Why do parrots have the ability to mimic?

Why do parrots have the ability to mimic? 

Parrots are not equally vocal, and many species likely imitate for different reasons. For example, African grey parrots in the wild are known to imitate other species of birds. My own observations of Amazon parrots from Mexico to Guyana to Peru revealed only imitations of each parrot's own species (and their own local dialects). When parrots are kept as pets, they learn their calls from their adoptive human social partners. Part of their appeal as pets is their ability to sing lower notes than smaller birds and so better reproduce human voices. In the wild, though, their calls may go much higher in pitch and much faster in tempo than any human tutor's voice. Regrettably, our desire for pet parrots has led to population declines of many species in their wild habitats.

But why do parrots and other birds rely on learning for vocal development instead of having each call developmentally hardwired, as with many other birds and animals? Some benefits of learning may include development of context-specific calls. Imitative vocal learning is also a reliable social display of neural functions—requiring good hearing, memory and muscle control for sound production—that may be under consideration by a potential mate or ally.

One consequence of vocal imitation is that local dialects can arise. In some cases, these regional calls may help males and females from similar areas find each other—or perhaps avoid each other. Song learning in some bird species allows territorial neighbors to know each other and helps to distinguish drifters from local territory holders. In an experimental captive population of budgerigars (small parrots from Australia, often referred to as parakeets), contact calls converged in a seeming adoption of a clan label. One study reports that budgerigars seemed to use call similarity in judging mates.

Playback studies of geographic dialects from wild parrot populations have shown that birds react more strongly to their local tongue. Maybe this is the best reason for these parrots to imitate: to better command the attention of a potential listener by producing sounds for which the listener already has a memory (or a "neural template"). The existence of a preformed perceptual template in the listener makes another parrot's imitations of him or her easier to perceive in a noisy environment. Imitations may even be directed to specific intended receivers.

Parrots, however, are not the only birds that learn by imitation. Indian mynah birds are also famed for their imitative capabilities, and in the U.S., northern mockingbirds sing repeated phrases with bits of calls appropriated from blue jays, robins, cardinals and other birds. These utterances are used in the springtime displays that inspired their common name as well as their scientific one: Mimus polyglottus.

The comparative study of parrots, and other vocally imitative animals, will help us to understand how evolution shapes neural mechanisms for complex social communication. Sadly, habitat loss and capture for the pet trade have pushed many parrot species to the brink of extinction. Parrots' great facility for learning (and the dialect variation it produces) underscores the need to save endangered species as whole populations, with their historically informative vocal traditions intact.

New Research Yields Clues about Makeup of Cancer Cells

New Research Yields Clues about Makeup of Cancer Cells

Two studies take different approaches to solving the problem of distinguishing cancerous from healthy cells, paving the way for earlier diagnosis and treatment 

 
CLUES: An atomic force microscope (AFM) "feels" the cells, by pushing against a cell's surface to determine its degree of softness.

 
CONNECTED: When an AFM is connected to an optical microscope, the two can be used to perform nanomechanical analysis of cancer and normal cells.

Breast cancer has proved especially difficult to find and fight due to the cancer cells' ability to blend in with healthy ones. Careful examination of the chemical makeup and shape of normal and diseased cells, however, promises to help doctors draw cancer out of the shadows.

Researchers at University of Michigan's Comprehensive Cancer Center in Ann Arbor report in Cell Stem Cell that they found a marker that can be used to identify cancer stem cells in breast tumors. Even though they account for only 5 percent of cells in tumors, stem cells (defined by their ability to generate identical cells and to morph into other cell types) are believed to play a key role in the spread of cancer.

The Michigan study, which began in late 2004, indicates cells from normal and cancerous breast tissue that contain high levels of the enzyme group aldehyde dehydrogenase (ALDH) acted like stem cells. Of the 577 human breast cancer tissue samples studied, those with tumors that tested positive for ALDH1—a specific form of the enzyme—were less likely to survive and were 1.76 times more likely to develop metastases than patients with ALDH1-negative tumors. ALDH1 was found in 19 percent to 30 percent of the study samples.

