Evolution can be a confusing term because it is used in more than one way. Many people in the general population have developed an incorrect understanding of evolution for a number of reasons. One is the misinformation spread by creationists by misrepresenting evolution, they may hope that it will be easier to get people to disregard it. Another is simple ignorance of the topic itself and the specific ways in which science uses certain terminology.
Because evolution is so complex, however, it is important to get a handle on the different ways in which the term can be used. There are, of course, broader uses we can talk about the evolution of the universe or the evolution of the planet Earth. In such cases, evolution simply refers to change over time, but that isnt what concerns us here.
Biology, in contrast, uses the term evolution a bit more specifically. At its most basic, evolution in biology can be used to refer either to the change in the gene pool of a population over time or to the concept of descent with modification. Here are some examples from basic biology texts:
- In fact, evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next. Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989.
- Biological evolution ...is change in the properties of populations of organisms that transcend the lifetime of a single individual. Douglas J. Futuyma in Evolutionary Biology, 1986.
The two definitions look a bit different, but they are expressing similar things the first is to a large extent more technical. An allele is a particular form of a gene and if a single gene is responsible for eye color, then one allele is for brown eyes, another allele is for blue eyes, and so on.
So, if the frequency of the allele for blue eyes changes in a population over time, that means that evolution has taken place. This may not seem like a very significant step in evolution, but the fact of the matter is most evolutionary steps are quite small large changes are the result of many, many smaller steps.
The second common use of the term evolution within biology is for the concept of common descent, the idea that all living beings are descended from a common ancestor. This typically occurs in the context of allele frequencies changing in populations over time, but there are also other factors as well. Thus, change in allele frequency over time is a narrow and technical definition of evolution while descent with modification is a broader understanding.
Lance F. contributed information for this.