For reasons that are not entirely clear, when animals make
their way to isolated islands, they tend to evolve relatively
quickly toward an outsized or pint-sized version of their
Line mainland counterpart.
5 tab]Perhaps the most famous example of an island giant-and,
sadly, of species extinction-is the dodo, once found on the
Indian Ocean island of Mauritius. When the dodo's ancestor
(thought to be a migratory pigeon) settled on this island with
abundant food, no competition from terrestrial mammals, and
10 no predators, it could survive without flying, and thus was
freed from the energetic and size constraints of flight. New
Zealand also had avian giants, now extinct, including the
flightless moa, an ostrich-like bird, and Haast's eagle
(Harpagornis moored), which had a wingspan up to 3
15 meters. Though Haast's eagle could fly-and presumably used
its wings to launch brutal attacks on the hapless moa-its body
mass (10–14 kilograms) pushed the limits for self-propelled
flight.
As extreme evolutionary examples, these island birds can
20 offer insights into the forces and events shaping evolutionary
change. In a new study, Michael Bunce et al. compared
ancient mitochondrial DNA extracted from Haast's eagle
bones with DNA sequences of 16 living eagle species to
better characterize the evolutionary history of the extinct
25 giant raptor. Their results suggest the extinct raptor
underwent a rapid evolutionary transformation that belies its
kinship to some of the world's smallest eagle species.
The authors characterized the rates of sequence evolution
within mitochondrial DNA to establish the evolutionary
30 relationships between the different eagle species. Their
analysis places Haast's eagle in the same evolutionary lineage
as a group of small eagle species in the genus Hieraaetus.
Surprisingly, the genetic distance separating the giant eagle
and its more diminutive Hieraaetus cousins from their last
35 common ancestor is relatively small.


According to the author of Passage 1, one of the reasons why dodo birds were so large is that they * (A) competed with larger birds, such as the Haast’s eagle. (B) had food sources that included large, terrestrial animals. (C) interbred with the larger, flightless moa. (D) had no natural predators on the island of Mauritius.