Unit 12: Evolution
Sec. 11.6 – Patterns in Evolution
Key Concept:
_________________________________________________
_________________________________________________

Evolution through natural selection is not
random.
o Natural selection can have ______________.
o The effects of natural selection add up over
time.
1. _________________ Evolution – describes
evolution toward ____________ traits in ____________ species.
2. _________________ Evolution – describes evolution toward ____________ traits in closely
____________ species.

Species can share each other over time.
o Two or more species can evolve together through _____________.
 Evolutionary paths become _____________.
 Species evolve in response to ___________ in each other.
o Coevolution can occur in ______________ relationships.
o Coevolution can
occur in
______________
relationships
sometimes called
__________ arm
races.

Species can become extinct.
o Extinction is the _____________ of a species from Earth.
o Background extinctions occur ____________ at a very low rate.
 Occur at roughly the same rate as ___________.
 Usually affects a ________ species in a small area.
 Caused by _________ changes in environment.
o Mass extinctions are ______ but much more intense.
 Destroy many species at a _________ level.
 Thought to be caused by ________________ events.
 At least ____ mass extinctions in last 600 millions years.

Speciation often occurs in patterns.
o A pattern of _______________ equilibrium exists in the fossil record.
 Theory proposed by Eldredge and Gould in 1972
 Episodes of speciation occur
_____________ in geologic time.
 Followed by long period of little
______________ change.
 Revised Darwin’s idea that
species arose through
___________ transformations.
o Many species evolve from _______
species during ___________
______________.
 Ancestral species diversifies into
many _____________ species.
 Descendent species usually
adapted to wide range of
environments.