The Beginning of Infinity: Explanations That Transform the World - David Deutsch (2011)
Chapter 14. Why are Flowers Beautiful?
My daughter Juliet, then aged six … pointed out some flowers by the wayside. I asked her what she thought wildflowers were for. She gave a rather thoughtful answer. ‘Two things,’ she said. ‘To make the world pretty, and to help the bees make honey for us.’ I was touched by this and sorry I had to tell her that it wasn’t true.
Richard Dawkins, Climbing Mount Improbable (1996)
‘Displace one note and there would be diminishment. Displace one phrase and the structure would fall.’ That is how Mozart’s music is described in Peter Shaffer’s 1979 play Amadeus. This is reminiscent of the remark by John Archibald Wheeler with which this book begins, speaking of a hoped-for unified theory of fundamental physics: ‘an idea so simple, so beautiful, that when we grasp it … how could it have been otherwise?’
Shaffer and Wheeler were describing the same attribute: being hard to vary while still doing the job. In the first case it is an attribute of aesthetically good music, and in the second of good scientific explanations. And Wheeler speaks of the scientific theory as being beautiful in the same breath as describing it as hard to vary.
Scientific theories are hard to vary because they correspond closely with an objective truth, which is independent of our culture, our personal preferences and our biological make-up. But what made Peter Shaffer think that Mozart’s music is hard to vary? The prevailing view among both artists and non-artists is, I think, that there is nothing objective about artistic standards. Beauty, says the adage, is in the eye of the beholder. The very phrase ‘It’s a matter of taste’ is used interchangeably with ‘There is no objective truth of the matter.’ Artistic standards are, in this view, nothing more than artefacts of fashion and other cultural accidents, or of individual whim, or of biological predisposition. Many are willing to concede that in science and mathematics one idea can be objectively truer than another (though, as we have seen, some deny even that), but most insist that there is no such thing as one object being objectively more beautiful than another. Mathematics has its proofs (so the argument goes), and science has its experimental tests; but if you choose to believe that Mozart was an inept and cacophonous composer then neither logic nor experiment nor anything else objective will ever contradict you.
However, it would be a mistake to dismiss the possibility of objective beauty for that sort of reason, for it is none other than the relic of empiricism that I discussed in Chapter 9 - the assertion that philosophical knowledge in general cannot exist. It is true that, just as one cannot deduce moral maxims from scientific theories, likewise nor can one deduce aesthetic values. But that would not prevent aesthetic truths from being linked to physical facts through explanations, as moral ones are. Wheeler was very nearly asserting such a link in that quotation.
Facts can be used to criticize aesthetic theories, as they can moral theories. For instance, there is the criticism that, since most arts depend on parochial properties of human senses (such as which range of colours and sounds they can detect), they cannot be attaining anything objective. Extraterrestrial people whose senses detected radio waves but not light or sound would have art that was inaccessible to us, and vice versa. And the reply to that criticism might be, first, that perhaps our arts are merely scratching the surface of what is possible: they are indeed parochial, but they are a first approximation to something universal. Or, second, that deaf composers on Earth have composed, and appreciated, great music; why could deaf extraterrestrials (or humans who were born deaf) not learn to do the same - if by no other means than by downloading a set of deaf-composer aesthetics into their brains? Or, third, what is the difference between using radio telescopes to understand the physics of quasars and using prosthetic senses (wired into the brain to create new qualia) to appreciate extraterrestrial art?
Experience may also provide artistic problems. Our ancestors had eyes and paint, which may have led them to wonder how paint could be used in a way that would look more beautiful.
Just as Bronowski pointed out that scientific discovery depends on a commitment to certain moral values, might it not also entail the appreciation of certain forms of beauty? It is a fact - often mentioned but seldom explained - that deep truth is often beautiful. Mathematicians and theoretical scientists call this form of beauty ‘elegance’. Elegance is the beauty in explanations. It is by no means synonymous with how good, or how true, an explanation is. The poet John Keats’ assertion (which I think was ironic) that ‘Beauty is truth, truth beauty’ is refuted by what the evolutionist Thomas Huxley called ‘the great tragedy of Science - the slaying of a beautiful hypothesis by an ugly fact - which is so constantly being enacted under the eyes of philosophers’. (By ‘philosophers’ he meant ‘scientists’.) I think Huxley, too was being ironic in calling this process a great tragedy, especially since he was referring to the refutation of spontaneous-generation theories. But it is true that some important mathematical proofs, and some scientific theories, are far from elegant. Yet the truth so often is elegant that elegance is, at least, a useful heuristic when searching for fundamental truths. And when a ‘beautiful hypothesis’ is slain, it is more often than not replaced, as the spontaneous-generation theory was, by a more beautiful one. Surely this is not coincidence: it is a regularity in nature. So it must have an explanation.
