Evolution refers to a change in the allele frequency of a population. A common misconception is that evolution is "progress" and is working toward some sort of goal. Often the conditions that lead to a certain change in allele frequency are later reversed and the allele frequency returns to its original state. For example, when southern Alberta experiences one of its periodic droughts, plants with a drought resistant phenotype will have an advantage over moisture-loving plants in the same species, and the drought-resistant alleles will become more common in the population. When the drought ends, the moisture-loving plants have the advantage and their alleles will become more common in the population. Neither phenotype is "better" and the species has not "progressed" - it has simply survived.

Natural Selection- basically, if an organism has a physical characteristic that gives it an advantage over other organisms AND it is a characteristic that can be passed to the next generation, that organism is said to be more 'fit' than its peers. For example, say there are a bunch of birds on and island and some have big beaks and some have small beaks.. Let’s say for some environmental reason, all of the small seeds on the island disappear and there are only large seeds left, so the birds with small beaks are unable to eat and most of them die. Now there are only a few small birds left to mate and make small bird babies, so in the next bird generation, there are more big birds than small ones. After several generations of this sort of thing, there will only be big birds left, and the bird population has evolved from big and little birds, to big birds only.
Populations do evolve (populations consist of many generations, and they have lots of genetic