Chemical species, evolutionary

In this introductory chapter, a broad overview is given of the history of chemical warfare on earth, and the compounds, species, and mechanisms involved. The impact of human-made compounds on the environment, which is the subject of this book, is an extremely recent event in evolutionary terms. It is important to take a holistic view, and to see the effects of human-made pollutants on the environment against the background of chemical warfare in nature. 

As explained in Chapter 1, the toxicity of natural xenobiotics has exerted a selection pressure upon living organisms since very early in evolutionary history. There is abundant evidence of compounds produced by plants and animals that are toxic to species other than their own and which are nsed as chemical warfare agents (Chapter 1). Also, as we have seen, wild animals can develop resistance mechanisms to the toxic componnds prodnced by plants. In Anstralia, for example, some marsupials have developed resistance to natnrally occnrring toxins produced by the plants upon which they feed (see Chapter 1, Section 1.2.2). 

The Protos warfare on their Lept neighbors depended heavily on chemicals, but ants are by no means unique in making extensive use of chemicals for communication and warfare. From one-celled organisms to complex plants and animals, many living creatures do the same. As species develop over evolutionary time, it is relatively easy for them to adapt their cellular machinery to producing chemicals for communication, warfare, and other purposes. These chemicals facilitate the way of life of organisms spread all across the biological spectrum. 

Other chemical studies did not find sex or seasonal differences in the composition of mammalian scents. No sex differences in the composition of mixtures of volatile compounds from glands have been found in the brushtailed possum, Trichosurus vulpecula, for example. The same profiles of low-molecular-weight branched carboxylic acids were found in paracloacal gland secretions of males and females (Woolhouse etal., 1994). Branched carboxylic acids also occurred in the preorbital gland secretion of a female sika deer [Ccrvus nippon) (Wood, 2004). Comparisons between the compositions of secretions in different, related species permit assumptions about functional adaptations and possible evolutionary pathways. Such comparisons are available for five Mustek species (Brinck etal., 1983), and three species of hyenas (Buglass etal., 1990). 

In other words, most organisms will have evolved to survive with chemical diversity in their environment. An organism exposed to a new natural or synthetic chemical will simply have one extra chemical in its environment. For reasons discussed in Chapter 5, the chances are extremely small that the new chemical will possess the particular properties that endow it with the potential to reduce the fitness of the organism. For billions of years, individuals of all species will, at intervals, have been exposed to a chemical that they have not encoimtered before. This will be a situation that might have happened many times in the lifetime of some individuals. It is certainly a circumstance that will have arisen many times in the recent evolutionary history of many species when species have increased their habitat range with the result that they inevitably encounter NPs that are novel to them. In other words, being exposed to new chemicals is a normal part of life. A good example of this fact comes from humans. Humans have been very... 

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