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Can SETI Succeed:
Carl Sagan and Ernst Mayr Debate

With the development of technology and our present understanding of the laws of nature, humanity is now in a position to verify or falsify the belief in extraterrestrial civilizations using experimental test. SETI is the quest for a generally acceptable cosmic context for humankind. In the deepest sense, this search is a search for ourselves.

Since the seminal paper by Giussepe Cocconi and Philip Morrison in 1959, the "orthodox view" among SETI proponents has been the following:

The Orion Nebula
Life is a natural consequence of physical laws acting in appropriate environments, and this physical process sequence as took place on Earth could occur elsewhere.

SETI proponents argue that our own galaxy has hundreds of billions of stars, and we live in a universe with billions of galaxies, so life should be common in this cosmic realm. There should be many habitable planets, each sheltering its brood of living creatures. Some of these worlds should develop intelligence and the technological ability and interest in communicating with other intelligent creatures.

Using electromagnetic waves, it should be possible to establish contact across interstellar distances and exchange information and wisdom around  the galaxy. Some fraction of the extraterrestrial civilization should be providing an electromagnetic signature that we should be able to recognize.

But because we have been unable to find a single piece of concrete evidence of alien intelligence yet, a philosophical battle has risen between those who might be called contact optimists who generally embrace the orthodox view of SETI and the proponents of the uniqueness hypothesis, which suggests that Earth is probably the only technological civilization in our galaxy.

Here we present both sides of the philosophical and scientific debate. First, one of the most prominent evolutionary specialists of this century, Ernst Mayr of Harvard University's Museum of Comparative Zoology, delivers the main arguments of the uniqueness hypothesis. Mayr notes that, since they are based on facts, the various degrees of uniqueness are a problem for SETI, not a hypothesis. The late Carl Sagan of The Planetary Society and Cornell University's Laboratory of Planetary Studies responds to Mayr's statements and expresses the optimist's view.

Which view is more palatable? Read on and decide for yourself.

The SETI debate originally appeared in the Planetary Society's Bioastronomy News, beginning with vol. 7, no. 3, 1995.)


Read Can SETI Succeed? Not Likely, by Ernst Mayr
Read The Abundance of Life-Bearing Planets, by Carl Sagan

Read Ernst Mayr's final comments
Read Carl Sagan's final comments
Return to SETI home


Enst Mayr

The Uniqueness Hypothesis:

Can SETI Succeed?
Not Likely

by Ernst Mayr


Carl Sagan

The View of
the Optimists:

The Abundance
of Life-Bearing Planets
by Carl Sagan