Genetics is the first biological science which got in the position in which physics has been in for many years. One can justifiably speak about such a thing as theoretical mathematical genetics, and experimental genetics, just as in physics. There are some mathematical geniuses who work out what to an ordinary person seems a fantastic kind of theory. This fantastic kind of theory nevertheless leads to experimentally verifiable prediction, which an experimental physicist then has to test the validity of. Since the times of Wright, Haldane, and Fisher, evolutionary genetics has been in a similar position.

If it were possible for us to have so deep an insight into a man's character as shown both in inner and in outer actions, that every, even the least, incentive to these actions and all external occasions which affect them were so known to us that his future conduct could be predicted with as great a certainty as the occurrence of a solar or lunar eclipse, we could nevertheless still assert that the man is free.

Philosophers have said that if the same circumstances don't always produce the same results, predictions are impossible and science will collapse. Here is a circumstance—identical photons are always coming down in the same direction to the piece of glass—that produces different results. We cannot predict whether a given photon will arrive at A or B. All we can predict is that out of 100 photons that come down, an average of 4 will be reflected by the front surface. Does this mean that physics, a science of great exactitude, has been reduced to calculating only the probability of an event, and not predicting exactly what will happen? Yes. That's a retreat, but that's the way it is: Nature permits us to calculate only probabilities. Yet science has not collapsed.

Predictions can be very difficult—especially about the future.

The best way to predict the future is to invent it.

There has never been an age so full of humbug. Humbug everywhere, even in science. For years now the scientists have been promising us every morning a new miracle, a new element, a new metal, guaranteeing to warm us with copper discs immersed in water, to feed us with nothing, to kill us at no expense whatever on a grand scale, to keep us alive indefinitely, to make iron out of heaven knows what. And all this fantastic, scientific humbugging leads to membership of the Institut, to decorations, to influence, to stipends, to the respect of serious people. In the meantime the cost of living rises, doubles, trebles; there is a shortage of raw materials; even death makes no progress—as we saw at Sebastopol, where men cut each other to ribbons&mdashand the cheapest goods are still the worst goods in the world.
With coauthor Jules de Goncourt (French writer, 1830-70)