Meaningful Scents Around the World: Olfactory, Chemical, Biological, and Cultural Considerations by Roman Kaiser (Wiley-VCH) In recent years, our knowledge of the anatomy and physiology of olfaction has grown enormously, accompanied by a growing appreciation of scent. This is reflected in the fact that the 2004 Nobel Prize in Medicine was awarded for discoveries of 'Odorant Receptors and the Organization of the Olfactory System'. This book naturally supports such developments, and takes the reader on a fascinating fragrant journey around the world to some of the exciting places the author has visited during his 30 years of olfactory research. Following an introductory section to the world of natural scents, including their biological meaning and history, the fragrance and flavor chemist, Roman Kaiser, who is renowned for his 'headspace' analytical technique, revisits some memorable scents. In doing so, he leads us to such exotic places as Lower Amazonia, Papua New Guinea, India, and many rain-forest biotopes in his quest for new molecules and new scent concepts, showing us along the way how a scent like tatami can be linked to culture. The third and final section describes the analysis of the compositions of the presented scents.
Excerpt: Patrick Süskind, in his world bestseller 'Perfume: The Story of a Murderer', creates a most unusual monster as the protagonist, a man without any odor of his own, but with a sense of smell so well developed that it is the sole content of his life. Grenouille, born into the waste of a fish market in 18th-century Paris, is the personification of olfaction and becomes the most talented perfumer. His nose not only perceives a scent as a whole, but also is able to analyze it as I do today with the latest analytical equipment. As he follows the trails of odors in his life, extracting the essences of flowers, spices, and virgins, his uncontrolled passion ends in a strange and fantastic climax. But this is not the real fiction of the novel – that is much more the postulation of a scentless living being. Scents are ultimately connected with living things – dense vegetation and high biodiversity go in parallel with high levels and wide diversity of scent molecules, the main reason that I have visited so many rainforest biotopes during the past ten years in my quest for new molecules and new scent concepts.
The sense of smell gives us a sense of other living beings, of our own species, or of animals and plants, and plays an important role in the forces ruling the living world, in 'sex and hunger', as brought to the point in one sentence by Jillyn Smith in her fascinating book 'Senses and Sensibilities'. A major part of communication between living things is based on exchange of volatile molecules, on semiochemical messengers. Thus, for example, the ultimate purpose of the scent of a flower, in conjunction with its shape and coloring, is to attract animal pollinators so as to ensure the preservation of the species. Social insects use semiochemicals to communicate about colony membership, sex, trails to food, and so on. As we will see, some Dracula species, mimicking fungi with their flowers, give off mushroom-like scents, thereby attracting females of fungus-fly species, a symbol for nature's complexity.
For humans, the sense of smell can be 'the super sense', or 'the mystic sense', but also 'the forgotten sense'. 'Super sense' because scent experiences can be stored with surprising vividness for a very long time, and on being re-experienced they can evoke strong, sudden emotions. For this reason, and because it works invisibly, it is also called the 'mystic sense'. Finally, it is justified to consider the sense of smell as forgotten by our culture – it is certainly the most undervalued. Cultural historians have shown that this was not always the case; the current low status of smell in the West
is most probably due to the 'qualification of the senses' by philosophers and scientists of the l8th and 19th centuries. The intellectual elite of this time declared vision as the superior sense, the sense of reason and civilization, while the sense of smell was placed on a much lower level, a primitive, brutish ability associated with savagery and even madness. This attitude of our culture towards the sense of smell, however, is only typical for the recent past. Museums are filled with scent artifacts from the important civilizations of the past – incense burners, flasks, vials, and philters – nor have all members of our society been able to live without full use of this sense, as is well illustrated by famous writers such as Charles Baudelaire (1821-1867), Joris Karl Huysmans (1848– 1907), and Marcel Proust (1871-1922).
During my involvement in natural-scent research over the past 30 years, I have been able to recognize strong indications of a retreat from the original Puritanism and a growing appreciation of scent. During this time, knowledge of the anatomy and physiology of olfaction has grown enormously, and just as I write this introduction, the 2004 Nobel Prize for Medicine has been jointly awarded to Richard Axel and Linda B. Buck for their discoveries of `Odorant Receptors and the Organization of the Olfactory System'. This will certainly secure the equality of smell with the other senses, and I sincerely hope that this book will adequately support this development. I would, therefore, now like to invite you on an enjoyable fragrant journey around the world, to visit some exciting places that will stay forever in my olfactory mind.
