'Why do you think it is...', I asked Dr. Cook ... 'that brain surgery, above all else—even rocket science—gets singled out as the most challenging of human feats, the one demanding the utmost of human intelligence?'
[Dr. Cook answered,] 'No margin for error.'

Clarke's Law of Evolution: It has yet to be proven that intelligence has any survival value.

Advertising may be described as the science of arresting the human intelligence long enough to get money from it.

Comprehension, inventiveness, direction, and criticism: intelligence is contained in these four words.

For most diagnoses all that is needed is an ounce of knowledge, an ounce of intelligence, and a pound of thoroughness.

If worms have the power of acquiring some notion, however rude, of the shape of an object and over their burrows, as seems the case, they deserve to be called intelligent; for they act in nearly the same manner as would man under similar circumstances.

Intelligence is a valuable thing, but it is not usually the key to survival. Sheer fecundity ... usually counts. The intelligent gorilla doesn't do as well as the less intelligent but more-fecund rat, which doesn't do as well as the still-less-intelligent but still-more-fecund cockroach, which doesn't do as well as the minimally-intelligent but maximally-fecund bacterium.

Intelligence is an extremely subtle concept. It's a kind of understanding that flourishes if it's combined with a good memory, but exists anyway even in the absence of good memory. It's the ability to draw consequences from causes, to make correct inferences, to foresee what might be the result, to work out logical problems, to be reasonable, rational, to have the ability to understand the solution from perhaps insufficient information. You know when a person is intelligent, but you can be easily fooled if you are not yourself intelligent.

Intelligence is like four-wheel drive. It only allows you to get stuck in more remote places.

Look round the world, contemplate the whole and every part of it: you will find it to be nothing but one great machine, subdivided into an infinite number of lesser machines, which again admit of subdivisions to a degree beyond what human senses and faculties can trace and explain. All these various machines, and even their most minute parts, are adjusted to each other with an accuracy which ravishes into admiration all men who have ever contemplated them. The curious adapting of means to ends, throughout all nature, resembles exactly, though it much exceeds, the productions of human contrivance-of human design, thought, wisdom, and intelligence.

Man has made use of his intelligence; he invented stupidity.

Man is an animal with primary instincts of survival. Consequently his ingenuity has developed first and his soul afterwards. The progress of science is far ahead of man's ethical behavior.

Mankind have been slow to believe that order reigns in the universe—that the world is a cosmos and a chaos.
… The divinities of heathen superstition still linger in one form or another in the faith of the ignorant, and even intelligent men shrink from the contemplation of one supreme will acting regularly, not fortuitously, through laws beautiful and simple rather than through a fitful and capricious system of intervention.
... The scientific spirit has cast out the demons, and presented us with nature clothed in her right mind and living under the reign of law. It has given us, for the sorceries of the alchemist, the beautiful laws of chemistry; for the dreams of the astrologer, the sublime truths of astronomy; for the wild visions of cosmogony, the monumental records of geology; for the anarchy of diabolism, the laws of God.

Mr Justus Liebig is no doubt a very clever gentleman and a most profound chemist, but in our opinion he knows as much of agriculture as the horse that ploughs the ground, and there is not an old man that stands between the stilts of a plough in Virginia, that cannot tell him of facts totally at variance with his finest spun theories.

No matter how much proponents of 'intelligent design' try to clothe their views in the apparel of science, it is what it is: religion. Whose intelligence? Whose design?

Our purpose is to be able to measure the intellectual capacity of a child who is brought to us in order to know whether he is normal or retarded. ... We do not attempt to establish or prepare a prognosis and we leave unanswered the question of whether this retardation is curable, or even improveable. We shall limit ourselves to ascertaining the truth in regard to his present mental state.

Outside intelligences, exploring the solar system with true impartiality, would be quite likely to enter the sun in their records thus: Star X, spectral class G0, 4 planets plus debris.

Science has not yet taught us if madness is or is not the sublimity of intelligence.

