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7.3 Evolution of Species
Key Ideas
► What
factors have contributed to the
diversity of species?
► How do new species form?
► How do scientists infer evolutionary
relationships among species?
► What causes the extinction of species?
A Variety of Species
► Over
time, different environments and
genetic variation have produced, through
natural selection, the variety of organisms
that exist today
► Habitat: specific environment that provides
the things the organism needs to live, grow,
and reproduce
► Genetic
Diversity : organisms within the
same species do not all have identical traits.
► Some genetic differences, or variations, may
result from mutations in DNA or
rearrangement of genes during meiosis
► All
the genetic variations in a species make
up the total “gene pool” of that species
► High variety in gene pools VS. Low variety
 Corn, cheetah
How do new species form?
new species can
form when a group of
individuals remains
isolated from the rest
of its species long
enough to evolve
different traits
 Geographic isolation –
one of the main
possible ways new
species form.
Inferring Species Relationships
► Scientists
have combined the evidence from
DNA, proteins structure, fossils, early
development, and body structure to
determine the evolutionary relationships
among species
► Elephant
and elephant shrew : the mouse-like
elephant shrews are more closely related to
elephants than rodents based on DNA
Extinction of Species
► Extinct:
no members of that
species are still alive.
(Woolly mammoths)
► Extinction if caused by a
change in a species’
environment. The members
of the species may not have
adaptations that allow them
to survive and reproduce in
the changed environment
► Climate
change : climate change can
destroy organisms’ habitats
 It has been the leading cause of extinction
► Adaptation
and survival – environmental
change does not always lead to extinction.
Some organisms may have traits that help
them survive in a changed env.
Some Q’s to think about…
► What
causes extinction?
► How can isolation lead to the formation of
new species?