Biological Meaning of Natural Scents
As a consequence of complex metabolic processes, a great number of relatively volatile substances are formed in at least 30% of all higher plant species. Because of their potential toxicity, they are stored as so-called 'essential oils' in special cells at the peripheries of flowers, leaves, or even roots. Their volatility allows these 'essential oils', consisting of anything from a handful to over 300 individual components, to be detected by the human or animal sense of smell. Humans generally experience them as fragrant scents, although some plants can give off offensive odors. Naturally, we cannot know how, for example, the pollinating animals experience the corresponding flower scents, although it seems reasonable to assume that they interpret them, regardless of how they are perceived by humans, as signals important for their own survival. Depending on the mechanism of scent release, fragrant plants may be divided into very roughly into the following two main groups:
Flowers give off their scents without any visible external stimulus. They control the scent release by an internal biological clock particular to each species. Environmental factors, including light intensity, day–night cycle, and temperature, act as triggering or inhibiting impulses, each affecting different species to varying degrees. Consequently, both the quantity and quality of the released scent often show a close correlation with time. As we shall see with the examples of some orchids, certain species even appear to be scentless during the day, but emit intense and usually very attractive scents after the onset of darkness (cf. Sect. 2.2 and 2.16). This phenomenon should be seen in the context of the biological significance of a flower's scent. Its ultimate purpose, in conjunction with the shape and coloring of the flower, is to attract animal pollinators so as to ensure the preservation of the species (Fig. 1.1). Co-evolution and adaptation between flower and pollinating insects have given rise to even more extreme time dependences in scent emanation. Thus, certain orchid species are only fragrant during the short time of dawning in the morning or twilight in the evening because they have totally adapted to the short visiting times of their associated crepuscular bee species (cf. Sect. 2.2).
In dramatic contrast with the night-active and crepuscular species, which, in most cases, are delightful to the human nose, are the putrid and fecal scents of those species of flowering plants that mimic carrion in both scent (stench) and color (generally reddish-brown to yellowish-brown), thus attracting carrion-feeding insects as pollinators. These are well represented in, for example, the very extensive orchid genus Cirrhopetalum, distributed across the whole of Southeast Asia. One unforgettable example is Cirrhopetalum robustum, which I encountered during a 'scent expedition' in the Lakekamu basin of Papua New Guinea, the flowers of which emit a particularly penetrating stench reminiscent of rotting flesh and overripe cheese. No less repulsive are the volatiles emitted by Stapelia species (Asclepiadaceae) native to southern Africa or the 15 or 50 Rafflesia species occurring in Malaysia and Indonesia, respectively. As we will discuss in more detail, certain species of this ecological group even mimic fungi in their flower scent and morphological appearance to get pollinated (cf. Sect. 2.21).
Like flies, beetles have been considered to represent archaic pollinators, although there are also some more highly evolved angiosperms that make use of beetle pollination. Since pollination takes place during feeding on pollen, floral tissue, nectar, or other floral exudates, their activity is often called 'mess and soil pollination'. One main group feels attracted by the amine-like and fecal odors given off by the typical carrion beetle blossoms as developed by Amorphophallus species. A second group is specialized in fruity odors and includes the striking Dynastine scarab beetles that pollinate the two spectacular Victoria species. These 'Royal Amazons' are discussed in Sect. 2.13.
Between these extremes, there lies an enormous variety of differently scented flowers pollinated by bees, wasps, and bumblebees. They include the familiar scents of lily of the valley, rose, sweet pea, primula, lime-blossom, mignonette, violet, hyacinth, narcissus, and carnation, and any of their countless possible combinations. As a part of their adaptation to these pollinators, the scent emanations of these flowers are dependent on daylight and warmth. As a further attractant, they often possess intense coloring, with violet, blue, yellow, and occasionally white serving as particularly attractive hues.
In the Hymenoptera pollinator group, the scents, shapes, and colors of flowers are actually associated with food in the form of nectar in ca. 80% of cases. In the remaining 20% of bee, wasp, and bumblebee species, the signals communicated by the associated flowers trigger completely different behavior patterns. A very exciting syndrome occurring within this group is discussed in Sect. 2.15.
To be or not to be scented may just depend on the presence or absence of the enzyme systems needed to metabolize, say, the color-giving carotenoids in a flower. In Sect. 2.4, for example, we encounter an orange-gleaming, but scentless, Marcgraviaceae. This species does not need a scent, because it is visited and pollinated by hummingbirds, which are much more attracted by bright colors between orange and red than by scents. Just afterwards, we discuss another representative of this family, occurring in the same habitat and possessing similar coloration. In this case, however, the enzyme systems needed to metabolize carotenoids and to synthesize other odorants are present, resulting in a fragrance attractive both to Hymenoptera species and to humans.
