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AAAS Science Assessment (http://assessment.aaas.org/topics)
Topic: Evolution and Natural Selection
Key Concept:
When inherited traits are favorable to individual organisms, the proportion
of individuals in a population that have those traits will tend to increase over
successive generations.
Sub-ideas:
Students are expected to know that:
1. There is variation in the inherited traits of organisms of the same species,
including traits that affect their ability to find food, avoid predators, and
attract mates.
2. Some inherited traits (e.g. bacterial resistance to antibiotics, skin
pigmentation in some organisms) may give individuals of a species an
advantage in surviving and reproducing in their environment compared
to other individuals of the same species (e.g. increased ability to find food
or nesting sites, avoid predators, attract mates, resist diseases).
Conversely, the individuals that do not have advantageous trait(s) are
more likely to be unable to survive and reproduce.
3. An organism’s survival influences its reproductive success. Usually, the
longer an organism lives (during its reproductive years), the more
chances it has to reproduce; therefore traits that improve chances of
survival (such as finding food or avoiding predators) also increase
chances of success in reproduction.
4. Changes in environmental conditions (such as the appearance of a new
predator, a slight change in temperature, or changes due to the eruption
of a volcano) can change which traits are more advantageous (or less
detrimental) in the new environment.
5. Because more of the individuals with favorable inherited traits survive
and reproduce than those that do not have them, and because the
favorable traits are passed on to the offspring, the proportion of
individuals with the favorable inherited traits increases in each
subsequent generation. This process is called natural selection.
6. There is no guarantee that any members of a population will be able to
survive and reproduce in a changed environment. Sometimes changes in
environmental conditions may cause an entire population of organisms to
die, or even an entire species to become extinct.
7. The process of natural selection does not lead to changes in the
characteristics of individual organisms. It only changes the characteristics
of populations (i.e. the proportion of individuals in the population having
certain inherited traits) over time.
8. After natural selection has operated on many successive generations of a
population, the descendants can be very different from their original
ancestors.
9. Even though organisms can be very different in both appearance and
behavior from their ancestors of many generations ago, they retain some
of the inherited traits of those early ancestors.
Boundaries:
1. Students are not expected to know the many ways speciation can occur in
a population.
2. Students are not expected to know the origin of variation among
individuals in a population (i.e. how genetic mutations happen).
Misconceptions:
Individual organisms can deliberately develop new heritable traits because they
need them for survival (Bishop & Anderson 1990; Passmore et al., 2002; Stern &
Roseman, 2004).
Suddent environmental change is required for evolution to occur (Nehm & Reilly,
2007).
Changes in a population occur through a gradual change in all members of a
population, not from the survival of a few individuals that preferentially
reproduce (Brumby, 1979; Bishop & Anderson, 1990; Anderson et al., 2002;
Stern & Roseman, 2004).
Evolution happens when individual organisms acclimate or "get used to" new
conditions gradually (Bishop & Anderson, 1990).
Change occurs in the inherited characteristics of a population of organisms over
time because of the use or disuse of a particular characteristic (Bishop &
Anderson, 1990).
Change to the characteristics of populations (i.e. the proportion of individuals in
the population having certain traits) of organisms is always random, and is not
influenced by the favorability of that change in a given environment (AAAS
Project 2061, n.d.).
Except for differences between males and females, and between young and old,
all organisms of the same species look and act the same (AAAS Project 2061,
n.d.).
All individuals within a population of organisms are the same. Differences among
them are trivial and unimportant. All members of a population are nearly
identical (Greene, 1990; Passmore & Stewart 2004; Anderson et al. 2002;
Shtulman, 2006).
The internal chemistry, appearance, and behavior of a species do not change,
even over long periods of time (AAAS Project 2061, n.d.).
Changes to the environment cannot lead to changes in the traits of species living
in that environment.
Change occurs in the inherited characteristics of populations of organisms over
time because organisms observe other more successful organisms and model
their appearance or habits (AAAS Project 2061, n.d.).