The passenger aircraft development over the last century reflects the evolution of flying animals.

According to Duke University mechanical engineer from Durham, North Carolina Adrian Bejan, evolution is not only a biological phenomenon, it is a physical phenomenon which is driven by physical laws. In birds, it includes aerodynamics.

Bejan based his argument on the "constructal law" theory which states that evolution involves both animate and inanimate systems in a way that it progressively provides easier access to the current flows around them such as water, air, electricity or blood.

"For a finite-size system to persist in time (to live), it must evolve in such a way that it provides easier access to the imposed currents that flow through it," Bejan said.

Scientists traditionally believe that it is impossible to witness biological evolution because it occurs on timescales that are much longer than a human life. However, researchers said that airplanes follow the evolution pattern of flying animals over a perceptible period of time.

The team found that airplanes follow the principle of bats, birds and other flying animals. This means larger designs are more efficient, faster and have a bigger range for flying. The airplane's mass is proportionate to the engine mass like how the heart, muscles and lungs of a flying animal are proportional to its body mass. The airplane's wingspan is also proportionate to the fuselage length and the needed amount of fuel is proportionate to its body size.

Through time, small planes evolved into various sizes with a particular niche each. The largest planes have become even larger. The evolution of animals is too slow for observation but the human-machine evolution of the airplane can be observed in a human lifetime. According to Bejan, animal and airplane evolution being predicted would mainly benefit biologists.

The researchers said that the next airplane design could be easily predicted based on this airplane evolution model. They predict the development of larger aircrafts with wingspans and engine sizes remaining proportionate to the fuselage sizes.

The study findings suggest that the process of evolution may be applied to other fields of study as well.