This diagram shows a very simple version of the evolutionary tree of life. Life begins a the bottom and evolves by branching off into the various major types ending with humans. Notice how we did not evolve from apes (primates) but where those two branches tie together is supposed to be our common ancestor. The reason there's no label there is that they haven't found it yet! But boy are they looking for it. There are candidates proposed all the time but they never seem to work out enough to fill in the the missing label. In fact, notice the absence of labels at all of the branching points. None, nada, zip. Could it be because that's not the way it happened?
There is another tree of life spoken of in the Bible.
Genesis 2:8-9 (NKJV)
The Lord God planted a garden eastward in Eden, and there He put the man whom He had formed. And out of the ground the Lord God made every tree grow that is pleasant to the sight and good for food. The tree of life was also in the midst of the garden, and the tree of the knowledge of good and evil.
Revelation 22:14 (NKJV)
Blessed are those who do His commandments, that they may have the right to the tree of life, and may enter through the gates into the city.