Name Date Period Evolution by Natural Selection Adapted from the University of California Los Angeles Life Sciences 1 Demonstration Manual Copyright 2010 by Drs Jennifer Doherty and Ingrid Waldron Department of Biology University of Pennsylvania1 Describe what is happening in figures 1 3 Is the population of mice different in figure 3 than in figure 1 Explain why Describe what is happening in figures 1 3 There are a group of mice on the ground and a bird is flying above them Some mice are gray while others are white The ground is also gray making the mice that are gray blend in As the bird flies over it only sees the white mice and eats them Eventually there will be more gray mice then white mice and over time the white mouse population will drop and the gray mouse population will rise Is the population of mice different in figure 3 than in figure 1 Explain why Yes The gray mice blend in with the ground so they have a higher chance of living while the white mice stand out and get eaten by the bird Living things that are well adapted to their environment survive and reproduce Those that are not well adapted don t survive and reproduce An adaptation is any characteristic that increases fitness which is 1 Teachers are encouraged to copy this student handout for classroom use A Word file which can be used to prepare a modified version if desired Teacher Preparation Notes comments and the complete list of our hands on activities are available at http serendip brynmawr edu sci edu waldron defined as the ability to survive and reproduce What characteristic of the mice is an adaptation that increased their fitness The color of the mice from white to gray makes them have a better fitness The table below gives descriptions of four female mice that live in a beach area which is mostly tan sand with scattered plants According to the definition given for fitness which mouse would biologists consider the fittest Explain why this mouse would be the fittest The tan mouse would be the fittest because it lives the longest and reproduces the most Color of fur that trait Black Tan Cream 2 months Age at death pups produced by each female 0 Running speed If a mouse s fur color is generally similar to its mother s color what color fur would be most common among the pups Tan because over time since the live longer an reproduce more they will have a higher chance to pass on 8 months 11 6 cm sec 2 months 0 5 cm sec 8 cm sec Tan and Black 4 months 3 7 cm sec A characteristic which is influenced by genes and passed from parents to offspring is called heritable Over many generations heritable adaptive characteristics become more common in a population This process is called evolution by natural selection Evolution by natural selection takes place over many many generations Evolution by natural selection leads to adaptation within a population The term evolution by natural selection does not refer to individuals changing only to changes in the frequency of adaptive characteristics in the population as a whole For example for the mice that lived in the beach area with tan sand none of the mice had a change in the color of their fur however due to natural selection tan fur was more common for the pups than for the mother mice In summary a heritable characteristic that helps an animal or plant to have more offspring which survive to reproduce will tend to become more common in a population as a result of evolution by natural selection Questions 1 Explain why a characteristic which helps an animal to live longer will generally tend to become more common in the population as a result of evolution by natural selection A characteristic that prolongs life span will become more common because it is passed on more often through reproduction Over time the ones that do not have as much of a life span will die off faster and their populations numbers will be dwarfed by a better color