Speciation, the process by which new species form, can occur when populations become geographically isolated. This can happen in several ways:
- Continental drift: As continents drift apart, once-connected populations may become separated. This is thought to explain the distribution of marsupials in Australia and South America.
- Vicariance: A physical barrier such as a mountain range or river divides a population, leading to allopatric speciation. This may explain the separation of North and South American deer species by the Isthmus of Panama.
- Dispersal: Individuals move to a new area and establish a new population, sometimes carried by wind, water, or land bridges. This is believed to explain the ancestors of Hawaiian honeycreepers.
- Climate change: Shifting climates can fragment habitats, making interbreeding difficult and potentially leading to speciation. This may have contributed to the division of African elephants into bush and forest subspecies.