What Can DNA Tell us about our `Universal Ancestor'?
Species with similar DNA codes are thought to be more closely related and share a more recent ancestry. Because all species have similar RNA, it is thought they have a common origin. Finding that Common Ancestor has proven elusive!
Below is a diagram, referred to as the Tree of Life due to the branches. The longer the branches, the greater the genetic distance between species.
While there is a link in the very middle, bringing all three of the Domains together, there is currently NO ORGANISM at that spot. If there had been a common ancestor as proposed, it has long since gone extinct.
Other important points.
Of the three Domains of Life, no one of these groups is
ancestral to the others.
We did not descend from present day Bacteria! Many
bacteria today are really quite evolved, for bacteria anyway.
Others have changed little, like the cyanobacteria.
Thermophiles have among the shortest branches to the `common
ancestor'. Perhaps the earliest life liked it hot, too?