The presence of ALDH1 in both normal and malignant stem cells supports the theory that they are the primary target of transformation to malignancy, says study senior author Gabriela Dontu, an assistant professor of internal medicine. "We believe it is only a very small population of cells that really are capable of unlimited growth and therefore drive cancer recurrence and metastasis," she says. "The fact that normal and cancer stem cells share a common feature gives more support that cancers arise from normal stem cells."

The clinical implications of this stem cell model of carcinogenesis "changes the way we approach early diagnostic prognosis and, very importantly, how we develop therapy," Dontu adds. As the research progresses, she and her colleagues plan to develop therapeutic strategies that might eliminate cancer stem cells in breast tumors and cancers from other tissues. The researchers acknowledge, however, that more work is needed before these findings can be applied in clinical tests or treatments.

In a related study, a group of University of California, Los Angeles, researchers are hunting specifically for the cancer cells in body cavity fluids. The team reports in the online edition of Nature Nanotechnology that conventional diagnostic methods—such as using cell markers—detect about 70 percent of cases in which cancer cells are present in the fluid, but miss the rest.

The U.C. Los Angeles researchers, using an optical microscope, found that normal and cancer cells extracted from chest cavity fluid of patients with lung, breast and pancreatic cancers looked very similar. But when they attached an atomic force microscope (AFM) to the ordinary optical scope, they were able to use its minute, sharp tip to "feel" the cells, by pushing against a cell's surface to determine its degree of softness, says study co-author Jianyu Rao, a researcher at U.C.L.A.'s Jonsson Comprehensive Cancer Center and an associate professor of pathology and laboratory medicine.

An AFM is not actually a microscope but rather a device with an extremely small silicon probe that can be attached to an optical microscope for imaging, measuring and manipulating matter at the nanoscale. "It's like a finger that feels the softness of a cell," says James Gimzewski, a U.C.L.A. professor of chemistry and biochemistry and a member of the school's California NanoSystems 

After probing a cell, the AFM assigns a value that represents how soft a cell is based on the resistance encountered. The researchers found that the cancer cells are much softer than normal cells, which come in varying degrees of stiffness. This was true of all the pancreas, lung and breast cells studied.

Rao and his colleagues want to use the touchy-feely AFM to test primary tumors for malignancy and study how different cancers behave. "Some tumor cells might be more rigid than others, meaning that they may be less metastatic," and thereby the patient is in less danger, Rao says.

Looking ahead, the AFM is most likely to be used not as an initial detection tool, but rather as a means of checking whether cancer is spreading or in remission. Fluid buildup is not necessarily an indication of cancer, so understanding the nature of the cells in this fluid is very important to determining possible treatments, according to the scientists. "We have to check the fluid to see if it's positive for cancer," Rao says, "because this can determine if a treatment needs to be more aggressive."

U.C.L.A. researchers are also using the AFM to study the effects of different drugs on cancer cells. "We want to see how cells change with the drugs that we use on them," says study co-author Sarah Cross, a U.C.L.A. graduate student in the chemistry and biochemistry department. The goal is to develop less toxic drugs than currently 

3-D Mammography Adds New Dimension to Breast Cancer Screening

3-D Mammography Adds New Dimension to Breast Cancer Screening

Stereo image technology allows doctors to view two digital mammograms as one 3-D picture, and promises to help them spot hard-to-detect tumors 

 
A BETTER ANGLE: BBN Technologies division scientist David Getty views a mammogram through a stereo display setup. The images are displayed on two high-resolution LCD monitors positioned at a 110-degree angle from one another, with a specially coated glass partition placed between them.  

 
HIDING IN PLAIN SIGHT: Unlike other areas of the body, the breast does not conform to a particular gross anatomy. Overlapping or neighboring healthy tissue can resemble malignancies or, conversely, may hide small growths.

A team of researchers is studying the use of stereographic imaging technology and three-dimensional (3-D) displays to detect breast malignancies missed by traditional mammographies, opening the door to earlier detection and treatment and reducing the number of false-positive results and follow-up tests.

