Principles of Evolution:
1. Natural Selection
- Require a “struggle for
existence”
- Occurs at individual
level
- “nature” selects
individuals to die or
survive
- Traits better adapted
for their environment
become more common
2. Adaptation: any heritable characteristic which
improves an organism’s chance of survival
- Does not arise in an
individual
- Requires variation
- Individuals selected
for/against based on
their adaptations
3. Fitness: the ability of an organism
to survive and reproduce
- Measured by relative
contribution to gene
pool
- Survival of the Fittest:
individuals best
adapted to the
environment survive
and reproduce
1. Variation: pheno/genotypic differences
between members of the same species
2. Struggle for Existence: the competition for
needed resources/reproduction
3. Fitness: the ability to survive and reproduce
– based on genetic contribution to gene pool
4. Adaptation: inherited characteristics that
improve an organism’s chances of survival
5. Survival of the Fittest: the organisms best adapted
to their environmental conditions survive and
reproduce
6. Natural Selection: organisms displaying the best
adaptations/traits become more common over
generations
Populations: units of evolution
- Individuals do not evolve
in a lifetime
-Nature selects some for
survival some for death
based on traits
* Rate of evolution =
change in certain allele
prevalence
- Gene pool: collection of
genes in a population at a
given time
Mutation: change in nucleotide
sequence of DNA
- Typically harmless
- If it affects protein =
harmful
- Rarely beneficial
- Leads to variations
- Usually not heritable,
unless it happens in
gametes
Evidence For Evolution:
1. Fossil Evidence
-Supports the theory –
especially in aquatic
organisms
-many holes still in the
fossil record
2. Homologous Structures: similar structures
with different functions/same embryological
origin
3. Vestigial Organs: organs/structures
which have lost function over geological
time
4. Embryological Similarities: all vertebrates
have similar embryological development
5. Radiometric Dating: the use of radioactive
elements to calculate the age of geological
substances
• Half life: the length of
time required for half of
the radioactive atoms in a
sample to decay into nonradioactive atoms
• Ex: Carbon-14 decays to
form carbon 12 (5730
years) – comparing the
amount of C14 to C12
allows us to age samples
6. DNA similarities: genomic data indicate that
all life forms are closely related to one another
Ex. Humans and Bananas
share 50% of the same
DNA
-Humans and Chimps=
98.5%
Types of Evolution:
Adaptive Radiation: process of a single species
or small group evolving into a diverse group of
organisms
Convergent Evolution: unrelated organisms
come to resemble one another
Coevolution: process by which two species
evolve in response to changes in each other
Gradualism: life is in a constant, small state of
flux and small changes evolve slowly into large
differences
Punctuated Equilibrium: life is stable, for long periods
of time but is interrupted with periods of dramatic
change
Speciation: creation of new species
Species: a group of individuals which bear
similar characteristics, can breed with one
another, and produce viable offspring
Two Types of Speciation:
1. Allopatric Speciation: a population
is separated and their genes drift apart
- Only occurs if
environmental
differences are
significant
- Genetic Drift: change in
allele frequency in a
population
2. Sympatric Speciation: new species
arise in the same area
- Arises due to changes in
sexual selection and
habitat preference
Genetic Drift: in populations, one allele
becomes more common in descendents