Species
Organism that has at least one characteristic
that is not shared with any other organism.
Characteristic
Controlled by proteins
Proteins
Made of amino acids
Order of amino acids
Determined by a gene
Gene
Series of nitrogen bases in a DNA
molecule
Mutation
Change in the nitrogen bases through
any number of causes
- Change gene
- Change amino acid / sequence
- Change protein
- Change characteristic
- Change organism
Evolution
•Change in gene frequency / species over time
•Unifying theory of biology based on scientific
observation
•Occurs in populations – not individuals.
Theories associated with evolution
Gradualism
Evolution in slow gradual steps
Punctuated equilibrium
short periods of rapid species formation
followed by long periods of little evolution
Coevolution
Interactions between species can
result in changes in the gene pool of
both species
Four Factors in Darwin’s Theory
- all species reproduce in excess of the
numbers that can survive
- all organisms compete for limited resources
- variations exist within a species
- environment selects for the more
advantageous variations
Needed for evolution to occur
1. Means of increasing Variation
Mutations – changes in nucleotide
sequence of DNA
Recombination – reshuffling of genetic
material during meiosis
Gene flow – gene frequency changes
due to immigration from other
populations
2. Means of decreasing variation
Natural selection – organisms with less
advantageous traits (genes) survive less often
and leave fewer off-spring.
Genetic drift – random events cause change
in gene frequency (small Populations)
founder effect
population bottlenecks
Gene flow – gene frequency changes due
to emigration
Microevolution
Change in a population’s alleles over a period
of time
B. List and describe three possible outcomes of natural
selection
Snail coloration
best adapted
to conditions
Average
Natural
selection
Number of individuals
Number of individuals
Directional Natural Selection
New average
Coloration of snails
Previous
average
Average shifts
Coloration of snails
Proportion of light-colored
snails in population increases
Figure 5-6 (1)
Page 102
Slide 8
Light snails
eliminated
Dark snails
eliminated
Natural
selection
Number of individuals
Number of individuals
Stabilizing Natural Selection
Snails with
extreme
coloration are
eliminated
Coloration of snails
Coloration of snails
Average remains the same,
but the number of individuals with
intermediate coloration increases
Figure 5-6 (2)
Page 102
Slide 9
Intermediate-colored snails
are selected against
Light
coloration
is favored
Dark
coloration
is favored
Natural
selection
Number of individuals
Number of individuals
Diversifying Natural Selection
Coloration of snails
Snails with light and dark
colors dominate
Coloration of snails
Number of individuals
with light and dark coloration
increases, and the number with
intermediate coloration decreases
Figure 5-6 (3)
Page 102
Slide 11
A. List limits of adaptation to change.
- A change in environmental conditions can lead to
adaptation only for traits already present in the gene pool
of population
- Even if a beneficial heritable trait is present in a
population, that population’s ability to adapt can be
limited by its reproductive capacity
- Even if a favorable genetic trait is present in a
population, most of the population would have to die or
become sterile so individuals with the trait could
predominate and pass the trait on.
Summarize some common misconceptions about
natural selection.
Survival of the fittest is survival of the strongest
Fittest is the measure of reproductive success not
strength
Evolution involves a “plan” that results in progressively
more perfect species
No plan or goal – only constant genetic
adaptation to conditions
Individuals will adapt to their environment
Biological adaptations are the result of genetic
characteristics not of conscious thought
Individuals have no choice in their genetic makeup, therefore they either have the characteristic or
not.
Macroevolution
Large changes recorded
in the fossil record
(large scale)
Speciation:
When a group of one species is cut off from the
rest of the population and gene flow is stopped.
Each group is acted on by local selective
conditions.
Kiabab Squirrel
Abert Squirrel
Conditions determine Characteristics
•Related organisms becomes less alike
•Distantly related organisms develop
similar characteristics
Observations that led to, and support
evolution
Fossils
Any preserved remnant or impression left
by organisms that lived in the past.
Relative dating – superimposition of
sedimentary rocks tells the relative age of
fossils
 Absolute dating – dating using half-lives of
radioactive isotopes (Potassium 40, Rubidium
87, Uranium 238, Carbon 14)
Transitional forms –
Archeoptryx and
similar bird-like
reptiles. Absence of
some forms can also
be used as an
argument against
evolution.
Homologous structures Structures that share a common ancestry.
Modified versions of the same structure.
Vestigial structures Remnants of an organisms evolutionary
past. The structure serves no major purpose
at this time.
DNA comparison
Protein comparison