1. Evolution is the change a population undergoes over time. The theory of natural selection is a mechanism of evolution. It that states the organisms among a population that have traits which allows them to have greater reproductive success will become more prevalent over time. Fitness is the term to measure how reproductively successful an organism is. Evolution by natural selection produces organisms that are adapted to their current, local environment but are not perfect. This can be demonstrated through the Italian wall lizard. Scientists conducted an experiment in 1971 where they placed ten pairs of Italian wall lizards onto the island of Pod Mrčaru, an island foreign to this species of lizard (Listverse 2011). After 36 years of letting the lizards roam the scientists discovered new adaptations in the lizards. On their homeland they ate predominately insects, whereas in the new habitat they are mostly vegetation. Due to this, their heads become longer, wider and taller while inhabiting the new island. Plants are tougher to eat and digest than insects, so a bigger head would give them an advantage over lizards that did not have a large head. The abundant food source allowed the lizards to reproduce easier (Johnson 2008). Another adaptation the lizards underwent pertains to their digestive system. They began to produce cecal valves in their guts because the lizards were eating many more plants than previously in their original environment. These valves slow the digestive process down, making it easier for the body to absorb all the nutrients possible from the hard-to-digest plants. These valves are thought by researchers to be caused by a random mutation (Johnson 2008). Mutations cause genetic variation in a population, which would explain why the lizards evolved so rapidly. This is significant because no other species of lizards have been found to have them but hatchlings, juveniles, and adult Italian wall lizards were all found to have them after being on the island (ScienceDaily 2008). The Italian wall lizard can then be said to have gone through evolution because it has undergone a genetic change over time. This evolution was necessary in order for the organism to survive in the new environment. This example demonstrates evolution by natural selection because it covers the three requirements of natural selection: variation of a trait, heritability, and differential reproductive success. Both head size and cecal valve presence show the variation from organism to organism, covering the first point. Certain traits may be more advantageous in the new environment, but it is still possible for some organisms to not develop them, or for them to develop at different rates, causing them to vary. Heritability just means that the traits can be passed down from parents to their offspring, which is the case for both head size and cecal valves. It also meets the requirement of differential reproductive success because only the organisms with larger heads and cecal valves can compete, survive, and reproduce adequately. Without these two functions the lizards would not be able to sustain themselves in a vegetation covered environment (Johnson 2008).
2. Researchers have discovered in prehistoric humans that the mutation that turns the lactase gene on permanently was not present, while now it is common (Berkeley 2007). Human’s ability to digest lactose has been evolved since humans domesticated cattle, which was approximately 7500 to 9000 years ago (Berkeley 2007). The evolution of lactose tolerance is occurring because more and more regions are adopting milk products as sources of nutrition. The mutation is random but was, and still is, favored by populations that have a convenient milk supply, as it is more advantageous to people in those regions (Berkeley 2007). Scientists believe that the allele for lactase persistence (lactose tolerance) most likely came in response to strong selection for the