The processes of science and art can look rather different: a new artistic creation rarely proves an old one wrong; artists rarely look at a scene through microscopes, or understand a sculpture through equations. Yet scientific and artistic creation do sometimes look remarkably alike. Richard Feynman once remarked that the only equipment a theoretical physicist needs is a stack of paper, a pencil and a waste-paper basket, and some artists, when they are at work, closely resemble that picture. Before the invention of the typewriter, novelists used exactly the same equipment.
Composers like Ludwig van Beethoven agonized through change after change, apparently seeking something that they knew was there to be created, apparently meeting a standard that could be met only after much creative effort and much failure. Scientists often do the same. In both science and art there are the exceptional creators like Mozart or the mathematician Srinivasa Ramanujan, who reputedly made brilliant contributions without any such effort. But from what we know of knowledge-creation we have to conclude that in such cases the effort, and the mistakes, did happen, invisibly, inside their brains.
Are these resemblances only superficial? Was Beethoven fooling himself when he thought that the sheets in his waste-paper basket contained mistakes: that they were worse than the sheets he would eventually publish? Was he merely meeting the arbitrary standards of his culture, like the twentieth-century women who carefully adjusted their hemlines each year to conform to the latest fashions? Or is there a real meaning to saying that the music of Beethoven and Mozart was as far above that of their Stone Age ancestors banging mammoth bones together as Ramanujan’s mathematics was above tally marks?
Is it an illusion that the criteria that Beethoven and Mozart were trying to meet were better too? Or is there no such thing as better? Is there only ‘I know what I like,’ or what tradition or authority designates as good? Or what our genes predispose us to like? The psychologist Shigeru Watanabe has found that sparrows prefer harmonious to discordant music. Is that all that human artistic appreciation is?
All these theories assume - with little or no argument - that for each logically possible aesthetic standard there could exist, say, a culture in which people would enjoy and be deeply moved by art that met that standard. Or that a genetic predisposition could exist with the same properties. But is it not much more plausible that only very exceptional aesthetic standards could possibly end up as the norm of any culture, or be the objective towards which some great artist, creating a new artistic style, spent a lifetime working? Quite generally, cultural relativism (about art or morality) has a very hard time explaining what people are doing when they think they are improving a tradition.
Then there is the equivalent of instrumentalism: is art no more than a means to non-artistic ends? For instance, artistic creations can deliver information - a painting can depict something, and a piece of music can represent an emotion. But their beauty is not primarily in that content. It is in the form. For instance, here is a boring picture:
and here is another picture with much the same content:
yet with greater aesthetic value. One can see that someone thought about the second picture. In its composition, framing, cropping, lighting, focus - it has the appearance of design by the photographer. But design for what? Unlike Paley’s watch, it does not seem to have a function - it only seems to be more beautiful than the first picture. But what does that mean?
One possible instrumental purpose of beauty is attraction. A beautiful object can be attractive to people who appreciate the beauty. Attractiveness (to a given audience) can be functional, and is a down-to-earth, scientifically measurable quantity. Art can be literally attractive in the sense of causing people to move towards it. Visitors to an art gallery can see a painting and be reluctant to leave, and then later be caused, by the painting, to return to it. People may travel great distances to hear a musical performance - and so on. If you see a work of art that you appreciate, that means that you want to dwell on it, to give it your attention, in order to appreciate more in it. If you are an artist, and halfway through creating a work of art you see something in it that you want to bring out, then you are being attracted by a beauty that you have not yet experienced. You are being attracted by the idea of a piece of art before you have created it.
Not all attractiveness has anything to do with aesthetics. You lose your balance and fall off a log because we are all attracted to the planet Earth. That may seem merely a play on the word ‘attraction’: our attraction to the Earth is due not to aesthetic appreciation but to a law of physics, which affects artists no more than it does aardvarks. A red traffic light may induce us to stop and stare at it so long as it remains red. But that is not artistic appreciation either, even though it is attraction. It is mechanical.
