Guest Author - Catherine Ebey
There is a different way of looking at biology. Classic taxonomy is now joined with phylogeny and the biological tree of life. Phylogenetics describes the evolutionary perspective of biology in which all living things are placed within a highly interconnected web of common ancestry. This beautiful notion of the connectedness of all species supports the evolutionary mode of thinking about life.
A phylogeny is a tree diagram of organism's place in evolution. A phylogeny may be constructed based on a common ancestor and its descendants. Each branch in the life tree represents a divergence from the original ancestor in which a new trait evolved that differentiated its descendants into a new species.
If you look at a basic phylogeny (try to find one with only three or four branches) you will see a “stem” at the bottom of the tree. This represents the first common ancestor of all the other organisms in the tree. As you look closely at the tree you will see different “branches” with different organisms assigned to them. Each split in the tree is called a node. This node represents where a new trait developed and the ancestor diverged into a new species. A node also represents the diverging species’ hypothetical common ancestor. A species’ hypothetical common ancestor is the closest genetically related ancestor to that new species.
For instance, if we were discussing plants the organism at the stem of the tree might represent the first photosynthetic organism. The first branch in the tree would represent the development of the ability to live on land instead of in water. These would be the plants in first group that split off from the main stem of the tree. The branch might represent where vascular tissue evolved, producing a new organism that could develop true roots, stems and leaves. The next node with its accompanying organisms might represent the development of seeds. The next node would represent the development of flowering plants.
All of these traits differentiated the ancestor into another species with a new adaptation to its environment. This new adaptation gives that organism another ability to add to its repertoire. This organism is now a new species because its DNA has fundamentally changed, so it can no longer reproduce within its ancestral species.
This life tree demonstrates the genetic connectedness of species. If you trace an organism’s genetic line, you can keep tracing back through their genetic and evolutionary history to discover links to past organisms. This is how these trees are constructed. These traits that differentiate species all have a genetic basis.
Discovering the inter-relatedness of organisms through genetic relatedness using phylogenetics draws attention to differences in grouping using traditional taxonomy and binomial nomenclature. Taxonomy uses similar morphological characteristics to group organisms together. Darwin branched out from this idea when he began using evolutionary relatedness to group organisms.
Both methods of classification are both valuable, but they use different grouping techniques. Each form of classification can be used for different purposes. Many scientists argue that the phylogenetic view is more biologically accurate because it traces evolutionary history through genetics.