Stereo mammography provides radiologists with a three-dimensional view of the internal structure of the breast by taking two images from slightly different angles—much the way our two eyes create depth perception, or moviemakers create 3-D IMAX films. These mammography images are displayed on two Planar Systems high-resolution—2,500-by-2,000 pixel—liquid crystal display (LCD) monitors attached one on top of the other at a 110-degree angle, with a specially coated glass partition between them. The glass allows a radiologist wearing slightly polarized glasses to see the lower monitor (placed at eye level) while simultaneously viewing a reflection of the second monitor (placed slightly above eye level and angled downward).

"The brain is able to put together these images taken from different vantage points and figure out where things are in terms of depth," says David Getty, division scientist at Cambridge, Mass.–based BBN Technologies, Inc., which developed the stereo mammography technology used during the trial. BBN began studying different technologies that could be applied to mammography in 1992.

According to study co-author Dr. Carl D'Orsi, a radiology professor at the Emory University School of Medicine in Atlanta, the new procedure would make it easier to find tiny tumors obscured by other tissue in the breast. "You're looking for something at the limits of human visibility," he says. "In other areas of the human body, you don't have to look for something that small" when screening for cancer. As a result, overlapping or neighboring healthy tissue can resemble malignancies or, conversely, may hide small growths.

As of July 2007, 1,093 patients at elevated risk for developing breast cancer were enrolled in Emory's clinical trial and had received both standard and stereoscopic digital mammography exams. A total of 259 suspicious findings were identified by the two tests and the patients were referred for additional diagnostic testing; 109 of the flagged spots turned out to be malignant lesions. Standard mammography missed 40 of the lesions that the stereoscopic exam found, whereas 24 slipped by the stereoscopic exam but were found by standard mammography. "It is possible that there were a few other lesions that existed and that were missed by both modalities," Getty says. Still, stereoscopic digital mammography reduced the amount of false-positive findings turned up by standard digital mammography by 49 percent.

But the images are not the only problem. New research shows that the ability—or lack of ability—to properly interpret mammograms also plays a role in their effectiveness. A report by Seattle-based Group Health Center for Health Studies, a nonprofit health care system, published this week in the Journal of the National Cancer Institute indicates that accuracy of readings depends on the experience and skill of radiologists interpreting them: Those who read diagnostic mammograms most accurately tended to be based at academic medical centers and / or have spent at least 20 percent of their time doing such assessments. Most mammograms in the U.S., however, are interpreted by general radiologists, who only spend a fraction of their time analyzing such x-rays.

That is not to say mammograms are easy to read. A radiologist or doctor often is hunting for early-stage cancer formations less than a half-centimeter (0.20 inch, or 0.50 centimeter) in diameter. Still, it is a skill in great demand. In 2004 (the most recent year for which numbers are available) 186,772 women and 1,815 men were diagnosed with breast cancer, according to the U.S. Department of Health and Human Services' Centers for Disease Control and Prevention.

Stereoscopic mammography systems could be built by simply adding a stereo display to existing digital mammography equipment, Getty says, noting that he and colleagues are meeting with mammography equipment manufacturers to gauge their interest and, also, are seeking funding for further technology development and clinical trials from the National Institutes of Health.

Stereo mammography holds even greater promise as mammography equipment manufacturers such as General Electric Co., based in Fairfield, Conn.; Siemens, AG, headquartered in Munich; and Bedford, Mass.–based Hologic, Inc., develop machines to perform breast digital tomosynthesis, which takes up to 20 images in an arc in front of each breast with each image separated by one or two degrees. Together, these images could be reconstructed and viewed through a stereo mammography system to create a 3-D image of the breast that can be examined from a number of different angles.

"Breast CT [computed tomography] scanning may be the ultimate, but that's a decade away," D'Orsi says. Getty is hoping that ultimately CT or magnetic resonance imaging (MRI) scans of internal organs—such as the prostate and lungs—will also be viewable this way.

Culture Speeds Up Human Evolution

Culture Speeds Up Human Evolution

Analysis of common patterns of genetic variation reveals that humans have been evolving faster in recent history 

 
FAST TRACK: Human evolution has sped up thanks to the population explosion caused by agriculture.

