From this question I note that pure-bloods are not actually really pure blooded according to the following quote:
“So-called pure-blood families maintain their alleged purity by disowning, banishing, or lying about Muggles or Muggle-borns on their family trees. They then attempt to foist their hypocrisy upon the rest of us by asking us to ban works dealing with the truths they deny. There is not a witch or wizard in existence whose blood has not mingled with that of Muggles, and I should therefore consider it both illogical and immoral to remove works dealing with the subject from our students’ store of knowledge.”
- The Tales of Beedle the Bard
One of the answers also notes that pure-bloods generally lie about Muggles or Muggle-borns on their family tree so that they can give the illusion they are pure-blood. Although the other answer notes pure-blood may actually just mean no Muggles of Muggle-borns within X generations.
However, this led me to an interesting thought: was there ever a time when there was a witch and/or wizard who was truly a pure-blood i.e. no Muggle of Muggle-born in their family tree? If this is the case does that mean witches and wizards are technically a separate species from Muggles?