Page 52 - Design in Nature

50 DESIGN IN NATURE

Trachea permeate the lung tissue. These so-
Syrinx called parabronchi eventually join up
Interclavicular together again, forming a true
sac
circulatory system so that air flows in
one direction through the lungs….
Although air sacs occur in certain
reptilian groups, the structure of the
lung in birds and the overall
Anterior
thoracic functioning of the respiratory system
sac is quite unique. No lung in any other
vertebrate species is known which in
Posterior
thoracic sac any way approaches the avian system.
Moreover, it is identical in all essential
Abdominal sac
details in birds… 19
Unidirectional airflow in the bird's lungs is In his book Evolution: A Theory in
facilitated by a system of air-sacs. These
sacs collect air and then pump it regularly Crisis, Michael Denton also points out to
into the lung. In this way, there is always
the impossibility of formation of such a
fresh air in the lungs. A complex
respiratory system such as this has been perfect system through progressive
created to satisfy birds' needs for high
evolution:
quantities of oxygen.
Just how such an utterly different
respiratory system could have
evolved gradually from the standard vertebrate design is fantastically
difficult to envisage, especially bearing in mind that the maintenance of
respiratory function is absolutely vital to the life of an organism to the
extent that the slightest malfunction leads to death within minutes. Just
as the feather cannot function as an organ of flight until the hooks and
barbules are coadapted to fit together perfectly, so the avian lung
cannot function as an organ of respiration until the parabronchi system
which permeates it and the air sac system which guarantees the
parabronchi their air supply are both highly developed and able to
function together in a perfectly integrated manner. 20

In short, the transition from terrestrial lung to avian lung is impossible
due to the fact that the lung that would be in a transitional developmental
stage would have no functionality. No creature without lungs can live for