basis of the phenomenon but also its prevalence. Men are mentioned occasionally. But sex researchers have found that the novel type of autoerotism shows up mainly in women. Ground zero for the research is Rutgers University, where scientists have repeatedly had female volunteers put their heads into giant machines and focus their attention on erotic fantasies — the scans reveal that the pleasure centers of their brains light up in ways indistinguishable from everyday orgasms. The lab atmosphere is no-nonsense, with plenty of lights and white coats and computer monitors. Subjects often thrash about so forcefully that obtaining clear images of their brains can be difficult. “Head movement is a huge issue,” Nan Wise, a doctoral candidate at Rutgers who helps run the project, said in an interview. “It’s hard to get a decent signal.” She said a volunteer’s moving her head more than two millimeters — less than a 10th of an inch — can make for a bad day in the lab. It is easy to dismiss this as a new kind of narcissism in search of scientific respectability, a kinky pleasure coming out of the shadows. Many YouTube videos now purport to show people using controlled breathing and erotic introspection to achieve what they describe as “thinking off” and “energy orgasms.” © 2013 The New York Times Company

Keyword: Sexual Behavior; Aggression
Link ID: 18720 - Posted: 09.30.2013

by Megan Gannon, Live Science Deep in the cloud forests of Central America, two species of singing mice put on a high-pitched opera to mark their territory and stave off clashes, researchers discovered. Alston's singing mouse (Scotinomys teguina) and the Chiriqui singing mouse (S. xerampelinus) have overlapping lifestyles in the cloud forests of Costa Rica and Panama. But the tawny cousins seem to establish geographic boundaries so they can avoid competing with each other. "A long-standing question in biology is why some animals are found in particular places and not others," study researcher Bret Pasch, a postdoctoral fellow at the the University of Texas at Austin, said in a statement. "What factors govern the distribution of species across space?" As it turns out, a little communication between individuals affects the spread of both species as a whole. Both species of singing mice produce vocalizations that are barely audible to humans. As video footage of the mouse-y opera from the foggy forest floor shows, the creatures throw their heads back and belt out songs in the form of rapidly repeated notes, known as trills. The Alston's mouse in the clip even looks likes it's taking a bow after its solo. © 2013 Discovery Communications, LLC

Keyword: Aggression; Aggression
Link ID: 18712 - Posted: 09.28.2013

Mark Peplow Hormone-disrupting chemicals may be far more prevalent in lakes and rivers than previously thought. Environmental scientists have discovered that although these compounds are often broken down by sunlight, they can regenerate at night, returning to life like zombies. “The assumption is that if it’s gone, we don’t have to worry about it,” says environmental engineer Edward Kolodziej of the University of Nevada in Reno, joint leader of the study. “But we’re under-predicting their environmental persistence.” “Risk assessments have been built on the basis that light exposure is enough to break down these products,” adds Laura Vandenberg, an endocrinologist at the University of Massachusetts in Amherst who was not involved in the study. “This work undermines that idea completely.” Endocrine disruptors — pollutants that unbalance hormone systems — are known to harm fish, and there is growing evidence linking them to health problems in humans, including infertility and various cancers1. But pinpointing specific culprits from the vast array of trace chemicals in the environment has proved difficult. Indeed, concentrations of known endocrine disruptors in rivers often seem to be too low to explain harmful effects in aquatic wildlife, says Kolodziej. He and his colleague David Cwiertny, an environmental engineer at the University of Iowa in Iowa City, decided to find out whether the breakdown products of endocrine disruptors could be boosting their environmental impact. Their team focused on trenbolone acetate, a synthetic anabolic steroid used as a growth promoter in more than 20 million cattle in the United States each year (this practice is banned in the European Union). © 2013 Nature Publishing Group

Keyword: Hormones & Behavior; Aggression
Link ID: 18711 - Posted: 09.28.2013

By Bruce Bower Cartoon ghosts have scared up evidence that the ability to visualize objects in one’s mind materializes between ages 3 and 5. When asked to pick which of two mirror-image ghost cutouts or drawings fit in a ghost-shaped hole, few 3-year-olds, a substantial minority of 4-year-olds and most 5-year-olds regularly succeeded, say psychologist Andrea Frick of the University of Bern, Switzerland, and her colleagues. Girls performed as well as boys on the task, suggesting that men’s much-studied advantage over women in mental rotation doesn’t emerge until after age 5, the researchers report Sept. 17 in Cognitive Development. Mental rotation is a spatial skill regarded as essential for science and math achievement. Most tasks that researchers use to assess mental rotation skills involve pressing keys to indicate whether block patterns oriented at different angles are the same or different. That challenge overwhelms most preschoolers. Babies apparently distinguish block patterns from mirror images of those patterns (SN: 12/20/08, p. 8), but it’s unclear whether that ability enables mental rotation later in life. Frick’s team studied 20 children at each of three ages, with equal numbers of girls and boys. Youngsters saw two ghosts cut out of foam, each a mirror image of the other. Kids were asked to turn the ghosts in their heads and choose the one that would fit like a puzzle piece into a ghost’s outline on a board. Over seven trials, the ghosts were tilted at angles varying from the position of the outline. The researchers used three pairs of ghost cutouts, for a total of 21 trials. © Society for Science & the Public 2000 - 2013

