Chapter 12. Sex: Evolutionary, Hormonal, and Neural Bases
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By Chelsea Whyte It was a gruesome scene. The body had severe wounds and was still bleeding despite having been lying for a few hours in the hot Senegalese savanna. The murder victim, a West African chimpanzee called Foudouko, had been beaten with rocks and sticks, stomped on and then cannibalised by his own community. This is one of just nine known cases where a group of chimpanzees has killed one of their own adult males, as opposed to killing a member of a neighbouring tribe. These intragroup killings are rare, but Michael Wilson at the University of Minnesota says they are a valuable insight into chimp behaviour such as male coalition building. “Why do these coalitions sometimes succeed, but not very often? It’s at the heart of this tension between conflict and cooperation, which is central to the lives of chimpanzees and even to our own,” he says. Chimps usually live in groups with more adult females than males, but in the group with the murder it was the other way round. “When you reverse that and have almost two males per every female — that really intensifies the competition for reproduction. That seems to be a key factor here,” says Wilson. Jill Pruetz at Iowa State University, who has been studying this group of chimpanzees in south-eastern Senegal since 2001, agrees. She suggests that human influence may have caused this skewed gender ratio that is likely to have been behind this attack. In Senegal, female chimpanzees are poached to provide infants for the pet trade. Fall from power Thirteen years ago, Foudouko reigned over one of the chimp clans at the Fongoli study site, part of the Fongoli Savanna Chimpanzee Project. As alpha male, he was “somewhat of a tyrant”, Pruetz says. © Copyright Reed Business Information Ltd.
Nicola Davis Girls as young as six years old believe that brilliance is a male trait, according research into gender stereotypes. The US-based study also found that, unlike boys, girls do not believe that achieving good grades in school is related to innate abilities. Andrei Cimpian, a co-author of the research from New York University, said that the work highlights how even young children can absorb and be influenced by gender stereotypes – such as the idea that brilliance or giftedness is more common in men. Are gendered toys harming childhood development? Read more “Because these ideas are present at such an early age, they have so much time to affect the educational trajectories of boys and girls,” he said. Writing in the journal Science, researchers from three US universities describe how they carried out a range of tests with 400 children, half of whom were girls, to probe the influence of gender stereotypes on children’s notions of intelligence and ability. In the first test, a group of 96 boys and girls of ages five, six and seven, were read a story about a highly intelligent person, and were asked to guess the person’s gender. They were then presented with a series of pictures showing pairs of adults, some same-sex, some opposite sex, and were asked to pick which they thought was highly intelligent. Finally, the children were asked to match certain objects and traits, such as “being smart”, to pictures of men and women. © 2017 Guardian News and Media Limited
By NATALIE ANGIER Whether personally or professionally, Daniel Kronauer of Rockefeller University is the sort of biologist who leaves no stone unturned. Passionate about ants and other insects since kindergarten, Dr. Kronauer says he still loves flipping over rocks “just to see what’s crawling around underneath.” In an amply windowed fourth-floor laboratory on the east side of Manhattan, he and his colleagues are assaying the biology, brain, genetics and behavior of a single species of ant in ambitious, uncompromising detail. The researchers have painstakingly hand-decorated thousands of clonal raider ants, Cerapachys biroi, with bright dots of pink, blue, red and lime-green paint, a color-coded system that allows computers to track the ants’ movements 24 hours a day — and makes them look like walking jelly beans. The scientists have manipulated the DNA of these ants, creating what Dr. Kronauer says are the world’s first transgenic ants. Among the surprising results is a line of Greta Garbo types that defy the standard ant preference for hypersociality and instead just want to be left alone. The researchers also have identified the molecular and neural cues that spur ants to act like nurses and feed the young, or to act like queens and breed more young, or to serve as brutal police officers, capturing upstart nestmates, spread-eagling them on the ground and reducing them to so many chitinous splinters. Dr. Kronauer, who was born and raised in Germany and just turned 40, is tall, sandy-haired, blue-eyed and married to a dentist. He is amiable and direct, and his lab’s ambitions are both lofty and pragmatic. “Our ultimate goal is to have a fundamental understanding of how a complex biological system works,” Dr. Kronauer said. “I use ants as a model to do this.” As he sees it, ants in a colony are like cells in a multicellular organism, or like neurons in the brain: their fates joined, their labor synchronized, the whole an emergent force to be reckoned with. © 2017 The New York Times Company
