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Research Roundup

Baboons May Have Influenced Human Evolution

We may take it for granted that humans can classify each other according to familial or social status, but how did those abilities evolve? In the November 14 issue of Science, Penn researchers reported that, much like humans, baboons identify each other based on complex rules that determine relationships between families and status or "rank" within their particular family.

"Humans organize their knowledge of social relationships into a hierarchical structure, and they also make use of hierarchical structures when deducing relationships between words in language," said Dr. Robert Seyfarth, professor of psychology, and one of the study's authors. "The existence of such complex social classifications in baboons, a species without language, suggests that the social pressures imposed by life in complex groups may have been one factor leading to the evolution of sophisticated cognition and language in our pre-human ancestors."

For the last 12 years, Dr. Seyfarth, Dr. Dorothy Cheney, professor of biology, and their colleagues have studied a troop of more than 80 baboons in the Okavango Delta of Botswana. Their research explores the cognitive mechanisms that might be the basis of primate social relationships and how such relationships may have influenced the development of human social relationships, intelligence and language.

Dominant baboons make threatening grunts, which lower-ranked baboons answer with supplicating screams. The researchers tape-recorded the calls of known individuals, then used a computer to mix and match the grunts and screams to make it seem as if a lower-ranked baboon was effectively dominating a higher ranked baboon.Then, in a playback experiment, the researchers played recorded interactions to individual baboons to see if there would be a response. Some playbacks mimicked the existing hierarchy, whereas others mimicked a rank-reversal, either between two members of the same family or between two members of different families.

"Rank-reversals run counter to their expectations, and a baboon will momentarily pause and give a look, just as you might if you didn't quite believe what you had just heard," said Dr. Thore Bergman, postdoctoral researcher in biology and lead author on the paper. "Our results demonstrated that these relationships were real and relevant to these baboons."

"Rank reversals within families are surprising, but rank-reversals between families are of potentially much greater importance and we see that the baboons recognize the significance of these events," Dr. Seyfarth said. "To do so, they must be astute observers, watching animals interact and deducing a social structure on the basis of what they've seen."

Strength and Conductivity of Nanotube-Laced Materials

Materials fortified with carbon nanotubes are strongest when the embedded filaments run parallel to each other, but electronic and thermal conductivity are best when the nanotubes are oriented randomly. That's the finding from a team of engineers at Penn who have developed a production technique that permits a finer and more precise dispersion of nanotubes within a material.

The results, which could give scientists the tools to customize nanotube-laced materials to meet their particular needs, are reported online and in the December 15 print edition of the Journal of Polymer Science Part B: Polymer Physics. Less than one-ten-thousandth the width of a human hair, carbon nanotubes possess unparalleled strength, superior heat-conducting properties and a unique ability to adopt the electrical properties of either semiconductors or metals, but so far they have failed to back up this theoretical potential with real-world applications.

"A major hurdle that has prevented us from mixing nanotubes into materials to take advantage of these remarkable properties is their stubborn tendency to bundle together," said Dr. Karen I. Winey, associate professor of materials science and engineering. "Uniform dispersion of nanotubes in materials is absolutely critical to harnessing their strength, electrical conductivity and thermal stability."

Dr. Winey and her colleagues used a technique called coagulation to mix single-walled carbon nanotubes evenly into a plastic, or polymer, called poly(methyl methylacrylate). In this method, nanotubes and PMMA are first mixed into a solvent, creating a fine suspension, and then plunged into distilled water. The PMMA rapidly precipitates out of this mixture, dragging the nanotubes with it and preventing them from clumping.

"At low concentrations the electrical conductivity of these nanocomposites was roughly 100,000 times better when the nanotubes were unaligned than when the nanotubes were well aligned," Dr. Winey said.

"While alignment is an asset for some mechanical properties, alignment is clearly a detriment for electrical properties," Dr. Winey said, "where adding more of the expensive nanotubes is not nearly as cost-effective as producing a random orientation of nanotubes in a composite." She was joined in the research by Dr. John E. Fischer, professor of materials science and engineering, and Fangming Du, a graduate student in chemical and biomolecular engineering.

