[Paleopsych] NYT: In Give and Take of Evolution, a Surprising Contribution From Islands

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In Give and Take of Evolution, a Surprising Contribution From Islands


    Islands hold a special place in the hearts of evolutionary biologists.
    When Charles Darwin visited the Galápagos Islands in 1835, he was
    stunned by the diversity of birds, which helped guide him to his
    theory of evolution by natural selection.

    Beginning in the middle of the last century, the ornithologist Ernst
    Mayr laid the foundation for the modern understanding of the way new
    species evolve, arguing that they mainly emerged when populations
    became geographically isolated. Mayr based his theory on his studies
    of birds from Pacific islands.

    Yet islands have generally been considered evolutionary dead ends.
    After animals and plants emigrated from the mainland, it was believed
    that they became so specialized for island life that they could not
    leave. They eventually became extinct, only to be replaced by new
    arrivals from the mainland.

    "They were like baubles of the evolutionary past," said Christopher E.
    Filardi, a biologist at the American Museum of Natural History.

    But Dr. Filardi and Robert Moyle, a colleague at the museum, have
    found evidence that islands can act as engines of evolution instead of
    dead ends.

    Animals can spread from island to island, giving rise to an explosion
    of new species, and even colonizing the mainland again. The results
    suggest that conserving biodiversity on islands is vital for the
    evolution of new species in the future.

    Dr. Filardi made this discovery by studying a group of Pacific island
    birds, known as monarch flycatchers, that were among the birds Mayr
    studied 80 years ago. Dr. Mayr could compare only the anatomy and
    colors of monarch flycatchers. Dr. Filardi, on the other hand, was
    able to analyze their DNA.

    He collected it from some species by going to remote islands, while
    Dr. Moyle extracted other samples from preserved flycatchers stored at
    the museum, going back to the 1800's.

    The scientists identified 13 species that shared a common ancestor in
    Australia or New Guinea between 2 million and 5.6 million years ago.
    The descendants of that ancient bird spread thousands of miles to
    islands as far-flung as Fiji and Hawaii. New species arose along the
    way, undergoing drastic changes at a rapid rate.

    In one lineage, the monarch flycatchers tripled their body size in
    less than a million years. "This stuff can happen really fast," Dr.
    Filardi said. This evolutionary wave returned to its origins when
    flycatchers from the Solomon Islands colonized Australia and New

    Dr. Filardi and Dr. Moyle published their results in the Nov. 10 issue
    of Nature.

    "Many aspects of island bird evolution are going to have to be
    rewritten," said Jon Fjeldsa, an ornithologist at the University of

    Other recent studies suggest that islands may also be engines of
    evolution for many other animals and perhaps even plants. In the June
    issue of The Journal of Biogeography, for example, Kirsten Nicholson
    of Washington University and her colleagues published a study of
    lizards that live in Central and South America.

    The team demonstrated that 123 mainland species are the descendants of
    an ancestor that lived in the West Indies.

    "I have a feeling that in the next 10 years we're going to see a lot
    more of this," Dr. Filardi said.

    Today monarch flycatchers and other island species are under serious
    threat from habitat loss and from rats and other animals introduced by
    humans. Rising seas from global warming could destroy some islands

    Dr. Filardi argues that the new findings make preserving island
    biodiversity even more urgent, because islands may be an important
    source of new biodiversity.

    "It's the potential that the earth has to reinvent itself in the
    future," he said. "Islands may have more to do with that than we ever

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