Gene flow transfers genes across what boundaries?

Gene flow is the process by which genetic material is transferred from one population to another, and it primarily occurs across population boundaries. This transfer can happen when individuals from different populations migrate and interbreed, introducing new alleles into the gene pool of the receiving population. As a result, gene flow can alter the genetic diversity and evolutionary trajectory of populations over time.

While species boundaries can influence gene flow—since it generally occurs between individuals of the same species or closely related species—gene flow is not limited to species boundaries alone. Similarly, geographical boundaries can affect the likelihood of gene flow due to physical barriers, but they do not define the concept itself. Ecological boundaries, which involve different habitats and ecological conditions, can also impact gene flow, particularly when species have specific habitat requirements that limit their movement. However, the fundamental mechanism of gene flow strictly relates to populations, hence the focus on population boundaries as the correct choice.