Wednesday, October 04, 2006

Mastodons in the news
A geologist and a physician have concluded from a study of 113 mastodon skeletons that tuberculosis was endemic in the big beasts during the late Pleistocene. Bruce Rothschild, the physician, fist noticed tuberculosis lesions on a metacarpal (front foot, palm bone) at a dig in 2001. Curious about how common tuberculosis might have been in mastodons, he sought out specimens in museums across the country and found evidence of the disease in over half of the individuals he examined.

One of the three major theories to account for the extinction of large mammals at the end of the last ice age is the hyperdisease theory. According to this idea, put forth by Ross MacPhee of the American Museum of Natural History, an epidemic of a highly virulent disease wiped out many of the now extinct species. MacPhee has suggested the possibility that the disease was carried by humans and their dogs from the old world into the new. While the idea is intriguing to some, so far no evidence of a pathogen has been found in the remains of the last Pleistocene giants.

Rothschild's tuberculosis doesn't quite fill the role of MacPhee's epidemic. The mastodons that Rothschild examined come from a couple thousand years time span. While tuberculosis isn't the sole cause of the extinction of the mastodons, it might be a contributing factor--one stressor among many. Combined with the shifting of their range as the climate changed and the introduction of a new predator (us) the combination might have been enough to push them over the edge. It's important to remember that, to be a cause of extinction, a stressor doesn't need to kill every individual in a species; it's enough to merely reduce their birth rate to below the number required for replacement. At that point, they go into a fatal decline.

Are these three stressors enough to account for the decline of the mastodons? Maybe. Could they also account for the extinction of any or all of the other species that died off at the same time? Also maybe, but much more research is required.

Rothschild's partner in this study, Richard Laub, points out that their work has relevance in beyond solving a ten thousand year old murder mystery. Tuberculosis is still a killer today. Understanding this ancient strain and its spread might help to understand modern antibiotic resistant strains and the danger of epidemics during a period of climate change. This is a perfect example of how research that appears to be completely academic can suddenly have useful applications in real life. It's another argument you can save to throw at that anti-science in-law or co-worker the next time they disparage pure science research.

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