Contraria sunt complementa.
Opposites are complementary.

Contrary to popular parlance, Darwin didn't discover evolution. He uncovered one (most would say the) essential mechanism by which it operates: natural selection. Even then, his brainstorm was incomplete until the Modern Synthesis of the early/mid-20th century when (among other things) the complementary role of genetic heredity was fully realized. Thousands upon thousands of studies have followed, providing millions of data points that support this understanding of how life on Earth has come to be as it is.

Galileo Galilei and Isaac Newton…. The relationship between these very different personalities is like that of two complementary stages of a rocket. Galileo, the argumentative “wrangler” who demanded that the universe be examined through a telescope rather than by means of a philosophy book, provided the first liftoff, and Newton, the secretive mathematician who searched among his notes to find a mislaid proof for universal gravitation, put the world into orbit.

History without the history of science, to alter slightly an apothegm of Lord Bacon, resembles a statue of Polyphemus without his eye—that very feature being left out which most marks the spirit and life of the person. My own thesis is complementary: science taught ... without a sense of history is robbed of those very qualities that make it worth teaching to the student of the humanities and the social sciences.

If in the description of an experimental arrangement the expression 'position of a particle' can be used, then in the description of the same arrangement the expression 'velocity of a particle' can not be used, and vice versa. Experimental arrangements, one of which can be described with the help of the expression 'position of a particle' and the other with the help of the expression 'velocity' or, more exactly, 'momentum', are called complementary arrangements, and the descriptions are referred to as complementary descriptions.

If the structure that serves as a template (the gene or virus molecule) consists of, say, two parts, which are themselves complementary In structure, then each of these parts can serve as the mould for the production of a replica of the other part, and the complex of two complementary parts thus can serve as the mould for the production of duplicates of itself.

In the firmament of science Mayer and Joule constitute a double star, the light of each being in a certain sense complementary to that of the other.

Knowledge and wonder are the dyad of our worthy lives as intellectual beings. Voyager did wonders for our knowledge, but performed just as mightily in the service of wonder–and the two elements are complementary, not independent or opposed. The thought fills me with awe–a mechanical contraption that could fit in the back of a pickup truck, traveling through space for twelve years, dodging around four giant bodies and their associated moons, and finally sending exquisite photos across more than four light-hours of space from the farthest planet in our solar system.

Physicists speak of the particle representation or the wave representation. Bohr's principle of complementarity asserts that there exist complementary properties of the same object of knowledge, one of which if known will exclude knowledge of the other. We may therefore describe an object like an electron in ways which are mutually exclusive—e.g., as wave or particle—without logical contradiction provided we also realize that the experimental arrangements that determine these descriptions are similarly mutually exclusive. Which experiment—and hence which description one chooses—is purely a matter of human choice.

Science investigates; religion interprets. Science gives man knowledge which is power; religion gives man wisdom which is control. Science deals mainly with facts; religion deals mainly with values. The two are not rivals. They are complementary.

The question of a possible physiological significance, in the resemblance between the action of choline esters and the effects of certain divisions of the involuntary nervous system, is one of great interest, but one for the discussion of which little evidence is available. Acetyl-choline is, of all the substances examined, the one whose action is most suggestive in this direction. The fact that its action surpasses even that of adrenaline, both in intensity and evanescence, when considered in conjunction with the fact that each of these two bases reproduces those effects of involuntary nerves which are absent from the action of the other, so that the two actions are in many directions at once complementary and antagonistic, gives plenty of scope for speculation.

There is no “pure” science itself divorced from human values. The importance of science to the humanities and the humanities to science in their complementary contribution to the variety of human life grows daily. The need for men familiar with both is imperative.

To us … the only acceptable point of view appears to be the one that recognizes both sides of reality—the quantitative and the qualitative, the physical and the psychical—as compatible with each other, and can embrace them simultaneously … It would be most satisfactory of all if physis and psyche (i.e., matter and mind) could be seen as complementary aspects of the same reality.

We should like to propose instead that the specificity of DNA self replication is accomplished without recourse to specific protein synthesis and that each of our complementary DNA chains serves as a template or mould for the formation onto itself of a new companion chain.
[Co-author with Francis Crick]

Without the slightest doubt there is something through which material and spiritual energy hold togehter and are complementary. In the last analysis, somehow or other, there must be a single energy operating in the world. And the first idea that occurs to us is that the 'soul' must be as it were the focal point of transformation at which, from all the points of nature, the forces of bodies converge, to become interiorised and sublimated in beauty and truth.