But, when analysed in sufficient detail, everything is mechanical. The laws of physics are sovereign. So, can one draw the conclusion that beauty cannot have an objective meaning other than ‘that which we are attracted to by processes in our brains and hence by the laws of physics’? One cannot, because by that argument the physical world would not exist objectively either, since the laws of physics also determine what a scientist or mathematician wants to call true. Yet one cannot explain what a mathematician does - or what Hofstadter’s dominoes do - without referring to the objective truths of mathematics.
New art is unpredictable, like new scientific discoveries. Is that the unpredictability of randomness, or the deeper unknowability of knowledge-creation? In other words, is art truly creative, like science and mathematics? That question is usually asked the other way round, because the idea of creativity is still rather confused by various misconceptions. Empiricism miscasts science as an automatic, non-creative process. And art, though acknowledged as ‘creative’, has often been seen as the antithesis of science, and hence irrational, random, inexplicable - and hence unjudgeable, and non-objective. But if beauty isobjective, then a new work of art, like a newly discovered law of nature or mathematical theorem, adds something irreducibly new to the world.
We stare at the red traffic light because doing so will allow us to continue our journey with the least possible delay. An animal can be attracted towards another animal in order to mate with it, or to eat it. Once the predator has taken a bite, it is attracted to take another - unless the bite tastes bad, in which case it will be repelled. So there we have a literal matter of taste. And that matter of taste is indeed caused by the laws of physics in the form of the laws of chemistry and biochemistry. We can guess that there is no higher-level explanation of the resulting behaviour than the zoological level, because the behaviour is predictable. It is repetitive, and where it is not repetitive it is random.
Art does not consist of repetition. But in human tastes there can be genuine novelty. Because we are universal explainers, we are not simply obeying our genes. For instance, humans often act in ways that are contrary to any preferences that might plausibly have been built into our genes. People fast - sometimes for aesthetic reasons. Some abstain from sex. People act in very diverse ways for religious reasons or for any number of other reasons, philosophical or scientific, practical or whimsical. We have an inborn aversion to heights and to falling, yet people go skydiving - not in spite of this feeling, but because of it. It is that very feeling of inborn aversion that humans can reinterpret into a larger picture which to them is attractive - they want more of it; they want to appreciate it more deeply. To a skydiver, the vista from which we were born to recoil is beautiful. The whole activity of skydiving is beautiful, and part of that beauty is in the very sensations that evolved to deter us from trying it. The conclusion is inescapable: that attraction is not inborn, just as the contents of a newly discovered law of physics or mathematical theorem are not inborn.
Could it be purely cultural? We pursue beauty as well as truth, and in both cases we can be fooled. Perhaps we see a face as beautiful because it really is, or perhaps it is only because of a combination of our genes and our culture. A beetle is attracted to another beetle that you and I may see as hideous. But not if you are an entomologist. People can learn to see many things as beautiful or ugly. But, there again, people can also learn to see false scientific theories as true, and true ones as false, yet there is such a thing as objective scientific truth. So that still does not tell us whether there is such a thing as objective beauty.
Now, why is a flower the shape that it is? Because the relevant genes evolved to make it attractive to insects. Why would they do this? Because when insects visit a flower they are dusted with pollen, which they then deposit in other flowers of the same species, and so the genes in the DNA in that pollen are spread far and wide. This is the reproductive mechanism that flowering plants evolved and which most still use today: before there were insects, there were no flowers on Earth. But the mechanism could work only because insects, at the same time, evolved genes that attracted them to flowers. Why did they? Because flowers provide nectar, which is food. Just as there is co-evolution between the genes to coordinate mating behaviours in males and females of the same species, so genes for making flowers and giving them their shapes and colours co-evolved with genes in insects for recognizing flowers with the best nectar.
During that biological co-evolution, just as in the history of art, criteria evolved, and means of meeting those criteria co-evolved with them. That is what gave flowers the knowledge of how to attract insects, and insects the knowledge of how to recognize those flowers and the propensity to fly towards them. But what is surprising is that these same flowers also attract humans.
