Extinct Dodo Related to Pigeons, DNA Shows
for National Geographic News
February 28, 2002
Scientists have determined, through DNA analysis, that the
long-extinct dodo belongs in the dove and pigeon family.
The dodo, poster bird for species extinction, has a pitiful reputation as a stupendously overweight idiot of a bird that couldn't even fly. But scientific evidence is slowly correcting that impression. Its new rep: an evolutionary success, perfectly adapted to its living conditions, thin and relatively fast, but still an early victim to the spread of man.
Dutch sailors began using the Indian Ocean island of Mauritius as a stopover in 1598; Within 80 years, the dodo was gone. Having evolved over millions of years to take maximum advantage of its splendid isolation, its size and inability to flee from predators ushered it into extinction in an evolutionary instant.
Molecular analysis of DNA retrieved from a dodo
specimen at the Oxford University Museum of Natural
History, England, confirms that the bird belongs firmly in the middle of the pigeon tree in evolutionary terms, reports a study published in the March 1 issue of the journal Science. Its closest living relative is the Nicobar pigeon, which lives in the Nicobar Islands and Southeast Asia, and it is part of a group of large island-dwelling birds that spend a great deal of time on the ground. Other modern representatives include the crowned pigeons of New Guinea and the tooth-billed pigeon of Samoa.
So why do scientists care whether a
long-extinct dumb fat bird found on only one island in the whole world was
related to a pigeon or an ostrich?
"Island taxa such as the dodo and
solitaire often represent extreme examples of evolution—and if we want to
examine how we, or the life around us, evolved then such animals are very
educational," said Alan Cooper, a zoologist at the University of Oxford and
one of the co-authors of the study. "By examining island birds we can
investigate how evolution works—because extreme examples are often the best
views of how something works."
Earlier scientists had speculated that the
dodo, and its closest relative, the also-extinct solitaire, descended from
migratory African pigeons that got lost and colonized the islands. The genetic
evidence clearly shows that the dodo and solitaire came from southeast Asia,
where all their close relatives remain.
The Oxford scientists can't tell when the dodo
arrived on Mauritius, or when it became flightless. Geological evidence
indicates that the island was created as a result of volcanic activity and
emerged from the water about 8 million years ago. Whether the birds flew, swam
or hitched a ride on floating debris like trees or clumps of seaweed, remains
unknown. The DNA evidence does indicate that the dodo and the solitaire
separated from a common ancestor about 25.6 million years ago. The common
ancestor separated from other Southeast Asian birds around 42.6 million years
Rescuing the Rep of the Dodo
Animals that evolve in isolation frequently
exhibit somewhat bizarre traits, and a giant flightless bird is surely on the
extreme end of avian evolution. But that doesn't make the dodo a failure. David
Quammen, in his seminal book on island biogeography and extinctions The Song
of the Dodo, calls the species an evolutionary success; it adapted well to
Having reached Mauritius, the birds adapted,
probably over several million years, to living on an island that had no
predators and a wealth of fruit lying on the ground. They gradually traded their
ability to fly for the ability to store larger amounts of fat that would carry
them through times of scarcity. To store the fat, they got bigger, making it
more difficult to fly. Surrendering the ability to fly, and thus to elude
enemies, he says, was an easy trade-off; there were no enemies to flee.
That all ended when the Portuguese and Dutch
began arriving in the 16th and 17th centuries. Having no reason to fear man, the
big ground-dwelling birds were easy prey. Numerous contemporary accounts
describe the birds as trusting and friendly—hardly bothering to get out of the
sailors' way, never mind trying to run and hide. But that was ecological naiveté,
says Quammen, not stupidity.
Although hunting certainly reduced populations,
it was the animals the sailors brought with them, especially pigs, rats, and
monkeys, that delivered the death blow to the species by preying upon their eggs
and chicks, if not the adults.
And while the dodo was definitely a big bird,
it probably wasn't nearly as fat and geeky as has been depicted. Most of what is
known about what the dodo looks like is derived from paintings and caricatures
from the 17th century.
Andrew Kitchener, a biologist and curator at
the Royal Museum of Scotland, has shown that the dodo was probably much thinner
and more lithe than has generally been depicted. Most of the sketches and
paintings were copies, not based on original observations. Some may be based on
birds in captivity in Europe that were unintentionally overfed, and fattened up
beyond what would occur in nature.
The derogatory catch phrase "Dumb as a
Dodo" has lived for more than 350 years; emerging science may slowly
reshape our understanding and give the long-dead bird some respect.