Keyword: Attention; Aggression
Link ID: 18706 - Posted: 09.26.2013

By Neuroskeptic The comparative anatomy of male and female brains is an incredibly popular topic. From teachers to cartoonists, everyone’s interested in it. One supposed dude-dame dimorphism is the width of the corpus callosum, the white matter bridge that connects the brain’s left and right hemispheres. Some studies suggest that women have a larger corpus callosum, relative to overall brain size, than men. This has led to a lot of speculation about how females, with their more ‘interconnected’ brains, are therefore better at things like multitasking: The corpus callosum is 30 percent more highly developed in the female brain… allowing information to flow more easily from one side of the brain to the other, which allows a woman to focus on more than one thing at a time. However, according to Eileen Luders and colleagues, that’s all a wash, because: Differences in Brain Volume Account for Apparent Sex Differences in Callosal Anatomy It’s been argued that women’s relatively larger corpus callosa may reflect the fact that men have larger brains, on average, and that the corpus callosum is relatively smaller in larger brains. In other words, the corpus callosum difference might be a side-effect of the true gender difference (perhaps the only one) – bigger male brains overall. Luders et al confirmed this with a clever technique: they looked in a large online brain database to find some extremely small male brains, and extremely large female ones. This, the two genders were matched on total size.

Keyword: Sexual Behavior; Aggression
Link ID: 18705 - Posted: 09.26.2013

By Felicity Muth In most animals, females are generally the ones that choose the males. This is a massive generalisation (for example, it doesn’t apply in this case), but I hope people who work on this topic will forgive me for it. Generally speaking, it’s the females that get to size up the males, check out whatever trait it is that’s attractive to them (be it weight, head feather colour, ability to sing, or muscle size) and then choose who they want to mate with. However, how animals (even insects) behave when choosing mates is by no means governed by fixed rules, and is influenced by many different things. I’ve previously written about fish that will change how they court females depending on who’s watching and male crickets that will change their victory displays after fighting with another male depending on their audience. Similarly, what a female chooses in a male mate isn’t totally free from influences outside the quality of the male in question. In some species, such as the field cricket, wolf spider and cowbirds, females with more experience choose differently to naïve females. But what other things might affect what females choose? Pretty much all animals come into contact and may be infected by parasites at some point in their life. Amazingly, parasites seem to affect the mating behaviour of animals in some unusual and unexpected ways. Some parasites castrate their hosts, or change who the host wants to mate with. Others can even cause sex-role reversals, such as in the bush cricket. © 2013 Scientific American

Keyword: Sexual Behavior; Aggression
Link ID: 18667 - Posted: 09.18.2013

By PAULINE W. CHEN, M.D. One afternoon at a school not far from the hospital where I was working, a teacher opened a utility closet and found a staff member passed out on the floor. He was clutching a small bloody mass in one hand, a sharp knife in the other, she reported, a red stain spreading rapidly at his middle. He had amputated his genitals. Once he’d been brought to our emergency room and resuscitated, the man refused further treatment. Doctors and nurses, concerned that if they waited any longer to reattach the severed part the surgery might not work, took the necessary steps to deem him mentally incompetent to make such decisions. “The guy was seriously nuts,” I remember one of the doctors saying afterward. “He kept screaming that he didn’t want ‘it’ back.” For days after the successful operation, the gruesome story was all anyone at the hospital could discuss. Most of us chalked it up to his being “certifiable,” and several wondered if maybe they should have skipped the surgery. “After all,” said one clinician, “isn’t that what he wanted?” But in all the chatter none of us mentioned a key part of the patient’s story: the unbearable suffering that must have pushed him to commit so brutal an act. In fact, anyone overhearing our conversations might have been hard pressed to find any of the warmth and sensitivity we routinely displayed toward patients with cancer, AIDS or heart disease. I remembered the man and our reactions this past week while reading “Falling Into the Fire: A Psychiatrist’s Encounters With the Mind in Crisis,” a thought-provoking new book by Dr. Christine Montross. Of all the afflictions that fall upon us, few remain as misunderstood and stigmatized as those that affect the mind. Copyright 2013 The New York Times Company

