Evolution & Natural Selection

1. Evolution & Natural Selection Chapters 15, 16, & 17

2. Important people associated with Evolution • James Hutton (1785)- proposed that earth was shaped by geological forces that took place over extremely long periods of time. He estimates the Earth to be millions of years old. • Lyell agreed with him and stated that volcanoes and earthquakes have and continue to change the earth. • Thomas Malthus (1798) – predicted the human population would grow faster than the space and food supplies needed to sustain them. • Example: War, famine, disease

3. Important people associated with Evolution • Jean-Baptiste Lamark (1809) – proposed that organisms changed over time due to use and disuse of certain organs/parts. The traits that were “used” in an organism’s lifetime could be passed on to their offspring. His theory was flawed! • Tendency towards perfection- continually changing to be successful. • Ex: birds acquired urge to fly • Use and Disuse- by using organ eventually change • Ex: birds in order to fly develop wings • Inheritance of Acquired Traits • Ex: Lift weights build muscles and offspring will inherit big muscles

4. Important people associated with Evolution • All of the previous peoples ideas influenced Darwin’s thinking… • Charles Darwin (1831) – Set sail on the H.M.S. Beagle. This voyage provided him with much of the data and evidence that lead to his theory of evolution • Darwin’s “Theory of Evolution” would turn the scientific world upside down!!!

5. Important people in pictures… James Hutton Charles Darwin Jean-Baptiste Lamark Thomas Malthus

6. Lamarck vs. Darwin http://www.angelfire.com/bug/darwinvslamarck/

7. What did Darwin observe??? • Extreme diversity existed among plant and animal species around the world. • The organisms found within a certain area were well suited to survive in that environment. • Living organisms he observed greatly resembled fossils that he found on his voyage.

8. What did Darwin observe??? • The Galapagos Islands  This tiny group of islands influenced Darwin the most! • Although the islands were close together, the climates and environments differed greatly. • Similar organism found on different islands had varying characteristics, like appearance and behavior, this is variation. • Examples: • Giant Galapagos Tortoises with varying shell shape. • Darwin’s Finches – beak shape differed among the birds.

9. What did Darwin observe???

10. What did Darwin observe???

11. Apaptations • A trait/characteristic that an organism is born with • All organisms have adaptations that help them survive and thrive • Structural adaptations are physical features of an organism like the bill on a bird or the fur on a bear. • Behavioral adaptations are the things organisms do to survive. For example, bird calls and migration are behavioral adaptations. • Physiological adaptations are chemical responses to stimuli to maintain homeostasis

12. adaptations

13. Natural Variation • Occurs in all populations • Sexual reproduction increases the chance of natural variation because of the gene shuffling of meiosis • Occurs far less frequently in asexual reproduction

14. Darwin presents his theory of Evolution • 1859 – Darwin published his work: On the Origin of Species • Two main points: 1. Species were not created in their present form, but evolved from ancestral species. 2. Proposed a mechanism for evolution: NATURAL SELECTION • Humans had been employing “artificial selection” for many years!

15. Artificial Selection • The selective breeding of domesticated plants and animals by man. • Question: What’s the ancestor of the domesticated dog? • Answer:WOLF

16. Evolution by natural selection • Struggle for Existence • Survival of the “Fittest” – Fitness results from adaptations that give an organism advantages for survival. The most “fit” organisms will survive and reproduce; passing along the advantageous characteristics to their offspring. These changes can only be seen after many generations! • Examples of adaptations that make organisms “fit”… • Descent with Modification – As organisms change over time; they become different, resulting in many varied species. This illustrates “common descent.” All living things have a common ancestor.

17. Evidence that supports Evolution • Fossil Record • Older fossils are in lower rock layers • Geographic Distribution of Living Species • Species evolve differently based on where they live. • Due to different climate changes adaptations resulted in differences. • Similar areas tended to have similar adaptations

18. Evidence that supports Evolution • Anatomy-body parts • Homologous Structures • Wing bat resembles forelimb of mammal, not bird • Bird wing resembles reptile forelimb Analogous Structures similar looking but evolutionary unrelatred Vestigial organs- no function now but did have a function in ancestors. Ex: appendix, tailbone

19. Evidence that supports Evolution • Similarities in Early Development • Embryos of related ancestors are similar in early stages • Biochemical Evidence • Common DNA and RNA sequences; genes

20. Speciation • Definition: forming a new species • What is a species? • Group of similar organisms that can breed and produce fertile offspring. • Isolating Mechanism • features of behavior , morphology, or genetics which serve to prevent breeding between species. • Reproductive Isolation • mechanisms that prevent two or more populations from exchanging genes • Isolating Mechanism = Reproductive Isolation= Formation of a new species

21. Major Types of Isolation • Behavioral Isolation – Two separate species are capable of interbreeding, but they do not because of behavioral differences. • Example  Meadowlarks, different songs to attract mates; courtship • Geographic Isolation – When one species becomes separated by some barrier (river, mountain, etc.) they may develop into two distinct species over time. • Example  Squirrel population split by Colorado River 10,000 years ago

22. Major Types of Isolation • Temporal Isolation – This mechanism occurs when species reproduce at different times (different mating times). • Example Orchids in the rainforest, only release pollen 1 day! • Reproductive Isolation- Can’t interbreed and have separate gene pools • Example  Lion and a Tiger make a Liger which is sterile.

