parafyletisenä

In evolutionary biology, the term *parafyletinen* (paraphyletic) refers to a group of organisms that includes an ancestral species and some, but not all, of its descendants. This concept is central to the study of phylogenetics, which examines the evolutionary relationships among organisms. A paraphyletic group is distinguished from a monophyletic group, which includes a common ancestor and *all* its descendants, and a polyphyletic group, which consists of organisms that share a trait but do not include their most recent common ancestor.

The classification of organisms into paraphyletic groups often arises when certain descendants are excluded due to shared derived traits or other criteria. For example, the term "reptiles" in traditional taxonomy is considered paraphyletic because it includes ancestral reptilian species but excludes birds, which are their direct descendants. Modern phylogenetic classifications often avoid paraphyletic groupings to better reflect evolutionary history, though some traditional names persist in common usage.

Paraphyletic groups can complicate phylogenetic analysis because they may obscure true evolutionary relationships. Scientists use methods like cladistics to identify and correct such groupings by constructing trees that represent the most accurate evolutionary connections. The recognition of paraphyletic classifications highlights the importance of updating taxonomic systems to align with current genetic and morphological evidence. While not inherently incorrect, paraphyletic groupings underscore the need for careful consideration in how biological diversity is categorized and understood.