The question of why larger animals consume relatively less energy compared to smaller animals has long puzzled biologists.
When thinking about tasks that aim to “illuminate the mysteries of the universe”, people often envision distant physics issues: astronomers observing far-off galaxies through telescopes, or experimental physicists “playing” with fundamental particles in particle accelerators.
As biologists attempt to unravel the profound mysteries of the universe, they often approach the explanation through physics. However, according to a new study published in the journal Science, sometimes physics—the study of the material world—also “throws up its hands” at certain biological questions.
For centuries, scientists have questioned why, relatively speaking, large animals burn less energy and require less food than smaller animals. Why does a tiny shrew need to consume food equivalent to three times its body weight, while a massive whale can be satisfied daily with just 5-30% of its body weight, primarily eating mollusks?
Relatively speaking, the tiny shrew is “greedier” than the giant whale.
While previous efforts to explain this “paradox” have leaned on physics and geometry, biologists believe the true answer lies in evolution. The key is optimizing the reproductive capacity of organisms.
A Puzzling Question, Even Physics Struggles
The first efforts to explain the phenomenon of “shrews eat a lot, whales eat little”, or more precisely, the disproportionate relationship between body size and metabolic needs, occurred nearly 200 years ago.
In 1827, two French scientists, Pierre Sarrus and Jean-François Rameaux, argued that energy metabolism should be proportional to the surface area of the body rather than its mass or volume. The issue is that metabolism generates heat, and the amount of heat an animal can dissipate into the environment depends on its body surface area.
Since Sarrus and Rameaux proposed their explanation, many other attempts have been made over the past 185 years.
African elephants consume even more modestly, with a daily intake of 4-7% of their body weight.
Perhaps the most famous of these is a study by American researchers Geoff West, Jim Brown, and Brian Enquist published in 1997. They proposed a model describing the transport of essential substances through a network of branching tubes, simulating a circulatory system.
They argued that their model provides “a theoretical, mechanical basis for understanding the central role of body size in all aspects of biology.”
The two explanations are academically similar. Like many other approaches proposed over the past century, they attempt to explain biological patterns by citing physical and geometric constraints.
The Issue Lies in Evolution
Living organisms cannot exist regardless of physical laws. However, evolution has proven adept at finding ways to overcome physical and geometric limitations.
In their new study, biologists at Monash University decided to examine what would happen to the relationship between metabolic rate and size if physical and geometric constraints were ignored.
They developed a mathematical model indicating that animals would spend the majority of their energy in early life on growth, and once they reached maturity, most energy would be devoted to reproduction.
They sought to determine which factors in animal life govern reproductive capacity throughout their lives and discovered that larger animals that conserve energy, like the aforementioned whales, are more successful in reproducing.
In other words, natural selection has done its work, making the physically puzzling situation understandable. The American biologist Theodosius Dobzhansky famously stated: “Nothing in biology makes sense except in the light of evolution.”
In summary, sometimes biology and the wonders of life create phenomena that seem like “miracles” in the material world.
