Darwin's theory of evolution by natural selection. Week 3

Transcription

1 Darwin's theory of evolution by natural selection Week 3 1

2 Announcements -HW 1 - will be on chapters 1 and 2 DUE:

3 Summary *Essay talk *Explaining evolutionary change *Getting to know natural selection 3

4 Common annoyances... *Immediately get to the point -don't start with a cheesy opener like "Webster's dictionary defines gene as " -Capitalizing: names of the fields are lower case: "...cultural anthropology, archaeology, physical anthropology,..." Tautologies It's Genus species = Homo sapiens 4

5 Solid essay outline 1. Introduction 1.1 Introduce the main subject of the essay 1.2 State your thesis 1.3 Briefly detail how the rest of the essay addresses/supports your thesis 2. Body of the essay - supporting your thesis (number of paragraphs varies with the differing questions) 2.1 Background or introduce the topic in detail (one paragraph) 2.2 Give support for your thesis 2.3 Give more support OR address potential objections to your thesis or support for the thesis 3. Conclusion 3.1 RESTATE thesis BRIEFLY recap/remind the reader that you've supported your thesis (in the body of the essay)

6 Key observations influencing Darwin -Every new generation has more offspring born than can survive (1) -There's constant competition for resources (2) -There's biodiversity among individuals in a generation (3) If all three of these circumstances are evident, then "favorable variations would tend to be preserved, and unfavorable ones to be destroyed. The result would be the formation of a new species" (Origin of Species) 6

7 Required conditions for natural selection to occur (i) Individuals in a population vary in inherited traits (ii) Some individuals are more fit, i.e., they have higher reproductive success because they have advantageous traits (iii) Selective pressures (environment, predation, etc) determine which traits are advantageous (iv) Over time, the proportion of individuals with advantageous traits increase while the proportion of individuals without such traits decreases 7

8 Important terms for evolution by natural selection Fitness: a measure of relative reproductive success of individuals -measured by an individual's genetic contribution to the next generation compared to other individuals Reproductive success: number of offspring an individual produces and rears to reproductive age Selective pressure: forces in the environment that influence reproductive success in individuals -what causes distinct species to develop 8

9 Natural selection in detail - analog with artificial selection Artificial selection -All domestic dogs share a common ancestry -There's extreme variation exhibited by dog breeds due to artificial selection 9

10 Required conditions for natural selection to occur (i) traits must be inherited if natural selection is to act on it (ii) natural selection cannot occur without population variation in inherited traits (iii) fitness is a relative measure that changes as the environment changes (iv) natural selection only acts on traits that affect reproduction 10

11 Required conditions for natural selection to occur (i) natural selection only acts on heritable traits (ii) natural selection cannot occur without population variation in inherited traits (iii) fitness is a relative measure that changes as the environment changes (iv) natural selection only acts on traits that affect reproduction 11

12 Natural selection in detail - Eight processes 8. Geographical isolation contributes to formation of new species as individuals adapt to different environments and respond to different selective pressures Influenced by observations and Wallace's biogeography 12

13 Example 1: Dog breeding Q: How could you turn a pack of wolves into Chihuahuas? Note: All dogs descended from wolves If you're given a pack of wolves to breed, how would you start breeding the wolves to eventually make a Chihuahua? 13

14 NS example exercises 1. Think about the question 2. Discuss question in pairs 3. Share answers to whole class Exercise 2: Peacock trains Q: How would you test whether peacocks with large spots on their trains have 'good genes'? 14

15 Competing hypotheses and social controversies about evolution Competing hypothesis: Intelligent Design -many criticisms but here are the three best criticisms 1. (quick) We can't differentiate between designed things and naturally occurring things. Which every rock in this picture is naturally formed except the 500th from the right in the bottom row. 2. Intelligent design is so vague it fails as a design inference 3. ID is a terrible explanation and outclassed by evolutionary theory 15

16 Competing hypotheses and social controversies about evolution Competing hypothesis: Intelligent Design -many criticisms but here are the three best criticisms 1. (quick) We can't differentiate between designed things and naturally occurring things. Which every rock in this picture is naturally formed except the 500th from the right in the bottom row. 2. Intelligent design is so vague it fails as a design inference 3. ID is a terrible explanation and outclassed by evolutionary theory 16

