Why Can't Humans Fly?

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The reason for why humans can't fly, is simple: the human's body is not adapted for that particular function. The human skeleton is adapted to do lots of other things but not fly.

On the other hand, there are animals who are specialised in this particular matter, these are actually the birds.

Birds are warm-blooded vertebrates just as humans, but they have fore-limbs modified to wings and have their skin covered with feathers. They have the power of flight.

The feathers are the single external feature that distinguishes birds from other vertebrates.

The feathers are produced from the skin which is loose and dry and they form an insulating layer around the bird's body, helping to keep its temperature constant, and repelling water.

The wings are specially developed for flight, having a large surface area and very little weight.

Humans have arms instead of wings and that is one of the reasons why they can not fly.

Some parts of the human's arm are similar to the bird's wing.

Birds wings consist of: 

The ball joints, followed by the humerus, then the ulna and radius, the carpals, and then 1st finger (where the bastard wing is located), 2nd and 3rd fingers. Ligaments surrounding this structure have attached, the primary and secondary feathers.

The human arm consist of: 

The head of the humerus, followed by the shaft of the humerus, the joint of the elbow, the ulna and radius, then joining the wrist bones to which the hand bones are attached. This follows by 5 finger bones.

The down feathers of the bird's wings are fluffy, trapping a layer of air close to the body.
The flight feathers and coverts, are broad and flat and offer resistance to the passage of air.

Features that humans do not have that adapt the bird for flying: 

1) The fore-limbs which are wings with a large surface area provided by feathers.

2) Large pectoral muscles for depressing the wings.

3) A deep, keel-like extension from the sternum for the attachment of the pectoral muscles.

4) Well developed coracoid bones which transmit the lift of the wings to the body.

5) A rigid skeleton giving firm framework for attachment of the muscles concerned with flying movements. Many of the bones which can move in mammals are fused together in birds.

6) Hollow bones which reduce the bird's weight.

7) A very efficient breathing system.

This is how flying works:

- The pectoral muscles contract.

- At this point the wing is pulled downwards.

- Air resistance then gives an up-thrust on the wing.

- The up-thrust is transmitted from the wing join to the caracoid bone.

- The whole body is then lifted.

The flight of a bird can be divided into flapping, where the pectoral muscles contract; and gliding, where the wings are out-spread and used as aero-foils.

The bastard wings are important during take-off. The up-stroke of the wings is much more rapid than the down-stroke. The way in which the primary and secondary feathers overlap produces a maximum resistance during the down-stroke and a minimum one on the up-stroke.

The tail feathers help to stabilise the bird in flight and are particularly important in braking and landing.

- On the up-stroke, air passes between vanes.
- On the down-stroke, air resistance closes the feathers.

This are the things that make birds so special and the reasons why they can fly and a man can NOT.

Our skeletons are very different as well as our locomotion.

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