written by Claire Lehmann I learned about Debra through reading her LA Times op-ed on the futility of gender neutral parenting. I got in touch with Debra because I wanted to learn more about her field of sex neuroscience, her own research and her thoughts on studying sex differences in the brain. Because the study of sex and sex differences is often fraught with political roadblocks, I also wanted to get a picture of how a neuroscientist-sex researcher approaches some of these contentious issues. Hi Debra, thanks for chatting to Quillette. Can you briefly tell us who you are — where you studied, who was your supervisor and what made you interested in neuroscience, in particular sex neuroscience? I am a sex researcher at York University in Toronto and I write about the science of sex for several media outlets, including Playboy. For my PhD, which I just defended, I worked with Dr. Keith Schneider, who has pioneered new methods in high-resolution fMRI and is the Director of the University of Delaware’s Center for Biomedical and Brain Imaging, and Dr. James Cantor at the University of Toronto, who is a world expert in the brain imaging of pedophilia. I remember opening up a textbook during my first neuroscience course as an undergraduate student, seeing images from an fMRI study, and thinking it was incredible. I decided to pursue neuroscience in grad school and had the opportunity to do a placement in sexology as part of my Master’s degree. That’s how I got hooked! And I haven’t looked back. © 2017 Quillette
In the mood? Feeling sexy and romantic has been linked to a hormone named kisspeptin. Researchers hope the chemical may help treat people with some sexual problems. Kisspeptin occurs naturally in the body, where it stimulates the release of other signalling chemicals that have been linked to reproduction. Now a study of 29 heterosexual young men has found that injections of the hormone enhance the brain’s response to sexual and romantic pictures of couples. After injection, MRI scans showed increased activity in the regions of the brain that are usually stimulated by sexual arousal and romance. But this activity was only prompted by arousing pictures – non-sexy images did not have the same effect. “Our findings indicate that kisspeptin could play a role in stimulating some of the emotions and responses that lead to sex and reproduction,” says Waljit Dhillo, at Imperial College London. “Ultimately, we are keen to look into whether kisspeptin could be an effective treatment for psychosexual disorders.” The team now plans to study the effects of the hormone in a larger group of people, including women as well as men. Journal reference: Journal of Clinical Investigation © Copyright Reed Business Information Ltd.
By NANCY L. SEGAL and SATOSHI KANAZAWA In 1973, the biologist Robert Trivers and the computer scientist Dan Willard made a striking prediction about parents and their offspring. According to the principles of evolutionary theory, they argued, the male-to-female ratio of offspring should not be 50-50 (as chance would dictate), but rather should vary as a function of how good (or bad) the conditions are in which the parents find themselves. Are the parents’ resources plentiful — or scarce? The Trivers-Willard hypothesis holds that when their conditions are good, parents will have more male offspring: Males with more resources are likely to gain access to more females, thereby increasing the frequency with which their genes (and thus their parents’ genes) are preserved in future generations. Conversely, male offspring that lack resources are likely to lose out to males that have more resources, so in bad conditions it pays for parents to “invest” more in daughters, which will have more opportunities to mate. It follows, as a kind of corollary, that when parents have plentiful resources they will devote those resources more to their sons, whereas when resources are scarce, parents will devote them more to their daughters. In short: If things are good, you have more boys, and give them more stuff. If things are bad, you have more girls, and give more of your stuff to them. Is this hypothesis correct? In new research of ours, to be published in the April issue of The Journal of Experimental Child Psychology, we suggest that in the case of breast-feeding, at least, it appears to be. In recent years, evidence has emerged suggesting that in various mammalian species, breast milk — which is, of course, a resource that can be given to children — is tailored for the sex of each offspring. For example, macaque monkey mothers produce richer milk (with higher gross energy and fat content) for sons than for daughters, but also provide greater quantities of milk and higher concentrations of calcium for daughters than for sons. © 2017 The New York Times Company
By Alice Klein Who needs men? A female shark separated from her long-term mate has developed the ability to have babies on her own. Leonie the zebra shark (Stegostoma fasciatum) met her male partner at an aquarium in Townsville, Australia, in 1999. They had more than two dozen offspring together before he was moved to another tank in 2012. From then on, Leonie did not have any male contact. But in early 2016, she had three baby sharks. Intrigued, Christine Dudgeon at the University of Queensland in Brisbane, Australia, and her colleagues began fishing for answers. Zoologger: The amphibious fish that mates with itself One possibility was that Leonie had been storing sperm from her ex and using it to fertilise her eggs. But genetic testing showed that the babies only carried DNA from their mum, indicating they had been conceived via asexual reproduction. Some vertebrate species have the ability to reproduce asexually even though they normally reproduce sexually. These include certain sharks, turkeys, Komodo dragons, snakes and rays. However, most reports have been in females who have never had male partners. There are very few reports of asexual reproduction occurring in females with previous sexual histories, says Dudgeon. An eagle ray and a boa constrictor, both in captivity, are the only other female animals that have been documented switching from sexual to asexual reproduction. © Copyright Reed Business Information Ltd.
