Darwin’s Theory of Evolutionas a Mechanistic Process • Darwin’s Idea of Common Descent • Darwin’s Idea of Gradualism • Darwin’s Idea of Multiplication of Species • Darwin’s Idea of Natural Selection
Darwin’s Idea ofCOMMON DESCENT • evolution = descent with modification • All organisms are related through descent from some unknown ancestor that lived in the distant past. • As the descendants spilled into various habitats over time, they accumulated diverse modifications (adaptations) that fit them to specific ways of life. • The history of life is like a tree. • The Linnean classification scheme reflected the branching genealogy of the tree of life, with organisms at the different levels related through descent from common ancestors.
The evolutionary history oforganisms can be portrayedas a tree growing throughtime.
Darwin’s Idea ofGRADUALISM • The origin of new species and adaptation are closely related processes. • A new species would arise from an ancestral form by the gradual accumulation of adaptations to a different environment. • e.g. Darwin’s finches ADAPTIVE RADIATION large ground finch small tree finch woodpecker finch
Darwin’s Idea ofMULTIPLICATION of SPECIES The existence of an enormous number of species some species are very similar (not as distinct from each other!) gradual changes in various characteristics as organisms became modified according to the conditions in which they lived
Darwin’s Idea of NATURAL SELECTIONas the Mechanism for Evolution • Overproduction - All species have a tendency and the potential to increase at a geometric rate. 2. Competition - The conditions supporting life are limited. - Only a fraction of the offspring in a population will live to produce offspring, so that the number of individuals in a population remains fairly constant. The environments of most organisms have been in constant change throughout geologic time.
3. Variation - Individuals in a population vary greatly in their characteristics.4. Adaptation - Some variations enable individuals to produce more offspring than other individuals.5. Natural Selection - Individuals having favorable traits will produce more offspring, and those with unfavorable traits will produce fewer offspring.• Speciation - Given time, natural selection leads to the accumulation of changes that differentiate groups from one another, such that a new species may arise.
Natural Selection Survival of the Fittest Other examples: 1. Insecticide resistance 2. Drug resistance in bacteria A population is the smallest unit that can evolve. Natural selection acts on individuals, but individuals do not evolve. Natural vs. Artificial Selection Camouflage as an example of evolutionary adaptation
Patterns of Evolution Divergent evolution – from one species to several different forms; adaptive radiation Convergent evolution – results in increased resemblance between unrelated species Coevolution – occurs when two or more species evolve in response to each other
Darwin’s Theory of Evolution in a nutshell Biological diversity is the product of evolution. The mechanism of modification has been natural selection working continuously over long periods of time.
At the time, Darwin did not understand the genetic basis forevolution. Variations arise from mutation and genetic recombination. Much of the variation observed in the individuals of a population is heritable.
The Synthetic Theory of Evolution (Neo-Darwinism) Variation mostly occurs as a result of gene mutations and genetic recombination. Evolution is the change in allele frequency within a population over time. gene allele frequency gene pool Ernst Mayr