Page 90 - The Evolution Impasse 2

88 Origin of the Avian Lung

REPTILE LUNG BIRD LUNG
REPTILE LUNG
BIRD LUNG
air in out air out

bron chia
al ve ol air in
par a bron chia

The anat o my of birds is very dif fer ent from that of rep tiles, their sup posed an ces tors.
Birds lungs fun tion in a to tal ly dif fer ent way from those of land-dwell ing an i mals. Land-
dwell ing an i mals breathe in and out from the same air ves sel. In birds, while the air en -
ters in to the lung from front, it goes out from the back. This dis tinct sys tem is spe cial -
ly made for birds, which need great amounts of ox y gen dur ing flight. It is im pos si ble for
such a struc ture to evolve from the rep tile lung.

Still an oth er fea ture re fut ing the one of the world's au thor i ties in this
ev o lu tion of the avi an lung is that its field, ex plains, be cause first, the avi an
struc ture leaves it nev er emp ty of lung is fixed rig id ly to the body wall
air, and fa ces the dan ger of col lapse and can not there fore ex pand in vol ume
and, sec ond, be cause of the small di am -
if it should be come emp ty. Michael
e ter of the lung cap il la ries and the re -
Denton has this to say:
sult ing high sur face ten sion of any liq -
Just how such a dif fer ent re spir a to ry
uid with in them, the avi an lung can -
sys tem could have evolved grad u al ly
not be in flat ed out of a col lapsed
from the stand ard ver te brate de sign
state, as hap pens in all oth er
with out some sort of di rec tion is,
ver te brates aft er birth. The
again, very dif fi cult to en vis age, es -
air cap il la ries are nev er col -
pe cial ly bear ing in mind that the
lapsed as are the al ve o li of oth er
main te nance of re spir a to ry
ver te brate spe cies; rath er, as they
func tion is ab so lute ly vi tal
grow in to the lung tis sue, the par -
to the life of the or gan -
a bron chi are from the be gin -
ism. Moreover, the
ning open tu bes filled with
unique func tion and 86
ei ther air or flu id.
form of the avi an
This sys tem, to tal ly dif -
lung ne ces si tates
fer ent from the lungs of rep tiles and
a num ber of ad -
di tion al unique ad ap ta tions dur ing oth er ter res tri al ver te brates, can not
avi an de vel op ment. As H. R. Dunker, have formed grad u al ly through un -
The Evolution Impasse II