Transcript Mutations
Mutations & Natural Selection Definition of Mutation = A random change in an organism’s DNA Can be inherited – passed down from a parent to their offspring Can be caused by carcinogens (cancer causing agents in the environment) Mutation = a random change in an organism’s DNA Circle one! #4. Mutations that occur in [ sex cells / body cells / any cell ] can be passed down to offspring. HINT 1 HINT 2 Where did you get your genes? You were once a zygote. Where did “zygote you” get genes from? HINT 3 What are the only cells that actually came from your parents to make you? What Can Mutations Do? Mutations can be POSITIVE (helpful) Some mutations can provide an advantage which helps the organism survive Mutations can be NEUTRAL (not harmful, not helpful) Neutral mutations do not affect the organism’s survival (the mutation does not help or hurt the organism) Mutations can be NEGATIVE (harmful) Negative mutations hurt the organism’s chances for survival Mutated blood cell (person with sickle cell anemia) Normal red blood cell Mutations can be POSITIVE (helpful) Some mutations can provide an advantage which helps the organism survive Some mutations can be helpful Some mutations can have no effect (NEUTRAL) Some mutations can be harmful A mutation may be POSITIVE, or NEUTRAL, or NEGATIVE depending on the environment Which bird would have the best chances of survival in a forest where all the leaves were BLUE? Some Important Terms Natural variation: differences among individuals of a species Artificial selection: nature provides the variation among different organisms, and humans select those variations they find useful. Natural selection: Over time, natural selection results in changes in inherited characteristics of a population. These changes increase a species fitness in its environment The Struggle for Existence: members of each species have to compete for food, shelter, other life necessities. Survival of the Fittest: Some individuals with certain traits better suited for the environment and will survive to reproduce the next generation. Darwin’s Theory of Evolution by Natural Selection The Theory of Evolution is the process by which different kinds of living organisms are thought to have developed and diversified from earlier forms during the history of the earth. Microevolution (natural selection; changes within species) Macroevolution (one species changes to another species) A theory is an idea or set of ideas that is intended to explain facts or events. Darwin’s Reasoning Darwin assumed that species can change over time (Lamarch); found fossils that seemed to fit this. Believed that the earth was very old (Lyell). A population can outgrow its resources (Malthus) competition for existence among offspring. Certain variations are more likely to survive and reproduce. “Fitness” = an organism’s relative ability to survive and produce fertile offspring. “Natural selection” = process by which nature “selects” the organisms that are the most useful. If artificial selection could change a domestic species over time, he believed natural selection could cause a species to “evolve” over time. Evolutionary Terminology Descent with Modification: Each living organism has descended, with changes from other species over time. Common Descent: were derived from common ancestors Giraffe Theory = An evolutionary explanation why giraffes have long necks. • Giraffes with longer necks had an advantage. They could reach leaves other giraffes could not. Therefore, the long-necked giraffes were more likely to survive and reproduce (greater fitness_. These giraffes passed the long-neck trait to their offspring. Each generation, the population contained more long-necked giraffes. Eventually, all giraffes had long necks. Giraffe Theory – HOWEVER… • Female giraffe necks are 2 feet shorter than males. If longer necks were needed to reach above the forage line, then they would have starved to death. • NO EVIDENCE in the fossil record of gradual increase the neck. • Giraffe neck is more than just a longer version of the okapi neck. • Giraffe “adaptational package”: exceptionally large heart (3 x’s man’s heart); blood pressure control; oversized lungs; respiratory rate 1/3 of humans; capillaries are very internal and 1/3 the size of humans. “Darwin’s Finches” The finches on the Galapagos Island are a great example of the way in which species' gene pools have adapted in order for long term survival via their offspring. Darwin's finches are thirteen to fourteen different species of finches living on the Galapagos Islands (considered an icon of evolution). Darwin had noticed that each island had its own variety of finch, with the most importance difference being the size and shape of their beaks used for different diets and lifestyles. “Darwin’s Finches” Some had large beaks used for cracking nuts and seeds, while others had slender beaks suited for catching insects etc. The explanation for this given by Darwin was that all the finches on the islands came from one original pair of finches, and that natural selection is responsible for the differences. Because of the variations in the finches he inferred that all species on earth had evolved from this process over billions of years. Current Research Researchers are now discovering that organisms can robustly adapt to different ecological niches without major changes in their DNA sequence. A team of Princeton scientists have won a prestigious award for 20 years of study of the finch's beaks. Just what was found? The two scholars, Drs. Peter and Rosemary Grant observed how, under drought conditions, birds with larger beaks were better adapted than others, thus their percentage increased. But this trend reversed when the cyclical conditions reversed. Furthermore, in times of drought, the normally separate species were observed to cross-breed. They are related after all. But is this really evolution? Even after the changes there is still the same array of beak sizes and shapes. This is variation and adaptation, not evolution. Actually, de-evolution has occurred; the observation is that there are larger groupings of species into what may be more reminiscent of the original kind. INTERPRETATION OF THE DATA IS KEY.