Darwin’s Voyage
A species is a group of similar organisms
that can mate with each other and
produce fertile offspring.
From his observations, Darwin inferred
that a small number of different plant
and animal species had come to the
Galapagos Islands from the mainland.
Adaptation - A trait that helps an
organism survive and reproduce.
Galapagos Finches Darwin made these
drawings of four species of Galapagos
finches. The beak of each finch is adapted to
the type of food it eats.
Evolution - The gradual change in a species
over time
Perhaps, Darwin thought, the species
gradually changed over many generations
and became better adapted to the new
conditions.
Scientific theory - A well-tested concept
that explains a wide range of observations.
Natural selection is the process by which
individuals that are better adapted to their
environment are more likely to survive and
reproduce than other members of the same
species.
Overproduction - most species produce far
more offspring than can possibly survive.
Competition - Since food and other resources
are limited, the offspring must compete with
each other to survive.
Variation - Any difference between
individuals of the same species.
Over a long period of time, natural
selection can lead to evolution.
Helpful variations gradually accumulate in a
species, while unfavorable ones disappear.
A new species can form when a group of
individuals remains separated from the rest
of its species long enough to evolve
different traits.
Homologous structures - Body parts that are
structurally similar in related species; provide
evidence that the structures were inherited
from a common ancestor.
Similarities in Early Development -
evolutionary relationships by comparing the
early development of different organisms.
Similarities in DNA - By comparing the
sequence of nitrogen bases in the DNA of
different species, scientists can infer how
closely related the species are.
Combining the Evidence - Scientists have
combined evidence from fossils, body
structures, early development, and DNA and
protein sequences to determine the
evolutionary relationships among species.
Branching tree - scientists think different
groups of organisms are related.