Download Struggle for Existence

Struggle for Existence
• Darwin was convinced artificial selection worked in
nature as the result of overproduction and competition
for resources = struggle for existence (members of each
species compete regularly to obtain food, living space,
and other necessities of life)
– Depends on an individual’s ability to survive and
reproduce = fitness
– Fitness results from adaptations = inherited
characteristics that increase an organism’s chance of
survival
– = “Survival of the Fittest!”
Natural Selection
• Survival of the fittest = Natural Selection!
– Traits are being selected and increasing over time
(over many generations without human
influences)
• Over time, natural selection results in changes
in the inherited characteristics of a
population. These changes increase a species’
fitness in its environment.
Descent with Modification
• Over time, natural selection
produces organisms with different
structures or functions resulting in
species that look different from
their ancestors
– Each living species has
descended with changes from
other species over time =
Descent with Modification
• Then, all living things must be
related!
– There’s a common ancestor of
all living things = Common
Descent
Evidence of Evolution
• Living things have been evolving on Earth for
millions of years. Evidence of this process
could be found in:
– The fossil record
– The geographical distribution of living species
– Homologous structures of living organisms
– Similarities in development
– DNA
Testing Natural Selections
• Back to the Galapagos Islands:
• For over 40 years, the Grants studied the
finches of the Galapagos Islands
The Grants’ work shows that the variation
within a species increases the likelihood of the
species’ adapting to and surviving
environmental change
What constitutes a new species?
• 1. Geographic
• 2. do not mate
Summary of Darwin’s Theory
• Individual organisms in nature differ, and some variation is
inherited (natural variation)
• Organisms in nature produce more offspring than can survive
and reproduce (overproduction)
• Members of each species compete for limited resources
• Unique organisms have different advantages and
disadvantages in the struggle for existence
• Individuals best suited to their environment survive and
reproduce, passing the characteristic to their offspring.
Individuals without the characteristic die
• Species change over time due to natural selection… new
species arise and others disappear
• Species alive today have descended with modification from
species of the past
• All organisms on Earth are united by a common descent