23. Evolution & Genetics: How are they linked??? • Darwin had a disadvantage when he developed his theory of evolution…he did not understand the mechanisms of heredity. • Today, we understand how genes, heredity, and evolution all tie together.

24. Evolution & Genetics: How are they linked??? • Gene Pool = the combined genetic info of all the members of a specific population. • Genetic Variation is Critical to Evolution • Mutations • Gene shuffling as a result of sexual reproduction

25. Evolution & Genetics: How are they linked??? • Single-Gene Traits vs. Polygenic Traits • Both lead to evolution, but polygenic traits (wide variety of phenotypes possible) lead to a more complex process of natural selection. • Genetic Equilibrium: when allele frequency remains constant in a population.

26. Evolution & Genetics: How are they linked??? • Hardy-Weinberg Principle: allele frequency remains constant in a population (no evolution)of these factors are present in the population. • Random mating • Population size very large • No movement in or out • No mutation • No natural selection

27. Evolution & Genetics: How are they linked??? • Three Major Types of “Natural Selection” • Directional Selection • Stabilizing Selection • Disruptive Selection

28. Directional selection • Form of natural selection by which the entire curve moves. • Occurs when individuals at one end of the distribution curve have higher fitness than individuals in the middle or at the other end of the curve. Key Directional Selection Low mortality, high fitness High mortality, low fitness Food becomes scarce.

29. Stabilizing Selection • Form of natural selection by which the center of the curve remains in its current position. • Occurs when individuals near the center of distribution curve have higher fitness than individuals at either end. Stabilizing Selection Key Low mortality, high fitness Selection against both extremes keep curve narrow and in same place. High mortality, low fitness Percentage of Population Birth Weight

30. Disruptive Selection • Form of natural selection in which a single curve splits into two. • Occurs when individuals at the upper and lower ends of a distribution curve have higher fitness than individuals near the middle. Disruptive Selection Largest and smallest seeds become more common. Key Population splits into two subgroups specializing in different seeds. Low mortality, high fitness Number of Birdsin Population Number of Birdsin Population High mortality, low fitness Beak Size Beak Size

31. What is Genetic Drift?? • Random change in allele frequency, based on the laws of probability. Example  Founder Effect • Founder Effect: change in allele frequencies as a result of the migration of a small subgroup of population.

32. History of Life • Fossil Evidence • Fossils provide proof of changes to life on earth • Relative dating – estimate fossil’s age compared to other fossils • Radioactive dating – age of fossil based on amount of remaining radioactive isotopes it contains • Geological Time

33. History of Life • Early History • Early atmosphere contained carbon dioxide, carbon monoxide, nitrogen, water vapor • Miller and Urey’s experiment show how a mixture of early atmospheric compounds could produce simple organic compounds found in living things • Rise of oxygen drove some life forms to extinction but many evolved and used oxygen for respiration and prospered • Endosymbiotic theory – eukaryotic cells arose from prokaryotic cells

34. History of Life • Geological Time Table • Paleozoic – Marine life • Devonian – animals invade land • Mesozoic – Dinosaurs and flowering plants • Cenozoic - Mammals

35. History of Life • Patterns of Evolution • Mass extinction •  Adaptive Radiation: Single species evolves into many species quickly • Ex. Dinosaurs and mammals • Convergent evolution – unrelated organisms resemble each other • Ex dolphin and shark • Coevolution – 2 species evolve in response to changes in each other • Ex flowers and insects • Punctuated Equilibrium – long stable periods interrupted by brief periods of rapid change • Changes in developmental genes- new research shows “hox” genes are master control genes and can control how evolution occurred.

36. The Miller-Urey Experiment Miller and Urey created a simulation of the predicted early atmosphere of the Earth. When they combined the atmospheric components with electricity, they produced organic compounds including amino acids.

37. The Evolution of Life Some scientists believe that RNA was the first genetic information The first life forms are thought to be single-celled prokaryotes (found from microfossils in rock) similar to bacteria. Later, photosynthetic bacteria produced oxygen. This oxygen combined with iron in the water, forming rust, which dropped to the ocean floor and left the ocean blue-green Most organisms evolved new metabolic pathways that would allow them to live in the new oxygen-rich environment.

38. The Evolution of Life Eukaryotic Cells evolved from prokaryotes that began evolving internal cell membranes. Some small prokaryote then entered a larger prokaryote to form a mutualistic relationship. These smaller prokaryotes were able to use oxygen (aerobic respiration) and evolved into what is now our mitochondria…recall that mitochondria have different DNA than the rest of the cell. This is called the Endosymbiotic Theory. The evolution of Sexual Reproduction allowed much more genetic variation among eukaryotes.

39. The Endosymbiotic Theory A descriptive Diagram: