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Scholarship & Creativity
Fossil is missing link in elephant lineage

A pig-sized, tusked creature that roamed the earth some 27 million years ago represents a missing link between the oldest known relatives of elephants and the more recent group from which modern elephants descended, according to an international team that includes U-M paleontologist William Sanders.
The teeth of the newly described Eritreum melakeghebrekristosi are a tip-off to its position as a missing link in the elephant family tree. (Photo courtesy William Sanders)

The group's findings, published in the Proceedings of the National Academy of Sciences, suggest that mastodons and the ancestors of elephants originated in Africa, in contrast to mammals such as rhinos, giraffes and antelopes, which had their origins in Europe and Asia and migrated into Africa. The dating of the new fossil, discovered in the east African country of Eritrea, also pushes the origins of elephants and mastodons 5 million years further into the past than previous records, Sanders says.

From 35 to 25 million years ago, representatives of the group known as proboscideans (which includes elephants, mastodons and their close relatives) lived only in Africa and Arabia, and most of them were palaeomastodonts. These animals were shorter and smaller than today's elephants, with short trunks and tusks and simple teeth that were all in place at the same time, as are human adult teeth.

After 25 million years ago, larger proboscideans such as mastodons and gomphotheres—the ancestors of modern elephants—dominated the scene. Elephant-sized, with long tusks and trunks, these advanced proboscideans had more complex teeth that emerged more slowly, so that each quadrant of the mouth had only one or two functional teeth in place at a time.

"The new fossil from Eritrea is important because it shows aspects of dental anatomy in common with the advanced group, including molars with more cusps and complex crowns and the delayed maturation and emergence of molars," says Sanders, an assistant research scientist in the Museum of Paleontology. But the creature that the new fossil represents also had characteristics in common with palaeomastodonts, namely smaller body size and a jaw structure that suggests shorter tusks and trunk.

"In age and anatomy it is exactly the sort of intermediate evolutionists would expect to bridge the gap between archaic and advanced proboscideans," Sanders says.

Sanders received financial support for participation in the project from a Scott Turner Award from the Department of Geological Sciences.

Suicide attempt rate for Blacks higher than previously reported

New research indicates that Blacks in the United States have a lifetime prevalence of attempted suicide of about 4 percent—a rate comparable with the general population but higher than previous estimates.

Findings from the first known national study about the prevalence of attempted suicide among Blacks appear in the Nov. 1 issue of the Journal of the American Medical Association.

Suicide is the 11th-leading cause of death among all Americans and the rates range across specific demographic subgroups. In recent years suicide and nonfatal suicidal behavior have emerged as crucial health issues for Blacks, particularly among older adolescents and young adults.

Sean Joe, assistant professor at the School of Social Work, and colleagues sought to determine national estimates of the lifetime prevalence and risk factors for suicidal thoughts, plans and attempts among Blacks of African American and Caribbean ethnicity in the United States. The researchers used data from the National Survey of American Life, a sample of 5,181 black respondents age 18 and older conducted between February 2001 and June 2003 by the Institute for Social Research Program for Research on Black Americans.

The estimated lifetime prevalence of suicide attempts among Blacks in the United States was 4.1 percent; for suicidal thoughts, 11.7 percent. By comparison, the most recent data from the National Institute of Mental Health for the period 1980-84 had the lifetime estimate of attempted suicide among Blacks at 2.3 percent.

In Joe's study, among those who reported suicidal thoughts, 34.6 percent made a suicide plan and 21 percent made an unplanned attempt.

Significant differences were found based on gender, with suicide attempts more prevalent among women (4.9 percent) than men (3.1 percent). The prevalence of suicide attempts was highest for Caribbean Black men (7.5 percent), followed by African American women (5 percent). Risk of a suicide attempt and suicidal thoughts were significantly associated with being younger, having a low education level, residing in the Midwest region of the United States, and having one or more psychiatric disorders.

To read the study go to: www.ns.umich.edu/htdocs/releases/story.php?id=1018.


One small snip from man; one giant leap for the genome

Snips of DNA of only 270 people from just four world locations provide a reliable map of genetic disease variations in the human genome for nearly all populations around the world.

U-M scientists evaluated worldwide coverage of a database of genetic markers and variations spread across the genome, called the HapMap, which was released one year ago by an international research consortium.

That team had identified about 4.5 million single-letter differences in DNA, called single nucleotide polymorphisms or SNPs (Snips) from the genomes of the Yoruba people in Nigeria, Chinese from Beijing, Japanese from Tokyo and a group of European-Americans. Each population's particular collection of SNPs is called a haplotype.

The HapMap database allows researchers to select markers that will be useful to their research and also to develop a standard set of markers to be used in studies of many diseases. Until now, however, the extent to which the genetic variants in the HapMap database represented the rest of the world's populations had not been studied.

"The variants in the HapMap provide a good set of markers to use to test for diseases such as diabetes in most human populations," says study author Noah Rosenberg, assistant professor in the Life Sciences Institute, the Bioinformatics Program and the department of Human Genetics at the Medical School.

Rosenberg's group studied genetic variation across populations to find the extent to which the genetic variants in the HapMap would apply to populations that were not part of that project. His team collected data from 927 individuals in 52 different world populations.

Researchers like Rosenberg will be able to use the HapMap to test genetic markers spread out across the genome to investigate differences related to that disease.

The paper, "A worldwide survey of haplotype variation and linkage disequilibrium in the human genome," was published Oct. 22 on the Nature Genetics Web site.

Kidney cancer detected and treated early, yet death rate continues to rise

The number of cases of kidney cancer has been rising over the last two decades, and new research from the U-M Comprehensive Cancer Center shows that this increase is driven largely by the detection of small, presumably curable, kidney masses. But even though the rising incidence has been paralleled by greater use of surgery for kidney cancer, this trend has not led to fewer people dying.

"With increased early detection and treatment of small tumors, we would expect to see a decrease in mortality associated with kidney cancer," says senior author Dr. Brent Hollenbeck, assistant professor of urology at the Medical School. "Surprisingly, that's not what we found."

The study, published in the Sept. 20 issue of the Journal of the National Cancer Institute, includes data from nine of the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) registries. In all, the researchers examined data from 34,503 patients with kidney cancer.

Over the study period (1983-2002), researchers observed a rise in the occurrence of kidney cancer for tumors of all sizes. But the greatest increases in kidney cancer incidence were among tumors 4 centimeters or smaller. Tumors of this size, often found in patients without any clinical signs or symptoms, are being detected more and more with the widespread use of magnetic resonance imaging and computerized tomography scans. These small tumors are considered curable, which has led to a rise in surgery for kidney cancer.

Even as early detection and surgical treatment increased, mortality rates rose dramatically, from 1.2 to 3.2 deaths per 100,000 people in the United States.

These seemingly contradictory findings can be explained in part through the rising incidence of larger, more lethal tumors, says lead author Dr. John Hollingsworth, fifth-year surgery resident with the Department of Urology.

Researchers say the data also suggest a proportion of these smaller, incidentally found kidney tumors may not merit surgical removal.

Other researchers on the study were Dr. David Miller, clinical lecturer in the Department of Urology, and Stephanie Daignault, a biostatistician with the Comprehensive Cancer Center.

The research was supported by the National Institutes of Health and the Johan and Suzanne Munn Endowed Research Fund of the Comprehensive Cancer Center.


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