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.
Stellar evolution
Planetary evolution
Organic evolution
Theory of Evolution states that all living organisms are evolutionary descendants of life-forms that existed during the past.

Charles Darwin

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"
Reproductive success


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.
Cell Division
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

Allopatric Speciation - speciation due to isolation of a population.
Isolation is due to physical barriers.
- oceans, mountains, etc.

Phyletic Gradualism

Speciation due to gradual changes.
One species gradually evolves into and is replace by another species.

Punctuated Equilibrium

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.

Classification Scheme


Human Classification
Domain Eukaryota eukaryotes
Kingdom Animalia animals
Phylum Cordata spinal cords
Subphylum Vertebrata vertebra
Class Mammalia mammals
Order Primates apes
Family Hominid bipedal apes
Genus Homo humans
Species sapien wise, knowing

Numbers of Identified Species
Insects 751,000
Arthropods (other than Insects) 123,161
Plants 248,438
Mollusks 50,000
Fungi 46,983
Protozoans 30,800
Algae 26,400
Fish 19,056
Flatworms 12,200
Roundworms 12,000
Segmented worms 12,000
Birds 9,090
Coelenterates 9,000
Reptiles 6,300
Echinoderms 5,000
Sponges 5,000
Bacteria 4,760
Amphibians 4,184
Mammals 4,000


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
- Mutations
- Predation
Evolution of one species into a new species is called pseudoextinction.

Mass Extinctions

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.

Additional Reading

Additional Readings in This Topic