factor demonstrating the impossibility of the reptile-bird
evolution scenario is the structure of avian lungs, which
cannot be accounted for by evolution.
In land-dwelling creatures, air flow is bidirectional.
Upon inhaling, the air travels through the passages in the
lungs (bronchial tubes), ending in tiny air sacs (alveoli).
The exchange of oxygen and carbon dioxide takes place here.
Then, upon exhaling, this used air makes its way back and
finds its way out of the lung by the same route.
In birds however, air is unidirectional. New
air comes in one end, and the used air goes at the other end.
Thanks to special air sacs all along the passages between
them, air always flows in one direction through the avian
lung. In this way, birds are able to take in air nonstop.
This satisfies birds' high energy requirements. This highly
specialized respiratory system is explained by Michael Denton
in his book A Theory in Crisis:
In the case of birds,
the major bronchi break down into tiny tubes which permeate
the lung tissue. These so-called parabronchi eventually
join up together again, forming a true circulatory system
so that air flows in one direction through the lungs. ...[T]he
structure of the lung in birds and the overall functioning
of the respiratory system is quite unique. No lung in any
other vertebrate species is known which in any way approaches
the avian system. Moreover, it is identical in all essential
details in birds as diverse as humming birds, ostriches
Bird lungs function in a way
that is completely contrary to the way the lungs of
land animals function. The latter inhale and exhale
through the same passages. The air in bird lungs, in
contrast, passes continuously through the lung in one
direction. This is made possible by special air sacs
throughout the lung. Thanks to this system, whose details
can be seen overleaf, birds breathe nonstop. This design
is peculiar to birds, which need high levels of oxygen
during flight. It is impossible for this structure to
have evolved from reptile lungs, because any creature
with an "intermediate" form between the two types of
lung would be unable to breathe.
BREATHING IN: The air which enters birds' respiratory
passages goes to the lungs, and to air sacs behind them.
The air which is used is transferred to air sacs at
||BREATHING OUT: When a bird breathes
out, the fresh air in the rear air sacs goes into the
lungs. With this system, the bird is able to enjoy a constant
supply of fresh air to its lungs.
There are many details in this lung system, which is shown
in very simplified form in these diagrams. For instance,
there are special valves where the sacs join the lungs,
which enable the air to flow in the right direction. All
of these show that there is a clear design at work here.
This design not only deals a death blow to the theory
of evolution, it is also clear proof of creation.Fresh
air moves out of the rear air sacs to the lungs.Stale
air is expelled from the front air sacs.
The important thing
is that the reptile lung, with its bidirectional air flow,
could not have evolved into the bird lung with its unidirectional
flow, because it is not possible for there to have been an
intermediate model between them. In order for a creature to
live, it has to keep breathing, and a reversal of the structure
of its lungs with a change of design would inevitably end
in death. According to evolution, this change must happen
gradually over millions of years, whereas a creature whose
lungs do not work will die within a few minutes.
Molecular biologist Michael Denton, from the
University of Otago in New Zealand, states that it is impossible
to give an evolutionary account of the avian lung:
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
In brief, the passage from a terrestrial lung
to an avian lung is impossible, because an intermediate form
would serve no purpose.
Another point that needs to be mentioned here
is that reptiles have a diaphragm-type respiratory system,
whereas birds have an abdominal air sac system instead of
a diaphragm. These different structures also make any evolution
between the two lung types impossible, as John Ruben, an acknowledged
authority in the field of respiratory physiology, observes
in the following passage:
The earliest stages
in the derivation of the avian abdominal air sac system
from a diaphragm-ventilating ancestor would have necessitated
selection for a diaphragmatic hernia in taxa transitional
between theropods and birds. Such a debilitating condition
would have immediately compromised the entire pulmonary
ventilatory apparatus and seems unlikely to have been of
any selective advantage.113
Another interesting structural design of the
avian lung which defies evolution is the fact that it is never
empty of air, and thus never in danger of collapse. Michael
Denton explains the position:
Just how such a different
respiratory system could have evolved gradually from the
standard vertebrate design without some sort of direction
is, again, very difficult to envisage, especially bearing
in mind that the maintenance of respiratory function is
absolutely vital to the life of the organism. Moreover,
the unique function and form of the avian lung necessitates
a number of additional unique adaptations during avian development.
As H. R. Dunker, one of the world's authorities in this
field, explains, because first, the avian lung is fixed
rigidly to the body wall and cannot therefore expand in
volume and, second, because of the small diameter of the
lung capillaries and the resulting high surface tension
of any liquid within them, the avian lung cannot be inflated
out of a collapsed state as happens in all other vertebrates
after birth. The air capillaries are never collapsed as
are the alveoli of other vertebrate species; rather, as
they grow into the lung tissue, the parabronchi are from
the beginning open tubes filled with either air or fluid.114
Parabronchial tubes, which enable
air to circulate in the right direction in birds' lungs.
Each of these tubes is just 0.5 mm. in diameter.
In other words, the passages in birds' lungs
are so narrow that the air sacs inside their lungs cannot
fill with air and empty again, as with land-dwelling creatures.
If a bird lung ever completely deflated, the
bird would never be able to re-inflate it, or would at the
very least have great difficulty in doing so. For this reason,
the air sacs situated all over the lung enable a constant
passage of air to pass through, thus protecting the lungs
Of course this system, which is completely different
from the lungs of reptiles and other vertebrates, and is based
on the most sensitive equilibrium, cannot have come about
with unconscious mutations, stage by stage, as evolution maintains.
This is how Denton describes this structure of the avian lung,
which again invalidates Darwinism:
The avian lung brings
us very close to answering Darwin's challenge: "If it could
be demonstrated that any complex organ existed, which could
not possibly have been formed by numerous, successive, slight
modifications, my theory would absolutely break down."115
Denton, A Theory in Crisis, Adler & Adler, 1986,
112 Michael Denton, A Theory in Crisis,
Adler & Adler, 1986, pp. 211-212. (emphasis added)
113 J. A. Ruben, T. D. Jones, N. R. Geist,
and W. J. Hillenius, "Lung Structure And Ventilation in Theropod
Dinosaurs and Early Birds," Science, vol. 278, p.
114 Michael J. Denton, Nature's Destiny,
Free Press, New York, 1998, p. 361.
115 Michael J. Denton, Nature's Destiny,
Free Press, New York, 1998, pp. 361-62.