Homo sapiens sapiens has spread across the globe and increased vastly in numbers over the past 50,000 years or so—from an estimated five million in 9000 B.C. to roughly 6.5 billion today. More people means more opportunity for mutations to creep into the basic human genome and new research confirms that in the past 10,000 years a host of changes to everything from digestion to bones has been taking place.

"We found very many human genes undergoing selection," says anthropologist Gregory Cochran of the University of Utah, a member of the team that analyzed the 3.9 million DNA sequences* showing the most variation. "Most are very recent, so much so that the rate of human evolution over the past few thousand years is far greater than it has been over the past few million years."

"We believe that this can be explained by an increase in the strength of selection as people became agriculturalists—a major ecological change—and a vast increase in the number of favorable mutations as agriculture led to increased population size," he adds.

Roughly 10,000 years ago, humanity made the transition from living off the land to actively raising crops and domesticated animals. Because this concentrated populations, diseases such as malaria, smallpox and tuberculosis, among others, became more virulent. At the same time, the new agriculturally based diet offered its own challenges—including iron deficiency from lack of meat, cavities and, ultimately, shorter stature due to poor nutrition, says anthropologist John Hawks of the University of Wisconsin–Madison, another team member.

"Their bodies and teeth shrank. Their brains shrank, too," he adds. "But they started to get new alleles [alternative gene forms] that helped them digest the food more efficiently. New protective alleles allowed a fraction of people to survive the dread illnesses better."

By looking for wide swaths of genetic material that vary little from individual to individual within these sections of great variation, the researchers identified regions that both originated recently and conferred some kind of advantage (because they became common rapidly). For example, the gene known as LCT gave adults the ability to digest milk and G6PD offered some protection against the malaria caused by Plasmodium falciparum parasite.

"Ten thousand years ago, no one on planet Earth had blue eyes," Hawks notes, because that gene—OCA2—had not yet developed. "We are different from people who lived only 400 generations ago in ways that are very obvious; that you can see with your eyes."

Comparing the amount of genetic differentiation between humans and our closest relatives, chimpanzees, suggests that the pace of change has accelerated to 10 to 100 times the average long-term rate, the researchers write in Proceedings of the National Academy of Sciences USA.

Not all populations show the same evolutionary speed. For example, Africans show a slightly lower mutation rate. "Africans haven't had to adapt to a fundamentally new climate," because modern humanity evolved where they live, Cochran says. "Europeans and East Asians, living in environments very different from those of their African ancestors and early adopters of agriculture, were more maladapted, less fitted to their environments."

And this speedy pace of evolution will not slow until every possible beneficial mutation starts to happen—the maximum rate of adaptation. This has already begun to occur in such areas as skin color in which different sets of genes are responsible for the paler shades of Europeans and East Asians, according to the researchers.

The finding raises many questions. Among them: "the medical applications of this kind of knowledge [as well as] exactly what most of the selected changes do and what drove their selection," Cochran says.

But the history of humanity is beginning to be read out from our genes, thanks to a detailed knowledge of the thousands of them that have evolved recently. "We're going to be classifying these by functional categories and looking for matches between genetic changes and historic and archaeological changes in diet, skeletal form, disease and many other things," Hawks says. "We think we will be able to find some of the genetic changes that drove human population growth and migrations—the broad causes of human history."

*This article wrongly characterized the HapMap genotype dataset used for this analysis as "genes" rather than "DNA sequences."

Do Women Who Live Together Menstruate Together?

Do Women Who Live Together Menstruate Together?

Does sisterhood among women extend to the monthly period? 

 
WOMEN'S PERIOD: Some have argued that women's menstrual cycles begin to synchronize when living together but evidence is spotty.

It's a classic girl-bonding scenario: While moaning to your roommate about uterine cramps, premenstrual syndrome or some other such periodic inconvenience you realize that she, unlucky girl, is having her period, too. Momentarily distracted, you take a collective step back to marvel at the wonders of human biology that have allowed your ovulation cycles to synchronize.

Though widely accepted as a fact of female life, many psychologists and anthropologists doubt the existence of such menstrual synchrony. Nearly half of the papers published on the topic find no evidence that close co-habitation draws menstrual cycles closer together. What's more, studies that do find an effect have been dogged by harsh criticisms of poor design and naive statistical analyses.

