But one possible valid answer; one that does NOT, however, address the issue at hand: why and wherefore does a huge amount of genetic material get carried forward - were it not for some underlying commonality?
On the practical level, we already know as humans we can evolve both plants and animals into more desireable forms by selectively breeding; so we already have before our very eyes proof of 'evolution' on a minor scale, therefore, we know it's possible ...
Do you know anywhere it is written or indicated that all plants/animals were created/based on one another - from all indications biblical animals could have equally been comprised of purely 'dog', 'cow' or 'horse' stuff as the elements we know they are comprised of ...