Darwin’s Theory of Natural Selection

Scenario #2 (1) The population of medium ground finches is highly variable in their individual beak size and shape. Some of the finches have smaller, shorter, weaker beaks and others have larger, deeper, stronger beaks. (5) A drought hits the island and there is no rain for 550 days. There is now a limited supply of seeds on the island. Fairly quickly all of the smaller, easier to crack seeds are eaten. (2) The finches that have smaller, shorter beaks go hungry and start to die off. (3) The medium ground finches with larger beaks are able to crack the larger, harder seeds, they live longer and reproduce offspring. (4) The offspring inherit their parent’s larger beaks. (6) The population of medium ground finches is now different. Overall a majority of the medium ground finches now have larger, deeper beaks and there are very few finches with smaller, shorter beaks. Questions 1. What is the key trait of selection among the finches? The beaks are the key trait that determines whether or not the finches live or die. 2. What are the finches competing over? They are competing over food. As the environment changed and certain seeds became scarce the finch’s beaks determined their ability to get food and therefore survive. Is the competition within or between species? The competition is within species. Individuals within the same species are the ones who will compete most fiercely over resources. General Information on the Assignment Is Lamark’s hypothesis scientific? Is it valid? To be scientific a hypothesis must be testable. Each of the components in Lamark’s hypothesis can be tested. Only some of Lamarck’s components are valid, in that they stand up to scientific testing. We know that environments change. We also know that individuals in all populations are variable in the traits that they possess. We know that individuals inherit the genetic material that their parents pass on, but they do NOT inherit any traits that were acquired within the parents lifetime (buff parents do not have buff babies!). Is Darwin’s hypothesis scientific? Is it valid? Darwin’s Theory is scientific and it is valid. Natural Selection has been tested over and over and over again and is still being tested in numerous populations of organisms and animals around the world today. Natural Selection is one of the four processes that we have to explain change of populations over time (the other three processes will be explained in Chapter 4).