Final answer:
Sympatric speciation is the process by which new species arise within a single, undivided population without geographic barriers, often through mechanisms such as polyploidy or behavioral isolation.
Step-by-step explanation:
The type of speciation that occurs within a single, undivided population is sympatric speciation. Unlike allopatric speciation, which involves geographic separation of populations, sympatric speciation happens within a shared habitat, without any physical barriers separating individuals of the population.
In sympatric speciation, reproductive isolation occurs through mechanisms that do not require geographic barriers. This can include changes in chromosome number (polyploidy), differences in feeding habits or ecological niches, and behavioral isolation. For example, a change in the number of chromosomes can lead to instant reproductive isolation within a population, as individuals with varying chromosome numbers cannot successfully interbreed. This helps a new species to evolve right within its parental population. Hence, even closely related organisms living in the same geographic region can slowly evolve into distinct species due to reproductive isolation mechanisms inherent to sympatric speciation.