Astronomers use physics to unravel the mysteries of the universe, and although it can also be used to uncover the secrets of biology, there are things that physics cannot explain. Biologists have asked for centuries why large animals burn less energy and require less food than small ones.
For instance, an enormous baleen whale can live by consuming 5% to 30% of its body weight in krill, while a tiny shrew needs to consume three times its body weight each day. Previous efforts try to use physics and geometry, but scientists from a new study believe that the answer is evolution. Their findings show that it is what maximizes an animal's ability to reproduce.
Relationship Between Metabolism and Size
The disproportionate relationship between metabolism and size was first proposed almost 200 years ago. According to Khan Academy, metabolism is inefficient and produces heat used by endotherms to warm themselves and keep a stable body temperature. The more active an animal is, the higher its metabolic rate.
French scientists Pierre Sarrus and Jean-François Rameauxin 1837 argued that energy metabolism should scale with the surface area rather than body mass or volume because the amount of heat an animal can dissipate depends on its surface area. After nearly two centuries, numerous explanations emerged for the observed scaling of metabolism.
One of these famous explanations was from US researchers Geoff West, Jim Brown, and Brian Enquist in 1997. They presented a model that describes the physical transport of essential materials like the one in the circulatory system. Their model shows a theoretical and mechanistic basis for how body size affects all aspects of biology.
Phys.org reported that the two models are philosophically similar as they try to explain biological patterns based on physical and geometric constraints.
Evolution Overcomes Physics and Geometric Constraints
It seems hard to defy the laws of physics regarding biology. However, evolution has remarkably found new ways to overcome the constraints of physics and geometry.
In the study titled "Metabolic Scaling Is the Product of Life-History Optimization," published in Science, researchers reveal what happened to metabolic rate and size if physical and geometric constraints were ignored.
They developed a mathematical model that shows how animals would use energy throughout their lifetimes and found that they would devote it to growing in their early years and then devote their increasing energy in adulthood to reproduce offspring.
Phys.org reported that the model was used to determine the characteristics of animals to increase their chances of being successful at reproducing. It shows that animals exhibited the kind of disproportionate scaling of metabolism with size as they do in real life.
The scientists concluded that disproportionate metabolic scaling is due to natural selection because it is more advantageous for lifetime reproduction. The findings also show that scientists have been looking in the wrong place for explanations and that the possibilities available to evolution are broader than expected.
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