Showing comparisons and similarities in DNA does not automatically equate that everything spawned from a common ancestor and down to spontaneous life.
If one was to write DNA code from scratch and design lifeforms, take the example of modern computer programming. Tell me who programs in binary today, using 01001110011000, starting at that point, to then come up with the most modern software today. Nobody. Core and shell parts of software and interfaces are used so as not to repeat the same crap over and over again, to be more efficient. So had life on Earth been by intelligent design, (God, aliens, spirits, other biological lifeforms, a person and we are all inside a computer simulation, etc), it would make sense for all to share DNA similarities to an extent.