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From: dean2@garnet.berkeley.edu (Dean Pentcheff)
Newsgroups: sci.bio
Subject: Re: Bats by a Mile
Summary: evolutioary constraint
Message-ID: <1991May25.184145.25738@agate.berkeley.edu>
Date: 25 May 91 18:41:45 GMT
Article-I.D.: agate.1991May25.184145.25738
References: <1991May17.044756.26698@ddsw1.MCS.COM> <1991May18.040410.15199@agate.berkeley.edu> <3075@cod.NOSC.MIL>
Sender: Dean Pentcheff
Reply-To: dean2@garnet.berkeley.edu (Dean Pentcheff)
Followup-To: sci.bio
Organization: Department of Integrative Biology, UC Berkeley
Lines: 31

>Dean Pentcheff writes:
>>Wouldn't the speed of sound in the medium have some effect?  Sound is
>>_much_ faster in water than in air.  Wouldn't that make it much more
>>difficult to measure distances by timing sound echos?
>
In article <3075@cod.NOSC.MIL> deichman@cod.NOSC.MIL (Shane D. Deichman) writes:
>Not if you were raised on just the one velocity, and had adapted to it....

This reflects a rather old fashioned view of evolutionary biology.  The
idea that organisms are optimally adapted systems for their environment
was discarded some time ago.  There are several reasons, some of which
have to do with the genetic variation available for selection to act
upon.  More obviously, organisms are constrained by the physical nature
of themselves and their  environment.  Sensory systems are bound to
operate within physical limits.  If sound is over four times faster in
water than in air (which it is), then the processing system has to be
four times more precise to achieve the same result.  Eventually, you
reach the limits of what neuronal systems can do.

One of the interesting differences I ran across is that sound in water
is "reciprocal," but not in air.  In the water, if a listener at point
A can hear sound from point B, a listener at B can hear sound from A
equally well.  This is not true in air.  Wind speeds are suffiently
high (relative to the speed of sound in air) that wind shear can
refract sound in a non-reciprocal way.  Water currents are much slower,
so the phenomenon is insignificant there.  Evolutionary adaptation
cannot sidestep this (or any other) physical phenomenon.

-- 
Dean Pentcheff  (dean2@garnet.berkeley.edu)
Department of Integrative Biology, University of California, Berkeley CA 94720