1 UNIT 5 PART 2: THE MODERN THEORY OF EVOLUTION The evidence shows that evolution occurred but not how or why. There have been different theories.

2 Lamarck’s Theory of Evolution He believed that species were not constant but that they changed, and that new species evolved from preexisting species. He thought these changes were caused by their need to adapt to changes in the environment. His theory had two principles: –Use and disuse –Inheritance of acquired characteristics

3 Use and Disuse The more a body part is used the stronger and more developed it becomes. Parts that are not used become weaker and less developed.

4 Inheritance of Acquired Characteristics Characteristics developed by use could be passed on to offspring. Lamarck said this was how giraffes got their long necks: by using them to stretch for food their necks became longer and that trait was passed on to offspring. Over time giraffe’s necks became longer and longer.

5 Weismann disproves Lamarck Weismann cut the tails off mice and bred them for over 20 generations. Each time the mice were born with tails. We now know that traits are passed on by genes which are not affected by life experiences.

6 Charles Darwin Sailed on the HMS Beagle as ship’s naturalist Collected and observed specimens from South America and the Galapagos Islands He thought that species changed slowly over time.

7 Darwin’s Finches Darwin believed that the species on the Galapagos Islands evolved from a species that came from the mainland. Each evolved to be different due to different environmental conditions on each island.

8 Darwin now had to figure out how evolution occurred He reasoned that because there is a struggle to survive, those who are better adapted to the environment (more fit) will survive to reproduce and those not as well adapted (less fit) won’t. This he called natural selection because it is nature that is selecting who survives. Wallace had the same idea and asked Darwin to look at his work. Their work was then published separately in 1859.

9 The Main Points of The Darwin- Wallace Theory of Evolution: Overproduction – produce more offspring than needed because only a few will survive. Competition – offspring must compete for food, water, shelter so only a few survive. Variation – differences in individuals. Some may affect the ability to compete.

10 ADAPTATIONS – because of variations some individuals will be better adapted to survive and reproduce than others. These individuals are the most fit. An adaptation is any kind of inherited trait that improves an organism’s chances of survival. These beaks are adaptations for eating different types of food.

11 The more variations that exist in a species the better that species chances of survival are if the environment changes. A change in the environment does not cause the variations – the variations must be present before the environment changes in order to be selected for. A selecting agent determines who survives. Natural selection – the environment selects those best adapted to survive and reproduce: survival of the fittest. These favorable traits will be passed on.

12 Types of Adaptations Structural – involve a part of the body Physiological – involve the metabolism Behavioral – involve actions Warning coloration – warns predators Camouflage – to blend in with environment Mimicry – copies something else

13 SPECIATION – over time favorable adaptations accumulate in species and unfavorable traits disappear. Eventually changes result in new species.

14 Speciation – the formation of new species There is a new species once a population has lost the ability to interbreed with its neighbors. Isolation is needed for speciation:  Geographic – a population is divided by a natural barrier such as a mountain or river. Over time each group adapts to its environment and its gene pool changes.  Reproductive – the loss of the ability to interbreed by two isolated groups. Can also be caused by changes in behavior, mating times, and sterility.

15 Populations Evolve Not Individuals Over time the allele frequencies change because of natural selection. Useful variations will increase; bad ones will decrease.

16 Two models of the Rate of Evolution Gradualism – evolution occurs slowly and continuously over long periods of time. Transitional forms are missing from the fossil record because they were less common. Punctuated Equilibrium – species stay the same for long periods (equilibrium) then have a short rapid evolution. Transitional forms are missing because there was not enough time.

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18 New traits can arise by: Mutation – If it is good, nature will select for it, otherwise it will go away. Genetic Recombination – during sexual reproduction Migration – individuals moving into or out of a population take their genes with them.

19 Adaptive Radiation (Divergent Evolution) The process by which a species evolves into a number of different species each in a new environment. Example: Darwin’s finches: adapted to trees or ground; seeds or insects

20 Convergent Evolution Natural selection causes unrelated species to resemble one another. This produces analogous structures.

21 Coevolution Two or more species evolve in response to each other. Example: Flowers and their pollinators

22 Industrial Melanism – The Peppered Moth The peppered moth in England had been well studied for a long time. The moth is mostly white, but “peppered” with dark specks. In 1845 a dark one was seen for the first time. By 1900, most of the moths around the cities were dark, while those in the country were mostly white. Why?

23 Case Study: Antibiotic Resistance When penicillin is used on bacteria for the first time 99.99% of the bacteria die. The.01% of the bacteria that survive have an adaptive variation that allowed them to survive penicillin. These bacteria multiply and their offspring will now be resistant to penicillin. Each time penicillin is used on the bacteria, more and more of them survive, until it is no longer effective. It is important to understand that the bacteria had the variation before they were exposed to penicillin, and not as a result of it. Penicillin is acting as the selecting agent.