Although not discussed in more detail in this book, nocturnal pollination by bats, an exclusively tropical phenomenon, should also be mentioned. While the typical nocturnal flowers pollinated by moths also mostly please our noses, the bat flowers often emit rather objectionable odors reminiscent of leek, garlic, rotten cabbage, mushrooms, and the like. As a consequence of co-evolution/adaptation, bat flowers are night-scented, practically always robustly structured, bell-shaped, and white or whitish in color. The bats obtain large amounts of nectar, pollen, or both as reward when visiting these flowers.
Much less was known until recently about the second group of fragrant plants, the so-called 'provoked scent releasers', in which volatiles are stored at the peripheries of leaves, stems, or even roots in especially designed glandular cells, or are formed in situ as a reaction to an external stimulus. Even elevated temperature caused by sunlight may be sufficient to burst these cells and to liberate the volatiles as scent. A well-known example is Dictamnus albus, which gives off a very characteristic lemon-peel type scent on being touched or exposed to elevated temperatures. According to one theory, a plant specimen of this Rutaceae native to the Near East might have been the burning bush of Moses. Indeed, on a hot summer day, the scent aura around a Dictamnus plant is quite intense, and it is said that it will burst into a blue flame on lighting with a match. Although I have tried hard, I have never been able to reproduce the phenomenon of the burning Dictamnus.
Until recently, not much more was known than that these 'essential oils' may influence the transpiration of a plant, that they might give protection against animal feeding, and that they might also be of importance for the plant because of their antibiotic properties. During the past ten years, however, many research groups have shown that these volatiles are of utmost importance for ecological interactions in nature. As representative of many fascinating papers, I would like to refer to the research done by André Kessler and Ian T Baldwin' of Germany's Max-Planck Institute for Chemical Ecology in Jena. In elegant experiments performed in Utah's Great Basin Desert, they were able to show that wild tobacco plants (Nicotiana attenuate) release scent chemicals as distress signals during attack by Manduca moth caterpillars, and that these scents attract 'bodyguard' insects that eat the predator's eggs and larvae. The airborne volatiles also stop adult Manduca moths from laying their eggs on this Nicotiana species. As a consequence, N. attenuate can reduce the number of pests by up to 90% by releasing these volatiles. One very important compound for such ecological interaction, methyl cis(Z)-jasmonate, also contributes significantly to many flower scents, as we will see during our fragrant journey around the world.
Historical Facts Concerning Natural Scents
Since the dawn of history, man too has been captivated by the scents – or perfumes – of plants. The origin of the word 'perfume' (Latin per fumum, literally 'through smoke') almost suggests that scents were initially meant asdivine. sacrificial offerings. In appealing to divine mercy, man had to sacri- lice to the gods his most precious possessions. These included fragrant resins, such as frankincense and myrrh, and, as civilization progressed, these increasingly took the place of sacrificial animals.
Thus, for example, the Epic of Gilgamesh, written in the 12th century B. C., and referring to events in the 28th or 27th century, describes how Utnapishti, the father of all men, gave thanks for his rescue from the Flood by burning cedar wood and myrrh, the sweet-smelling odor of which pleased the gods. Since then, the smell of incense has pervaded human history up to the present. One of its most refined sources – agarwood, the wood of the gods.
The Egyptians were experts in the manufacture and use of scented plant drugs and essential oils (including distillates). These substances were used not only in ritual contexts, but also for medical and cosmetic purposes. The Egyptian Ebers Papyrus (Smith Papyrus), written as early as 1600 B. C., contains the recipes for 100 such concoctions. This great appreciation of scents in Egyptian culture is not surprising in view of the importance it attributed to an attractively scented flower, the blue lotus of the Nile (Nymphaea caerulea; cf. Sect. 2.14). Some thousand years later, Confucius in ancient China lauded the beauty and scents of certain terrestrial orchid species, which he referred to as 'kin' . He compared their flowers to the perfect human being and their scents to the joys of friendship.
In the old Indian Epic of Mahabharata, the highest goddess praises herself as the 'Scent of Earth'. The miniature painting in the style of the Mogul period shown in Fig. 1.5 offers good reason to assume that both gods and humans in this culture were especially fond of flowers and their scents. It might show the Princess Sumbawati, who knew a paradise-like place in the Southern Himalayas, where all her favorite plants grew, opening their flowers at defined times of day or night, and filling the air with indescribable pleasing scents. The happy souls who were allowed to rest at this place were healed of all mental and physical diseases, and their hearts became light again.
