ABSTRACT
Microevolution, as we have seen, occurs due to changes in allele frequencies from one generation to another. Macroevolution, however, encompasses processes that often take thousands of generations, resulting in major changes in the average phenotypes of populations. These processes can be quite complex, incorporating long-term microevolutionary processes, but additionally involving other considerations, such as major extinction events. These other considerations may be systematic, but they may also be somewhat random. A full consideration goes well beyond the bounds of our concern with human biology, but some basic concepts are relevant. First, however, a discussion of how organisms are classified is warranted.
