Question

What are monophyletic and paraphyletic groups?

Short answer

Monophyletic groups, or clades, are sets of species that share a common ancestor and include all its descendants. They represent the natural evolutionary relationships between species and are illustrated through phylogenetic trees. Paraphyletic groups, on the other hand, share a common ancestor but do not include all its descendants, creating an artificial group that doesn't represent the natural relationships between species. An example of these groups can be seen in Amniotes (monophyletic), which include all birds and reptiles and their common ancestor, and Reptilia (paraphyletic), which includes reptiles but arbitrarily excludes birds.

Step-by-step solution

Definition of Monophyletic Groups

Monophyletic groups, also known as clades, are a set of species that share a common ancestor and include all the descendants of that ancestor. In other words, every species within a monophyletic group can trace its lineage back to a single common ancestor. This relationship is often represented as a branching tree-like diagram called a phylogenetic tree, where the common ancestor is at the base of the tree and the descendant species are at the ends of the branches.

Definition of Paraphyletic Groups

Paraphyletic groups, on the other hand, are a set of species that share a common ancestor but do not include all the descendants of that ancestor. Some species, which evolved from the common ancestor, are excluded from the group. This creates an artificial group that does not represent the natural evolutionary relationships among the species. Paraphyletic groups are often formed due to subjective or arbitrary criteria that exclude some species from the group.

Example of Monophyletic and Paraphyletic Groups

To illustrate the concept of monophyletic and paraphyletic groups, let's use an example. Birds and reptiles are a classic example of these two groups. A monophyletic group, or clade, would be the group that includes all birds and reptiles and their common ancestor. This group is referred to as 'Amniotes,' which includes all living and extinct animals descending from that common ancestor. In a phylogenetic tree, the common ancestor is at the base, and all the descendant species (birds and reptiles) are at the ends of the branches. A paraphyletic group would be a group that includes reptiles but excludes birds. In this case, it's the group referred to as 'Reptilia,' an artificial group that does not represent the natural evolutionary relationships between the species because it excludes birds, which evolved from the same ancestor as reptiles. Through this example, we can see how monophyletic groups represent the natural evolutionary relationships between species, while paraphyletic groups fail to do so by excluding some descendants of the common ancestor.