With the passage of time, people eventually learned how to extract the scents of many plants in highly concentrated form as essential oils. The technique of distillation may already have been known to the Indus Valley civilization as early as 3000 B.C., but it was to be another 4000 years before the Arabs rediscovered this process. After further developments during the Middle Ages, it eventually assumed industrial forms in the 19th century, shows a typical example of the apparatus used at that time to isolate essential oils by steam distillation.
In this process, the scented plant material – e.g., flowering lavender branches, chips of sandalwood, or even scented roots such as those of vetiver grass – is added to water and heated in the boiler. The fragrant volatiles evaporate with the steam and are subsequently returned to liquid form in the condenser. The obtained essential oil, which is insoluble in water, floats on the surface and can easily be separated off.
The more-sensitive and -valuable flower scents, such as those of jasmine, rose, and tuberose, however, are usually extracted with a highly volatile solvent to produce, after various concentration stages, a 'flower absolute'. This method did not come into use until organic chemistry made the appropriate solvents available in the 19th century. To obtain, for example, 1 kg of rose scent in the form of essential oil or absolute by this classical method, 3 –5 tons of Rosa centifolia flowers have to be picked by hand and processed. In the case of jasmine (Jasminum grandiflorum), some 8 to 10 million individual flowers, weighing a total of 1 ton, are required for 1 kg of absolute. It is not surprising, therefore, that both of these natural products, 1 which are used in many perfumes, command as much as CHF 4,000-8,000 per kilogram. Nevertheless, among the 500 or so regularly used essential oils and absolutes, there are also some that can be obtained in much greater quantities with much less effort. Lavender oil, for example, only costs CHF 60-140 per kg, depending on the type and year.
Investigation of Natural Scents
Until the middle of the 19th century, such natural extracts of scented flowers or other plant parts, together with – to a certain extent – those of animal secretions, were the only raw materials used in the creation of fragrances. No wonder that chemists working in the fragrance industry have been investigating these natural products extensively since the dawn of modern organic chemistry. As a result of this (continuing) research work, perfumers now have at their disposal not only the 500 or so regularly used natural products for the preparation of their creations, but at least double this number of synthetic fragrance compounds that have originated in one way or another from natural products.
In spite of all these synthetic and natural products available off the shelf, the huge range of fascinating natural scents that surround us is still a great source of stimulation and is as yet far from exhausted. For a long time, however, many of these scents could not be analytically investigated because they could not be captured in sufficient amounts and/or in adequate quality.
By the 1970s, methods of instrumental analysis, particularly capillary gas chromatography (GC) and mass spectrometry (MS), had reached such a high level of sensitivity, thanks to modem electronics, that the analytical investigation of micro-samples could also be envisaged. This gave incentives to look for methods that would allow the scents emitted by living flowers/plants to be trapped in a quality as perceived by the human nose. These requirements were not met by destructive isolation methods such as micro-extraction/distillation, which might influence the original scent. The method of choice was instead specified as a close-to-nature trapping technique that, for the first time, would enable the analytical investigation of rare and endangered species. Such a method was soon developed, the emanated scent being trapped on a small amount of suitable adsorbent porous polymer such as Porapak or Tenax, or on charcoal, followed by solvent extraction.
In the mid 1970s, we thus implemented a long-term research program at Givaudan with the aim of investigating and, in promising cases, subsequently synthetically reconstituting such original and attractive scents that are not available as commercial essential oils or related products. The method has since proved to be effective, and over the past ten years has been specially adapted to field experiments conducted under extreme conditions such as those found in rainforests.
To collect the flower scent of, say, Pachira insignis, a fascinating Bom-bacaceae native to the neotropics, a single flower is inserted into a glass vessel of adapted size and shape without damaging the flower. The scented air surrounding the flower is then drawn through the adsorption trap by means of a battery-operated pump over a period of 30 min to 2 h (30 ml min-1), depending on the intensity of the scent. The adsorption trap, containing 2-5 mg of adsorbent, in this case Porapak Super-Q, is placed as close as possible to the scent source within the glass vessel. While air and moisture pass through these micro-traps unhindered, the scent is adsorbed and accumulated in amounts of 10-200 pg during the collection time. For flowers or plant parts with very complex shapes, it is more practical simply to isolate the scent source from the environment to the extent possible with a suitably shaped object, such as a glass funnel. The adsorption trap is then centered as near as possible to the position where the scent release is judged to be maximum. Afterwards, the adsorbed scent is eluted with an appropriate amount of a suitable solvent, usually 20-60 ug[11 of hexane/acetone 10:1, directly into a micro-ampoule, which is then sealed and kept cool until the return to the laboratory. Finally, the obtained samples are investigated by a combination of capillary gas chromatography and mass spectrometry (GC/MS), together with complementary methods.
