Why Can’t We Fly?

Human chest muscles, called pectorals, only make up 1 percent of an average person’s body weight. A bird’s pectorals are an amazing 30 percent to half of its total weight.

Strong pectorals bolster bird wings as they cut through the air, pushing birds forward and propelling them into the sky.

But that’s not the only difference between a person’s physique and a bird’s build that keeps people on land and birds in the sky.

In order to take flight, people would have to undergo a significant redesign of the chest muscles, chest cavity, bones, skin, feet and organs.

Light as a feather is an expression that can describe birds’ body parts in general.

“The respiratory tract goes into the bone to help reduce the weight,” said Dr. Julia K. Whittington, medical director of the Wildlife Medical Clinic at the University of Illinois at Urbana-Champaign. “Air sacs fill a bird’s body to keep it cool as well as light weight for flight. “

Bone structure is very different between human and avian species.

“Several of the major bones, the femur (leg bone) and humerus (arm bone), are hollow. These are called pneumatic bones,” Whittington said.

A side view of a bird would show that its whole body is designed to fly: it looks like a compressed tear drop. Even the beak is streamlined for flight, representing a slimmer version of the jaw bone.

Whittington said the bird skeleton is reinforced for flight. “The fused skeleton along the spine gives stability like a boat,” she said. Tail feathers act like a brake or rudder for steering, she explained.

“If you watch a bird’s flight in slow motion it’s truly incredible. Each independent flight feather can be adjusted for flight,” she said.

Feathers are one of the most significant differences between humans and birds.

“Feathers are modified scales,” Whittington said, adding their origins date to a bird’s ancestor — the dinosaur.

Feathers can keep a bird warm or waterproof, depending on the bird species. They are shaped differently on the top sides and bottom sides to best create lift and propulsion through the air.

Another holdover from dino days is the egg. Baby birds develop in an egg outside the mother, although one bird species, the kiwi, incubates eggs inside its body.

Some birds never got the hang of hover or glide with the Earth far below. Ostriches and penguins are two types of birds that are permanently grounded.

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