Carl Sagan

The well-meaning contention that all ideas have equal merit seems to me little different from the disastrous contention that no ideas have any merit.

A mutation in a DNA molecule within a chromosome of a skin cell in my index finger has no influence on heredity. Fingers are not involved, at least directly, in the propagation of the species.

There is a popular contention that half or more of the brain is unused. From an evolutionary point of view this would be quite extraordinary: why should it have evolved if it had no function? But actually the statement is made on very little evidence.

Absence of evidence is not evidence of absence.

Note that in all this interaction between mutation and natural selection, no moth is making a conscious effort to adapt to a changed environment. The process is random and statistical.

Without these experimental tests, very few physicists would have accepted general relativity. There are many hypotheses in physics of almost comparable brilliance and elegance that have been rejected because they did not survive such a confrontation with experiment. In my view, the human condition would be greatly improved if such confrontations and willingness to reject hypotheses were a regular part of our social, political, economic, religious and cultural lives.

The integrity of the experimenters in the face of this unexpected finding is breathtaking. (It is difficult to imagine any experiment that would convince leading practitioners of many political or religious philosophies of the superiority of a competing doctrine.)

The search for patterns without critical analysis, and rigid skepticism without a search for patterns, are the antipodes of incomplete science. The effective pursuit of knowledge requires both functions.

There is no doubt that right-hemisphere intuitive thinking may perceive patterns and connections too difficult for the left hemisphere; but it may also detect patterns where none exist. Skeptical and critical thinking is not a hallmark of the right hemisphere. And unalloyed right-hemisphere doctrines, particularly when they are invented during new and trying circumstances, may be erroneous or paranoid.

Natural selection has served as a kind of intellectual sieve, producing brains and intelligences increasingly competent to deal with the laws of nature. This resonance, extracted by natural selection, between our brains and the universe may help explain a quandary set by Einstein: The most incomprehensible property of the universe, he said, is that it is so comprehensible.

At any rate, both because of the clear trend in the recent history of biology and because there is not a shred of evidence to support it, I will not in these pages entertain any hypotheses on what used to be called the mind-body dualism, the idea that inhabiting the matter of the body is something made of quite different stuff, called mind.

Evolution often uses this strategy. Indeed, the standard evolutionary practice of increasing the amount of genetic information as organisms increase in complexity is accomplished by doubling part of the genetic material and then allowing the slow specialization of function of the redundant set.