Lysenkoism is held up by bourgeois commentators as the supreme demonstration that conscious ideology cannot inform scientific practice and that "ideo… - Richard Lewontin

With great perception, Sagan sees that there is an impediment to the popular credibility of scientific claims about the world, an impediment that is almost invisible to most scientists. Many of the most fundamental claims of science are against common sense and seem absurd on their face. Do physicists really expect me to accept without serious qualms that the pungent cheese that I had for lunch is really made up of tiny, tasteless, odorless, colorless packets of energy with nothing but empty space between them? Astronomers tell us without apparent embarrassment that they can see stellar events that occurred millions of years ago, whereas we all know that we see things as they happen. (…) Our willingness to accept scientific claims that are against common sense is the key to an understanding of the real struggle between science and the supernatural. We take the side of science in spite of the patent absurdity of some of its constructs, in spite of its failure to fulfill many of its extravagant promises of health and life, in spite of the tolerance of the scientific community for unsubstantiated just-so stories, because we have a prior commitment, a commitment to materialism. It is not that the methods and institutions of science somehow compel us to accept a material explanation of the phenomenal world, but, on the contrary, that we are forced by our a priori adherence to material causes to create an apparatus of investigation and a set of concepts that produce material explanations, no matter how counter-intuitive, no matter how mystifying to the uninitiated. Moreover, that materialism is absolute, for we cannot allow a Divine Foot in the door. The eminent Kant scholar Lewis Beck used to say that anyone who could believe in God could believe in anything. To appeal to an omnipotent deity is to allow that at any moment the regularities of nature may be ruptured, that miracles may happen.

The division between those who try to learn about the world by manipulating it and those who can only observe it had led, in natural science, to a struggle for legitimacy. The experimentalists look down on the observers as merely telling uncheckable just-so stories, while the observers scorn the experimentalists for their cheap victories over excessively simple phenomena. In biology the two camps are now generally segregated in separate academic departments where they can go about their business unhassled by their unbelievers. But the battle is unequal because the observers' consciousness of what it is to do "real" science has been formed in a world dominated by the manipulators of nature. The observers then pretend to an exactness that they cannot achieve and they attempt to objectify a part of nature that is completely accessible only with the air of subjective tools.

To say that genetic differences are relevant to hetero- and homosexuality is not, however, to say that there are “genes for homosexuality” or even that there is a “genetic tendency to homosexuality.” This critical point can be illustrated by an example I owe to the philosopher of science, Elliott Sober. If we look at the chromosomes of people who knit and those who do not, we will find that with few exceptions, knitters have two X chromosomes, while people with one X and one Y chromosome almost never knit. Yet it would be absurd to say that we had discovered genes for knitting. The possession of two X chromosomes causes an embryo, with rare exceptions, to develop into an anatomical and physiological female, while the possession of a Y chromosome leads almost always to male development, and in our culture women are taught to knit while men are not. The beauty of this example is its historical (and geographical) contingency. Had we made the observations before the end of the eighteenth century (or even now in a few Irish, Scottish and Newfoundland communities), the result would have been reversed. Hand knitting was men’s work before the introduction of knitting machines around 1790, and was turned into a female domestic occupation only when mechanization made it economically marginal.