Charles Darwin: Theory of Evolution as a Mechanistic Process

1. JRMG Bio1 2008 Charles Darwin: Theory of Evolution as a Mechanistic Process

2. Darwin’s Idea of Common Descent • Descent with modification A.K.A EVOLUTION • common ancestor/prototype • Accumulated diverse modifications or adaptations

3. The finches posed questions to Darwin: did they descend from one mainland ancestor, did islands allow isolated populations to evolve independently, and could present-day species have resulted from changes occurring in each isolated population

4. Darwin’s Idea of Common Descent • Life history is like a tree • Common trunk: multiple branching and re-branching • Common ancestor in each fork of branching • lineage of common descent • Extinct species

5. TAXONOMY: Tree of Life • Carolus Linnaeus • Species are fixed • Ordered the great diversity of organisms into “groups subordinate to groups” • Kingdom Phylum Class Order Family Genus Species

6. Reflected the genealogy of the tree of life

8. Darwin’s Idea of Multiplication of Species • species either split into or bud off other species • geographical isolation of a founder species. Founder effect. The frequency of the a allele is low in the initial population, but a small subset, in which one individual is Aa, is removed from the large population and founds a new population. The frequency of a is markedly higher in this new population, due to its relatively high frequency in the founders

9. Darwin’s Idea of Multiplication of Species • different ecological niches provide different ways of living • different plants and animals come to fill different niches with different shapes and behaviors.

11. Darwin’s Idea of Gradualism • changes through the gradual change of population rather than the sudden production of new individuals • species arise: • Through gradual accumulation of adaptations to a different environment

13. e.g. Darwin’s finches  ADAPTIVE RADIATION

15. Rapid evolution may arise: • Isolation of small population • Migration of small group in a new environment • Through mass extinction • Because of geological barriers

16. Darwin’s Idea of Natural Selection • Compared processes in nature with artificial selection • Developed a scientific hypothesis to explain how evolution occurs • Struggle for existence (Malthus) • Members of each species compete regularly to obtain food and living space and other necessities in life • Central to his Theory of Evolution

17. Survival of the Fittest • key factor in the struggle for existence • Fitness • ability to survive and reproduce • result of adaptation • central to the process of evolution by natural selection

18. LOW FITNESS • Either DIE or LEAVE FEW OFFSPRINGS • HIGH FITNESS LEVEL • many OFFSPRINGS • referred to as: NATURAL SELECTION • accumulation of changes that differentiate groups from one another, such that a new species may arise

19. DARWIN’s MISSING INGREDIENT • Darwin did not understand the genetic basis for variation • variations • mutations • genetic recombination • mutation as a raw material for evolution

20. OTHER THINGS TO BE CONSIDERED • Natural vs. Artificial selection • Importance of population in evolution • smallest unit that can evolve • Natural selection acts on individuals but INDIVIDUALS DO NOT EVOLVE

21. Darwinian View of LIFE • Diverse forms have arisen • DESCENT WITH MODIFICATION FROM ANCESTRAL SPECIES • Biological diversity • Mechanism of modification • NATURAL SELECTION

22. Patterns of Evolution • Mass extinction • 99% of the species ever lived are now extinct • wiped out whole ecological systems* • Cretaceous extinction • Large asteroid struck the earth • Can be caused by eruptions of many large volcanoes (Permian and Cretaceous) , changing of positions of continents and changing of sea levels

23. Patterns of Evolution • Adaptive Radiation • single species or small group of species has evolved into several different forms that live in different ways • Ex. Darwin’s Finches Dinosaurs Mammals

25. Patterns of Evolution • Convergent Evolution • unrelated organisms come to resemble one another • Natural selection may mold different body structures • structures tend to function the same way and look similar • Analogous structures • same look and function • Different embryonic origin

28. Patterns of Evolution • Coevolution • two species evolve in response to the changes in each other over time • Ex. Fig trees and wasps

29. Patterns of Evolution • Developmental Genes and Body Plans • Hox genes

30. Process of Speciation • Species • group of organisms that can interbreed and produce a fertile offspring • Share a common gene pool • As new species evolve populations become reproductively isolated from each other • Reproductive isolation • Can be: Behavioral, Geographical and Temporal

31. Process of Speciation • Behavioral isolation • Capable of interbreeeding but has different courtship rituals or behavior • Ex. Eastern and western meadowlark • Geographical isolation • Two populations are separated by geographic barriers • Acted by natural selection • Ex. Abert and Kaibab Squirrels

32. Process of Speciation Behavioral Geographical

33. Process of Speciation • Temporal isolation • Two or more species reproduce at the different times

34. DIANE DODD’s Experiment