STEPHEN JAY GOULD: THE PATTERN OF LIFE'S HISTORY

No one can claim that the spandrels under the dome are adaptations for anything. I suppose it's a good idea to put some plaster there — otherwise the rainwater is going to come in — but the fact that they're tapering triangular spaces is a side consequence of the adaptive decision to mount the dome on four arches. It's space left over. It's a side consequence; it isn't an adaptation in itself.

When I looked at these spandrels, I realized that every set of spandrels — there are six in San Marco — had a very sensible iconography linked with the dome. Under the main dome, for example, there are four evangelists in the spandrels. Four spandrels, four evangelists. Under each of the four evangelists is one of the four biblical rivers — the Tigris, the Euphrates, the Nile, and the Indus — and they are personified as a man, and the man holds an amphora, a water jar, and he pours water onto a single flower in the tapering triangular space below. It's a beautiful design. But no one would argue that the spandrels exist to house the evangelists. The spandrels are nonadaptive, side consequences. Since they are there anyway, you might as well fill them with useful and sensible structures.

Many biologists would say, "Well, of course, that's right. We know there are spandrels, or bits and pieces, left over, but they're just nooks and crannies, funny little corners; they don't have any importance." But that's not true; the fact that something is secondary in its origin doesn't mean it's unimportant in its consequences. Those are entirely separate subjects.

Spandrels often turn out to be more important, in terms of the consequences in history of a structure, than the actual immediate reasons for their having been there in the first place. For example, the dome of San Marco is radially symmetrical; there is no reason to ornament the dome in four-part symmetry for structural reasons, yet every dome but one in San Marco is ornamentally structured in four-part symmetry, in harmony with the spandrels below. The spandrels are not just nooks and crannies; they actually determine the iconographic program of the dome itself. Just as with the human brain: most of what the brain does are probably spandrels — that is, the brain got big by natural selection for a small set of reasons having to do with what is good about brains on the African savannas. But by virtue of that computational power, the brain can do thousands of things that have nothing to do with why natural selection made it big in the first place, and those are its spandrels.

Because I began this paper with an architectural example, no one would confute it, because it wasn't a threat to their conventional thinking. If I'd started with an organic example, it would have raised the hackles of all the people trying to be strict Darwinians.

Arthur Cain was the summer-up of the whole session. There's a line in Durrell's Alexandria Quartet where the narrator, Pursewarden, says that he's a Protestant in the only meaningful sense of the term — that he likes to protest. Well, moderators are supposed to be moderate, I suppose. Arthur Cain was not. He devoted his entire summary of the conference to a vitriolic attack on this paper, essentially saying that Dick and I knew that adaptation was true because we had to, because it obviously is true. Arthur said that we had attacked it because, although we knew it to be true, we so disliked the political implications of sociobiology, which is based on it, that we abrogated our credentials as scientists.

That was so off the wall that it was just amazing. When I got up to give my re-reply, the second coordinator of the conference was standing in front of the podium — which had the motto of the Royal Society, "Nullius in verba," on it — and I asked him to step aside. He was annoyed: why was I asking him to move, that was not fair. But he later realized why I had. Now, I'm stupid about certain things that scientists are supposed to be good at. I'm not particularly quantitative; I'm numerate but not innovative. I'm not a great experimentalist. But I pride myself on having immersed myself in Western culture and having learned some languages, and knowing certain aspects of humanism that many scientists don't take up.

I asked him to step aside, and I said that I thought Arthur had been entirely wrong, that he'd completely misunderstood the motives of my talk, and that I was doing nothing but trying to uphold the motto of the Royal Society, which had sponsored this meeting. The reason that was an effective strategy was that I knew that most people, most members, didn't know what the motto "Nullius in verba" meant. It looks like it means "Words do not matter" or "Do not pay any attention to words," since nullius means "nothing" and verba is "word." So most people think it means that words mean nothing and you have to do the experiment.

But nullius is genitive singular; it can't mean that. It means "of nothing" or "of no one." I knew what the motto meant. I knew that it was a fragment of a statement from Horace — a famous quotation from a poem, in which he says, "I am not bound to swear allegiance to the dogmas of any master." Nullius addictus jurare in verba magister. It's "Nullius in verba," or "In the words of no (master)." It's just a fragment from a larger line.

