Changes

A '''species''' is a group of living beings or organisms having sufficient genetic similarity to be able to produce fertile offspring.<ref>A group of organisms belong to the same biological species if they are capable of producing fertile offspring. [http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/Def-S/species.html Holgrem Lab], Northwestern University, Illinois </ref>

A '''species''', according to the [[classification system]] used by biologists, is a group of living organisms having sufficient genetic similarity to be able to produce fertile offspring.<ref>A group of organisms belong to the same biological species if they are capable of producing fertile offspring. [http://www.biochem.northwestern.edu/holmgren/Glossary/Definitions/Def-S/species.html Holgrem Lab], Northwestern University, Illinois </ref>

For example, a [[tiger]] and a [[clam]] are different species, because they cannot produce offspring. A [[German Shepherd]] and a [[Beagle]] can produce offspring, because they are different breeds within one species.

For example, a [[tiger]] and a [[clam]] are classified as different species, because they cannot produce offspring. A [[German Shepherd]] and a [[Beagle]], although different ''breeds'', are classified as being the same species because they can produce fertile offspring.

However, the definition of "species" has changed over time and is sometimes problematic.

However, the definition of "species" has changed over time and is sometimes problematic.