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Staar Category 3 Key 2

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B.

7 The student knows evolutionary theory is a scientific


SS STAAR Reporting Category 3- explanation for the unity and diversity of life.

BIOLOGICAL EVOLUTION & CLASSIFICATION


B.7 (D) Analyze and evaluate how the elements of natural selection, including inherited variation, the
potential of a population to produce more offspring than can survive, and a finite supply of environmental
resources, result in differential reproductive success.

I. Peter and Rosemary Grant Studies: Natural Selection in action


In1973, Peter and Rosemary Grant began studying Darwin’s finches on a tiny volcanic island in the
Galapagos called Daphne Major. They captured various finches to measure, weigh, and record their diet.
The finches had a range of traits in body size and beak size and shape. Some beaks were small and less
powerful; others were large and more powerful.
In 1977, the island suffered a harsh drought and affected the vegetation. This lead to a drop in the
amount of seeds available. Most of the smaller, softer seeds were quickly eaten. What was left was larger,
tougher seeds that were generally left untouched by the birds. The birds that were able to eat these
seeds were the birds that had larger and more powerful beaks. The birds with smaller beaks were less
likely to survive. The following generations included more offspring with larger beaks than usual; and
fewer offspring with smaller beaks.

1. Define natural selection: Daphne Major


Individuals with traits that are best suited for their environment
will survive and pass on their traits to their offspring.

For each element of natural selection listed in the table below, list
how the finches in the Grant study apply:

Element of natural How it applies to the finches in the Grant study


selection
2. Inherited variation Some beaks were larger than others; the larger beaks were more powerful
than the smaller beaks.

3. Potential for a The generation of birds following the drought mostly had larger beaks; the
population to produce birds with smaller beaks were dying off, which was changing the allelic
more offspring than can frequency of the population.
survive
4. Finite supply of There are only a certain amount of resources available; this creates a
environmental resources competition among population members for resources required
for survival.

5. Genetic variation is the differences of phenotypes found within populations. Explain why this is crucial
for the survival of a species: If the genetic variation among beaks did not exist, it may have been the case
that the birds with larger beaks were not present. This would have potentially erased the species as the
smaller beaks could not consume the food source available after the drought.
STAAR Biology Review © Biology Roots, LLC www.biology-roots.com
B.7 The student knows evolutionary theory is a scientific
SS STAAR Reporting Category 3- explanation for the unity and diversity of life.

BIOLOGICAL EVOLUTION & CLASSIFICATION


II. Genetic diversity is essential for the survival of a species:
Traits may become more common in a population through the process of natural selection.
Having more traits to select from increases the species chance for survival. In other words, genetic
variation is essential for the survival of a species.

Example: There is a large population of Tasmanian devils in Australia, but


they lack variation in one gene that regulates a part of their immune system
called theThere
Example: histocompatibility complex.ofThere
is a large population is a spread
Tasmanian devilsof
inaAustralia,
disease known
but they lack variation in one gene
as DFTD
that (devilafacial
regulates part oftumor
theirdisease),
immune which
systemhas caused
called the approximately 90%complex. There is a spread of a
histocompatibility
of the Tasmanian
disease known as devil
DFTDpopulations
(devil facialto sufferdisease),
tumor from thiswhich
deadlyhasdisease. They
cause approximately 90% of the Tasmanian
are now
devil considered
populations to an endangered
suffer species.disease. They are now considered an endangered species.
from this deadly

6. How is the lack of genetic variation for the one gene causing the Tasmanian devil numbers to decline?
In other words, how might a more diverse histocompatibility immune gene help the Tasmania devil
species? The immune gene for the devils is not capable of fighting off the tumor disease; if there were a
slightly different variation of the gene present, it may be able to defend the devils from this disease.

Example: A species of moth called the peppered moth can be dark or light in color. The lighter moths
would camouflage on the lighter colored trees and the lichens, which caused most of the dark moths to
be eaten by birds. Originally, most of the populations were light colored. During the Industrial Revolution,
soot from the burning of fossil fuels darkened the trees. Dark-colored moths were now at an advantage
as they camouflaged on the darkened trees. The light colored moths were the ones that were now easily
seen by birds and preyed upon.

7. What genetic variation is present in the peppered moths? The genetic variation found in the peppered
moths is the color: light vs. dark.

8. Predict what would have happened to the moth population if this genetic variation did not exist:
If there were a lack of genetic variation, we can assume the dark colored moths would not exist, and the
peppered moth population would most likely be nearly erased.

9. As more environmental protection regulations are enforced, the amount of smog has decreased,
causing trees to become a lighter color again. What do you think has happened to the moth population
since the Industrial Revolution? There has most likely been a rise in the number of light colored moths.

STAAR Biology Review © Biology Roots, LLC www.biology-roots.com Light variation


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