Phylogenetics is the study of evolutionary relationships between different organisms.
Phylogenetic trees are diagrams that describe these relationships. These trees are similar to a family tree; a family tree visualises relationships between individuals based on inheritance, whereas phylogenetic trees visualise relationships between organisms based on shared characteristics.
Phylogenetic trees are presented in many forms. Common forms include...
Ladder
Tree
...and more. While each form can represent equivalent information, some forms are easier to read than others.
The tree form is often the most intuitive to read, and leads to the least number of misconceptions.
Phylogenetic trees are made up of roots, nodes, branches, and tips.
The root indicates the start of the tree, and the start of time. Branches represent independent lines of evolution. Tips are labelled, descendent taxa.
Nodes are points of bifurcation that represent common ancestors. These nodes are representative of evolution’s underlying principle: common descent.
Should you go back far enough, all existing and extant organisms would share a most recent common ancestor, termed the last common ancestor (LCA).
The fewer number of nodes between taxa, the more closely related taxa are; the taxa share a more recent LCA.
When creating a phylogenetic tree, the principle of parsimony tells us that the simplest answer is the best. In other words, the tree with the fewest number of evolutionary changes is the most likely.
For example, it is more likely that wings evolved a single time in birds, rather than multiple times in separate lineages.
Phylogenetic trees can be oriented in many ways. Upwards...
Downwards
...even horizontally. It’s important to remember that the orientation of the tree does not matter. And trees presented in different orientations can be informationally equivalent to one another.
Evolution and phylogenetics are closely intertwined. An important feature of evolution is time; evolutionary processes occur over millions, and billions of years. As a result, a branch or node on a phylogenetic tree represents the result of millions of years of evolution. Deep time refers to evolutionary and physical geological processes that happen on large geologic scales. To truly understand evolution, and phylogenetics as a result, it is important to understand the vastness of deep time. In the next section of TreeDeep, we'll explore a tree of life through the passage of geological time. We'll explore the most recent 1 billion years of Earth's history.
Explore a Tree of Life
