Monophyly
In
phylogenetics, a group is
monophyletic (
Greek: "of one race") if it consists of a common ancestor and all its descendants. A taxonomic group that contain organisms but not their common ancestor is called
polyphyletic, and a group that contains some but not all descendants of the most recent common ancestor is called
paraphyletic.
 |
The grouping of reptiles and birds is generally believed to be monophyletic. |
For example, all organisms in the genus
Homo are believed to have come from the same ancestral form in the family
Hominidae, and no other descendants are known. Thus the
genus Homo is monophyletic. If, on the other hand, it were discovered that
Homo habilis had developed from a different ancestor than
Homo sapiens, and this ancestor were not included in the genus, then the genus would be polyphyletic. Since
biologists by and large prefer groups to be monophyletic, in this case, they would likely either split the genus or broaden it to include the additional forms.
Some
evolutionary taxonomists use the term
holophyletic to describe this sort of group and instead use monophyletic in its older sense, where it refers to both holophyletic and paraphyletic groups.
*
taxonomy*
Linnaean taxonomy*
cladistics*
evolutionary taxonomy