The flower frequently has such a shape that the micro-trap can be introduced directly into the flower without use of a glass vessel, as sometimes practiced with so-called `SPME (Solid-Phase Micro-Extraction) fibers' by other researchers. However, both the `SPME-fiber' method, which we have been using for many years for routine-type measurements, and the headspace.
Furthermore, the complementary investigation of a micro-extract of the fragrant plant tissue in question – if available at all for this purpose – is always helpful since it facilitates the estimation of the quantitative data and allows a better insight into the less volatile portion of the natural scent. Such micro-extracts may be obtained either by extracting the flowers/plants with highly purified solvents such as hexane in the classical way or with liquid carbon dioxide in modern, highly convenient computer-controlled laboratory systems.
By applying these methods over the past 25 years, we have investigated more than 1,900 flower, plant, fruit, wood, and herb scents out of a selection of ca. 9,000 species of scented plants evaluated during this time. Publications on, for example, the scents of orchids and of cacti6, and, more generally, on new or uncommon volatile compounds in the most diverse floral scents, and on scents found in rainforests give partial overviews of these investigations, trapping techniques with subsequent thermodesorption have the fatal disadvantage that only one injection into the GC/MS system per experiment is possible, allowing only a rough overview analysis. Working in the fragrance industry requires one to be totally scent-oriented, which means that at least a second and third injection are needed for the so-called `GC-sniffing', in order to localize trace constituents often of decisive olfactory importance. Thanks to the enormous advances made in instrumental analysis, even NMR spectroscopy can be involved today in the structural elucidation of new scent components of such micro-samples, provided that 1 –5 ug can be isolated by preparative capillary GC. In practice, this is only realistic with samples obtained by trapping and subsequent solvent elution.In a very similar way, fragrant molecules can also be adsorbed from all types of aqueous solutions – such as fruit juices, plant saps, or environmental fluids – by so-called SPE (Solid-Phase Extraction) methods. The aqueous solution (40 – 80 ml) is passed through a small amount of a porous polymer capable of adsorbing the aroma compounds, while the more polar components such as hydroxy acids/carboxylic acids or sugars pass through unhindered. Subsequently, the aroma part is recovered by elution with a suitable solvent and the obtained eluate is investigated as already described for the headspace samples.
Biology of Floral Scent edited by Natalia Dudareva, Eran Pichersky (CRC) The first book of its kind, Biology of Floral Scent provides comprehensive coverage of state-of-the-art floral scent research. This book explores the major aspects of floral scent biology including its function and significance for plants and pollinators, composition, enzymology, evolution, and commercial aspects. It employs a modern approach that incorporates molecular biology, enzymology, chemistry, entomology, genetic engineering, and functional genomics. By combining literature on plant reproduction into a single volume, this text provides an easy reference for plant biologists, natural products chemists, cell and molecular biologists, ecologists, and entomologists.
As with nearly all living creatures, humans have always been fascinated by floral scents. Yet, while we have been producing, perfumes for at least 5000 years to serve myriad purposes from religious to sexual to medicinal, the limitation of our olfactory faculty has greatly hindered our capacity to clearly and objectively measure smells. Only recently have the advances been made in practical methodologies and affordable instrumentation that allow us to collect, separate, and identify those volatile compounds that have aromatic impact. These advances have led to much intensive investigation that has resulted in many highly insightful and useful discoveries.
Biology of Floral Scent provides the first comprehensive treatment of this rapidly evolving field. It reviews the impressive research being done across several disciplines, incorporating molecular biology, enzymology, chemistry, entomology, genetic engineering, and functional genomics.
Organized into a single volume covering every major aspect of floral scent research, this landmark work
Explores the functions and significance of scent in the interactions between plants and pollinators
Details plant composition and enzymology, explaining how and where various scent compounds are made and how they are emitted
Offers insight into plant evolution
Discusses commercial applications, including the use of recently identified scent genes to genetically engineer flowers to produce new scents
Meeting the needs of plant scientists, cell and molecular biologists, natural product chemists, pharmacognosists, and entomologists, as well as students in these fields, this work provides the background, findings, and insight that will stimulate new research to further advance an understanding of floral scent biology.
