When a new species form by geographic isolation, it is called geographical speciation or allopatric speciation. Geographical isolation is a physical separation which prevents gene flow between distinct populations (on the island and on continent). The island populations will eventually diverge from a single species that migrated to the island. The members of the populations, which once belonged to the same species, will no longer be able to mate and produce offspring. Eventually, the formation of new species will occur, for example kangaroos, koala, and wombats, form that one species.
This example illustrates adaptive radiation
Adaptive radiation is a process in which closely related organisms that evolves from an ancestral species become more diverse, and separate to form new groups that are adapted to various niches with specialized modes of life. Adaptive radiation occurs as a result of changes in the environment and may create many new niches, new resources, or new problems.
Evoultion from a common ancestor
Marsupials are a group of animals with a distinctive characteristic: these animals carry the young offspring in a pouch. This pouch did not appear independently in each of the species, this pouch was present many millions of years ago in the last common ancestor of all marsupials.
The last common ancestor of marsupials -the most recent species from which all the marsupials organisms are directly descended- already had this trait (carrying the young offspring in a pouch) and this trait was therefore inherited to all the descendant species.
Correct answer on edg. is
Adaptive Radiation :)
Adaptive radiation refers to an evolutionary process in which organisms diversify from one ancestral species, which leads to different other forms and species. This tends to happen when organisms are pressured to adapt to a new environment.
Australian terrestrial mammals such as kangaroos, koalas, and wombats, are examples of this process. According to research, these iconic marsupials went through adaptive radiation in response to the expansion of grassland that occurred in the mid-Pliocene. Another example (the most famous one) is the case of Darwin's finches, which all evolved from a single species but then changed in response to their environment.
adaptive radiation due to them adapting
The correct answer is adaptive radiation.
Adaptive radiation is a process of rapid diversification of an ancestral species into a large number of descendant species in a different environment with adaptive morphological and physiological traits.
Over 200 species of Marsupials mice, moles, flying squirrels and flying phalanger are found in Australia continent which was formed as a result of adaptive radiation from ancestral species to occupy the different niches of Australia.
Thus, adaptive radiation is the correct answer.