Keyword: Sexual Behavior
Link ID: 23110 - Posted: 01.17.2017
By Virginia Morell Only three known species go through menopause: killer whales, short-finned pilot whales, and humans. Two years ago, scientists suggested whales do this to focus their attention on the survival of their families rather than on birthing more offspring. But now this same team reports there’s another—and darker—reason: Older females enter menopause because their eldest daughters begin having calves, leading to fights over resources. The findings might also apply to humans, the scientists say. “What an interesting paper,” says Phyllis Lee, a behavioral ecologist at the University of Stirling in the United Kingdom, who was not involved in the study. “It brings two perspectives on menopause neatly together, and provides an elegant model for its rarity.” The new work came about when Darren Croft, a behavioral ecologist at the University of Exeter in the United Kingdom, and his colleagues looked back on their 2015 killer whale menopause study. “That showed how they helped and why they lived so long after menopause, but it didn’t explain why they stop reproducing,” he says, noting that in other species, such as elephants, older females also share wisdom and knowledge with their daughters, but continue to have calves. © 2017 American Association for the Advancement of Science.
By Alice Klein Mothers hold their children more on the left and wild mammals seem to keep their young more on that so too, at least when fleeing predators. Now it seems many mammal babies prefer to approach their mother from one side too – and the explanation may lie in the contrasting talents of each half of the brain. In mammals, the brain’s right hemisphere is responsible for processing social cues and building relationships. It is also the half of the brain that receives signals from the left eye. Some researchers think this explains why human and ape mothers tend to cradle their babies on the left: it is so they can better monitor their facial expressions with their left eye. Now, Janeane Ingram at the University of Tasmania, Australia, and her colleagues have looked at whether animal infants also prefer to observe their mum from one side. The team studied 11 wild mammals from around the world: horses, reindeer, antelopes, oxen, sheep, walruses, three species of whale and two species of kangaroo. Whenever an infant approached its mother from behind, the researchers noted whether it positioned itself on its mum’s left or right side. They recorded almost 11,000 position choices for 175 infant-mother pairs. Infants of all species were more likely to position themselves so that their mother was on their left. This happened about three-quarters of the time. © Copyright Reed Business Information Ltd.
By Virginia Morell Japanese macaques and sika deer live comfortably together on Japan’s Yakushima Island: The deer eat fruit the monkeys drop from the trees, and the monkeys groom and sometimes hitch a ride on the deer. But a couple years ago, one of the macaques took this relationship to a new level. Unable to get a mate of his own kind, this low-ranking snow monkey used the deer’s back for his pleasure (as pictured, and also shown in this not-suitable-for-work video). He did not penetrate her, but did ejaculate, and the deer then licked her back clean, researchers report in the current issue of Primates. The monkey was later seen attempting to mount another deer, but she objected and threatened him. He also guarded his unlikely love interests, chasing away any other male monkeys who came near. Scientists have only reported one other case of sexual relations in the wild between unrelated species. That one involved male Antarctic fur seals coercing king penguins; once, after sating his lust, the seal ate the bird. In both cases, scientists suspect that the males were unable to acquire a mate of their own kind, and seasonal hormonal surges led them to seek love elsewhere. © 2017 American Association for the Advancement of Science.
