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This Week in Science: Jul 24, 2015

In this week's Science, Alan Leshner argues for a re-evaluation of the structure of graduate education in science. He notes that fewer than half of new PhDs in the field will not end up pursuing careers in academia despite the focus on graduate training on such a goal, highlighting the need for the current education system to adopt new programs that address the career needs of today's students. Leshner, CEO emeritus of the American Association for the Advancement of Science, warns of resistance to such changes, but stresses the benefits to future science students.

Also in Science, a team led by Danish scientists reports on the comparative analysis of genomes from ancient and modern individuals from the Americas, Siberia, and Oceania, which uncovered new details about how the ancestors of present-day Native Americans entered the Americas. The investigators' data suggest that these ancient migrants came in a single wave from Siberia no earlier than 23,000 years ago and after no more than 8,000 years of isolation in Beringia. They also theorize that ancestral Native Americans, after arriving in the Americas, diversified into two genetic branches about 13,000 years ago, one restricted to North America and another spread out across both North and South America, which gave rise to today's diverse Native American populations. GenomeWeb has more on this and a related Nature study here.

Finally, a group of Australian and US researchers presents a study indicating that rapid phases of a warming climate played a significant role in the extinction of megafauna — animals greater than 100 pounds — during the last glacial period. The data contradict the theory that human hunting and land alteration had the biggest impact on these animals. By comparing ancient DNA with radiocarbon data on severe climate events in the Late Pleistocene that were obtained through Greenland ice cores and other sources, the researchers discovered a close relationship between extinctions and the rapid climate changes associated with interstadial warming events. GenomeWeb also covers this here.