Keyword: Schizophrenia; Aggression
Link ID: 18648 - Posted: 09.16.2013

By GINA KOLATA It is the scourge of many a middle-aged man: he starts getting a pot belly, using lighter weights at the gym and somehow just doesn’t have the sexual desire of his younger years. The obvious culprit is testosterone, since men gradually make less of the male sex hormone as years go by. But a surprising new answer is emerging, one that doctors say could reinvigorate the study of how men’s bodies age. Estrogen, the female sex hormone, turns out to play a much bigger role in men’s bodies than previously thought, and falling levels contribute to their expanding waistlines just as they do in women’s. The discovery of the role of estrogen in men is “a major advance,” said Dr. Peter J. Snyder, a professor of medicine at the University of Pennsylvania, who is leading a big new research project on hormone therapy for men 65 and over. Until recently, testosterone deficiency was considered nearly the sole reason that men undergo the familiar physical complaints of midlife. The new frontier of research involves figuring out which hormone does what in men, and how body functions are affected at different hormone levels. While dwindling testosterone levels are to blame for middle-aged men’s smaller muscles, falling levels of estrogen regulate fat accumulation, according to a study published Wednesday in The New England Journal of Medicine, which provided the most conclusive evidence to date that estrogen is a major factor in male midlife woes. And both hormones are needed for libido. “Some of the symptoms routinely attributed to testosterone deficiency are actually partially or almost exclusively caused by the decline in estrogens,” said Dr. Joel Finkelstein, an endocrinologist at Harvard Medical School and the study’s lead author, in a news release on Wednesday. © 2013 The New York Times Company

Keyword: Obesity; Aggression
Link ID: 18637 - Posted: 09.12.2013

Sarah Zhang Fathers with smaller testes are more involved in child care, and their brains are also more responsive when looking at photos of their own children, according to research published online today in the Proceedings of the National Academy of Sciences1. Evolutionary biologists have long observed a trade-off in male primates between mating efforts to produce more offspring and the time males spend caring for their progeny. For instance, male chimpanzees, which are especially promiscuous, sport testes that are twice as big as those of humans, make a lot of sperm and generally do not provide paternal care. By contrast, male gorillas have relatively small testes and protect their young. The latest study suggests that humans, whose paternal care varies widely, show evidence of both approaches. The analysis1 incorporates measures of testicular volume, brain activity and paternal behaviour, notes Peter Gray, an anthropologist at the University of Nevada, Las Vegas, who was not involved in the study. “We’ve got something that pulls those strands together, and it does so in a really interesting way.” The research team — led by James Rilling, an anthropologist at Emory University in Atlanta, Georgia — set out to investigate why some fathers are more involved in child care than others. The researchers recruited 70 fathers of children aged between one and two years, and scanned the men’s brains and testes in a magnetic resonance imaging (MRI) machine. The fathers and the children's mothers also filled out surveys rating the fathers' commitment to child care. © 2013 Nature Publishing Group

Keyword: Sexual Behavior; Aggression
Link ID: 18629 - Posted: 09.10.2013

By BENJAMIN EWEN-CAMPEN This may seem obvious. But in evolutionary terms, the benefits of sexual reproduction are not immediately clear. Male rhinoceros beetles grow huge, unwieldy horns half the length of their body that they use to fight for females. Ribbon-tailed birds of paradise produce outlandish plumage to attract a mate. Darwin was bothered by such traits, since his theory of evolution couldn’t completely explain them (“The sight of a feather in a peacock’s tail, whenever I gaze at it, makes me feel sick!” he wrote to a friend). Moreover, sex allows an unrelated, possibly inferior partner to insert half a genome into the next generation. So why is sex nearly universal across animals, plants and fungi? Shouldn’t natural selection favor animals that forgo draining displays and genetic roulette and simply clone themselves? Yes and no. Many animals do clone themselves; certain sea anemones can bud identical twins from the sides of their bodies. Aphids, bees and ants can reproduce asexually. Virgin births sometimes occur among hammerhead sharks, turkeys, boa constrictors and komodo dragons. But nearly all animals engage in sex at some point in their lives. Biologists say that the benefits of sex come from the genetic rearrangements that occur during meiosis, the special cell division that produces eggs and sperm. During meiosis, combinations of the parents’ genes are broken up and reconfigured into novel arrangements in the resulting sperm and egg cells, creating new gene combinations that might be advantageous. © 2013 Salon Media Group, Inc.

