My TARDIS booth explanation.
If I remember correctly, I was discussing with someone why there were so many thousands upon thousands of different animals on the planet (different genera, not species), and I speculated that maybe the unicorn or satyr was an animal whose responsibility was to repopulate the Earth by giving birth to different genera.
Get pregnant, have a cow; get pregnant again, have a horse; get pregnant again, have a giraffe; and so on.
But I really wasn't comfortable with it.
Finally! there is a limit to Goddidit! lolz