How Populations Evolve: Chapter 13

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1. Give the general meaning of the word evolution and the specific meanings of the word as used by biologists:

• Change in the genetic make-up of a population over time
• Development of new species from preexisting species
• Relationships between different species over geological time ("Grand scale")

Comments: All organisms are believed to be related by genealogical descent. This follows as we have noted repeatedly from what we see around us as expressed by cell theory. Darwin did not even like the word evolution but instead preferred the term 'modification with descent'.

Often times people distinguish between microevolution and macroevolution but there is clear distinction between them and saying you believe in microevolution but not macroevolution has been compared to believing in the existence of feet but not miles.

2. Discuss the following related to Darwin's cultural and Scientific Context:

Define the typological species concept and relate it to Plato's parable of the Cave.

• Identify and tell the contribution of the following people to pre-Darwinian thinking about evolution:
• Aristotle and Plato vs Anaximander
• Georges Buffon
• Lamarck
• Charles Lyell

3.  List and discuss Darwin's three radical ideas:

• Variation is important in how evolution operates.
• Biological evolution happens to populations not individuals.
• The environment can serve as the 'designer' of evolutionary adaptations.

• Evolution as a process of adaptation.
• Inheritance of Acquired characteristics, as an incorrect mechanism about how evolution operates.

• Voyage of the Beagle
• Explain the two conclusions of the new geology of Charles Lyell. p 247
• Define the principle of gradualism

Comment: The principle of gradualism is more properly expressed as the principle of uniformitarianism(uniformity) which says that the physical principles governing how the universe appears to work today operate pretty much the same through space and time. Of course, logically this might not be strictly true, but science accepts this idea because it empirically works in science just as in everyday life.

A good application of the principle of uniformity is our current understanding of the age of the Earth. Geologists today following Lyle's assumption routinely use different systems of isotopes to date rocks and ultimately to estimate the age of the Earth. A good discussion is at:http://www.talkorigins.org/faqs/faq-age-of-earth.html

6. List the main conclusions Darwin raised in Origin of Species:

• All species today are descended from ancestral species - Modification with descent.
• Natural selection is the mechanism for modification with descent.
• The biological adaptations shown by organisms today are the result of natural selection.
• Define and give examples of sexual selection.

Darwin also understood the importance of what he called sexual selection and that certain adaptations such as the Peacock's tail may be the result selection for mates. For a modern experimental analysis see La Bas, Hockham and Ritchie(2004) Evolution(58):1763Ð1772: http://evol.allenpress.com/evolonline/?request=get-document&issn=0014-3820&volume=058&issue=08&page=1763

Comment: As Darwin understood, and organism's behavior is subject to natural selection as well and can be viewed as an adaptation. See for instance: www.psypress.co.uk/pip/ resources/chapters/PIP_evolution.pdf . This is a pdf file so you will need Acrobat's reader.

7. Identify the importance of the following lines of evidence of evolution. pp 249-253

• The fossil record
• Biogeography
• Comparative anatomy
• Comparative Embryology
• Molecular Biology

An additional resource is the Talk.Origins archive .

• Define biogeography and  give examples of the questions raised by biogeography. 
  
• Explain the significance of the Galapagos finches. p 254
  
• Explain what fossils are and explain why fossils are important in the study of evolution.
  
• Explain how we know older fossils are in deeper layers of sedimentary rock.
  
• Define comparative anatomy and explain the concept of homology Vs analogy.
  

Comments:

Your book does not properly define homology. One of the deep dark secrets about homology is that homology as a concept predates evolution. Homology is better defined as a strong pattern of developmental correspondence and structural correspondence between structures between different species. From this correspondence or similarity we infer common ancestry. Sometimes structures that appear homologous really aren't when the details are closely examined.

 A strong case for homology is made when we find complex structures that have a different function but have a strong pattern of structural correspondence. Analogous structures have a similar function but do not have the same deep correspondence in development and structure. For instance the eyes of some squids look very much like vertebrate eyes at first glance. But the developmental details are quite different. I might point out that the squid example give lie to the claim of creationists that there are no transitional forms say between simple eyes and complex eyes, since all can be found in squids!

Analogy is related to an important pattern in biogeography namely that distantly related organisms in similar environments often show similar adaptations to the broad features of the environment and conversely that closely related organisms in terms of homology may show quite different adaptations to the broad features of their environment. Here is a good example. Which plants are cacti?

8.  Explain the two key observations that Darwin connected in his theory of natural selection. p 255

• Explain why variation in traits is  important for natural selection.
• Discuss the role of the environment in natural selection.
• Explain why it is incorrect to say "pesticides have created pesticide resistant insects". See p 256
• Compare artificial selection to natural selection. See my Natural Selection Made Easy link.

9.  Explain how populations of insecticide resistant insects and antibiotic resistant bacteria evolve via natural selection.

• population
• gene pool
• heritable variation
• sources of  genetic variation
• polymorphisms

11. Explain the 'bookkeeping steps in calculating allele frequencies in the gene pool.

• Calculate allele frequencies given genotype frequencies in a population or for incomplete dominance situations such as the snap dragon example(not in text)
  
• Explain the Hardy Weinberg Equilibrium concept.
• Define micro-evolution from the population genetics perspective. p 260
• Use the Hardy Weinberg relationship to estimate allele frequencies in situations of complete dominance.
  

12. Discuss the five main mechanisms of evolution:

• Genetic drift
• Explain the importance of genetic drift and the bottleneck effect in conservation of rare species.
• Gene flow
• Mutations
• Natural Selection
• Explain Darwinian fitness. p 264
• Describe the three major outcomes of natural selection: Directional, diversifying(disruptive), stabilizing
• Non random mating(not in text).

Comment: There are several distinct types of non random mating. First of all organisms may mate with their neighbors. In human populations this was quite common until recently. Next organisms may select mates based on certain characteristics. Selection for bright plumaged birds by females of many bird species is based on innate preferences for certain forms and colors.Darwin coined the term sexual selection which is still in use today.

Here is a very recent article linking estrogen levels in women to male preferences with regards to female beauty: http://www.sci-tech-today.com/story.xhtml?story_id=003000002IFI

There is good evidence that human females select mates based on certain characteristics as well. So in humans at least sexual selection is done by both genders. :-)

13. Explain the population genetics of sickle cell anemia.

14. Some key points to remember: Evolution refers to a process and a theory.

• Evolution is a process that is as well established as any in modern science.
• The theory of evolution is incomplete.
• Microevolution = genetic change in a population.
• Natural selection is believed to be the mechanism by which complex adaptations develop and spread.
  
• Natural selection is only one agent of evolution.
  
• Speciation = the processes by which new species or kinds develop.
• Macroevolution = large scale patterns of relationships over geological time.