Keyword: Sexual Behavior; Aggression
Link ID: 18571 - Posted: 08.28.2013

By Felicity Muth Humans love their victory displays. You only have to watch a game of football (or soccer to US-readers) to see some victory displays of the most ridiculous kind. Why do people do such things? If there was no crowd there, it is unlikely that they would perform such displays. But is it for the sake of the sex they are wishing to attract, or perhaps to put people they are competing with in no doubt of their accomplishment? Other animals, of course, also compete with each other, for food, resources and mates. And, like humans, how they behave once they win or lose a competition may depend on who’s around to see it. Male spring crickets fight with each other for territories and females Male spring field crickets fight with other males. The winners tend to do a lot better with the lady crickets, as the winners may gain the best territory, and because females of this species prefer dominant males. Now for the part that may surprise you: the males that win these fights will perform a victory display just like humans – after beating another male, the male winner performs an aggressive song and jerks his body in a particular way to show off that he’s won this fight. But, like with humans, the question arises: why do males do these victory displays? Is it to show the loser male that he has lost, or to show other males and females that he’s won? © 2013 Scientific American

Keyword: Sexual Behavior; Aggression
Link ID: 18569 - Posted: 08.27.2013

By Jessica Shugart Sometimes it pays to be mediocre. A new study shows that sheep with a 50/50 blend of genes for small and big horns pass along more of their genes over a lifetime than their purely big-horned brethren, who mate more often. The finding offers rare insight into an enduring evolutionary paradox—why some traits persist despite creating a reproductive disadvantage. The results, published online August 21 in Nature, reveal that while big-horned sheep mated most successfully each season, small-horned sheep survived longer. Rams who inherited one of each type of gene from their parents got the best of both worlds: they lived longer than bigger-horned sheep and mated more successfully than those with the smallest horns. As a result, middle-of-the-road sheep passed on more of their genes over time. “They’re the fittest of them all,” says Jon Slate of the University of Sheffield in Scotland, who led the study. “This is a marvelous combination of using the most modern tools available to confirm classic older views of sexual selection,” says evolutionary geneticist Allen Moore of the University of Georgia in Athens, who was not involved in the study. Traits such as bold peacock feathers and giant antlers evolved to garner the attention of prospective females and boost reproductive success. Yet if each generation of females continues to pick the most stellar males, Charles Darwin wondered, how do sub-par versions of a trait continue to persist? “It’s something that has preoccupied evolutionary biologists ever since,” Slate says. © Society for Science & the Public 2000 - 2013

Keyword: Evolution; Aggression
Link ID: 18550 - Posted: 08.22.2013

By Patrick Cooney The Disney film Finding Nemo lied to your kids! The people at Disney would simply argue that they altered reality to create a more entertaining storyline, but read below for the true story, and you tell me which you think is more entertaining. How Finding Nemo started: Father and mother clownfish are tending to their clutch of eggs at their sea anemone when the mother is eaten by a barracuda. Nemo is the only surviving egg, and he grows up in his father’s anemone before getting lost on a crazy adventure! How Finding Nemo should have started if it were biologically accurate: Father and mother clownfish are tending to their clutch of eggs at their sea anemone when the mother is eaten by a barracuda. Nemo hatches as an undifferentiated hermaphrodite (as all clownfish are born) while his father transforms into a female clownfish now that his female mate is dead. Since Nemo is the only other clownfish around, he becomes male and mates with his father (who is now female). Should his father die, Nemo would change into a female clownfish and mate with another male. Although a much different storyline, it still sounds like a crazy adventure! As you can see, the first minute of Finding Nemo, outside of the talking fish part, is the only biologically accurate part of the movie. Considering that Disney demonstrated reproduction and the killing of the mother in the first minute of the movie, how did it decide that a natural sex change is outside the bubble of viewable material? © 2013 The Slate Group, LLC

Keyword: Sexual Behavior
Link ID: 18549 - Posted: 08.22.2013

by Ed Yong In the image above, all the eggs in the top row are laid by cuckoos and those in the bottom row belong to their victims. These uncanny similarities help cuckoos to fob off their parental duties by laying their eggs in the nests of other species. If the hosts can’t tell the difference between their eggs and the foreign ones, they’ll end up raising the cuckoo chick as their own. And they pay a hefty price for their gullibility, since cuckoo chicks often kill or outcompete their foster siblings. The relationship between cuckoos and their hosts is a classic example of an evolutionary arms race. Cuckoos, should evolve eggs that more closely match those of their hosts, while the hosts should evolve keener senses to discriminate between their own eggs and a cuckoo’s. The greater honeyguide isn’t a cuckoo but uses the same tactics—it parasitises the nests of little bee-eaters by laying eggs of the same size and shape. But this mimicry doesn’t help it to fool the bee-eaters, which seem to accept any old egg no matter how different it looks. Instead, Claire Spottiswoode from the University of Cambridge has found that the parasitic honeyguides are fighting an evolutionary arms race against… each other. Bee-eaters build their nests underground, usually within abandoned aardvark burrows. When honeyguides invade, they’ll puncture the bee-eater’s eggs before laying their own. This kills some of the eggs outright and weakens others. If any chicks survive to hatching, they’re finished off by the honeyguide chick, which stabs its foster siblings to death with a vicious hooked bill.

Keyword: Sexual Behavior; Aggression
Link ID: 18538 - Posted: 08.21.2013