From:    Mark Isaak
To:      All                                    Msg #92, Jun-18-93 08:10PM
Subject: Polar Bear Hair

Organization: The Aurora Group, Palo Alto, CA
From: isaak@aurora.com (Mark Isaak)
Message-ID: <1993Jun19.041030.281@aurora.com>
Reply-To: isaak@aurora.com (Mark Isaak)
Newsgroups: talk.origins


I finally found the reference I remembered to the myths about polar bear
hair.  It's in "Letters", _Scientific American_, Sept. 1988, pg. 8, by D. M.
Lavigne, Dept. of Zoology, Univ. of Guelph, Ontario.  (In the process, I
also found a letter (from Aug. 1991) debunking the idea that humans are the
only mammals which can't drink and breathe simultaneously.  But I digress.)
I quote the polar bear letter herewith, in its entirety:

    To the Editors:
      "Solar Polar bears" ["Science and the Citizen," March] is only the
    latest version of a story that has been in circulation now for almost 10
    years.  The fact that the story is largely fictional seems to go
    unnoticed.
      The solar-polar-bear tale is a classic example of scientific
    folklore.  Each time it is told, new elements are added, but the
    essential ingredients remain the same.  Obviously the story has wide
    appeal, and most readers, including many scientists, it seems, are not
    aware of its problems.  "It must be true," they say; "I saw it in the
    newspaper"--or in _Time_ (December, 1978), _Natural History_ (October,
    1981) or _BBC Wildlife_ magazine (February, 1988).  Now that it has
    reached _Scientific American_, can textbooks be far away?
      Space does not allow me to outline the entire history of this
    legend, but I should like to put your own story into perspective.  It
    has been known since the late 1960's that the pelts of certain white
    animals are capable of trapping sunlight and converting some of it into
    warmth on sunny days in cold environments.  The white hairs reflect and
    transmit much of the visible and near-infrared rnadiation (the major
    components of sunlight) down through the pelt, where it is absorbed by a
    dark skin.  Skin temperatures well above the deep body temperature (37
    degrees C) have been recorded in such animals.  The heat that is emitted
    from this warm skin then becomes trapped by the white hairs, warming the
    layer of insulating air in the pelt.  Such a "greenhouse effect" is not
    unique to seals or polar bears; it was reported in certain arctic and
    subarctic plants and "woolly bear" caterpillars as early as 1955.
      The seminal work that spawned the legend of "solar polar bears" was
    a more recent observation (but not as recent as suggested in your
    story).  Working at the University of Guelph in the early 1970's, Nils
    Oritsland and I found that the pelts of several white animals, including
    whitecoated harp seal pups and polar bears, _absorb_ much of the
    ultraviolet component in sunlight.  (Short-wave UV rays make up less
    than 10 percent of sunlight; they contribute to the synthesis of vitamin
    D, cause sunburning and tanning and in highly reflective environments
    may cause damage to the human cornea, a condition known as snow
    blindness.)  Since ice and snow reflect UV, we found that UV photographs
    could reveal "black" seal pups and polar bears and also military
    equipment painted "white" for camouflage in the Arctic--but with
    UV-absorbent paint!  (Other details of our work as they were outlined in
    the story are incorrect, but since these details are not essential
    elements of the legend, I shall not go into them here.)
      With this brief overview we can now evaluate your version of the
    solar-polar-bear legend.  Your piece states that polar-bear fur is a
    "natural collector that convert part of the solar-radiation spectrum
    into heat with an efficiency exceeding 95 percent."  It does not say
    specifically which part of the solar spectrum might be involved, but I am
    not familiar with any such data.  The information with which I am
    familiar suggests that polar-bear hair is not nearly as efficient as
    contended in utilizing visible and near-infrared components of sunlight,
    and not nearly as efficient as certain seal pelts.  Even cow pelts
    appear to be more efficient in this regard than polar-bear fur.
      Your piece also states that the polar bear is the "most efficient
    absorber" of the UV component in sunlight, but this is also not correct.
    Every white bird and mammal we have examined absorbs UV with wavelengths
    of between about 290 nanometers (the shortest wavelength found in
    sunlight) and 320 nm., and dark-colored birds and mammals are much more
    effective than any white animals, including polar bears, in absorbing
    the entire range of UV wavelengths in sunlight (between 290 and 400
    nm.).
      The observation that individual polar-bear hairs are "actually
    colorless, not white," attributed to Richard E. Grojean sometime within
    the past seven years, was actually published by Oritsland and Keith
    Ronald in 1978.  Their observations pertained _only_ to visible and
    near-infrared radiation, not to UV.  And to compare a polar-bear hair to
    a "quartz fiber" is nonsense.  Quartz transmits near-UV (that is why
    quartz lenses are used for UV photography), whereas, as the piece
    correctly notes, polar-bear hair absorbs UV.
      It is for this reason that mechanisms proposed to explain how
    polar-bear hairs trap UV radiation to gain heat will not work.  In early
    versions of the legend it was proposed that the UV somehow entered the
    hollow core of the polar-bear hair, which then functioned as a "light
    pipe" to direct the radiation to the skin.  Of course, since the UV is
    absorbed by the protein in the outer layers of the hair, little if any
    of it would actually reach the hollow core to be transmitted magically
    down the light pipe.  Presumably in an attempt to overcome this problem,
    the legend has been modified, as is shown in the diagram for your piece.
    Now it is proposed that the UV is captured by the outer solid part of
    the hair (labeled "Transparent shaft") and aimed "toward the skin."
    Once again there is a serious problem:  the "shaft" of the polar-bear
    hair is _not_ transparent to UV; it absorbs it.
      Yet if a UV-absorbent material could significantly improve the
    efficiency of solar collectors, then, as I have indicated above,
    researchers would choose a highly UV-absorbent dark pelt rather than a
    white polar-bear pelt for the purpose.  Indeed, if one wants to fill
    solar collectors with hairlike fibers in order to _absorb_ more of the
    solar spectrum, why not fill the collectors with black hairs?
      This brings me to what is perhaps the most perplexing aspect of this
    bit of folklore: the tenuous connection between UV radiation and heat
    from the sun.  No one to my knowledge has demonstrated that UV
    contributes anything to thermoregulation in polar bears and other
    mammals.  And since UV is only a small part of incident solar radiation,
    it seems peculiar to concentrate on this part of the spectrum in order
    to improve solar collectors or, as in earlier versions of the legend,
    cold-weather clothing for the military.
                                 D. M. Lavigne
    Department of Zoology
    University of Guelph
    Guelph, Ontario

--
Mark Isaak           "There lives more faith in honest doubt,
isaak@aurora.com      Believe me, than in half the creeds." - Tennyson