When you think of the American Southwest, you probably think of cacti, both big and small. If you were to visit the American Southwest today, you might be disappointed with the lack of variation among cactus species, especially right off the major highways. In 1926, Route 66 was the nation's first major highway to allow visitors to visit the Southwest. Like many tourists, these visitors wanted to take home a memento of their travels. Many people would pull over and begin looking for their own living souvenirs. Since many of the tourists did not have the necessary tools to extract a spiny cactus out of the soil, they usually had to make a conscious decision about what type of cactus they should dig up. The cacti with too many spines were seen as too difficult to dig out, and the visitors likely didn't have gloves to protect their hands. The cacti with too few spines were seen as homely and were often overlooked. Therefore, the tourists found a cactus that was between these two extremes. Over the last century, the phenotypic variation within these small cacti has changed (at least in areas accessible by these highways). Factors of Evolution
1. There is genetic variation within the population due to inheritance of a mutation.
2.There is competition for limited resources.
3.Organisms that are better suited to their environment are able to survive and reproduce.
4.Species produce more offspring than can survive in an ecosystem.