What is meant by the "species problem"?
(1) The exact definition of species is still controversial.
(2) The exact mechanisms of speciation is not known.
(3) The number of species present is much more than identified species.
(4) The extinction of species is taking place at an alarming rate.
(1) The species problem is the set of questions that arises when biologists attempt to define what a species is. Such a definition is called a species concept; there are at least 26 recognized species concepts.