Selection I) Populations and species evolve, meaning that their heritable characteristics change through time.
More precisely, evolution is defined as changes in allele frequencies over time.
Evidence for Evolution:
1) Evidence for Change through time:
a) Fossil record: (first measured in relative age through sedimentary rock then through radiometric
ii) Transitional form – “law of succession” – is a fossil species with traits that are intermediate
between those of older and younger species
a) Vestigial traits – a reduced or incompletely devolved structure that has no function or reduced
function but it is clearly similar to functioning organs or structures in closely related species
b) Current EXAMPLES: Evolving Bacteria, insect and plant resistance
2) Evidence that species are related:
a) Geographic relationship
a. Galapagos Mockingbirds – must have evolved from same ancestor therefore are part of a
b) Homology – a similarity that exists in species descended from a common ancestor. 3 levels:
a. Genetic homology – a similarity in the DNA sequences of different species
b. Developmental Homology –a similarity in embryonic traits – observed in the overall
morphology (form) of the embryos and in the fate of particular embryonic tissues.
c. Structural Homology – similarities in adult morphology (i.e. arms)
II) Natural Selection occurs when individuals with certain alleles produce the most surviving offspring in
a population. An adaptation is a genetically based trait that increases the ability of an individual to
produce offspring in a particular environment.
Evolution – a change in the allelic frequencies of a population over time
Process of Evolution by Natural Selection: occurs when (1) heritable variation leads to (2) differential
success in survival and reproduction
Adaptation – A trait that increases the fitness if an individual in a particular environment
*Finches: Although beak size showed no net change, beak shape changed dramatically (more pointier)
and overall body size got smaller III) Evolution by natural Selection is not progressive, and it does not change the characteristic of the
individuals that are selected, it changes only the characteristics of the