August 8, 2000

Sidney Liebes

Elisabet Sahtouris

Brian Swimme

Re: A Walk Through Time and the "Recovery" of Biodiversity


You have created a work of art! I have never seen such a beautiful book, and that includes books on art. It is a pleasure to look at, a pleasure to read, and a pleasure to learn from.

As an environmentalist, I am constantly looking for "ammunition" – facts and ideas that can help convince people to protect the treasure that is wild nature. In particular, I want to convince people to care about preserving biodiversity and endangered species. That is one reason I bought and read your book.

Therefore, I am peeved to see you use the word "recover" in relation to the aftermath of an extinction event. (E.g. on page 132, "It takes 25 million years for Earth to recover its biodiversity, much of it with new creatures".) It gives the reader the impression that extinction is "not so bad" after all, because the Earth can "recover". The word hides several misconceptions. First, extinct species cannot "recover". They will most likely never appear again, no matter how long we wait. So where is the "recovery"?

Second, you seem to imply that biodiversity is measured by the number of species that exist. There are actually at least two different quantitative aspects to biodiversity: the number of species, and their degree of divergence. This was pointed out by Stephen Jay Gould in his wonderful book, Wonderful Life: there used to be several distinct groups of arthropods; after an extinction event, only four survived. We may have more species now, but we may never regain the amount of diversity (divergence) that we once had. So where is the "recovery"?

Third, even if we somehow regained the same degree of diversity among living things, would it really compensate for what was lost? Personally, I like the species that we have now. I don’t care that after their extinction we may gain some new ones. So where is the "recovery"? How would you feel if I said that you had lost your spouse, or child, but then you "recovered"?

I know that this term is commonly used in this regard, but I think that you will agree that it is a misnomer.

Other than that little quibble, I love your book. Thank you for writing it!


Michael J. Vandeman, Ph.D.


Liebes, Sidney, Elisabet Sahtouris, and Brian Swimme, A Walk Through Time – From Stardust to Us – The Evolution of Life on Earth. New York: John Wiley & Sons, Inc., c.1998.

Vandeman, Michael J.,, especially "Wildlife and the Ecocity" and "Wildlife Need Habitat Off-Limits to Humans".