Encyclopedia of Evolution.pdf - Online Reading Center

Galton, Francis
constituted a premier example of adaptive radiation. Since
Peter and Rosemary Grant began their studies in the 1970s,
the finches have provided some of the most detailed information
in the world about natural selection; isolating
mechanisms; and hybridization.
• Mockingbirds. A single founding population, probably of the
Ecuadorian long-tailed mockingbird Mimus longicaudatus,
has evolved into four species of mockingbirds on the Galápagos:
Nesomimus trifasciatus, N. macdonaldi, N. melanotis,
and N. parvulus. They are distinct from one another in coloration
and behavior; they differ enough from their mainland
ancestors that they have been placed in a different genus,
Nesomimus, from the genus Mimus of which the North and
South American mainland mockingbirds are members.
• Land iguanas, or lava lizards. Seven species of land iguanas
have evolved on the Galápagos Islands (see figure on page
171).
• Tortoises. The giant tortoises after which the Galápagos
Islands are named are the most famous animals in the
islands. Several of the islands have recognizably different
kinds of tortoises—a fact that the governor of the islands
pointed out to Charles Darwin when he visited. The tortoises
move very slowly and live for a long time; a slow metabolism
is a major part of their adaptation to these islands.
Darwin rode on some when he visited. A few of the tortoises
alive today may have been alive when Darwin visited.
• Daisy trees. The Galápagos Islands have 13 species of
Scalesia trees, in the composite (daisy) family Asteraceae.
Almost all members of this huge, worldwide family of
plants are herbaceous (like the familiar daisies, dandelions,
thistles, and ragweeds)—except on islands, such as the
Channel Islands of California, St. Helena in the Atlantic,
Hawaii, and the Galápagos. These daisy trees are somewhat
flimsy and small as trees go and probably could not
compete with trees from plant families with a long evolutionary
history of producing trees, such as pines and oaks.
On these islands, there are relatively few trees, which has
allowed natural selection to produce tree-sized daisies.
• Tree cactuses. Cactuses in mainland North and South
American deserts do not have bark; the six species of Galápagos
prickly pear cactuses, however, do. The bark may
have evolved as protection against the abundant sea animals
that rest in their sparse shade.
There are also species that are unique to the Galápagos
Islands, although they have not undergone as much adaptive
radiation as can be seen in the animals mentioned above.
Two hundred of the 700 species of Galápagos plants are
unique, including the Galápagos tomato. Marine iguanas are
highly unusual in the reptile world because they swim and eat
algae. The Galápagos penguin is the only penguin that lives in
a warm environment. There are Galápagos species of sharks,
doves, hawks, rats, bees, butterflies, centipedes, martins, and
flycatchers.
Other animals such as frigate birds travel widely in the
oceans and have not evolved into unique forms confined to
the islands. The isolation of the islands makes them a haven
for birds and mammals that travel the oceans.
The Galápagos Islands offer very little in the way of natural
resources. They have been used for centuries as a place
where ships could stop, but they were not even very good for
this, for they have very little freshwater. The tortoises were
actually a popular attraction for sailing ships. Because of their
slow metabolism, the tortoises could survive for many weeks
in the cargo holds of the ships and could supply fresh meat
on long voyages. When Darwin visited, one of the islands
was used as a prison colony. Since none of the native animals
had economic value to the Europeans, they introduced livestock
such as goats that could survive the harsh island conditions.
Today, populations of feral goats continue to damage
the natural vegetation.
Further Reading
Kricher, John. Galápagos: A Natural History. Princeton, N.J.: Princeton
University Press, 2006.
Galton, Francis (1822–1911) British Evolutionary psychologist
Sir Francis Galton was a cousin of Charles Darwin (see
Darwin, Charles) and was one of the first scientists to apply
evolutionary principles to human genetics. He was the major
force behind the development of eugenics. Eugenics presupposes
that there are genetic differences in intelligence between
races, and that the “lower” races, which have lower intelligence,
should have restricted immigration quotas and be discouraged
from breeding. Although there are genetic influences
upon intelligence, modern geneticists have concluded that
these influences do not correspond in any way to races or to
cultures. Eugenics has become almost synonymous with racism
and is not taken seriously by modern scientists. Galton’s
championing of eugenics has eclipsed his reputation, causing
many modern scholars to overlook his many legitimate and
important contributions to science.
Born January 16, 1822, Galton began his studies, as did
many other 19th-century British scientists, as a medical student.
His lack of interest and his undistinguished performance
prevented him from starting a practice. Instead, he traveled in
the Middle East and Africa. He gathered many data about the
land, people, and climate as he traveled. His data were characterized,
perhaps more than anyone else’s (even Darwin’s)
by careful measurements and by statistical sampling methods
and relatively large data sets.
Upon his return to England, he used the things he had
learned while traveling, and the statistical methods that he
had refined, to undertake research in different fields. He created
some of the first weather maps and made significant
contributions to meteorology. During his studies of human
measurements, he noticed that each individual has a unique
fingerprint, and he convinced Scotland Yard to adopt a fingerprinting
system—the first in the world and now used
universally. In order to analyze his eugenics measurements,
Galton developed some important statistical techniques,
which led to the development of regression. These methods,
which analyze the probability that an association between
two variables is not simply due to chance, are essential to
modern scientific research (see scientific method) even