After months of this daily grind in a hot, inhospitable place, the Grants head back to Princeton to interpret the data." (12-14).
Weiner describes Endler's work: "What the Grants are to Darwin's finches, Endler is to guppies. His guppies live in northeastern South America, in the small streams that zigzag down the mountains of Venezuela, Margarita Island, Trinidad, and Tobago, flashing through steep, undisturbed green forests and then the broad spreads of the old cacao and coffee plantations, on their way to the Caribbean Sea and the Atlantic".(12) Weiner discusses the guppies: "When Endler analyzed his guppy surveys, he discovered a pattern. The spots on each guppy look chaotic, but the spots of all the populations of guppies in a stream, taken together, from the headwaters down to the base, have a kind of order. The spots on each population of guppies bear a simple relationship to the number of guppy eaters in their part of the stream. The more numerous the guppies' enemies were, the smaller and fainter the guppies' spots. The fewer their enemies, the larger and brighter their spots were" (13).
As Endler shows, environments influences characteristics, the same can be seen in human environments. The guppies are basically shaped by their environment. The environment has a strong impact on the youth and guppies. The prevalence of youth gangs in a place will most likely increase the number of youth who are involved in gang activities. Similarly, the presence of guppies in a place gives way to a community of guppies that are present there.
In the United States alone, almost 5,000 communities report having juvenile gangs (Moore and Terrett, 6). These communities have a total of 31,000 juvenile gangs with a membership of around 850,000 young people. These numbers shows that juvenile gangs are present on local communities throughout the United States (Moore and Terrett, 6). Similarly, guppies tend to stay together in a particular stream. Endler studied the streams which are natural laboratories for the study of natural selection of guppies. Weiner writes further "Endler developed standardized methods of identifying the guppies and measuring guppy spots. His method of study is as careful Grants' methods with Darwin's finches. He learned to anesthetize and photograph each guppy he caught. Then from the photographs he recorded the color and position of each spot of every male guppy, dividing each guppy into dozens of sectors to make a standardized guppy map that is easy to read, to tally, and to enter into a computer." (14-15).
There are factors that affect the presence of gangs and guppies. In the case of guppies, Weiner cites that "Endler found guppies and at least a few of their enemies in almost every section of almost every stream, from the headwaters near the summit of each mountain to the plains and plantations below. Neither the guppies nor the guppy eaters can swim up a waterfall, nor the population of each section of stream tend to stay put" (16).
There are predisposing factors for youth gangs. "Poverty and marginalization" are major factors that signal the presence of youth gangs in a community (Duffy and Gilig, 25). Duffy and Gilig explain that marginalization is a term that refers to the state of