Author:
           
            Wesley R. Elsberry
Email:
            welsberr@inia.tamug.tamu.edu
Date:
            1998/01/16
Forums:
            talk.origins 



In article ,
Mr. C.  wrote:
>In article <34BC3E8A.20FE@pop.seanet.com>, "kale@pop.seanet.com"
> wrote:

[...]

K> Karl,

K> Welcome back from where ever it is you ran to.  You left in such a hurry 
K> that you forgot to supply me with the sources you used to put together 
K> your cetacean evolution post.

KC>The problem is that I CRUSHED your cetacean evolution
KC>theory. My post clearly showed where the evolutionist had made
KC>their mistakes.  Instead of answering the post YOU have hid
KC>behind your so-called demand. sheeze.

If by "cetacean evolution" Karl is referring to his "dolphin
echolocation disproves evolution!" post, that has been
responded to in such a manner that Karl could do no better than
"Is not!" in email responses.  I encouraged Karl to post his
responses to the newsgroup, so they could get archived at
DejaNews and the like.  No posts appeared.  Karl claimed that
the evolution of cetacean biosonar was impossible.  What I
support below is that plausible pathways in function exist
since relatively unspecialized mammalian auditory systems can
perform well in biosonar target discrimination tasks, and that
click production can be seen as a co-opted development from
social communication.  Here's my post on the topic:

In article ,
Karl  wrote:

KC>Dolphins are incredible animals which exhibit an intricate
KC>communication and detection system in the form of underwater
KC>sonar.  

Hey... finally a Scicre argument that takes place in the field
of my dissertation research.

If it is sonar, then it is not communication.  Sonar and
communication are functional categories.  Vocalizations can be
whistles (tone-based) or clicks (pulse-based).  Communication
may occur via either type of vocalization.  In dolphins,
no significant role has been found for whistles in biosonar.

KC>Using specialized mechanism in the nasal passages just
KC>below the blowhole enables them to emit short, pulse-type
KC>sounds. 

Please identify your source for this information.  I'm
intrigued, because if Karl is referring to Ted "Grizz"
Cranford, Bill Van Bonn, Tricia Kamolnick, Monica Chaplin, and
Jennifer Carr's endoscopic research on the location of the
vocalization emission source, that stuff was just recently
presented at the International Bio-Acoustics Council meeting in
October.  This would represent the first time that a SciCre-ist
had used research that I personally witnessed in an argument.
Of course, Karl could be referring to hypotheses and
speculation presented earlier as if these were confirmed and
generally known to be true.

The "specialization" is some ridged folds known as the "monkey
lips".

KC>The clicks are beamed forward, with the oily melon serving as
KC>an acoustic lens and the bony forehead as a reflector.  

Apparently referencing more of Cranford's work with computed
tomography of the melon and acoustic propagation modelling.

KC>As mentioned above these clicks are used as a form of
KC>underwater sonar.  

Not all clicks are sonar.  Some may be used in communication.
Blackwood and Evans presented on this issue just this year
at the Animal Behavior Society meeting.

KC>Using these sonar clicks they are able to detect objects
KC>underwater by using 'echolocation' in which the sounds
KC>are reflected off solid surfaces back to their 'sensitive
KC>ears' which are in the area of their lower jaw, known as an
KC>"acoustic window." 

Phbbbbbt.  The dolphin's ears are in the same place as in
other mammals.  There may be an acoustic window through the
lower jaw, but that does not move the ears.

KC>Inside is a specialized fatty tissue which connects to the
KC>inner ear. 

Specialized?  Does Karl have a reference for that claim?

KC>The jawbone itself is hollow, and filled with an oily fluid
KC>that also conducts sound efficiently. Inside the dolphins inner
KC>ear, an extra large number of nerve cells help account for this
KC>animals ability to hear such a wide-range of frequencies.  

Wever suggested in 1972 that the higher numbers of ganglion
cells in the dolphin inner ear compared to humans aids in
representation of high frequency information.  However, getting
high frequency sound to activate those neurons requires a bit
more.  The change in width of the dolphin's (Tursiops
truncatus) basilar membrane is about 14x.  In humans, the
change in width is about 6.25x.  The stiffness of the basilar
membrane in Tursiops is also greater than in humans.  These two
factors are, IMO, more important to the reception of a wide
range of sound and high frequency sound than simple number of
ganglion cells present.  One point in favor of this is that the
absolute numbers of inner and outer hair cells, the sensory
transducers which activate those ganglion cells, are of
comparable numbers in Tursiops (3451 | 13933) and humans (3475
| 11500) (Au 1993 pp.28-30).

KC>By interpreting these echoes, dolphins can distinguish the
KC>direction, distance, speed, size, shape and even the density of
KC>an object.

I'd like references to add to my collection on "speed" and
"density" discrimination.  See below for comments on passive
determination of direction in dolphins.

KC>The problem is, how did this incredibly complex system
KC>evolve.  Just the evolution of the sonar transmitting
KC>portion boggles the mind.  

As has been noted, some minds are easier to boggle than 
others.

