EVOLUTION THEORY - THE CONCEPT, THE RECORD, THE FACT

Lecture Slides

• WHAT IS EVOLUTION?

• Refers to the processes by which life has changed through time.

• The record preserved in the rock is the data base from which interpretations and models are developed to explain that change

• The theory links a multitude of biological phenomena and is underpinned by the geological record.

• Darwinian Evolution

• Organismal acquisition of small adaptive changes allowing species to alter slowly over time from one form to another

• Darwinian hypotheses inferred these changes would eventually result in new sp.

• Individuals that survived were best adapted would pass those "adaptive" features to the next generation.

• Fossils & Darwin

• Believed that when the fossil record did not support this gradual change, that the fossil record must be incomplete.

• Concepts formulated BEFORE genetics was recognized.

• Modern Synthesis: NeoDarwin

• Genetic theory, population ecology, and other biological facts modified the concept that included:

• Variation from random changes in the gene pool

• Selection favors the survival and continuance of particular variants at the expense of others;

• Changes within lineages result from gradual accumulation of favorable heritable variations;

• Interbreeding maintains a gene pool that provides genetic homogeneity and stability

• CENTRAL NeoDarwinian TENETS

• Reductionism - the gradual substitution of gene frequencies through time

• Panselectionism - all adaptions are in someway selective; natural selection is "The Force"

• Extrapolationism - genetic changes at one level (molecular) could be scaled up

• Gradualism - small changes in phenoptype over generations can result in new body plans and new species

• MUTATIONS

• Recombination varies the gene pool

• May spontaneously change to a new allele (homozygous or heterozygous) resulting in mutation.

• Chemical change in the DNA helix.

• WHERE DO MUTATIONS OCCUR?

• Simple mutation by change in one nucleotide base or pair base.

• Chromosomal mutations affect 10's to 1000's of base pairs and may involve inversion, rearrangement, addition, or deletion.

• OTHER MUTATIONS

• MAY have have large scale phenotypic effects or may be neutral

• There are mobile genetic elements (jumping genes) whereby DNA sequences are capable of moving along chromosomes.

• Allows for radical and rapid alteration of the pattern of gene expression.

• Advantage or Disadvantage?

• Advantageous mutations can only spread through a population if

• It is recurrent and passed to new organisms

• It carries some selective advantage

• The population is small enough.

• Disadvantageous mutations can result in extinction

• Structural & Regulatory Jeans

• Structural genes code for each individual protein and structure in the body; many neutrally code.

• Effectiveness depends upon regulatory genes - switches that turn on and off development.

• Small mutation in a regulatory gene can result in significant change in development. The result is "a place for everything, and everything in its place."

• Homeotic genes

• Production of 'normal' parts in odd places

• Hox genes are a subset of homeotic genes that control developmental sequencing in a particular segment of the body plan.

The American Geological Insitute recently has published Evolution and the Fossil Record that is available in .pdf format. Obtain and Read this reference for class.

Framsticks is a project in which evolutionary mutation is taken as the basis for adaption of stick organisms in an artificial world. The program is designed to similuate evolutionary mechanisms operating in the natural world.

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