Charles Darwin: Theory of Evolution as a Mechanistic Process

1. Charles Darwin: Theory of Evolution as a Mechanistic Process JRMGUCE 2009

2. Charles Darwin: Theory of Evolution as a Mechanistic Process • Darwin’s Idea of Common Descent • Darwin’s Idea of Multiplication of Species • Darwin’s Idea of Gradualism • Darwin’s Idea of Natural Selection

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

4. 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???

5. 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

6. TAXONOMY: Tree of Life Carolus Linnaeus - Species are fixed - Ordered the great diversity of organisms into “groups subordinate to groups”

7. Reflected the genealogy of the tree of life

8. Darwin’s Idea of Multiplication of 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 • species either split into or bud off other species • geographical isolation of a founder species.

10. 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

12. 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

14. 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

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

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

29. 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

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

31. Process of Speciation

32. Process of Speciation

33. DIANE DODD’s Experiment