chapter 22 descent with modification: a darwinian view
DESCRIPTION
“The Origin of Species” Darwin’s book focused on 2 main ideas: 1.“descent with modification” explains life’s unity and diversity. 2.Natural Selection – competition for limited resources results in differential survival. Individuals with favorable phenotypes are more likely to survive and produce more offspring, passing traits to the next generation.TRANSCRIPT
![Page 1: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/1.jpg)
Chapter 22
Descent with Modification: A Darwinian View
![Page 2: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/2.jpg)
Charles Darwin (1809-1882)
• Traveled on the ship the H.M.S. Beagle and served as an observer and naturalist.
• Had an interest in geologic distribution of species and fossils.
• Reassessed his trip and theorized that new species arise from ancestral forms by gradual accumulations of adaptations to a different environment.
![Page 3: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/3.jpg)
“The Origin of Species”Darwin’s book focused on 2 main ideas:1. “descent with modification” explains life’s
unity and diversity.2. Natural Selection – competition for
limited resources results in differential survival. Individuals with favorable phenotypes are more likely to survive and produce more offspring, passing traits to the next generation.
![Page 4: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/4.jpg)
![Page 5: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/5.jpg)
Natural Selection• Simplistically, evolution is defined as a
change in gene frequency within a population.
• Gene frequencies change in response to changes in the environment. These changes act as a selective mechanism on populations.
• Environments can be more or less stable, affecting the evolutionary rate and direction. Different genetic variations can be selected in each generation.
![Page 6: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/6.jpg)
![Page 7: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/7.jpg)
• An adaptation is a genetic variation that is favored by selection and manifested as a trait that provides the organism with an advantage in a particular environment.
• Phenotypic variations are not directed by the environment but occur through random changes in the DNA and through new gene combinations.
• Some variations significantly increase or decrease the fitness of an organism and the population.
![Page 8: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/8.jpg)
African cowpea seeds
![Page 9: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/9.jpg)
![Page 10: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/10.jpg)
Artificial Selection• Humans impact variation in other species.
![Page 11: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/11.jpg)
![Page 12: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/12.jpg)
Evidences for evolution
Scientific evidence of biological evolution uses information from geographical, geological, physical, chemical and mathematical applications.Morphological homologyBiochemical/genetic similaritiesFossil recordMathematical models and simulations
![Page 13: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/13.jpg)
Homologous Structures
![Page 14: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/14.jpg)
• Morphological homologies are features shared by common ancestry.
• Vestigial structures are remnants of functional structures, which can be compared to fossils and provide evidence for evolution.
![Page 15: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/15.jpg)
![Page 16: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/16.jpg)
![Page 17: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/17.jpg)
![Page 18: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/18.jpg)
Biochemical/genetic similarities
• DNA nucleotide and protein sequences provide evidence for evolution and ancestry.
![Page 19: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/19.jpg)
![Page 20: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/20.jpg)
Mathematical models
• Phylogenetic trees, graphical analyses of allelic frequencies can be used to support evo relationships.
![Page 21: Chapter 22 Descent with Modification: A Darwinian View](https://reader033.vdocuments.us/reader033/viewer/2022050803/5a4d1b187f8b9ab059992674/html5/thumbnails/21.jpg)
Key Points to Remember1. Individuals DO NOT evolve, a population
evolves through its interaction with the environment.
2. Evolution can only be measured as changes in relative proportions of heritable variations in a population over a succession of generations.
3. Natural selection can amplify or diminish heritable traits only.
4. Environmental factors vary from place to place and time to time.