Download Aim 45 BLANK - Manhasset Schools

Unit 6: Evolution
Name:
Date:
Aim #45 Extinction: How can we analyze the rate of Evolution and what causes organisms to go extinct?
Evolution involves changes that give rise to a variety of organisms, some of which continue to change through time while
others die out. Most of the diversity of life on Earth today is believed to be the result of natural selection occurring over a
vast period of geologic time. The amount of change is linked to changes in the environment.
I.
How Fast Does Evolution Take Place?
Evolution does not necessarily mean long-term progress is going to go in a certain direction. Evolutionary changes
often appear to be like the growth of a __________________. Some branches ______________________ from the
beginning with little or no change, many __________________ altogether, and others branch out repeatedly,
sometimes giving rise to more _________________ organisms.
Which concept is best supported by this diagram?
a. Evolutionary pathways proceed only in one set
direction over a short period of time
b. All evolutionary pathways will eventually lead to
present-day organisms
c. All evolutionary pathways are the same length and they
all lead to present-day organisms.
d. Evolutionary pathways can proceed in several
directions with only some pathways leading to presentday organisms.
a) For some species the rate of evolution is very _______________.
Ex: Horseshoe crab has shown little change in fossils of its ancestors from 300 million years ago.
b) For some species, the rate of evolution is very ______________.
Ex: The horse has evolved tremendously over the past 60 million years.
Which statement about the rates of evolution for different species is in agreement with the
theory of evolution?
a. They are identical, since the species live on the same planet.
b. They are identical, since each species is at risk of becoming extinct.
c. They are different, since each species has different adaptations that function within a changing
environment.
d. They are different, since each species has access to unlimited resources within its environment.
II.
Factors Affecting the Rate of Evolution
What are the factors that cause a species to evolve quickly? slowly? Regardless of the factors causing evolution, it
may take millions of years for any species to accumulate enough differences from its ancestors to be classified as a
new or different species.
What causes a FAST Rate of Evolution?
What causes a SLOW Rate of Evolution?
___________ environmental change and __________
___________ environmental change and __________
changes in the environment
changes in the environment
______________ reproductive rate
_____________ population
______________ reproductive rate
VS.
_____________ population
Variation _________ present among species
Variation _________ present among species
___________ mutations exist
___________ mutations exist
____________ offspring born
____________ offspring born
___________ lifespan
___________ lifespan
Rapid changes in the environment often lead to rapid changes in species. Explain why:
III.
Extinction:
The fossil record shows that most of the species that have lived on Earth no longer exist
a) What can cause Extinction to occur?
 Drastic changes in the
(unstable)

Lack of _________________________ in a species

Adaptive characteristics are _____________________________ for survival
** In an environment that is constantly changing, how come species are more likely to survive if they possess variations?
c)
1) State a relationship between human
population growth & the rate of extinction
2) State one possible reason for the change
in the number of species extinctions
between 1890 to 1990