Keyword: Sexual Behavior
Link ID: 23074 - Posted: 01.10.2017
By Ellen Hendriksen Pop quiz: what’s the first thing that comes to mind when I say “ADHD”? a. Getting distracted b. Ants-in-pants c. Elementary school boys d. Women and girls Most likely, you didn’t pick D. If that’s the case, you’re not alone. For most people, ADHD conjures a mental image of school-aged boys squirming at desks or bouncing off walls, not a picture of adults, girls, or especially adult women. Both scientists and society have long pinned ADHD on males, even though girls and women may be just as likely to suffer from this neurodevelopmental disorder. Back in 1987, the American Psychiatric Association stated that the male to female ratio for ADHD was 9 to 1. Twenty years later, however, an epidemiological study of almost 4,000 kids found the ratio was more like 1 to 1—half girls, half boys. © 2017 Scientific American
National Institutes of Health (NIH) researchers have discovered molecular mechanisms that may underlie a woman’s susceptibility to disabling irritability, sadness, and anxiety in the days leading up to her menstrual period. Such premenstrual dysphoric disorder (PMDD) affects 2 to 5 percent of women of reproductive age, whereas less severe premenstrual syndrome (PMS) is much more common. “We found dysregulated expression in a suspect gene complex which adds to evidence that PMDD is a disorder of cellular response to estrogen and progesterone,” explained Peter Schmidt, M.D. of the NIH’s National Institute of Mental Health, Behavioral Endocrinology Branch. “Learning more about the role of this gene complex holds hope for improved treatment of such prevalent reproductive endocrine-related mood disorders.” Schmidt, David Goldman, M.D., of the NIH’s National Institute on Alcohol Abuse and Alcoholism, and colleagues, report on their findings January 3, 2017 in the journal Molecular Psychiatry. “This is a big moment for women’s health, because it establishes that women with PMDD have an intrinsic difference in their molecular apparatus for response to sex hormones – not just emotional behaviors they should be able to voluntarily control,” said Goldman. By the late 1990s, the NIMH team had demonstrated (link is external) that women who regularly experience mood disorder symptoms just prior to their periods were abnormally sensitive to normal changes in sex hormones — even though their hormone levels were normal. But the cause remained a mystery.
By Alice Callahan Can psychiatric medications alter the mother-baby bond? I am having a baby in a month and am on an antidepressant, antipsychotic and mood stabilizer. I don't feel a natural instinct to mother or connect to my baby yet. Could it be because of my medications? It’s normal for expectant parents to worry if they don’t feel a strong connection to the baby right away. “Those kinds of mixed fears and anxieties are really common in most pregnancies, certainly first pregnancies,” said Dorothy Greenfeld, a licensed clinical social worker and professor of obstetrics and gynecology at Yale School of Medicine. Bonding is a process that takes time, and while it can begin in pregnancy, the relationship between parent and child mostly develops after birth. Psychiatric conditions, and the medicines used to treat them, can complicate the picture. Antidepressants, the most widely used class of psychiatric drugs, do not seem to interfere with a woman’s attachment to the fetus during pregnancy, as measured by the amount of time the mother spends thinking about and planning for the baby, a 2011 study in the Archives of Women’s Mental Health found. On the other hand, the study found that women with major depression in pregnancy had lower feelings of maternal-fetal attachment, and this sense of disconnection intensified with more severe symptoms of depression. “Depression can definitely affect a person’s ability to bond with their baby, to feel those feelings of attachment, which is why we encourage treatment so strongly,” said Dr. Amy Salisbury, the study leader and a professor of pediatrics and psychiatry at the Alpert Medical School at Brown University. “That’s more likely to interfere than the medication itself.” There is less research on the effects of other types of mental health medications on mother-baby bonding, but psychiatric medications can have side effects that might interfere with parenting. For example, a small percentage of people taking mood-stabilizing medications have feelings of apathy, and that could hinder the bonding process, said Dr. Salisbury. And some mental health medications, depending on dosage and combination, might make a person feel too sedated. But again, letting mental illness go untreated is likely far riskier for both the mother and the baby. © 2016 The New York Times Company
By Laura Beil, Justin Shamoun began to hate his body a few weeks into seventh grade. He was a year younger than his suburban Detroit classmates, having skipped a grade. Many of his peers were entering puberty, their bodies solidifying into sleek young men. Justin still had the doughy build of a boy. After gym class one day, someone told Justin he could probably run faster if he weren’t so fat. The remark crushed him. Ashamed, he started hiding his body under ever-baggier clothes and making excuses to skip P.E., the pool, anywhere required to expose bare skin. Finally, he decided to fix himself. He dove headlong into sports and cut back on food. Before long, he was tossing his lunch into the garbage and picking at his dinner. He ate just enough to blunt his hunger, until the time came when he ate barely at all. The thought that he had an eating disorder never occurred to him. Long considered an affliction of women, eating disorders — the most deadly of all mental illnesses — are increasingly affecting men. The National Eating Disorders Association predicts that 10 million American men alive today will be affected, but that number is only an estimate based on the limited research available. The official criteria for diagnosing eating disorders were updated to be more inclusive of men only in 2013. And last year, Australian researchers writing in the Journal of Eating Disorders noted that “the prevalence of extreme weight control behaviors, such as extreme dietary restriction and purging” may be increasing at a faster rate in men than women. © 2016 Scientific American
