Identify factors that have contributed to
the diversity of species.
 Explain how new species form.
 Explain how scientists infer evolutionary
relationships among species.
 Explain what causes the extinction of
species.


Over time, different
environments and
genetic variation
have produced,
through natural
selection, the variety
of organisms that
exist today.

An organism’s habitat is the specific
environment that provides the things the
organism needs to live, grow, and
reproduce.
Organisms within the same species do
not all have the same traits
 All genetic variations in a species make
up the total “gene pool” of that species.

Many species have a great variety of
diversity in their gene pools.
 These species can often adapt to
changes in the environment.

In some species, most of the organisms
are genetically similar.
 These species have difficulty surviving
environmental changes.


A new species can form when a group of
individuals remains isolated from the rest
of its species long enough to evolve
different traits.
One of the main ways new species form.
 Isolation, or complete separation,
happens when some members of a
species become cut off from the rest of
the species.


Scientists have combined the evidence
from DNA, protein structure, fossils, early
development, and body structure to
determine the evolutionary relationships
among species.
Scientists infer that the species inherited
many of the same genes from a
common ancestor.
 The more similar the DNA sequences, the
more closely related the species are.


A species is extinct if no members of that
species are still alive.

Extinction is 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 is the leading cause of
extinction.

Some organisms in a species may have
traits that help them survive in a
changed environment.