Module: Natural Selection
DCI: LS4.B (A) Natural selection occurs only if there is both (1)
variation in the genetic information between organisms in a population and (2)
variation in the expression of that genetic information - that is, trait
variation - that leads to differences in performance among individuals.
DCI: LS4.B (B) The traits that positively affect survival are more
likely to be reproduced, and thus are more common in the population.
PE: HS-LS4-2 Construct an explanation based on evidence that the
process of evolution primarily results from four factors: (1) the potential for
a species to increase in number, (2) the heritable genetic variation of
individuals in a species due to mutation and sexual reproduction, (3)
competition for limited resources, and (4) the proliferation of those organisms
that are better able to survive and reproduce in the environment.
[Clarification Statement: Emphasis is on using
evidence to explain the influence each of the four factors has on number of
organisms, behaviors, morphology, or physiology in terms of ability to compete
for limited resources and subsequent survival of individuals and adaptation of
species. Examples of evidence could include mathematical models such as simple
distribution graphs and proportional reasoning.] [Assessment Boundary:
Assessment does not include other mechanisms of evolution such as genetic drift, gene flow through
migration, and co-evolution.]
PE: HS-LS4-3 Apply concepts of statistics and probability to
support explanations that organisms with an advantageous heritable trait tend
to increase in proportion to organisms lacking this trait.
[Clarification
Statement: Emphasis is on analyzing shifts in numerical distribution of traits
and using these shifts as evidence to support explanations.] [Assessment
Boundary: Assessment is limited to basic statistical and graphical analysis.
Assessment does not include allele frequency calculations.]
The ideas are:
- natural selection only occurs if 2 conditions are met
- traits that make an individual more likely to survive will become more common in a population over time
- There are four tenants of natural selection.
Possible Question Starters:
Which of these describes conditions under which natural selection will take place?
- there is variation between individuals, some variations lead to a survival advantage, etc.
The frequency of a certain trait in a population will increase if...?
Which of the following would provide evidence to support the idea that the behavior of an organism affects its chances for survival?
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