So in regard to mental qualities, their transmission is manifest in our dogs, horses and other domestic animals. Besides special tastes and habits, general intelligence, courage, bad and good tempers. etc., are certainly transmitted.

Some recent philosophers seem to have given their moral approval to these deplorable verdicts that affirm that the intelligence of an individual is a fixed quantity, a quantity that cannot be augmented. We must protest and react against this brutal pessimism; we will try to demonstrate that it is founded on nothing.

The 'stream' we call science always flows forward; sometimes reactionary beavers block its flow, but the stream is never defeated by this; it accumulates, gathers strength; its waters get over the barrage and continue on their course. The advancement of science is the advancement of God, for science is nothing but human intelligence, and human intelligence is the most valuable treasure God has bequeathed us.

The brighter you are, the more you have to learn.

The equation of animal and vegetable life is too complicated a problem for human intelligence to solve, and we can never know how wide a circle of disturbance we produce in the harmonies of nature when we throw the smallest pebble into the ocean of organic life.

The human race, whose intelligence dates back only a single tick of the astronomical clock, could hardly hope to understand so soon what it all means.

The present state of the system of nature is evidently a consequence of what it was in the preceding moment, and if we conceive of an intelligence that at a given instant comprehends all the relations of the entities of this universe, it could state the respective position, motions, and general affects of all these entities at any time in the past or future. Physical astronomy, the branch of knowledge that does the greatest honor to the human mind, gives us an idea, albeit imperfect, of what such an intelligence would be. The simplicity of the law by which the celestial bodies move, and the relations of their masses and distances, permit analysis to follow their motions up to a certain point; and in order to determine the state of the system of these great bodies in past or future centuries, it suffices for the mathematician that their position and their velocity be given by observation for any moment in time. Man owes that advantage to the power of the instrument he employs, and to the small number of relations that it embraces in its calculations. But ignorance of the different causes involved in the production of events, as well as their complexity, taken together with the imperfection of analysis, prevents our reaching the same certainty about the vast majority of phenomena. Thus there are things that are uncertain for us, things more or less probable, and we seek to compensate for the impossibility of knowing them by determining their different degrees of likelihood. So it was that we owe to the weakness of the human mind one of the most delicate and ingenious of mathematical theories, the science of chance or probability.

The trouble with the world is that the stupid are cocksure and the intelligent full of doubt.

There is nobody so irritating as somebody with less intelligence and more sense than we have.

We ought then to consider the present state of the universe as the effect of its previous state and as the cause of that which is to follow. An intelligence that, at a given instant, could comprehend all the forces by which nature is animated and the respective situation of the beings that make it up, if moreover it were vast enough to submit these data to analysis, would encompass in the same formula the movements of the greatest bodies of the universe and those of the lightest atoms. For such an intelligence nothing would be uncertain, and the future, like the past, would be open to its eyes.

What we call man is a mechanism made up of … uncrystallized matter … all the colloid matter of his mechanism is concentrated in a countless number of small cells. … [T]hese cells [are] dwelling places, communes, a walled town within which are many citizens. ... [T]hese are the units of life and when they pass out into space man as we think we know him is dead, a mere machine from which the crew have left,so to speak. ... [T]hese units are endowed with great intelligence. They have memories, they must be divided into countless thousands of groups, most are workers, there are directing groups. Some are chemists, they manufacture the most complicated chemicals that are secreted by the glands.

[My study of the universe] leaves little doubt that life has occurred on other planets. I doubt if the human race is the most intelligent form of life.

[Thomas Henry] Huxley, I believe, was the greatest Englishman of the Nineteenth Century—perhaps the greatest Englishman of all time. When one thinks of him, one thinks inevitably of such men as Goethe and Aristotle. For in him there was that rich, incomparable blend of intelligence and character, of colossal knowledge and high adventurousness, of instinctive honesty and indomitable courage which appears in mankind only once in a blue moon. There have been far greater scientists, even in England, but there has never been a scientist who was a greater man.