By Heather M. Snyder For more than 25 years, Mary Read was a successful nurse in Lititz, Pennsylvania. But in 2010, at the age of 50, she started having trouble with her memory and thinking, making it difficult for her to complete routine tasks and follow instructions at work. The problems worsened, bringing her career to an abrupt end. In 2011, her doctor conducted a comprehensive evaluation, including a cognitive assessment, and found that she was in the early stages of younger-onset Alzheimer’s, which affects hundreds of thousands of people under 65. A year earlier, Elizabeth Wolf faced another sort of upheaval. The 36-year-old community health program director was forced to abandon her own career, home and community in Vermont when both of her parents were diagnosed with Alzheimer’s three months apart. Wolf took the difficult decision to move back into her childhood home in Mount Laurel, New Jersey in order to become their primary caregiver. These stories are not unusual. Alzheimer’s dementia disproportionately affects women in a variety of ways. Compared with men, 2.5 times as many women as men provide 24-hour care for an affected relative. Nearly 19 percent of these wives, sisters and daughters have had to quit work to do so. In addition, women make up nearly two-thirds of the more than 5 million Americans living with Alzheimer’s today. According to the Alzheimer’s Association 2016 Alzheimer’s Disease Facts and Figures, an estimated 3.3 million women aged 65 and older in the United States have the disease. To put that number in perspective, a woman in her sixties is now about twice as likely to develop Alzheimer’s as breast cancer within her lifetime. © 2016 Scientific American
Morwenna Ferrier Is my face attractive? Don’t answer that. Not because I’m ducking out of this, but because you can’t. Attractiveness is subjective, perhaps the most subjective question of all; that we outsource the answer to Google (and we do, in our droves) is ironic since it depends on a bias that is impossible to unpack. Yet in searching the internet for an answer, it also reveals the question to be one of the great existential tensions of our time. Because, as we all know, being attractive is absolutely 100% the A-road to happiness. If you are Googling to rate your attractiveness, then you are probably working on the assumption that you aren’t. You’re also, possibly, more vulnerable and susceptible to being told that you aren’t. In short, you’re a sitting duck, someone who had a sore throat and who asked good old Dr Google for advice only to be told it was cancer. Still, it’s only in investigating precisely why Google is the last person you should ask – being a search engine therefore insentient – that you can start cobbling together an idea of what attractiveness really is. It’s worth starting with semantics. Beauty is not attractiveness and vice versa, though we commonly confuse the two. Beauty (arguably) has a template against which we intuit and against which we measure ourselves. It is hinged around genetics and a particular look associated with this politically correct (and largely western-governed) model. Darwin wouldn’t agree: “It is certainly not true that there is in the mind of man any universal standards of beauty with respect to the human body,” he said. But a lot has changed since his time. © 2016 Guardian News and Media Limited
Keyword: Sexual Behavior
Link ID: 23030 - Posted: 12.28.2016
Laura Sanders Pregnancy changes nearly everything about an expectant mother’s life. That includes her brain. Pregnancy selectively shrinks gray matter to make a mom’s brain more responsive to her baby, and those changes last for years, scientists report online December 19 in Nature Neuroscience. “This study, coupled with others, suggests that a women’s reproductive history can have long-lasting, possibly permanent changes to her brain health,” says neuroscientist Liisa Galea of the University of British Columbia in Vancouver, who was not involved in the study. Researchers performed detailed anatomy scans of the brains of 25 women who wanted to get pregnant with their first child. More scans were performed about two months after the women gave birth. Pregnancy left signatures so strong that researchers could predict whether women had been pregnant based on the changes in their brains. The women who had carried a child and given birth had less gray matter in certain regions of their brains compared with 20 women who had not been pregnant, 19 first-time fathers and 17 childless men. These changes were still evident two years after pregnancy. A shrinking brain sounds bad, but “reductions in gray matter are not necessarily a bad thing,” says study coauthor Elseline Hoekzema, a neuroscientist at Leiden University in the Netherlands. A similar reduction happens during adolescence, a refinement that is “essential for a normal cognitive and emotional development,” says Hoekzema, who, along with colleagues, did most of the work at Universitat Autònoma de Barcelona. Following those important teenage years, pregnancy could be thought of almost as a second stage of brain maturing, she says. |© Society for Science & the Public 2000 - 2016.
