Updates; January 2009; Scientific American Magazine; by Philip Yam; 1 Page(s)

Extinction by Disease Theories for what killed off the woolly mammoth and other North American megafauna some 11,000 years ago have long focused on climate change and human hunting pressure. But in 1997 another possible culprit was proposed: hyperlethal disease introduced to the immunologically naive behemoths by dogs or vermin that accompanied humans when they arrived in the New World [see ¿Mammoth Kill¿; SciAm, February 2001]. Now Alex D. Greenwood of Old Dominion University and his colleagues have produced the first evidence of disease-induced extinction among mammals. The team¿s genetic analyses indicate that two species of rat endemic to Christmas Island in the Indian Ocean went extinct because they contracted a deadly pathogen from black rats, which arrived via the SS Hindustan in 1899. Less than a decade after the black rats landed, the endemic rats were gone. The findings appear in the November 5 PloS ONE.

Cloning Mice on Ice Too bad Christmas Island is not near the North Pole. Rats that went extinct on that island might then have left frozen remains for cloning¿an idea advanced to save species [see ¿Cloning Noah¿s Ark¿; SciAm, November 2000]. In a new study scientists in Japan created healthy clones from mice preserved for 16 years at ¿20 degrees Celsius without chemical protection from ice. They took nuclei primarily from thawed brain cells and put them into host cells, which led to a line of embryonic stem cells from which the researchers ultimately bred 13 mice. Freezing and thawing ruptures cells and damages DNA, but the work, reported online November 3 in the Proceedings of the National Academy of Sciences USA, reveals that significant genomic information survives. Whether the success can help resurrect woolly mammoths is unclear, but it offers hope at least for smaller extinct species.