This is so familiar a fact that it is hard to see how amazing it is. But think of all the countless hideous animals in nature, and think also that all of them who find their mates by sight have evolved to find that appearance attractive. And therefore it is not surprising that we do not. With predators and prey there is a similar co-evolution, but in a competitive sense rather than a cooperative one: each has genes that evolved to enable it to recognize the other and to make it run towards or away from it respectively, while other genes evolve to make their organism hard to recognize against the relevant background. That is why tigers are striped.
Occasionally it happens by chance that the parochial criteria of attractiveness that evolved within a species produce something that looks beautiful to us: the peacock’s tail is an example. But that is a rare anomaly: in the overwhelming majority of species, we do not share any of their criteria for finding something attractive. Yet with flowers - most flowers - we do. Sometimes a leaf can be beautiful; even a puddle of water can. But, again, only by rare chance. With flowers it is reliable.
It is another regularity in nature. What is the explanation? Why are flowers beautiful?
Given the prevailing assumptions in the scientific community - which are still rather empiricist and reductionist - it may seem plausible that flowers are not objectively beautiful, and that their attractiveness is merely a cultural phenomenon. But I think that that fails closer inspection. We find flowers beautiful that we have never seen before, and which have not been known to our culture before - and quite reliably, for most humans in most cultures. The same is not true of the roots of plants, or the leaves. Why only the flowers?
One unusual aspect of the flower-insect co-evolution is that it involved the creation of a complex code, or language, for signalling information between species. It had to be complex because the genes were facing a difficult communication problem. The code had to be, on the one hand, easily recognizable by the right insects, and, on the other, difficult to forge by other species of flower - for if other species could cause their pollen to be spread by the same insects without having to manufacture nectar for them, which requires energy, they would have a selective advantage. So the criterion that was evolving in the insects had to be discriminating enough to pick the right flowers and not crude imitations; and the flowers’ design had to be such that no design that other flower species could easily evolve could be mistaken for it. Thus both the criterion and the means of meeting it had to be hard to vary.
When genes are facing a similar problem within a species, notably in the co-evolution of criteria and characteristics for choosing mates, they already have a large amount of shared genetic knowledge to draw on. For instance, even before any such co-evolution begins, the genome may already contain adaptations for recognizing fellow members of the species, and for detecting various attributes of them. Moreover, the attributes that a mate is searching for may initially be objectively useful ones - such as neck length in a giraffe. One theory of the evolution of giraffe necks is that it began as an adaptation for feeding, but then continued through sexual selection. However, there is no such shared knowledge to build on across the gap between distant species. They are starting from scratch.
And therefore my guess is that the easiest way to signal across such a gap with hard-to-forge patterns designed to be recognized by hard-to-emulate pattern-matching algorithms is to use objective standards of beauty. So flowers have to create objective beauty, and insects have to recognize objective beauty. Consequently the only species that are attracted by flowers are the insect species that co-evolved to do so - and humans.
If true, this means that Dawkins’ daughter was partly right about the flowers after all. They are there to make the world pretty; or, at least, prettiness is no accidental side effect but is what they specifically evolved to have. Not because anything intended the world to be pretty, but because the best-replicating genes depend on embodying objective prettiness to get themselves replicated. The case of honey, for instance, is very different. The reason that honey - which is sugar water - is easy for flowers and bees to make, and why its taste is attractive to humans and insects alike, is that we do all have a shared genetic heritage going back to our common ancestor and before, which includes biochemical knowledge about many uses of sugar, and the means to recognize it.
Could it be that what humans find attractive in flowers - or in art - is indeed objective, but it is not objective beauty? Perhaps it is something more mundane - something like a liking for bright colours, strong contrasts, symmetrical shapes. Humans seem to have an inborn liking for symmetry. It is thought to be a factor in sexual attractiveness, and it may also be useful in helping us to classify things and to organize our environment physically and conceptually. So a side effect of these inborn preferences might be a liking for flowers, which happen to be colourful and symmetrical. However, some flowers are white (at least to us - they may have colours that we cannot see and insects can), but we still find their shapes beautiful. All flowers do contrast with their background in some sense - that is a precondition for being used for signalling - but a spider in the bath contrasts with its background even more, and there is no widespread consensus that such a sight is beautiful. As for symmetry: again, spiders are quite symmetrical, while some flowers, such as orchids, are very unsymmetrical, yet we do not find them any less attractive for that. So I do not think that symmetry, colour and contrast are all that we are seeing in flowers when we imagine that we are seeing beauty.