KC>What function would it serve without a functioning oily
KC>mellon?  

Communication has been mentioned before.  Communication does
not require high directivity.  Biosonar does require
directivity of the signal, which an acoustic lens *enhances*.
Communication can use both whistles and clicks.  More 
efficient click production for communication could have 
driven the specialization of the "monkey lips", which could
then be exapted for biosonar use.

KC>How would it produce the sonar without the specialized
KC>mechanism functioning properly?  

One doesn't need an acoustic lens for some information to
be gained from the environment via sound.  Humans are not
specialized echo-locators, yet a sensory aid for the blind
exists which consists of a pinger.  The person using this
device comes to be able to detect a variety of obstacles
in their path.  The pinger is not a system that is
specialized in the same sense as the dolphin transmitting
system, and yet useful information is obtained.  There is
wide variation in the structure of pulses used in biosonar
by cetaceans.  Suggestions that only the specific modern
form produced by Tursiops spp. are useful are risible.

KC>Now comes the second part.  How did the dolphin evolve the
KC>ability to receive the sonar through its jawbone?  

Karl can ask to borrow his significant other's vibrator, turn
it on, and hold it against his jaw.  Surprise!  One can hear
such sound through the magic of bone conduction.

KC>How did it evolve to be filled with oil?  

If oil serves better as a conductor than marrow, one can
speculate about a graded series of changes with marrow
having progressively greater fat content.

KC>What good was the receiving system when the echo
KC>transmitting system wasn't completely evolved? 

First, communication still happens.  Many cetaceans species
are quite social, including T. truncatus.  Second, partial
function compared to present capabilities is still good
stuff.  Pseudorca can resolve differences in metal
cylinders done to 1/3000th of an inch, but no one in their
right mind would argue that their biosonar was without use
if it only resolved 1/2 of an inch.  Evolutionary adaptation
via natural selection (Hi, Larry!) proceeds via *relative*
fitness.  If the trait of detecting an object at ten feet in
murky water puts those who have it at a relative advantage to
others, it could be retained and spread in the population.
Third, passive acoustic localization of prey items is known
to happen in Tursiops.  The more sensitive the receiving 
system, the better it is for passive localization.  The more
sensitive the receiving system, the more likely it is that
even poor transmission of an active signal will result in
useful information.  The dolphin's passive localization
can place a source within 1.5 to 5 degrees of its actual
position in the horizontal plane, and between 2 and 3.5
degrees in the vertical plane (Au 1993 pp.50-51).

Experiments with humans have shown that subjects listening to
simulated dolphin biosonar ensonification of targets (at
1/128th speed) do just as well on the tasks as the dolphins did
originally (Fish 1976 cited by Au 1993 p.182).  Yet humans do
not have a receiving system tuned for biosonar tasks.  This
suggests that the relatively unspecialized auditory system of
humans is quite capable of handling crude echolocation, which
the auditory prostheses for the blind also confirm.  The
mammalian auditory system in general probably doesn't need any
specialization to start taking advantage of biosonar.

KC>Why evolve the transmitting section if the receiving jawbone
KC>section wasn't completely evolved either?

While the jawbone contributes to perception, it isn't the
only pathway, and even without specializations it would
have contributed to bone conduction.

Again, communication requires projection of sound.  Another
IBAC presentation concerned the apparent targeting of
communication to specific other dolphins in a group, which
would mean that higher directivity of outgoing sound would be
favored if such communications change reproductive success.
The simple task of communicating at a distance would favor
high intensity sound production, which would lead to an
increased likelihood that useful information could be
obtained from the environment by even an unspecialized
receiving system.

KC>Next we have to connect both systems to the brain.  Then
KC>again why would the brain connect to a system that doesn't
KC>function, 

Come again?  Ears in mammals were already connected to the
brain before the ancestors of cetaceans headed back to the sea.
The production of sound for communication was already linked
to the brain.  

KC>or should I say couldn't function in it's early
KC>evolutionary stages?

It functioned for hearing of other sorts first.  The connection
to the brain just is not an issue for those who have more than
a couple of live neurons to rub together.

KC>It doesn't take a rocket scientist to figure out
KC>evolution didn't happen.

I'd say it takes a complete ignoramus.



For information on the sonar of dolphins, I'd recommend

Au, Whitlow W. L.  1993.  The Sonar of Dolphins.  Springer-Verlag.

It's the definitive resource on the topic, with extensive 
bibliographies and summaries of significant research.  Chapters
cover the receiving and transmitting systems, characteristics
of the signals, capabilities, and modelling.  There's even
a chapter comparing dolphin and bat biosonar.  My copy set me
back $83 hot off the presses in 1993, but that's Springer-Verlag
for you.  Hopefully, I'll remember to get Whit to autograph
mine at the marine mammal meeting in Monaco next year.

-- 
Wesley R. Elsberry, 6070 Sea Isle, Galveston TX 77554. 
Student in Wildlife & Fisheries Sciences. http://www.rtis.com/nat/user/elsberry
"you mush faced bum i said and clawed out a piece of his ear" - mehitabel