Evolutionary biology

Coffee!!: Why are polar bears white?

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Conventional, and fairly obvious, wisdom would suggest that the bear avoids being noticed by its prey by blending in with the landscape and moving through the snow on silent feet. Evolving that way should be easy enough – the colour gene drops out, and …

We readily assume that the prey is on land, casting a wary eye around. Not necessarily. Some remarkable BBC footage suggests it may not be so simple:

You can see it, no problem, but you must click the BBC link. – d.

Here, you will hear the bear stomping and see it clearly visible above clear ice – as it would be to a seal approaching a blowhole. Presumably, the seal – apprised of an unexpected caller – goes to another of its many blowholes. But once the bear sits down to wait quietly at one … which one is it? The bear, observed, is apparently lucky one time in ten, by invisible patience alone. I don’t see that anything would change if the bear was green or purple or …

Is it possible that white coats are favored because they are less conspicuous to other bears, who tend to be crabby and territorial much of the time?

10 Replies to “Coffee!!: Why are polar bears white?

  1. 1
    DarelRex says:

    Thought I heard somewhere that the white (actually clear) hairs channel sunlight to the bear’s skin, which is black and absorbs the light strongly. Helps the bear keep warm.

  2. 2
    bornagain77 says:

    DarelRex,

    some notes:

    # Koon, Daniel W., “Power of the polar myth”, New Scientist, Vol. 158, No. 2131, p. 50 (April 25, 1998). “[Koon and Hutchins’] research revealed that the popular notion was not correct, they found that less than .001 percent of red light and less than a trillionth of the violet light transmitted traveled the length of a typical, inch-long hair. Even less ultraviolet light made it from the tip to the base of the hair…As writer Bertrand Russell pointed out, even Aristotle–the most famous scientist of his day–claimed that women have fewer teeth than men, though it never occurred to him to check Mrs. Aristotle’s mouth. The moral of Koon’s study is that a little dose of skepticism never hurts.

    and this:

    The hypothesis emerged with a study in the mid-1970s by zoologists from two universities, the University of Guelph in Canada and the University of Oslo in Norway. The scientists discovered that polar bear pelts reflect very little ultraviolet light, which is invisible light that causes tans and sunburns. A few decades later, a team of researchers from the Boston area proposed that polar bears were using the ultraviolet light to warm their skin. Their hypothesis was based on the fact that polar bear hair is transparent. They claimed the hair might work as a fiber-optic cable, through which light energy travels like electricity through a power wire. Though they did not test the theory, it found its way into the mainstream, inspiring articles in the Christian Science Monitor, the New York Times, and Time magazine.

    Koon decided to test if a polar bear’s hair could actually conduct light. Koon and a student, Reid Hutchins, got a few hairs from a male polar bear that lives at a zoo in Rochester, New York. Their research revealed that the popular notion was not correct, they found that less than .001 percent of red light and less than a trillionth of the violet light transmitted traveled the length of a typical, inch-long hair. Even less ultraviolet light made it from the tip to the base of the hair.

    Thus DarelRex, I guess the theory for the bear hair being a fiber optic cable is false, while the anomaly of why polar bears absorb the heating ultraviolet light so efficiently, compared to other types of hair, remains a unexplained mystery.

  3. 3
    Collin says:

    off-topic

    Flower now has largest genome

    http://news.yahoo.com/s/ap/201.....est_genome

  4. 4
    Robert Byers says:

    Its reasonable to conclude polar bears are white for the same reason the rabbits, foxes etc are. the simple conclusion first.
    It must be related to seen/unseen issues.
    yet what is the mechanism that turned them all white within a short period of time. is it happanchance selection?
    i think the colours of animals has never been explained rightly by selection issues.
    I suspect a innate trigger affects creatures upon immigration to new areas.
    In other words all hair colours are attuned to the colours of the envirorment by laws not yet discovered.
    Speculation.

