I have been asked this questions by many biology students and even non-biologist without a pretty straightforward answer to give. We are quite accustomed to phylogenetic trees where a common ancestor becomes two different species and these new species become, each one, two more. But, Why is not possible that a species might divide in three different species? Or four? Or more?
What arguments support this conception of the evolutionary process? Also, if somebody has a good article explaining this, please provide me with the link or citation so I can refer my fellow biology students to it.