Environmental Science 101

"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


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”
Reproductive success


Flaw in Darwin’s theory: unable to explain how favorable traits were retained or passed on to offspring.
Genetics can explain
All cells contain chromosomes
- complex double strands of DNA
- deoxyribonucleic acid
- information about organism
Chromosomes divide when cell divides (replicates itself)
Resulting cells contain same DNA information as original (clone)


Changes in DNA can occur, altering the information – Mutation.
Mutations which occur in reproductive cells will be passed on to next generation.
Result from:

Mutations - Speciation

Mutations are random with respect to fitness.
Mutations may be:
New species evolve from old species if enough mutation occurs within a population – Speciation.

Types of Speciation

Allopatric Speciation: due to isolation (physical barriers) of a population.
Peripatric Speciation: small groups of individuals break off from the larger group and form a new species
Parapatric Speciation: species is spread out over a large geographic area; isolation by distance
Sympatric Speciation: new species evolve from a single ancestral species while inhabiting the same geographic region

Phyletic Gradualism vs. Punctuated Equilibrium

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.

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

Comparative Anatomy: comparison of anatomical structures.
Embryology: study of features and phenomena exhibited in the formation and development of embryos.
Fossils: remains or traces of ancient life.


Science of arrangement or classification
System for naming organisms
Classification scheme based on Species: group of organisms having structural, functional and developmental similarities; able to interbreed, produce fertile offspring.
Evolutionary relationships

The End of Evolution

Extinction: total disappearance of a species
Extinctions occur because of:
Pseudoextinction: Evolution of one species into a new species
Mass Extinction: when large numbers of species all die out at the same time.
An estimated 99.9% of all species that ever lived are now extinct.