Historical Geology 102
"This preservation of favourable individual differences and variations, and the destruction of those that are injurious, I have called Natural Selection, or Survival of the Fittest. Variations neither useful nor injurious would not be affected by natural selection . . ."
Charles Darwin, The Origin of Species by Means of Natural Selection, 1872
Evolution is defined as change through time.
Theory of Evolution states that all living organisms are evolutionary descendants of life-forms that existed during the past.
Charles Darwin - Origin of Species
Evolution based on natural selection.
Individuals within a species with favorable adaptations will have the best chance of survival and for transmitting those traits to the next generation.
"Survival of the Fittest"
Flaw in Darwin's theory - unable to explain how favorable traits were retained or passed on to offspring.
Genetics can explain why.
All cells contain chromosomes - complex double strands of DNA.
DNA stores information about the organism - a recipe.
Chromosomes divide when the cell divides (replicates itself).
The two resulting cells then contain the same information as the original.
Changes in the DNA can occur, altering the information - mutation.
Mutations which occur in the reproductive cells will be passed on to the next generation.
Mutations result from:
errors in DNA repair
damage by radiation
Mutations - Speciation
Mutations are random with respect to fitness.
Mutations may be: harmful, neutral or beneficial.
Depends on the environment.
New species evolve from old species if enough mutation occur within a population - speciation.
Allopatric Speciation - speciation due to isolation of a population.
Isolation is due to physical barriers.
- oceans, mountains, etc.
Speciation due to gradual changes.
One species gradually evolves into and is replace by another species.
Species remain stable for long periods of time then change very rapidly over a very short period of time.
Read the original article where the theory was first presented. Punctuated Equilibrium: An Alternative to Phyletic Gradualism by Niles Eldredge and Stephen Jay Gould
Styles of Evolution
Divergent Evolution - diversification of a species into two or more species.
Parallel Evolution - development of similarities in two or more closely related descendants.
Convergent Evolution - development of similarities in two or more distantly related groups.
Evidence of Evolution
Classification / Taxonomy - grouping of organisms based on shared characteristics.
Comparative Anatomy - comparison of anatomical structures.
Embryology - study of the features and phenomena exhibited in the formation and development of embryos.
Geographic Distributions - location of species in relation to related or similar species.
Fossils - remains or traces of ancient life.
The science of arrangement or classification.
Basic classification scheme is based on Species.
Species - a group of organisms having structural, functional and developmental similarities and are able to interbreed and produce fertile offspring.
|Phylum Cordata||spinal cords|
|Family Hominid||bipedal apes|
|Species sapien||wise, knowing|
|Numbers of Identified Species|
|Arthropods (other than Insects)||123,161|
Taxonomy is a system for naming organisms.
It is also a way to study evolutionary relationships.
Organisms in a Genus are more closely related than organisms in an Order.
The End of Evolution
Extinction - the total disappearance of a species.
Extinctions occur because of:
- Changes in the environment
Evolution of one species into a new species is called pseudoextinction.
Mass extinctions occur when large numbers of species all die out at the same time.
It is estimated that 99% of all species that have ever lived are now extinct.
Current mass extinction is resulting in an estimated loss of 18,000 species every year.