The Theory of
Evolution
Charles Darwin
(Working off the information and data
collected from other scientists)
Charles Darwin and Natural
Selection
Charles Darwin (1809-1882): studied
evolution. Evolution is the change in
populations over time. Fossil evidence
formed the basis of the early
evolutionary concepts.
Many explanations about how species
evolve have been proposed, but the
ideas first published by Charles
Darwin are the basis of modern
evolutionary theory.
 Charles
Darwin sailed off on the HMS
Beagle at the age of 21, which journey
for five years. There he was the ships
naturalist, studying and collecting
species along the route. Darwin
became curious about the possible
relationships among the species he
collected.

On the Galapagos Islands Darwin made
several observations which led him to
believe that species can change over time.
After several years of studying and
researching other scientist methods and
experiments as well as conducting his own
he realized that several individuals struggle
to survive.
Darwin gained insight into the
mechanism that determined which
organisms survive in nature from
his pigeon-breeding experiments.
Breeding organisms with specific
traits in order to produce offspring
with identical traits is called
artificial selection. Darwin
believed there was a force in nature
acting like artificial selection.

Natural Selection is a mechanism for
change in populations. It occurs when
organisms with certain variations survive,
reproduce, and pass their variations to the
next generation. Organisms without there
variations are less likely to survive and
reproduce. As a result, each generation
consists largely of offspring from parents
with these variations that aide survival.
Darwin published the first book about
evolution called The Origin of Species by
Natural Selection.
Interpreting evidence after Darwin: One of
the problems if that evolutionary processes are
difficult for humans to observe directly. The
short scale of human life spans makes it difficult
to comprehend evolutionary processes that
occur over millions of years. Evolution is more
commonly defined by modern biologists as any
change in the gene pool of a population.
Adaptations: Evidence for Evolution

Adaptation is any variation that aids an
organism’s chances of survival in its
environment. For example, thorns are an
adaptation of some plants and distinctive
colorings are an adaptation of some animals.
Peppered Moths

According to Darwin’s theory adaptations in
species develop over many generations.
Structural adaptations for mole rats to survive
underground are large teeth and claws. Mimicry
is a structural adaptation that enables one
species to resemble another species. One form
of mimicry is to acquire physical features to
resemble a harmful species. Predators will then
avoid them, fearing that they are dangerous.
 Camouflage
is another adaptation that
enables a species to blend with their
___________________. Because
well-camouflaged organisms are not
easily found by predators, they survive
to reproduce.

Physiological adaptations can develop
rapidly. For example, medicines can evolve
very rapidly. Physiological adaptations are
changes in an organism’s metabolic
processes. Besides bacteria what’s another
example of a species who has underwent
physiological adaptations?
________________________________
Other Evidence for Evolution
• Fossils are an important source of evolutionary
evidence because they provide a record of early
life and evolutionary history. Even though
paleontologists have missing pieces in their
fossil record, they still understand the overall
picture. As the fossil record becomes more
complete, the sequences of evolution become
more clear.

Structural features with common
evolutionary origin are called homologous
structures. Homologous structures can
be similar in arrangement, in function, or
in both. Evolutionary biologists view
homologous structures as evidence that
organisms evolved from a common
ancestor. You can compare the butterfly
wing with a bird. They are not similar in
structure, but they are similar in function.

EX. Bat wing, whale flipper, and dog paw
 The
body parts of organisms that do
not have common evolutionary origin
but are similar in function are called
analogous structures.

Example: Bird wing & bat wing are both for
flight but they are structurally different
Another type of body feature that suggests
evolutionary relationships is a vestigial
structure. This is a body structure that
has no function in a present-day organism
but was probably useful to an ancestor.
 Ex. Human tailbone, whale pelvis

 An
embryo is the earliest stage of
growth and development of both
plants and animals. Similarities among
the young embryos suggest evolution
from a distant, common ancestor.

Today many scientists use the results of
biochemical studies to help determine the
evolutionary relationships of species.
Since Darwin’s time, scientists have
constructed evolutionary diagrams that
show levels of relationships among
species.