The sense of smell is the most basic and universal sense. Even bacteria have mechanisms to detect the presence of chemicals in their environment. The scents that emanate from flowers have been noticed by humans since antiquity; a fact that has been documented in ancient texts. In 3000 B.C., when the Egyptians were learning to write and make bricks, they were already making primitive perfumes and using them for religious rituals. Humans' admiration for the fragrances of flowers has made these volatile substances into many commercial products. Volatiles are heavily used in the perfume, cosmetics, and fragrance industries, which are continually researching new and unusual volatile compounds and scents. Consumers are also constantly searching for new scented ornamental crops. However, the biosynthesis of floral volatiles and the roles of floral scents in plants are topics that have only recently begun to receive serious scientific attention. While we can certainly detect scent molecules in the air, the sheer number of such scents, and their complexity, confound us. Our olfactory sense is simply not good enough to separate the components and identify each one with any certainty. The consequences of our inability to clearly and objectively measure smells with our nose mean that, in the absence of appropriate instrumentation, scientific research in this area is greatly impeded.
Recent advances in practical methodologies and affordable instrumentation to collect, separate, and identify volatile compounds have allowed floral scent research to become a standard scientific research topic accessible to many investigators, which in turn has resulted in many exciting new discoveries. Thus the fourteen chapters of this book summarize and represent the progress in our current understanding of the major areas of investigation into floral scent: the techniques used to study it, how the various scent compounds are made, where they are made and how they are emitted from the flower, the effect of floral scent on the various ecological interactions between insects and flowers, and finally, how researchers are using the newly identified scent genes to genetically engineer flowers that will produce new scents. The editors realize that there is much more to be learned in this area and they hope that this book will stimulate new research to advance our understanding of floral scent biology.
Sensory Processes by David Soderquist (Sage Publications) provides an introductory text that emphasizes all the sensory systems from a neuroscience perspective. The text is designed to meet a new and relatively unique niche in the neurosciences. The first two chapters provide the basic neural and physiological foundations for the remaining chapters. The text then continues by focusing on the neurological processes associated with each sensory modality. Although the emphasis is on the neurological aspects of each sensory system, perception is not disregarded. Perceptual processes are introduced and discussed from a neurological perspective. A unique aspect of the text is the inclusion of anomalies and dysfunctions for each sensory modality. In addition, a Glossary provides definitions for each highlighted term or concept discussed in the chapters. Given this approach, the content of the book is most likely to attract individuals interested in neuroscience, psychology, and biology. Sensory Processes, however, also recommends itself to those in other disciplines (anthropology, pre-medicine, pre-dentistry, pre-veterinarian)For over three decades Soderquist taught graduate and undergraduate courses in psychology. Although the courses have varied in their depth of presentation, content, and titles (Introductory Psychology, Perception, Sensation and Perception, Sensory Processes, Biological Psychology, Auditory Perception, Animal Psychophysics), they all focused on or emphasized particular perceptual aspects of human and animal existence. Because perception is one of the major intellectual pursuits of psychologists, it is well recognized that "There is nothing that is in the intellect that is not first in the senses" (Blaise Pascal).
The Human World in the Physical Universe by Nicholas Maxwell (Oxford University Press) How is it possible for the world as we experience it to exist embedded in the physical universe? How can there be sensory qualities, consciousness, freedom, science and art, friendship, love, justice - all that which gives meaning and value to life - if the world really is more or less as modern science tells us it is? This is the problem that is tackled by this book. The solution proposed is that physics describes only a selected aspect of all that exists - that aspect which determines the way events unfold. Sensory qualities, inner experiences, consciousness, meaning and value, all these exist but lie beyond the scope of physics, and of that part of science that can be reduced to physics. Furthermore, these human features of the world are to be explained and understood, not scientifically, but "personalistically," a kind of understanding distinct from, and not reducible to, science. This view that the world is riddled with what may be called "double comprehensibility" leads to a proposed solution to the philosophical mind/body problem, and to the problem of free will; it leads to a reinterpretation of Darwin's theory of evolution, and to an account of the evolution of consciousness and free will. After a discussion of the location of consciousness in the brain, the book concludes with a proposal as to how academic inquiry might be changed so that it becomes a kind of inquiry rationally designed to help humanity create a more civilized human world in the physical universe.