What is a Phylogenetic Relationship

A “Phylogenetic relationship” can be defined as being a reference to a timeline in the past that a species shared common ancestors.

Our understanding about phylogenetic relationships hinges on the patterns we see within evolutionary changes occurring along the passage of time. Darwin called it “descent with modification.” As we study each species we look for shared traits that have evolved within a lineage which suggests a common relation.

This can be documented by using a “Tree of Life” which is created by using a succession of branching, where we can observe that one species separates into these two distinct elements. This will then branch off further on and then again. Eventually there will be many small branches emanating from an original source.

It is widely accepted that the original organism was most likely a kind of worm. This worm divided into two separate worm species, and then went on to divide again and again, with each division bringing new, independent lineages which carried on evolving. After hundreds of millions of years the original worm has evolved in many millions of different species.

For example, when looking at the lineage of a bird, we move back in time and follow the branching back to where they connect, observing how close the intersection is in relation to a reptile or a mammal.

We find that by travelling back through these connectives we can find that animals and plants that bear no resemblance to each other in our modern world can often have a common ancestor and share traits that have endured over a course of time.

This can be especially evident in species such as birds and reptiles. Birds are the most successful of the dinosaurs, because they developed wings and avoided extinction 65 million years ago. Related to the crocodilians of our modern period, they share many things in common, such as being egg layers and nest builders and possessing the ability to “sing” for a mate and protect their territories.

In fact crocodiles have a much closer relation to birds and dinosaurs than they do to lizards and turtles.

Through using sophisticated DNA research it is now even possible to gain an understanding of micro organisms where we had very little visual knowledge to take any knowledge from.

Over the last couple of decades it has been established that there are three main branches to the “Tree of Life”; Bacteris, Archaea and the Eukaryotes.

Understanding the pattern of past evolutionary events, gives us a unique insight into the biological history of every living creature on Earth. Scientists recognize the huge advantage this research gives us by helping to identify and trace the origins of infectious diseases such as: HIV, the Ebola and West Nile viruses, anthrax, and influenza.

By making Phylogenetic comparisons with animals such as the chimpanzee, mouse, zebra fish we are able to gather important and groundbreaking knowledge of the structure and function of the human genome, which in turn can help us to fight against a wide amount of human disorders.


Travels in the Great Tree of Life. Peabody Museum of Natural History http://www.peabody.yale.edu/exhibits/treeoflife/index.html (accessed 25/03/2009)

Tree Of Life Wb Project. What is Phylogeny? http://www.tolweb.org/tree/phylogeny.html (Accessed 25/03/2009)