Evolution's greatest mistakes
10 August 2007
NewScientist.com news service
Claire Ainsworth and
Michael Le Page
http://www.newscientist.com/channel/life/mg19526161.800-evolutions-greatest-mistakes...
Bad ventilation
THE ascent of Mount Everest's 8848 metres without bottled oxygen in 1978 suggests that human lungs are pretty impressive organs. But
that achievement pales in comparison with the feat of the griffon vulture that set the record for the highest recorded bird flight
in 1975 when it was sucked into the engine of a plane flying at 11,264 metres.
Birds can fly so high partly because of the way their lungs work. Air flows through bird lungs in one direction only, pumped through
by interlinked air sacs on either side. This gives them numerous advantages over lungs like our own. In mammals' two-way lungs, not
as much fresh air reaches the deepest parts of the lungs, and incoming air is diluted by the oxygen-poor air that remains after we
breathe out. Our air passages end in air sacs, or alveoli, which unlike the tubes of bird lungs have to be relatively large to
ensure adequate air flow. This means less surface area for gas exchange. Large alveoli also need thick walls for support, but these
reduce gas exchange. As a result, humans have delicate alveolar walls that are prone to become damaged, leading to a condition
called emphysema.
Verdict: Bird lungs are far superior to ours and, the more they are studied, the longer the list of their advantages becomes. We
mammals might have been even more successful had we inherited or evolved similar lungs.
