Name: Class: Date:
NATURAL SELECTION
Introduction
Charles Darwin (1809 – 1882) was an English naturalist who first developed a theory of evolution that
has laid the groundwork for modern biological thinking. Darwin grew up in a time when the scientific view
of the natural world was dramatically shifting. Geologists were suggesting that Earth was more ancient
than previously thought and had changed over time. Biologists were suggesting that life on Earth was
also changing. In this climate, Darwin developed a scientific theory of evolution that explains how modern
organisms evolved over long periods of time through descent from common ancestors.
Darwin’s Fateful Journey
In the year 1831 and at the age of 22, Charles Darwin joined a 5-year trip around the world as the official
naturalist on the ship H.M.S. Beagle. The main purpose of the Beagle’s voyage was to map the coastline
of South America. The ship traveled around the coast of South America to the Galapagos Islands. From
there, the ship pursued a westerly course passing the southern coast of Australia, then going north to the
southern coast of Asia, and then south along the southern coast of Africa back to England.
Darwin role was to collect specimens of plants and animals and make observations about what he saw.
No one knew it at the time, but this journey would become one of the most important scientific voyages in
history because it led Darwin to develop his ideas about evolution.
What Darwin Observed Aboard the Beagle
Darwin filled his notebooks with observations about the characteristics and habitats of the different
species that he saw. But Darwin wasn’t content just to describe the biological diversity that he saw: he
wanted to explain it in a scientific way. Darwin looked for larger patterns in his data, and as he traveled,
he noticed three major patterns of biological diversity (see table on the following page).
As an example, on the Galapagos islands, a collection of closely-spaced islands off the coast of Ecuador,
Darwin observed that one type of bird, a finch, lived on all of the islands. However, finches living on each
island had slightly different beaks. On one island, they finches had heavy beaks. These finches primarily
ate heavy seeds that they cracked open with their strong beaks. On another island, the finches had
thinner, sharper beaks. These finches probed local plants for small insects. After careful study, Darwin
concluded that the finches’ beaks had adapted to the type of food available on each island.
