Introduction
Speciation refers to the creation a new species. Through this process, the
earliest groups of similar organisms were able branch out and populate the world
with millions of different varieties of life. Though vital to the concept of
evolution, the term "species" has been defined several different ways throughout
history. The oldest definitions were based on the physical similarity of
individuals. Today, however, the main defining characteristic of a species is
reproductive isolation.
Types of speciation are defined by way in which populations become isolated.
Sympatric speciation occurs when populations of a species that share the
same habitat become reproductively isolated from each other. Allopatric
speciation occurs when populations of a species become geographically
isolated. Allopatric speciation is the most common form of speciation seen
today. Parapatric speciation, which is extremely rare, occurs when populations
are separated by an extreme change in habitat rather than a physical barrier.
However, such processes of speciation are insufficient to explain the diversity
of life we see on earth today. Many modern species instead owe their existence
to the phenomenon of adaptive radiation, the process by which several new
species evolve rapidly through repeated colonization of a new habitat.
