natural selection

how is the diversity of life explained

the theory of evolution

what did Aristotle believe?

he believed species to be fixed (unchanging). Each form was perfect and permanent.

What did Carolus Linnaeus believe?

each species was designed for a specific purpose.

founder of taxonomy

developed the binomial format for naming species

what did Georges Cuvier believe?

believed in catastrophism, each strata boundary indicates a sudden event or catastrophe that would explain the loss of species in the next layer. from one layer to the next, new species appeared while other disappeared.

what did James Hutton and Charles Lyell believe?

uniformitarianism- mechanisms of change are constant over time. The perceived changes on Earth’s surface resulted from slow continuous actions.

what did Jean-Baptiste de Lamarck believe

believed that parts of the body that are used extensively become larger and stronger, while those that are not used deteriorate. An organism could pass these modifications to its offspring.

Who published The Origin of Species and when?

Charles Darwin in 1859.

what are the major observations of The Origin of Species?

1. there is a unity to life

2. within life, there is also diversity

3. Organisms seem well-suited to their particular enviornment

4. descent with modification

what is descent with modification?

Descent with modification means that species share common ancestors, and as their descent populations spread into different environments over many generations, inherited traits change so that each lineage becomes adapted to its particular way of life

natural selection

process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than do other individuals because of those traits. Natural selection acts on individuals, but only populations evolve.

how is natural selection possible

can only act on variation with a genetic component. Genetic variation is the differences amongst individuals in the composition of their genes or other DNA sequences. Without genetic variation, evolution cannot occur.

What are the sources of genetic variation?

• Mutation: a change in the nucleotide sequence of an organism’s DNA

• Alteration of gene number or position: chromosomal changes that delete, disrupt or rearrange loci

• Sexual reproduction- crossing over, independent assortment of chromosomes, fertilization

why doesn’t the perfect organism exists?

1. selection can act only on existing variations- natural selection only favors the fittest phenotypes among those currently in the population

2. evolution is limited by historical constraints- evolution does not ignore the ancestral anatomy and build a new structure from scratch, rather evolution adapts existing structures to new situations

3. adaptations are often compromises- organisms face trade-offs in which the ability to perform one function may reduce the ability to perform another

4. chance, natural selection, and the environment interact

what evidence supports the theory of evolution?

• direct observations of evolutionary change

• homology- similarity resulting from common ancestry. for example vestigial structures.

• fossil record- for example, can show the transition from land to sea in the ancestors of cetaceans

• biogeography- the geographic distribution of species provides evidence for evolution