Download Darwin`s Theory: Natural Selection

Darwin’s Theory:
Natural Selection
(14.1-14.3)
The basics…
 Evolution: process by which modern
organisms have descended from
ancient organisms (change over time)
 Scientific Theory: a well-supported,
testable explanation of phenomena
that have occurred in the natural
world
Voyage of the Beagle
 1831: Darwin set sail from
England aboard the
H.M.S. Beagle as a
Naturalist
 Throughout the voyage he
went ashore and collected
plant and animal
specimens
 He also read scientific
literature and kept
journals
The Galapagos
 Characteristics of plants and animals varied
noticeably among the different islands.
Darwin’s Observations
Summary of Observations
 Many plants and animals are especially
well-suited to the environments they
inhabit
 Organisms tend to have many more
offspring than are able to survive.
Influences on Darwin
Hutton & Lyell: Geologic forces that shape the
earth occur very slowly, so earth must be more
than a few thousand years old; Geologic forces
continue to act on the earth
Malthus: Population growth exceeds food
supply growth leading to struggle for existence
** If the Earth has changed, life probably
has too. If people experience struggle for
existence, other organisms probably do as
well.
Lamarck:
 Tendency for
Perfection
 Use and Disuse
 Acquired Traits
Lamarck believed
changes acquired in a
lifetime could be
passed on leading to a
change in a species.
Applying Lamarck’s Hypothesis:
Evaluating Lamarck
Strength’s
• Species weren’t static
and changed over time
• Species were related
through common
ancestry
• Helped paved way for
Darwin by bringing
evolution to the
forefront of scientific
debate
Weakness’s
• Lamarck didn’t know
about genes and how
traits were inherited
• An organism’s
behavior has no
effect on its heritable
characteristics
On the Origin of Species
 Proposed a mechanism for
evolution called natural
selection
 Presented evidence that
evolution has been taking place
for millions of years and
continues today
 1858, Darwin received a
manuscript from Alfred Russell
Wallace proposing similar ideas,
he finally decided to publish.
Book was released in 1859
Artificial Selection
• Selection by humans for
breeding of useful traits
from natural variation
among different
organisms
• Natural selection works
essentially the same
way, but the
environment, not
humans determines the
desirable traits.
Process of Natural Selection
(S.N.A.S.D.)
 Struggle for Existence: Organisms generally have
more offspring than resources can support
 Natural Variation: Even within a species there will be
distinct differences between individual organisms
 Adaptation: Some variations provide individuals with
an advantage that increases their chances of survival.
 Survival of the Fittest: Those with the adaptations
are more likely to survive and reproduce
 Descent with Modification: Genes for the beneficial
adaptations are passed on and the trait becomes
increasingly more common in each new generation of the
species
Evidence of Evolution I
The Fossil Record
Geographic Species Distribution
Homologous Structures
Vestigial Structures:
organs that are so reduced that
they are just traces (vestiges) of
homolgous structures in other
species
Evidence of Evolution II
Similarities in Development
Biogeochemical Factors (DNA)