"That's all I'm doing," I said. "I'm saying that we are not bound to swear allegiance to the dogmas of any master; I'm here to present an alternative viewpoint that's consistent with your own society. How can you castigate me?"

The paper gets a lot of citations, but I don't know how many of its citations mean that it was actually used. In the game of citation analysis, you know that there are a certain number of citations that are, in a sense, honorary; that is, people will write a paper in which they want to support an adaptationist's perspective, and they feel that in fairness they have to cite at least one thing to show they know there's an opposing literature. The spandrels paper is the classic one, so they cite it. Whether or not they actually take it seriously I don't know. But it's become the standard source of a broader view of the causes of evolutionary form.

The paper provides a context for my current views on constraint — the importance of geometric and historical constraint, as opposed to a strictly adaptationist view of the world. The "exaptation" argument arises very much out of the spandrels principle, and I wish I'd developed the word when I wrote the paper. There's a problem — most Darwinians don't acknowledge it, since it doesn't work out as a problem for them — because "adaptation," as the word is used, has two distinctly different meanings. It's the process whereby a structure is designed by natural selection for a use, but often the word is also used for the structure itself. I have my foot here. It works well. Is it an adaptation, simply because it works well? Strict Darwinians don't have a problem using the same word both for the structure that works well and for the process that gets you there, because they think that the process is the only way you can get the working structure.

Under the spandrel principle, you can have a structure that is fit, that works well, that is apt, but was not built by natural selection for its current utility. It may not have been built by natural selection at all. The spandrels are architectural by-products. They were not built by natural selection, but they are used in a wonderful way — to house the evangelists. But you can't say they were adapted to house evangelists; they weren't. That's why Elisabeth Vrba and I developed the term "exaptation." Elisabeth is a paleontologist at Yale University, who has collaborated with both Niles Eldredge and me, and who did the most interesting work on punctuated equilibrium.

Exaptations are useful structures by virtue of having been coopted — that's the "ex-apt" — they're apt because of what they are for other reasons. They were not built by natural selection for their current role. Strict Darwinians cannot deny the principle. Their usual response is to say that it's minor, just a gloss, exaptations are rare, they're just nooks and crannies, they're not important. But in the spandrels argument it's essential that they are important. Just because something arises as a side consequence doesn't condemn it to secondary status.

Arthur Cain brought up the subject of political implications. In a sense, I brought it on myself, but I'll defend how it happened. Niles Eldredge and I wrote the first punctuated- equilibrium paper in 1972. I wrote a follow-up in 1977, in which I tried to analyze some of the theory's social and psychological sources, because they're in every theory of gradualism, and I had tried to argue that gradualism is a quintessential notion of Victorian liberalism. I thought it would be so ridiculous and — to use a biblical term — vainglorious to claim that gradualism, at least in part, was not a truth of nature but recorded a social context, and then to argue that "punctuated equilibrium is true; it's just a fact of nature." There obviously had to be a social context for punctuated equilibrium, too. I thought it only fair to write about what might have been some of the sources of punctuated equilibrium, and since there's a long tradition in Hegelian and Marxist thought for punctuational theories of change, it was clearly not irrelevant that I had been brought up by a Marxist father. I'd learned about these things.

That's not the reason the punctuated-equilibrium theory exists — if only because Niles developed most of the ideas, and he didn't have any such background. But it is relevant that I, rather than someone else, thought of it, in that my own background is probably a relevant fact. It was necessary for me to say that; it would have been absurd to claim that gradualism is politically influenced but punctuated equilibrium is a fact of nature. People seize upon that one statement.

Historians of science make a distinction between what they call context of justification and context of discovery, and it's fair enough. There's a logic of justification, which is independent of the political and social views of the people who develop the ideas. But if you want to ask why certain people develop ideas rather than other people, and why they develop them in this decade rather than that decade, then for those questions, which are about context of discovery rather than context of justification, surely the personal side is very relevant; it has to be explored and understood. But it has very little bearing on whether the idea is right or not. The fact that I learned Marxism from my father may have predisposed me toward being friendly to the kind of ideas that culminated in punctuated equilibrium; it has absolutely nothing to do with whether punctuated equilibrium is true or not, which is an independent question that has to be validated in nature.