Transition to Adulthood Delayed

Becoming an adult takes longer today than in previous decades, with many not achieving all the traditional markers--starting a career, forming a new household, starting a family--until after age 30, according to a study by the Network on Transitions to Adulthood. The Network, funded by the MacArthur Foundation, is directed by Dr. Frank Furstenberg, professor of sociology.

According to the study, a demographic shift has occurred, almost without notice, but with important ramifications for the job market, the marriage market and public policy. To examine the experiences of youth as they move toward adulthood, Dr. Elizabeth Fussell, a demographer at Tulane University, and Dr. Furstenberg used 1900-1990 U.S. Census data on youth aged 16-30 along with sample data from the Census Bureau's 2000 Current Population Survey.

Dr. Fussell and Dr. Furstenberg's report The Transition to Adulthood During the 20th Century: Race, Nativity and Gender includes findings on the shifting path to adulthood for native-born, foreign-born, white and black men, and women.

Among the study's other findings:

  • For men, the ability to support and thus form a family has declined. In the industrialized economy of the first half of the 20th century, most men were able to attain such independence by age 20.
  • Women, too, have seen a shift toward delayed marriage and more independent living while working or attending school.
  • Another trend for women is the growing proportion postponing marriage, but not necessarily motherhood, until after age 30.
  • Differences between black, white and foreign-born populations in education and labor market opportunities have narrowed since the 1960s. The lives of blacks increasingly resemble those of their white peers as they have become more fully and equally integrated into society's institutions. Nevertheless, fewer minority youth than native-born whites are participating today in education and work, a fact that deserves further investigation.
  • Even after marriage, men and women continue to combine a variety of roles more often than in the past, such as attending school and working, both before and after becoming parents.

The results of the study are to be published in the forthcoming book On the Frontier of Adulthood: Theory, Research, and Public Policy, edited by Richard A. Settersten, Frank Furstenberg and Ruben G. Rumbaut (University of Chicago Press).

Electronic Scale Lowers Mortality Rates

Patients with advanced heart failure who reported daily to health-care professionals any changes in weight or symptoms associated with the illness had significantly lower mortality rates than their unmonitored peers, according to a national study led by investigators in the Heart Failure and Cardiac Transplant Program at Penn's Medical Center. The findings were published in the October issue of American Heart Journal.

"The findings were a surprise," said Dr. Lee R. Goldberg, assistant professor of medicine, and principal investigator for the study. "We set out to determine whether the rate of hospitalization for patients who reported their weight and symptoms to health-care personnel on a daily basis might be lower than the rate for unmonitored patients. Instead, we found the hospitalization rates were essentially the same for both groups--but there was a striking disparity in their mortality rates over the period of the study."

Over six months, the nurse-monitored group sustained 11 deaths, while the unmonitored group sustained 26 deaths--a 56 % difference in mortality rates. Dr. Goldberg said the impact on mortality was demonstrated despite "aggressive medical management for both patient groups," and it held true for patients of heart transplant centers as well as community medical practices.

Patients in the AlereNet daily monitoring system group relied on a technology system that included an electronic scale and personalized response mechanism tied into their home telephone line. They were instructed to weigh themselves and to answer a set of five questions tailored to their individual symptoms twice each day. The information was sent to a control center and reviewed by nurses once daily over the course of the study.

Patients in the standard care group were advised to weigh themselves daily and keep a log of weight gains and losses, and they were instructed to contact their personal physician about weight increases above a prescribed amount or about any worsening symptoms. They were also asked to bring their weight log with them to the study's regularly scheduled cardiologist visits.

"We are not certain what caused the disparity in mortality rates," Dr. Goldberg said. "But the sole difference in the two groups appears to be the daily monitoring by trained nurses in the AlereNet group, which means those patients may have been more likely to benefit from rapid medical intervention."



Almanac, Vol. 50, No. 18, January 20, 2004