Which molecule is responsible for the wide diversity of life on earth?

A phylogeny is an evolutionary ”tree” of related
organisms that can be constructed by using
information obtained from the genetic material.
Genetic information is contained in all living cells,
in the form of long DNA molecules that take the
shape of connected double- stranded spirals
(DNA stands for deoxyribonucleic acid). DNA
spirals, or “helixes”, are tightly compressed in the
nucleus of every cell. Their information is
organized into a code made up of four small
molecules — the building blocks of DNA. The
molecules, called nucleotides, are labelled:
A (adenine), C (cytosine), G (guanine) and T
(thymine).
It is possible to draw conclusions about the
evolution of a group of plant or animal species,
and the relationships among them, by comparing
selected pieces of DNA.