Continuing our series on the intellectual impact of Darwinism, John Barrow argues that the reason we find such things as parks, cosy alcoves and paintings of flowers so aesthetically pleasing is because they are pointers to the savannah grasslands in which our ancestors hunted.

Our ancestors spent millions of years of their history in tropical savannah habitats - grassy plains with few trees. So when we admire pictures of such landscapes is it because they set off a deep-seated emotional reaction in us, linked to appreciation of a type of environment which once enhanced our chances of survival?

Instinctive aesthetic reactions to the world could not have evolved and persisted if, on the average, they contributed negatively to survival, but responses that enhance the chances of survival will persist. This is why rotten meat tastes unpleasant to us, while sugars are sweet. Some of the most interesting evolved responses are those associated with our responses to the environment.

Our hunter-gatherer ancestors did not have direct access to infallible measures of the safety, nor the fertility, of a particular environment. They did not take soil samples or monitor the crime levels. All they could do was respond to a variety of indicators correlated to safety and survival. Thus the appearance of clouds on the horizon is a welcome sight in a dusty savannah grassland. Their appearance is strongly correlated with coming rain and a local abundance of food. Even when you have running water in abundance, a disposition towards finding cloud patterns pleasant would remain as an inherited adaptation, which once had positive survival advantage over a feeling of cloudy disinterest.

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Psychologists have carried out a number of controlled experiments on children and adults to discover which environments they prefer. By using photographs, it is possible to remove extraneous factors (like the presence of water or animals) and show the viewers habitats of which they have had no direct experience. Among very young children the savannah environment was the favourite (the desert was the least). But older teenagers, who had experienced other environments (like deciduous woodland or rain forests) often liked them as much as the savannah. The overall pattern of the studies suggests that, among the very young, there is an innate aesthetic preference for the savannah landscape; this preference is then modified by experience of other environments as the subjects grow older. When experience is limited then the savannah landscape is the most pleasing.

The savannah displays many faithful cues for safe human habitation; cues recreated in our urban parks. There is scattered tree cover, which offers shade and shelter from danger, interspersed with grasses; yet there are long vistas with frequent undulations that allow good views and rapid orientation. Most food sources are close to the ground, whereas in a forested environment life is out of reach, high above the ground in the forest canopy.

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If the environment is deemed safe for further exploration, then other features highlight the most attractive sites. The topography must allow us to navigate easily; landmarks, bends, and variations are welcome to the eye, so long as they do not create confusing complexities, or hide dangers. We recognise the encouragement to explore that any mysterious element in the terrain creates, like the tempting path that winds out of sight. Its further exploration will only be safe if it combines adventure with automatic caution and an instinct to recoil from danger.

Our surprising fascination with risk attracts us to all manner of cultural embellishments - from horror stories and roller-coaster rides, to paintings of shipwrecks and disaster movies; it springs from an inherited urge to explore and understand environments as fully as possible from the safest possible vantage point. The fact that these hazards are potentially fatal is the reason that a desire to inform oneself more fully as to their nature has selective advantage over an attitude of apathetic indifference.

There is a clear adaptative advantage to be gained by choosing environments which offer places of security and unimpeded views of the terrain - which allow one to see without being seen - tempered by a mysterious invitation to explore. Their attractiveness informs many of our aesthetic preferences, from architecture to landscape painting. Expansive views and cosy inglenooks, daunting castles, the treehouse, the Little House on the Prairie, the mysterious door in the wall of the secret garden: so many of the classically seductive landscape scenes combine symbols of safety with the prospect of uninterrupted panoramic views or the enticement to explore, tempered by verdant pastures and water. These comfortable, pastoral scenes appeal to our instinctive sensibilities because of the selective advantages that such environments first held for our ancient forebears. Their style figures prominently in the aesthetics of our best-appreciated landscape gardening, public parks, and gardens, where it is calculated to aid relaxation and induce feelings of well-being.

Architects like Frank Lloyd Wright emphasised canopies and refuges within buildings, often setting them in opposition to panoramic vistas, or even cascades of water, in order to heighten the feeling of security that these cosy alcoves create. Sloping ceilings, overhangs and porches are all architectural features which accentuate the feeling of refuge from the outside world; while balconies, bays, and picture windows meet our desire for a wide-ranging prospect which allows us to see without being seen. The skilful use of trees and water can reinforce these features. Their denial in many urban building projects has had disastrous consequences that are all too plain to see.

Our aesthetic preferences are a fusion of instinct and experience. We would expect that, in the absence of experience and special influence, our innate sensitivities for these life-supporting features of natural scenes would influence our artistic preferences. Indeed, simple landscapes and still-life scenes are often preferred by those with no special interest in art. A taste for the avant garde, or the abstract, is a fruit of experience overriding instinct. Even then, what appeals in man-made art is often the symbolic play, or counterplay, on those same adaptative features that have, for so long, informed traditional artistic images.

Our sensitivity to so many of the transient features of our environment - the lengthening shadows that signal the end of daylight; the darkening clouds or rushing winds that herald cold or storm; the distant horizon that hides the unknown "over the hills and far away" - are all pointers that once rewarded response and appreciation. Our artistic fascination with sunsets and cloud patterns; our sensitivity to the nuances of light and shadow in the representation of the natural world; the menacing metaphor of the storm and the tempest: all of these instinctive feelings make sense as residues of reactions to changes in the environment that require rapid evaluation. Shadow reveals new information about distance and depth; it allows a more detailed appraisal of the environment. Danger lurks in the shadows; survivors are more likely than not to be especially sensitive to it. Alertness to the sunset and the shadows that warn of coming darkness, and the need to ensure warmth and safety, has clear advantage over disinterest. Reaction to the appearance of the sun when it is far from rising and setting, by contrast, offers far less information of vital importance to living things.

