Re: Evolution is alive and well

Glenn R. Morton (grmorton@waymark.net)
Sun, 18 Oct 1998 12:16:59 -0500

At 05:15 PM 10/12/98 PDT, Adam Crowl wrote:
>Personally I think this is a bit of an ask. What does it require to
>answer? Imagine how a new organ might develop - lungs beginning as some
>invagination along the alimentary canal. Where did that beginning begin?
>What caused it?
>
>As a Darwinian I'd say it began as some mutation in the developmental
>process, and it gave its possessor some slight advantage, or was not
>disadvantageous. Over time that was enough. Say a fish gulps air. At
>first it uptakes gases via the blood vessels and somatic cells lining
>its stomach. Any increase in area is advantageous, at first, but a
>bigger stomach doesn't work as well. Instead a separate cavity is better
>and over time and generations this increases in size and vascularisation
>- ultimately creating a dizzying diversity of "lungs" amongst fish and
>tetrapods. And some either lose lungs [chondrichtyans] or change them
>into swim bladders [teleosts].

Hi Adam,

This is not what paleontology and comparative anatomy says about the origin
of the lungs.

"The lungs developed from the swim bladders of fish. The larynx first
evolved as a device to protect the lungs from the influx of water and
foreign objects. The basic physiologic factors that structure the way in
which human beings produce intonational signals follow from these
phylogenetic events." ~ Philip Lieberman, The Biology and Evolution of
Language, (Cambridge: Harvard University Press, 1984), p. 99

and

"Air-breathing fish instead filled their swim-bladder/lung by swallowing
air, which then was transferred to their bloodstream from the swim bladder
serving as a lung. The change in function of the swim bladder constitutes
a functional branch-point. The new behavior is disjoint with the previous
behavior of fish. Life out of water is quite different and novel compared
with a watery existence.
"Given these new conditions of life--life out of water--there are
selective advantages for the further development of the larynx. The
presence of the larynx itself yields the possibility for further changes.
As Negus points out, the next stage in the evolution of the larynx was the
development of fibers to pull the larynx open to allow more air into the
lungs during breathing. Further stages of evolution yielded cartilages
that facilitate the opening movements of the larynx. The elaboration of the
larynx yields a second functional branch-point when it can act as a
sound-generating device. The process of phonation, in which the vocal
cords move rapidly inward and outward to convert the steady flow of air
from the lungs into a series of 'ppuffs' of air, can occur in the larynges
of animals like frogs. negus's comparative studies again demonstrate that
many of the larynges of many animals are specialized for phonation at the
expense of respiration." ~ Philip Lieberman, The Biology and Evolution of
Language, (Cambridge: Harvard University Press, 1984), p. 265

Now, the big change between a lung and a swim bladder needed to improve gas
exchange, is the invagination of the swimbladder surface. A swim bladder
with a smooth surface has a minimal surface area in which gases can be
exchanged. One which lots of invaginations increases the surface area and
increases the gas exchange rate.
glenn

Adam, Apes and Anthropology
Foundation, Fall and Flood
& lots of creation/evolution information
http://www.isource.net/~grmorton/dmd.htm