Adaptive radiation occurs when an ancestral species diversifies rapidly into several new and different species. This happens when a species is introduced into a new ecosystem where many empty ecological niches exist. The original species reproduces and survives under these new conditions, which allows for speciation. As discussed earlier, the original population will undoubtedly have variation.

Organisms with different characteristics, or phenotypes, will begin to inhabit each available niche. Over time, the species will adapt to the different environments. Sixty million years ago, the mass extinction of dinosaur species at the end of the Cretaceous Period left many ecological niches for our own mammalian ancestors to populate. One mammal from Madagascar, the tenrec, is another example of this phenomenon.

Tenrecs are distant cousins of Central African shrews. It is believed that the common ancestor of the present-day species came to Madagascar some 60 or 70 million years ago, at about the time dinosaurs disappeared and the evolution of mammals was just beginning to take place. Madagascar had very few mammals evolving there at that time, lemurs, a few rodents, and the ancestors of pygmy hippopotamuses.

With no large predators in the habitat, tenrecs multiplied and populated the island, appropriating themselves of the jungle at the Western edge of Madagascar. Thanks to this successful speciation, there are now about 30 different species of tenrecs.