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With the darkness comes the importance of fire; flickering flames still fascinate us. The fire was the focus of life after dark, offering warmth and safety, fellowship and light. It inflames strong emotions by its paradoxical offer of comfort and threat of danger. This odd mixture of fear and fascination appears elsewhere. Large animals are strangely attractive, yet threatening. Once, they were both a danger and an abundant source of food. Our instinctive attraction to them, tempered by fear and respect, looks like a remnant of a reaction that increased the likelihood of survival. Animals were the key to our primitive ancestors' survival. It is not surprising that instinctive reactions to them evolved and spread. Those reactions underlie our penchant for animal symbolism: the dominance of the lion, the soaring freedom of the eagle, the fleetness of the gazelle - these are some of the symbols that draw on our environmental history.

For tropical savannah dwellers, daily changes of light and temperature are regular and rapid, but other critical changes are slow and subtle. The most unpredictable element of the savannah landscape is the seasonal variation of the rainfall. We would therefore expect to find human adaptations sensitive to seasonal change and to imminent rainfall and emerging fruitfulness. We find emotional responses to the seasonal changes in the colours of leaves and shrubs: people flock to New Hampshire in the fall. We find flowers beautiful, therapeutic, and romantic. What hospital ward would be without them? What more frequent gift for a loved one? What more common "still life" subject?

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We do not eat flowers, but the appearance of flowers is a useful cue which allows different plants to be rapidly identified and distinguished. If no flowers are present, then plants are all green, and can be distinguished only by detailed inspection. Flowers also give information about the ripeness of fruit. Thus, while plants burst into flower for reasons that have nothing to do with our likes or dislikes, the fact that a sensitivity to flowers has a purpose, which is adaptative, provides us with a clue to the origin of what would otherwise be an entirely mysterious fascination.

Flowers, like all living things possess obvious symmetry. Our general sensitivity to symmetry and the acuteness of our visual detection of it might well have origins in the simple fact that almost all living things possess at least lateral symmetry while inanimate objects do not. A sensitivity to symmetrical patterns in a confused or camouflaged scene is a life-saving sense, picking out potential predators, prey, or mates. Indeed, one can appreciate why it might pay to be a little over-sensitive in this respect. Better to be thought paranoid once in a while than end up as someone else's lunch.

It has become fashionable to regard human aesthetic preferences as totally subjective responses to learning and nurture. This now seems barely credible. Our sensitivities and emotional responses have not been created out of nothing. The evaluation of environments was a crucial instinct for our distant ancestors - one upon which their very survival hinged. The adaptative responses that we have inherited from them form a basis over which our subsequent social experience is overlaid. In many of the visual arts, we see remnants of past imperatives, now overlain with symbol or subverted into opposition, perhaps, but undeniably present in our representations of natural landscapes. Even where artistic representations are heavy with artificial symbolism of a religious or romantic sort one can often find a background resonance with echoes of our innate emotions. The backgrounds in portraits and religious works often contain scenes which combine images of safety, danger, and wide-open space. Adjusting the balance of these ingredients stirs finely balanced emotions. It sheds light upon our attraction by symbols in art, and reveals why particular images can so effectively be pressed into service to conjure up emotional responses. Art would not be a universal human activity if there were no universal emotional responses and resonances.

Speculating wildly for a moment, suppose extraterrestrials evolved by natural selection, (as many would argue they must) then we would expect that their environment would have presented quite different challenges to our own. They would need to have met those challenges by inheriting instinctive reactions to their environment that had survival value. We might expect that they would also retain heightened emotional responses to those aspects of their environment whose appreciation would be advantageous to their survival. Knowing something of their environment and their range of senses, we could expect images of safe havens, clear vantage points, and danger, to produce instinctive responses from them. If they provided us with examples of their artistic creations and preferences, then we might begin to understand them. While their symbols of safety, danger, and panorama might have been so transmogrified by their social practices and physiology as to be now unrecognisable, if traces remain, we would have taken the first steps towards understanding how their minds work.

The source of our affection for natural landscapes also sheds light upon our responses to unnatural landscapes. The ubiquity of powerful computer systems has created an explosion of computer graphics which adorn galleries, bedrooms, and bookcovers. This technology has focused most intensely upon the creation of computer-generated fractal landscapes, which display striking statistical similarities to natural scenes. Yet, despite their superficial impressiveness and their display of structure on all scales, they are not landscapes that draw you into them or which demand a second look. Our discussion of the human adaptation to landscape features helps us to understand our responses to computer-generated scenes. Their focus on the fractal texture of landscapes excludes any recognition of the importance of mingled symbolic associations of prospect, refuge and hazard. They are dominated by wide-ranging vistas and horizons, but lack the deliberate inclusion of refuge symbols and inducements to explore. They fail to resonate with our evolutionary adaptation for emotional response to particular landscape symbols. They are simply not landscapes that we feel drawn to enter.

John D. Barrow is professor of astronomy at the University of Sussex. His book, The Artful Universe, will be published by Oxford University Press on November 15.

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