# of This Bean That Survived = population size – total kills
This exercise illustrates the effect of natural selection on populations of predators and prey. Part 1: Natural Selection Exercise-Generation 1 One example is the presence of geographical barriers such as mountain ranges or islands that prevent gene flow between separated populations. There is a variety of isolating mechanisms that can prevent gene flow from occurring. Given sufficient time, a population that is isolated from the original population can diverge physically and/or behaviorally to the point where it is a distinct species. Reproductive isolation occurs by some mechanism that can isolate diverging populations so as to prevent interbreeding. If these four processes are coupled with reproductive isolation, then speciation (the formation of a new species) can occur. Individuals with favorable characteristics have a competitive advantage and are more likely to pass their genes on to the next generation. Natural selection can be viewed as differential reproduction. Put Darwin’s observations together and you get natural selection, a process favoring survival and reproduction of the most fit individuals in a population.
This is not necessarily true of our common use of the word! Be careful here, because the word “fitness” does not refer to physical fitness or healthiness! This word is being used in a very specific way to mean “successful reproduction.” Fit individuals make more babies.