This series hasn't been released on DVD yet (reasons found on the Internet vary from Creationist conspiracy to the more plausible explanation that the BBC doesn't actually own the rights to the incidental music, and re-scoring would cost too much.) At any rate, the series can still be found on the Internet in various forms -- even at the almost legitimate site Veoh.com. I think it is worth seeing, although the dated 1970s vibe does seep through -- one person coming to my party thought I was showing "Planet of the Apes" (to be fair, it was during a scene set in a rocky region of South America.)
Pictured, Charles Darwin (Malcolm Stoddard, right) reveals to his friend Joseph Hooker (Paul Chapman, left) his suspicions that species may not be immutable.