Download Notes Natural Selection File

Natural Selection
• The process by which organisms that are
better suited to their environment than others
produce more offspring.
• As a result of natural selection, the proportion
of organisms in a species with characteristics
that are adaptive to a given environment
increases with each generation. Therefore,
natural selection modifies the originally
random variation of genetic traits in a species
so that alleles that are beneficial for survival
predominate, while alleles that are not
beneficial decrease.
Species
• basic category of biological classification,
composed of related individuals that resemble
one another, are able to breed among
themselves, but are not able to breed with
members of another species.
Selective Pressure
• Environmental pressures on populations;
drought, climate change, new predator,…
• Selective pressure can cause some individuals
to fail or produce few offspring while others
survive and produce large numbers of
offspring.
• The pressure selects which individuals will
survive and which will fail.
“Survival of the fittest”
• The organisms with adaptations that allow it to
acquire resources and reproduce more effectively
than another is the one that will survive.
OR
“Survival of the fittest” thus means the organisms
that fit best with their surroundings will thrive and
reproduce.
Content Statement
• Diversity of species occurs through gradual
processes over many generations. Fossil
records provide evidence that changes have
occurred in number and type of species.
Content Statement cont.
• Fossils provide important evidence of how life
and environmental conditions have changed.
Content Statement cont.
• Changes in environmental conditions can
affect how beneficial a trait will be for the
survival and reproductive success of an
organism or an entire species.
Content Statement cont.
• Throughout Earth’s history, extinction
of a species has occurred when the
environment changes and the individual
organisms of that species do not have the
traits necessary to survive and reproduce in
the changed environment. Most species
(approximately 99 percent) that have lived on
Earth are now extinct.
Extinction
The dying out or termination of a
species.
Extinction occurs when species are
diminished because of environmental
factors or because of evolutionary changes
in their members (genetic inbreeding, poor
reproduction, decline in population
numbers).
Mass Extinctions
• An adaptation is a trait that allows an organism to
survive. Adaptations are due to natural selection
and the changing of environments that favors one
trait over another. Variation in a population can
eventually lead to adaptation if there is a
selecting factor. An example of an adaptation is
color adaptation. Animals that are harmless
mimic the color schemes of dangerous animals to
protect themselves. (Snakes) (Youtubehttps://www.youtube.com/watch?v=L4tJ3bYmfx
w)
• The adaptations we see today are the “happy
accidents,” the ones that worked to the
organism’s advantage and helped it survive.
• Adaptations determine the relationships
organisms have with their environment.
• It is possible for offspring to vary somewhat
from their parents, as well as from their
siblings.
• The variation may or may not contribute to
the improved survival of the individual
sporting the variation
The fossil record documents the variation in a
species that may have resulted from changes in
the environment. The fossil record is contained
within the geologic record (ESS grade 8).
Combining data from the geologic record and
the fossil record, Earth’s living history can be
interpreted.
Charles Darwin