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Prof. Kevin Kinney Quoted in San Diego Union-Tribune

September 8, 2004

September 8, 2004, Greencastle, Ind. - "Which comes first: metabolism or size?," is one of the questions asked in an article published in today's edition of the San Diego Union-Tribune. " 'It's a kind of chicken-and-egg question,' said Kevin Kinney, an assistant professor of biology at DePauw University in Indiana. 'There's no way to definitively answer that. The better view is to think about the size of life as a constant compromise. Organisms are always looking for the optimum size for their lifestyle.' "

The newspaper's Scott LaFee writes, "Life comes in all sizes, from extraordinarily large to microscopically small, with millions of versions of medium in between." The story points out, among other things, that "The difference in mass between an average-sized bacterium and a 100-foot-long blue whale is 1021. A hypothetical super-organism 1021 times larger than a blue whale would be 100 times larger than Earth." LaFee asks, "What is the maximum size of life? What's the minimum? Does size really matter?."

Besides Dr. Kinney, the piece includes quotes from Steven Vogel, a professor of zoology at Duke University.

"Unlike physics or math or chemistry, biology seems to be governed by few all-encompassing principles, especially in regard to size," states LaFee. "The rule that life span tends to lengthen and metabolism to slow down proportionate to size is one such principle. Another, some say, is the so-called quarter-power law, which posits that life scales geometrically in four dimensions -- width, length, depth and mass -- rather than just the first three. The idea is hotly contested by skeptics, who are unpersuaded by current arguments and evidence, not to mention the numerous exceptions to the rule. For example: The heart of a 1-ounce mouse beats roughly 600 times per minute. The mouse lives an average of three years. An elephant's heart beats just 30 times per minute, but a 5-ton elephant will likely live 60 years or more. In both cases, if the animals' pulse rate is scaled inversely as the quarter-power of the animal's mass, this notable fact is produced: The total number of heartbeats in a mouse's and an elephant's average life span will be roughly the same, about 946 million times. Used this way, the quarter-power law can be used to estimate life span. But other species, such as people, mess up the equation. A human heart, beating a normal 65 times per minute, hits the 946 million mark somewhere around the 27th year of life, far short of the average human life span. 'Nobody has been able to explain why this is so,' said Kinney. 'And humans aren't the only exception. Anteaters are way, way off the chart. Quarter-power scaling is a great rule, but it doesn't explain why some species last so much longer than others.'"

Later, the text continues, "Measuring life and understanding how it works is not without practical application. The quarter-power scaling law, for example, has been used to extrapolate drug dosages from animal models to human patients. How organisms of different dimensions function or simply survive, said Kinney, has real-world relevance in sports, medicine and engineering. 'Anteaters shouldn't live as long as they do,' said Kinney, 'so maybe there's something we can learn about how they do it and apply it to ourselves. Some termites build huge mounds that they somehow keep cool. Maybe there's a lesson for skyscraper design in them.'"

The complete article can be accessed at the Union-Tribune's Web site by clicking here.

Source: San Diego Union-Tribune

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