A sort of mirror image of that objection is that there are other things in nature that we also find beautiful - things that are not results of either human creativity or co-evolution across a gap: the night sky; waterfalls; sunsets. So why not flowers too? But the cases are not alike. Those things may be attractive to look at, but they have no appearance of design. They are analogous not to Paley’s watch, but to the sun as a timekeeper. One cannot explain why the watch is as it is without referring to timekeeping, because it would be useless for timekeeping if it had been made slightly differently. But, as I mentioned, the sun would still be useful for keeping time even if the solar system were altered. Similarly, Paley might have found a stone that looked attractive. He might well have taken it home to use as an ornamental paperweight. But he would not have sat down to write a monograph about how changing any detail of the stone would have made it incapable of serving that function, because that would not have been so. The same is true of the night sky, waterfalls and almost all other natural phenomena. But flowers do have the appearance of design for beauty: if they looked like leaves, or roots, they would lose their universal appeal. Displace even one petal, and there would be diminishment.
We know what the watch was designed for, but we do not know what beauty is. We are in a similar position to an archaeologist who finds inscriptions in an unknown language in an ancient tomb: they look like writing and not just meaningless marks on the walls. Conceivably this is mistaken, but they look as though they were inscribed there for a purpose. Flowers are like that: they have the appearance of having been evolved for a purpose which we call ‘beauty’, which we can (imperfectly) recognize, but whose nature is poorly understood.
In the light of these arguments I can see only one explanation for the phenomenon of flowers being attractive to humans, and for the various other fragments of evidence I have mentioned. It is that the attribute we call beauty is of two kinds. One is a parochial kind of attractiveness, local to a species, to a culture or to an individual. The other is unrelated to any of those: it is universal, and as objective as the laws of physics. Creating either kind of beauty requires knowledge; but the second kind requires knowledge with universal reach. It reaches all the way from the flower genome, with its problem of competitive pollination, to human minds which appreciate the resulting flowers as art. Not great art - human artists are far better, as is to be expected. But with the hard-to-fake appearance of design for beauty.
Now, why do humans appreciate objective beauty, if there has been no equivalent of that co-evolution in our past? At one level the answer is simply that we are universal explainers and can create knowledge about anything. But still, why did we want to create aesthetic knowledge in particular? It is because we did face the same problem as the flowers and the insects. Signalling across the gap between two humans is analogous to signalling across the gap between two entire species. A human being, in terms of knowledge content and creative individuality, is like a species. All the individuals of any other species have virtually the same programming in their genes and use virtually the same criteria for acting and being attracted. Humans are quite unlike that: the amount of information in a human mind is more than that in the genome of any species, and overwhelmingly more than the genetic information unique to one person. So human artists are trying to signal across the same scale of gap between humans as the flowers and insects are between species. They can use some species-specific criteria; but they can also reach towards objective beauty. Exactly the same is true of all our other knowledge: we can communicate with other people by sending predetermined messages determined by our genes or culture, or we can invent something new. But in the latter case, to have any chance of communicating, we had better strive to rise above parochialism and seek universal truths. This may be the proximate reason that humans ever began to do so.
One amusing corollary of this theory is, I think, that it is quite possible that human appearance, as influenced by human sexual selection, satisfies standards of objective beauty as well as species-specific ones. We may not be very far along that path yet, because we diverged from apes only a few hundred thousand years ago, so our appearance isn’t yet all that different from that of apes. But I guess that when beauty is better understood it will turn out that most of the differences have been in the direction of making humans objectively more beautiful than apes.
The two types of beauty are usually created to solve two types of problem - which could be called pure and applied. The applied kind is that of signalling information, and is usually solved by creating the parochial type of beauty. Humans have problems of that type too: the beauty of, say, the graphical user interface of a computer is created primarily to promote comfort and efficiency in the machine’s use. Sometimes a poem or song may be written for a similar practical purpose: to give more cohesiveness to a culture, or to advance a political agenda, or even to advertise beverages. Again, sometimes these purposes can also be met by creating objective beauty, but usually the parochial kind is used because it is easier to create.
The other kind of problem, the pure kind, which has no analogue in biology, is that of creating beauty for its own sake - which includes creating improved criteria for beauty: new artistic standards or styles. This is the analogue of pure scientific research. The states of mind involved in that sort of science and that sort of art are fundamentally the same. Both are seeking universal, objective truth.
