1. THE THEORY OF NATURAL SELECTION Chapter 13 Section 1 Grade 10 Biology Spring 2011

2. Objectives Identify several observations that led Darwin to conclude that species evolve Relate the process of natural selection to its outcome Summarize the main points of Darwin’s theory of evolution by natural selection as it is stated today Contrast the gradualism and punctuated equilibrium models of evolution

3. Bell Ringer Write down what you already know about evolution

4. Biography of Darwin Darwin was a poor student, disinterested in subjects his father wanted him to engage in Attended medical school but was repelled by surgeries and often skipped lectures Was often found outdoors collecting biological specimens Completed a degree in theology but was interested in natural sciences

5. Biography of Darwin In 1831, Darwin was recommended for a position as a naturalist on the HMS Beagle

6. Science Before Darwin Idea that each species is a divine creation that exists, unchanging, as it was originally created Scientists had begun to seek to explain the origins of fossils  Tried to explain their observations by altering traditional explanations of creation  Others proposed various mechanisms to explain how living things change over time

7. Science Before Darwin Lamarck’s theory  Over the lifetime of an individual, physical features increase in size because of use or reduce in size because of disuse  These changes are then passed on to offspring  Is incorrect, but correctly pointed out that change in species is linked to “physical condition of life”

9. Darwin’s Observations Read Lyell’s book Principals of Geology, that proposed that the surface of the Earth changed slowly over many years Visited different places, where he saw things that he thought could be explained only by a process of gradual change  Extinct Armadillo fossils similar but not identical to present species

10. Darwin’s Observations Galapagos Islands  Many plants and animals resembled those of coast  Hypothesized that ancestors of Galapagos species migrated to islands from South America long ago and changed after they arrived  Called it decent with modification- evolution

11. Growth of Populations Malthus  Wrote that human populations are able to increase faster than the food supply can  Unchecked populations grow by geometric progression  Food supplies grow by arithmetic progression  Proposed human population do not grow unchecked because death caused by disease, war, and famine slows population growth

12. Growth of Populations Population: consists of all the individuals of a species that live in a specific geographical area and that can interbreed

13. Evolution by Natural Selection Darwin realized Malthus’s hypothesis about human population applied to all species Every organism has potential to produce many offspring during its lifetime In most cases, only a limited number of offspring survive to reproduce

14. Evolution by Natural Selection Darwin connected Malthus’s ideas with his own observations and ideas Individuals that have physical or behavioral traits that better suit their environment are more likely to survive and will reproduce more successfully than those that do not have such traits  Natural Selection

15. Natural Selection

16. Evolution by Natural Selection In time, the number of individuals that carry favorable characteristics that are also inherited will increase in a population  Nature of population will change- evolution

17. Evolution by Natural Selection Proposed organisms differ from place to place because their habitats present different challenges to and opportunities for survival and reproduction Adaptation: is an inherited trait that has become common in a population because that trait provides a selective advantage

18. Publication of Darwin’s Work 1844, Darwin wrote down his ideas about evolution and natural selection Published in 1858 Presented with Alfred Wallace who was coming to the same conclusion as Darwin was about natural selection and evolution

19. Darwin’s Theory 1. Inherited variation exists within the genes of every population or species (the result of random mutation and translation errors) 2. In a particular environment, some individuals of a population or species are better suited to survive (as a result of variation and have more offspring- natural selection)

20. Darwin’s Theory 3. Over time, the traits that make certain individuals of a population able to survive and reproduce tend to spread in that population 4. There is overwhelming evidence from fossils and many other sources that living species evolved from organisms that are extinct

21. Darwin’s Ideas Updated Change Within Populations:  Now know genes are responsible for inherited traits  Certain forms of a trait become more common in a population because more individuals in the population carry the alleles for those forms  Natural selection causes the frequency of certain alleles in a population to increase or decrease over time  Mutations and recombination of alleles that occurs during sexual reproduction provide endless sources of new variations of natural selection to act upon

22. Darwin’s Ideas Updated Species Formation:  The environment differs from place to place  Populations of the same species living in different locations tend to evolve in different directions  Reproductive isolation: condition in which two populations of the same species do not breed with one another because of geographic separation, difference in mating periods, or other barriers to reproduction  May eventually become unable to breed together

23. Darwin’s Ideas Updated The Tempo of Evolution:  Gradualism: model of evolution in which gradual change over a long period of time leads to species formation  Suggested that successful species may stay unchanged for long periods of time (Gould and Eldredge)  Major environmental events in the past have caused major evolution to occur in spurts  Punctuated equilibrium: model of evolution, in which periods of rapid change in species are separated by periods of little or no change  Evidence for both

25. Review 1. T/F Malthus and Lyell influenced Darwin in his ideas of natural selection 2. T/F The number of individuals that carry favorable characteristics that are also inherited will increase in a population 3. T/F The smallest scale that evolution happens on is the individual

26. Answers 1. T/F Malthus and Lyell influenced Darwin in his ideas of natural selection 2. T/F The number of individuals that carry favorable characteristics that are also inherited will increase in a population 3. T/F The smallest scale that evolution happens on is the individual  Smallest scale is at the population level, individuals don’t evolve, populations do