Tree of life.
<P>
   Based  on  rRNA  gene sequences, organisms are divided into 3 domains:
   Bacteria, Archaea, and Eukarya.
<P>
   Eukarya  and  Archaea  share  a  common ancestor, and are more closely
   related to each other than to Bacteria.
<P>
   Note:
   Archaea  and Bacteria are "prokaryotes" that lack organelles such as a
   nucleus.
<P>
   The  lack  of  organelles  is  not  a  shared  derived character, thus
   "prokaryotes" do not constitute a monophyletic clade.