And both, I believe, are seeking it through good explanations. This is most straightforwardly so in the case of art forms that involve stories - fiction. There, as I mentioned in Chapter 11, a good story has a good explanation of the fictional events that it portrays. But the same is true in all art forms. In some, it is especially hard to express in words the explanation of the beauty of a particular work of art, even if one knows it, because the relevant knowledge is itself not expressed in words - it is inexplicit. No one yet knows how to translate musical explanations into natural language. Yet when a piece of music has the attribute ‘displace one note and there would be diminishment’ there is an explanation: it was known to the composer, and it is known to the listeners who appreciate it. One day it will be expressible in words.
This, too, is not as different from science and mathematics as it looks: poetry and mathematics or physics share the property that they develop a language different from ordinary language in order to state things efficiently that it would be very inefficient to state in ordinary language. And both do this by constructing variants of ordinary language: one has to understand the latter first in order to understand explanations of, and in, the former.
Applied art and pure art ‘feel’ the same. And, just as we need sophisticated knowledge to tell the difference between the motion of a bird across the sky, which is happening objectively, and the motion of the sun across the sky, which is just a subjective illusion caused by our own motion, and the motion of the moon, which is a bit of each, so pure and applied art, universal and parochial beauty, are mixed together in our subjective appreciation of things. It will be important to discover which is which. For it is only in the objective direction that we can expect to make unlimited progress. The other directions are inherently finite. They are circumscribed by the finite knowledge inherent in our genes and our existing traditions.
That has a bearing on various existing theories of what art is. Ancient fine art, for instance in Greece, was initially concerned with the skill of reproducing the shapes of human bodies and other objects. That is not the same as the pursuit of objective beauty, because, among other things, it is perfectible (in the bad sense that it can reach a state that cannot be much improved on). But it is a skill that can allow artists to pursue pure art as well, and they did so in the ancient world, and then again during the revival of that tradition in the Renaissance.
There are utilitarian theories of the purpose of art. These theories deprecate pure art, just as pure science and mathematics are deprecated by the same arguments. But one has no choice about what constitutes an artistic improvement any more than one has a choice as to what is true and false in mathematics. And if one tries to tune one’s scientific theories or philosophical positions to meet a political agenda, or a personal preference, then one is at cross purposes. Art can be used for many purposes. But artistic values are not subordinate to, or derived from, anything else.
The same critique applies to the theory that art is self-expression. Expression is conveying something that is already there, while objective progress in art is about creating something new. Also, self-expression is about expressing something subjective, while pure art is objective. For the same reason, any kind of art that consists solely of spontaneous or mechanical acts, such as throwing paint on to canvas, or of pickling sheep, lacks the means of making artistic progress, because real progress is difficult and involves many errors for every success.
If I am right, then the future of art is as mind-boggling as the future of every other kind of knowledge: art of the future can create unlimited increases in beauty. I can only speculate, but we can presumably expect new kinds of unification too. When we understand better what elegance really is, perhaps we shall find new and better ways to seek truth using elegance or beauty. I guess that we shall also be able to design new senses, and design new qualia, that can encompass beauty of new kinds literally inconceivable to us now. ‘What is it like to be a bat?’ is a famous question asked by the philosopher Thomas Nagel. (More precisely, what would it be like for a person to have the echo-location senses of a bat?) Perhaps the full answer is that in future it will be not so much be the task of philosophy to discover what that is like, but the task of technological art to give us the experience itself.
Aesthetics The philosophy of beauty.
Elegance The beauty in explanations, mathematical formulae and so on.
Explicit Expressed in words or symbols.
Inexplicit Not explicit.
Implicit Implied or otherwise contained in other information.
MEANINGS OF ‘THE BEGINNING OF INFINITY’ ENCOUNTERED IN THIS CHAPTER
- The fact that elegance is a heuristic guide to truth.
- The need to create objective knowledge in order to allow different people to communicate.
There are objective truths in aesthetics. The standard argument that there cannot be is a relic of empiricism. Aesthetic truths are linked to factual ones by explanations, and also because artistic problems can emerge from physical facts and situations. The fact that flowers reliably seem beautiful to humans when their designs evolved for an apparently unrelated purpose is evidence that beauty is objective. Those convergent criteria of beauty solve the problem of creating hard-to-forge signals where prior shared knowledge is insufficient to provide them.