[Paleopsych] NYT: In Give and Take of Evolution, a Surprising Contribution From Islands
checker at panix.com
Wed Nov 30 23:24:40 UTC 2005
In Give and Take of Evolution, a Surprising Contribution From Islands
By CARL ZIMMER
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
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
"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
More information about the paleopsych