So after reading articles like "People Use Just 8.2% of Their DNA" etc., and thinking a bit... I got this idea:

What if DNA is actually like a software source code repository? You know, it has "master" branch - which is most stable and up-to-date version of program but also it has other branches, experimental ones and of course it has huge amount of "junk" - i.e. backed up version of files from previous changes to code that is not used in any way in actual program.

So what if first primitive single-cellar organisms had super primitive and very short DNA, then it got improved, but original DNA was not erased, but backed up every time new mutation (commit in software SCCS) appeared.

Theoretically, the more primitive organism is, the shorter DNA it should have. For example, some very old sharks that still survive from Mesozoic era should have shorter DNA than modern sharks... Is this confirmed by actual experiments?

This explains why human DNA is mostly so similar to dog DNA, fish DNA etc. Because we all evolved from same primitive cells! Base of our "repository" was same!

Also this explains why human embryo come though all this steps of been single cell, multi-cell, fish, amphibian, mammal etc.

I'm no expert in biology by any means, and I suspect that this idea was around for long time, but I'm not sure... What do you think?