By Claire Asher We pride ourselves on our big brains, but when it comes to figuring out whether people or other animals with particularly big brains do better than others, the evidence has been lacking. Now, for the first time, a study in red deer is showing that bigger brained mammals tend to be more successful in the wild, and that brain size is a heritable trait that they can pass on to their offspring. Corina Logan from the University of Cambridge and her team have looked at the skulls of 1314 red deer (Cervus elaphus) from the Isle of Rum. The complete life histories of the deer are well known thanks to the Isle of Rum Red Deer Project, which has been collecting data on the island for more than 40 years, spanning seven deer generations. “This kind of study has not been conducted before because it requires long-term data from a large number of individuals,” says Logan. Heritable heads The team found that the ratio of skull volume to body size was highly heritable, explaining 63 per cent of variation between individuals. Female deer with larger skulls lived significantly longer and raised more offspring to adulthood, though it’s not clear yet why bigger brains are advantageous to females. © Copyright Reed Business Information Ltd.
By Sam Wong Size matters. Bigger genitals mean more mating success for male mosquito fish, a relative of the guppy. But the development of longer male organs prompts females to evolve bigger brains to help them escape overeager mates. Mating among mosquito fish is far from romantic. The male makes no effort to court partners, instead sneaking up and attempting to copulate by force up to a thousand times a day. It uses a modified anal fin, the gonopodium, to deliver sperm into the female. In this sort of mating system, the relationship between males and females can resemble that between predators and prey, which commonly involve an evolutionary arms race where adaptations on one side are closely matched by changes on the other. For example, big-brained predators tend to prey on big-brained prey, as the two try to outsmart each other. Séverine Buechel and colleagues at Stockholm University in Sweden wondered if a similar arms race was going on between male and female mosquito fish. Do females evolve bigger brains to defend against sneaky males, and do males evolve bigger brains in response? To test this, the team looked at what happened to brain size when males were bred to have longer gonopodia. Male mosquito fish have long gonopodia compared with related species in which coercion is not the dominant mating strategy, and males with longer gonopodia tend to be more successful at mating. The researchers found that breeding more well-endowed males led to bigger-brained females. But there was no arms race: male brains didn’t get bigger at the same time. © Copyright Reed Business Information Ltd.
Barbara J. King Birdsong is music to human ears. It has inspired famous composers. For the rest of us, it may uplift the spirit and improve attention or simply be a source of delight, fun and learning. But have you ever wondered what birds themselves hear when they sing? After all, we know that other animals' perceptions don't always match ours. Anyone who lives with a dog has probably experienced their incredible acute hearing and smell. Psychologists Robert J. Dooling and Nora H. Prior think they've found an answer to that question — for, at least, some birds. In an article published online last month in the journal Animal Behaviour, they conclude that "there is an acoustic richness in bird vocalizations that is available to birds but likely out of reach for human listeners." Dooling and Prior explain that most scientific investigations of birdsong focus on things like pitch, tempo, complexity, structural organization and the presence of stereotypy. They instead focused on what's called temporal fine structure and its perception by zebra finches. Temporal fine structure, they write, "is generally defined as rapid variations in amplitude within the more slowly varying envelope of sound." Struggling to fully grasp that definition, I contacted Robert Dooling by email. In his response, he suggested that I think of temporal fine structure as "roughly the difference between voices when they are the same pitch and loudness." Temporal fine structure is akin, then, to timbre, sometimes defined as "tone color" or, in Dooling's words, the feature that's "left between two complex sounds when the pitch and level are equalized." © 2016 npr