Menstrual synchrony was first demonstrated in a 1971 paper published in Nature by Martha McClintock. The University of Chicago psychologist had observed during her undergraduate days in an all-female dorm that close friends tended to get their periods at the same time.

To test the idea formally, she asked 135 college girls living in dorms to recall their period start dates at three times throughout the academic year. She found that close-friend groups had periods significantly closer together in April (later in the year) compared with October: lessening from an average of 6.4 to 4.6 days apart.

The phenomenon was dubbed "the McClintock effect" and is widely held as the first example of pheromones—unconscious chemical signals that influence behavior and physiology—among humans.

Many subsequent researchers went on to reproduce the results from McClintock's original experiment in people, rats, hamsters and chimpanzees. But a cohort of studies that found no evidence for menstrual synchrony began to grow, too.

The father–son team of Leonard and Aron Weller, both at Bar-Ilan University in Israel, conducted the most studies on humans; they looked at college dorm roommates, athletes, lesbian couples, mothers, sisters, friends and even office colleagues throughout the 1990s. Sometimes they found signs of synchrony and other times not, with no explanation why. "The answer is not clear," the elder Weller says. "At one time before we started doing our research it was sort of a truism. But if it exists it is certainly not ubiquitous."

In 1992 H. Clyde Wilson, now an emeritus professor of anthropology at the University of Missouri–Columbia re-analyzed McClintock's first experiment, along with a few others that used a similar design. He found that all had inflated the difference between period start dates at the beginning of their studies. Correcting this and other methodological errors stripped away significance from McClintock's original results, he wrote.

And McClintock's former colleague, psychologist and mathematical modeler Jeffrey Schank at the University of California, Davis, found in a highly controlled rodent pheromone study that their model of two pheromones—one that pulls ovulation forward and one that delays it—driving synchrony didn't work. "That was very disappointing to me," he says. "I really wanted those models to work out."

The insurmountable hurdle in all the studies, he says, is that women often have persistent cycles of different lengths. As such, they can never truly synchronize, just randomly phase in and out of synchrony over the months as their cycles diverge and converge.

Last year, he co-authored a study in Human Nature following 186 female Chinese students living in dorms for an entire year, the longest menstrual synchrony study yet. He saw no evidence for the phenomenon, but plenty of random overlaps that could be seen as synchrony if viewed through a shorter time window.

McClintock, however, remains resolute. Focusing on narrow definitions of precise synchrony misses the greater point, she says: whether the social environment of women can affect the timing of ovulation, not menstruation per say, no matter in which direction or what pattern. "I don't think there is any doubt that social interaction among women and body compounds from women can change the way the ovary functions," she says.

McClintock points to her 1998 Nature paper, which found that women exposed to cotton pads soaked with underarm secretions collected from donors undergoing the first and second (follicular and luteal) phases of their cycles resulted in significantly altered menstrual cycle lengths in the test women. The results, however, rested on a knife-edge of statistical significance, Schank says, and could have been due to chance.

But a team of Japanese researchers at Yokohama City University, led by Kazuyuki Shinohara, also found in a series of papers that donor women undergoing these two phases of the menstrual cycle release compounds that when inhaled by other women can significantly impact the frequency in the latter of pulses of luteinizing hormone (LH), which helps control the timing of ovulation and cycle length.

Similarly, a 2004 study from McClintock's group found that odors from breast-feeding women alter the timing of the cycles and LH surges in childless women.

McClintock is still actively researching the area. The most important questions, she says, are exploring the underlying mechanisms behind variation in the social effects on ovulation: Why do some women not respond? Why are some phases of the menstrual cycle more sensitive to external stimuli?

"I completely agree with Jeff [Schank]. There are no perfectly lock-phased cycles that are sustained over 20 cycles; that is very rare. But given what I know about the causes of menstrual synchrony means I expect it to be rare," she says. "So the fact that it is rare doesn't mean that it doesn't exist."

But until the relevant pheromones and their biochemical receptor pathways are better described, the current bulk of evidence suggests that popular notions of menstrual synchrony are more college town myth than dorm room reality.