The species problem is a mixture of difficult, related questions that often come up when biologists define the word "species". Definitions are usually based on how individual organisms reproduce, but biological reality means that a definition that works well for some organisms (e.g., birds) will be useless for others (e.g., bacteria).
One common, but sometimes difficult, question is how best to decide which species an organism belongs to, because reproductively isolated groups may not be readily recognizable; cryptic species may be present.
Another common problem is how to define reproductive isolation, because some separately evolving groups may continue to interbreed to some extent, and it can be a difficult matter to discover whether this hybridization affects the long-term genetic make-up of the groups.
Many of the debates on species touch on philosophical issues, such as nominalism and realism, as well as on issues of language and cognition.
The current meaning of the phrase "species problem" is quite different from what Charles Darwin and others meant by it during the 19th and early 20th centuries. For Darwin, the species problem was the question of how new species arose: speciation.
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Famous quotes containing the words species and/or problem:
“Genius detects through the fly, through the caterpillar, through the grub, through the egg, the constant individual; through countless individuals the fixed species; through many species the genus; through all genera the steadfast type; through all the kingdoms of organized life the eternal unity. Nature is a mutable cloud which is always and never the same.”
—Ralph Waldo Emerson (1803–1882)
“I tell you, sir, the only safeguard of order and discipline in the modern world is a standardized worker with interchangeable parts. That would solve the entire problem of management.”
—Jean Giraudoux (1882–1944)