On Thu, 19 Jun 2003 03:28:40 +0000 (UTC), oxiran{at}yahoo.com (Richard)
wrote:

>r norman  wrote in message
news:...
>> On Wed, 18 Jun 2003 02:35:30 +0000 (UTC), oxiran{at}yahoo.com (Richard)
>> wrote:
>
>Thanks for the very thorough answer. That is what I expected the
>answer to be from my understanding of my high school biology (taken
>many years ago).
>
>Is this true then: When animals came out of the water and started
>breathing air, the behavior of coming out of the water did not cause
>genetic changes.  The behavior of coming out of the water created an
>opportunity for certain random genetic changes to improve the animals
>survival rate, and that is why the changes took place.
>
>Thanks again.
>Richard

The transition from aquatic to terrestrial life didn't come about in
the way you describe.  That is, the behavior of moving onto land was
not passed to the offspring so that they would be better at living on
land.  Rather, those aquatic animals that had the genetic machinery to
be able to survive on land were able to live on land and that genetic
machinery was passed to their offspring.

That ability consisted primarily of two things, both present in a
specific line of fish.  First, a sac branching off the digestive
system.  The fish would swallow air, passing it into the sac and using
it to assist in respiration.  This structure (closely related to the
swim bladder of many fish) is found in the lungfish and helps it to
survive when the ponds it lives in dry up during the hot summer
months. The second is sets of pectoral and pelvic fins with a
particular internal bony structure that are able to allow the fish to
hobble across the land trying to return to the water.  This structure
is found in the lobe-fin fish.

A fish with both characters would be able to survive long enough when
its pond dried up to be able to get back to water.  So any genetic
mutation that let the fish survive longer on land would be advantagous
under those conditions and would be selected for.  So the genetic
ability preceded the behavior.  It is not the result of the behavior.
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