Which of the following is a form of speciation without geographic barriers?

• A. Allopatric speciation
• B. Parapatric speciation
• C. Gradualism
• D. Sympatric speciation

Answer: (D)

Speciation without geographic barriers happens when new species arise within the same location, often through ecological differences or chromosomal changes that create reproductive isolation despite contact. Sympatric speciation fits this idea best because it describes species formation that occurs in a single population without a physical barrier splitting it apart. Mechanisms include disruptive selection where different subgroups prefer different habitats or resources, or polyploidy in plants that instantly creates reproductive isolation from the parent population.

Allopatric speciation requires a geographic barrier that splits populations. Parapatric speciation involves neighboring populations with limited gene flow across a gradient, still tied to some geographic separation. Gradualism is about the rate of evolutionary change, not the presence or absence of geographic barriers.