The Tree of Life is much like a family tree, except that its branches are not adorned with the names and birth dates of a few dozen people. Instead it bears all of the millions of species that exist on earth today, and those that have existed throughout the nearly four billion years of earth’s history. It answers the questions: How are we humans related to animals, plants and bacteria? How are animals, plants and bacteria related to each other?

As recently as ten (10) years ago, the Tree of Life could be thought of as a seedling. Ten years ago, much of the information known today did not exist, science has made remarkable advances in the field of genome sequencing, it has only been in the last five years that scientists have been able to sequence so many genes, and with the advancement of technology relationships between organisms are known today that scientists were not aware of.

The discovery of these relationships is leading to marked growth of the Tree of Life; the Tree marks the beginning of a new era in Biology. It is the basis for all kinds of new endeavors of a synthetic sort: comparing species, behaviors, developing patterns, meaning of different parts of the biological organization and so on.

The Tree has practical applications that are already in use by science. The Tree of Life presents a clear picture of the relationships between viruses, how they circulate in the human population, and how they arrived in the population in the first place.

Evolutionary relationships can be represented by a variety of trees such as the
the Cladogram, Additive, and the Ultrametric Trees. The most basic tree is the cladogram which gives the recency of common ancestry that is given the three sequences, A, B, C. This sequence means that A and B share a common ancestor more recently than either does with C.

Additive trees contain additional information, namely branch lengths. These are numbers associated with each branch that corresponds to some attribute of the sequence such as amount of evolutionary change.

Ultrametric trees are a special kind of additive tree in which the tips of the trees are all equidistant from the root of the tree. This type of tree can be used to express evolutionary time, stated in years or indirectly as the amount of sequence divergence using a molecular clock.