A CENTURY OF PROGRESS 135
organisms. Elton also recognized
that particular groups of organisms
occupied certain niches in the food
chain for periods of time. Elton’s
niches include not only the habitats
but also the resources upon which
the occupying organisms rely for
sustenance. The dynamics of
energy transfer through trophic
(feeding) levels were studied by
the American ecologists Raymond
Lindeman and Robert MacArthur,
whose mathematical models
helped change ecology from
primarily a descriptive science
into an experimental one.
The green movement
A boom in popular and scientific
interest in ecology in the 1960s
and 1970s led to the development
of the environmental movement
with a whole range of concerns,
stimulated by powerful advocates
such as the American marine
biologist Rachel Carson. Her 1962
book Silent Spring documented the
harmful effects on the environment
of man-made chemicals such as
the pesticide DDT. The first image
of Earth seen from space, taken
by Apollo 8 astronauts in 1968,
awakened public awareness of
the planet’s fragility. In 1969, the
organizations Friends of the Earth
and Greenpeace were established,
with the mission to “ensure the
ability of the Earth to nurture life
in all its diversity.” Environmental
protection, along with clean andRachel Carson (far right) made a
significant contribution to the science
and public understanding of ecology
by drawing attention to the destructive
impact of pollution on the environment.
renewable energy, organic foods,
recycling, and sustainability, were
all on the political agenda in both
North America and Europe, and
national conservation agencies
were established based on the
science of ecology. Recent decades
have seen growing concern over
global climate change and its
impact on the environment and
present ecosystems, many of
which are already threatened
from human activity. ■Alexander von
HumboldtBorn in Berlin to a wealthy and
well-connected family, Humboldt
studied finance at the University
of Frankfurt, natural history and
linguistics in Göttingen, language
and commerce in Hamburg,
geology in Freiburg, and anatomy
in Jena. The death of his mother in
1796 provided Humboldt with the
means to fund an expedition to
the Americas from 1799 to 1804,
accompanied by botanist Aimé
Bonpland. Using the latest
scientific equipment, Humboldt
measured everything from plants
to population statistics and
minerals to meteorology.On his return, Humboldt was
honored across Europe. Based in
Paris, he took 21 years to process
and publish his data in over 30
volumes, and then synthesized
his ideas in four volumes titled
Kosmos. A fifth volume was
completed after his death in
Berlin at 89. Darwin called him
“the greatest scientific traveller
who ever lived.”Key works1825 Journey to the Equinoctial
Regions of the New Continent
1845–1862 Kosmos