If that statement is true, how can any evolutionist understand anything about any creature as he does not know how life began to exist?
If you do not know how something began to exist, how can you know the linage of it?
By using what you do know. If we have some lineage:
A --> B --> C --> D --> E --> F
Where A is where it began to exist and F is today, you could know all sorts of stuff about:
B --> C --> D --> E --> F
While knowing nothing about A
You could easily follow the stories in the Bible, like say the lineage of the Exodus, without knowing anything about Genesis.