I have fond memories of the original series, not just because it was so well done but because I worked for Don Meier Productions, in Chicago, c. 1977-78. It was a great place to work for a first job out of college. (At the wages they paid, though, I was pretty much forced to move on.)
The show had been in production for 15 years at that point, and was a well-oiled machine. The ever-dapper Don Meier had cinematographers scattered around the globe shooting raw footage. The footage was sent to the offices on Chicago's Magnificent Mile, where very experienced editors would piece together each show. Then, the writer (Allan Eckert?) would create a script that conformed to the visuals -- just the reverse of how fictional stories are shot and produced (although this may still be the method used with wildlife and other documentaries).
One of my jobs was to edit in the commercial segues, usually spoken by Marlin Perkins ... "Just as the mother lion protects her cubs, you can protect your family with Mutual of Omaha ..."
It was a treat to watch these pros at work, and to learn from them. Animal Planet and all the animal-related shows on the Discovery Channel owe much to these pioneers. Though it would be great to see the old shows (and Marlin, Jim, Stan) on TV again, I believe the advances in animal photography and documentary production make that, sadly, unlikely.