Why does natural selection favour only few species?

November 4th, 2008 - 3:08 pm ICT by IANS  

Washington, Nov 4 (IANS) Why does natural selection favour few plants and animals species to the exclusion of others?The answer lies in the rate of metabolism of a species - how fast a species consumes energy, per unit of mass and per unit time, according to a University of California (UC) Riverside-led research team.

The researchers studied 3,006 species, the largest ever analysed by a single team. The list encompasses much of the biological diversity on the planet — from bacteria to elephants, and algae to sapling trees.

They surprisingly found the mean metabolic rate of the species at rest fell on a narrow range of values - 0.3 to 9 watts per kg.

“This narrow range is in dramatic contrast to the 20 orders of magnitude difference in the body mass of the species we studied,” said Bai-Lian Li, a professor of ecology at UC Riverside, who led the study with two colleagues.

“At physiological rest, the biosphere appears to run, on average, predominantly at the optimal rate defined by this narrow range of values. This remarkable phenomenon is likely associated with the pervasive biochemical universality of living matter, and could provide us with clues to understanding how life is organised.”

According to Li, the metabolic optimum explains the ubiquitous and seemingly unrelated features of life organisation we see all around us - complex adaptations such as animal breathing and flat, green leaves, according to an UC release.

“Organisms whose designs fit the physiological window have been favoured by natural selection across all of life’s major kingdoms,” Li said.

“Species had to invent diverse tricks to remain near the metabolic optimum, from which the progressive evolutionary increase in body size - from prokaryotes to largest vertebrates and plants - was continually taking them away,” Li added.

Unlike the genetic code and protein composition, metabolic rate cannot be inherited from a common ancestor. Rather, a particular range of metabolic rates is maintained by natural selection.

Li’s associates are Anastassia M. Makarieva and Victor G. Gorshkov of the Russian Academy of Sciences, St. Petersburg.

These results appeared in the Tuesday issue of the Proceedings of the National Academy of Sciences.

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