17 Competing hypotheses and social controversies about evolution Competing hypothesis: Intelligent Design -many criticisms but here are the three best criticisms 1. (quick) We can't differentiate between designed things and naturally occurring things. Every rock in this picture is naturally formed except the 5th from the right in the bottom row. 17

18 Competing hypotheses and social controversies about evolution 2. Intelligent design is so vague it fails as a design inference 18

19 Competing hypotheses and social controversies about evolution What's a good design inference then? Design inferences are based on our background experience with human intentions Intentions: goals, aims, and desires a person has Examples 1. Pug, chicken, grizzly bear, camel spider -It's obvious the first two are the products of human design because we have background experience with humans designing animals for pets 19

20 Competing hypotheses and social controversies about evolution What's a good design inference then? Design inferences are based on our background experience with human intentions Intentions: goals, aims, and desires a person has Examples 2. Arrowhead, fishing hook, etc - our background knowledge that humans design tools to hunt allows archaeologists to infer design in arrowheads and other artifacts found at archaeology digs 20

21 Competing hypotheses and social controversies about evolution What's a good design inference then? Design inferences are based on our background experience with human intentions Intentions: goals, aims, and desires a person has Examples 2. Arrowhead, fishing hook, etc - our background knowledge that humans design tools to hunt allows archaeologists to infer design in arrowheads and other artifacts found at archaeology digs 21

22 Competing hypotheses and social controversies about evolution 3. ID is a terrible explanation and outclassed by evolutionary theory Good explanations have the following characteristics *Disconfirmable - there can be evidence against it *Testable - the explanation makes predictions that (i) we can test scientifically and (ii) past the tests *Background knowledge - the explanation is consistent with facts independent of those it is trying to explain 22

23 Genes, DNA, cells and the biological basis for life Week 4 23

24 Constraints on the 19th century version of natural selection 1. There needs to be variation among the individuals of a population for natural selection to act Constraint: Darwin was unable to explain why there's variation seen among populations 2. Adaptations (favorable traits) are inherited from parent to offspring Constraint: Darwin was unable to explain how the process of inheritance works 24

25 Genetics Genetics studies gene structure and action Genetic mechanisms undergird evolutionary change 25

26 Cells - General Composition Organelles - substructures in the cell performing various functions E.g., protein synthesis, energy storage, waste disposal, etc. Nucleus - contains DNA and RNA Ribosomes - organelles in part made up of RNA; involved in protein synthesis Mitochondria - powerhouse of the cell - produces energy; think: cell's engines; also has DNA: mtdna 26

27 Cells - Two types Somatic cells - body tissues e.g., organs, brain, bone, and muscle Sex cells (gametes) - unites with another gamete from each parent which forms a zygote. They transmit genetic information from parents to offspring. Zygote - Potential to develop into a new organism, contains all the chromosomes (46 for us) 27

28 Proteins Function - attach to various molecules to perform different functions Hemoglobin (Hb) - binds w/ oxygen and transports it around the body Collagen - (tissue composition) - most common protein in the body Enzymes - regulate chemical reactions; E.g., digestive enzyme lactase breaks down lactose into simpler sugars. Hormones - affect different tissues and organs. E.g., Insulin made by specialized pancreas cells causes the absorption of glucose in liver cells 28

29 DNA DNA (deoxyribonucleic acid) - Double-stranded host of the genetic code RNA (ribonucleic acid) - single-stranded molecule messenger (mrna) transfer (trna) DNA + RNA contain the genetic information controlling the cell's functions 29

30 DNA Structure -nucleotides stacked on top of each other form the double-stranded twisted ladder-like structure Nucleotides: composed of a sugar, a phosphate (sides), and a nitrogenous base (rungs) Bases - form complementary bonds Adenine bonds with Thymine Guanine bonds with Cytosine 30

31 Protein Synthesis DNA determines the structure and function of proteins Proteins: made of chains of amino acids Function is determined by the number and arrangement of amino acids making up the chain Amino acids - building blocks of proteins 31