  5. 5
    bornagain77 says:

    Robert Byers,

    The mechanism for polar bear ‘sub-speciation’ was rapid:

    Post details: Polar bears and mammalian speciation – May 2010
    Excerpt: “Recent genetic studies have shown that polar bears evolved from within brown bears, and that a genetically unique clade of brown bear populations that live exclusively on the Admiralty, Baranof, and Chichagof (ABC) islands of southeastern Alaska’s Alexander Archipelago are more closely related to polar bears than to other brown bears.” “The stable isotope data, phylogenetic analysis, and the geological and molecular age estimates of the Poolepynten specimen indicate that ancient polar bears adapted extremely rapidly both morphologically and physiologically to their current and unique ecology within only 10-30 ky following their split from a brown bear precursor,,,
    http://www.arn.org/blogs/index.....speciation

    Thus you are warranted to postulate some epigentic, ‘evironmental clue’, mechanism as for the rapid adaptation. Yet it must be kept in mind that even though the speciation for brown bears was rapid, that the speciation also came at a cost of the genetic information that was already present in the brown bear population:

    Genetics – Polar Bear
    Excerpt: microsatellite data that can be compared suggest there may be less genetic variation among populations of polar bears than among populations of black bears and brown bears (Paetkau et al. 1995, 1999). Paetkau et al. (1999) also found genetic distances among polar bear populations were at the lower extreme of the distances reported for the gray wolf (Canus lupus), another widely distributed carnivore.

    Evidence from patterns in mtDNA also may hint at somewhat less genetic variation among polar bear populations than among populations of other bears. Cronin et al. (1991) reported only one basic polar bear mtDNA lineage, whereas black and brown bears each have two very divergent lineages. The older species (black and brown bears) appear to have more genetic variation across their ranges than the more recently derived polar bears.

    Greater morphological variation among populations of brown bears (e.g., very large individuals, such as those living on Kodiak Island and coastal Alaska, vs. smaller interior or arctic bears) also appears to reflect more genetic variation than is present among polar bears (Stirling and Derocher 1990; Talbot and Shields 1996a, 1996b). Morphological variation among polar bears is minimal throughout their range. Paetkau et al. (1999)
    http://www.polarbearsinternati.....e/genetics

    etc.. etc..

  6. 6
    bornagain77 says:

    correction:

    even though the speciation from brown bears was rapid

  7. 7
    Heinrich says:

    In other words all hair colours are attuned to the colours of the envirorment by laws not yet discovered.

    So why do polar bears born in zoos retain their white colour?

  8. 8
    Robert Byers says:

    Bornagain 77
    Its fine to find genetic differences between bears of great differences. It could only be that way. yet that doesn’t explain the origin of the change or sppeed.
    It wasn’t from thousands of years but instant that browns went white. why otherwise go white if you can live so long in intermediate stages. unlikely and , number crunching , impossible.
    A creationist wants toi find polar bears are all alike. This because the change was instant and then sticks in the gear. Other bears switch about due to very different needs and so more variable.
    Genetics is only a language of bodies and not a trail of former bodies leading to present bodies. thats just extrapolation.
    Like in peoples colour differences it was a innate change and not from selection with dying losers.

  9. 9
    Robert Byers says:

    Heinrich
    They would keep their colour if the original reason they changed was a innate sudden change. So important that the body instantly adapted. They survive fine in zoos and so the trigger is never pulled.
    Nedd is the origin of biological change and not mere location.

  10. 10
    bornagain77 says:

    Byers you state:

    ‘Genetics is only a language of bodies and not a trail of former bodies leading to present bodies. thats just extrapolation.’

    This is only true in a limited context for we can presently observe examples of ‘sub-speciation’ where the sub-speciation event is brought about by loss of genetic diversity from a parent species. So it is a very limited extrapolation to infer sub-speciation within the tight constricts of ‘loss of information’, or moreover within the tight constricts of the principle of Genetic Entropy. It is quite another thing altogether for neo-Darwinists to extrapolate the common descent of all life on earth by a natural process for the creation of information that no one has ever seen before.

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