The paper analyses the conflict between wildlife conservation and its accompanying land-use in an East African context. In the model there are two agents. First, there is an agency managing the wildlife and the habitat of the wildlife, which is referred to as parkland. On the other hand, there is the group of agro-pastoralists living in the vicinity of the wildlife habitat, whose land-use is referred to as rangelands. The parkland is used for tourism production and hunting, while the rangelands are used for agro-pastoral production. Both agents will find it beneficial to expand their land-use, so there is a land-use conflict. This is analysed in two steps. First, social optimality is studied; then we study the utilization of the wildlife and its accompanying land-use when there is no unified resource policy and the park agency follows its self-interest. The effects on the two different management schemes of changing economic conditions, such as the recommendations of the CITES convention and a programme subsidizing agro-pastoral production, are discussed.

International transfers to developing countries are sometimes advocated on the ground that they contribute to tropical forest conservation. Here we demonstrate that the effectiveness (and attractiveness) of this instrument is reduced if the restrictive assumption of deterministic prices is relaxed. With stochastic prices, the steady-state forest stock in the absence of transfers is greater, implying that the marginal benefit of additional hectares conserved is less. In addition, the ‘wealth effect’ of transfers counteracts the ‘freeing-up effect’, which implies that per unit of subsidy fewer hectares of tropical forest are protected. Both effects reduce the attractiveness of transfers as a policy instrument for Western governments to combat tropical deforestation.

Although improvements in human health represent a crucial aspect of development worldwide, many trends associated with development and global change appear to be reducing health security. In this article, we define the human epidemiological environment and describe key biophysical, economic, sociocultural, and political factors that shape it. The potential impact upon the epidemiological environment of aspects of both development and global change are then examined: the influences of human population size, mobility, geographic distribution, and nutritional status; modernization; loss of indigenous medicinal knowledge; microbial evolution of antibiotic resistance; land conversion and biodiversity loss; agricultural intensification; stratospheric ozone depletion; and climate change. Human vulnerability to infectious disease is often strongly and deleteriously influenced by ongoing, intensifying changes in these factors. An unprecedented level of communication and cooperation between experts, institutions, and nations is required to respond to the increasing threat of epidemic disease, which points to a promising area for enhanced interdisciplinary collaboration.

Daily and Ehrlich have described the current state of our epidemiological environment in chilling detail. While their point is that human beings interact and affect the epidemiological environment in a variety of ways, the development of antibiotic resistance in bacteria strikes us as one aspect that we can begin to analyse immediately. The evolution of resistance to antibiotics is a function of their use by humans. The more we use, the more selective pressure is placed upon bacteria to develop resistance. This is further complicated by how they are used. Both the duration and the amounts used affect the change in the level of resistance. Finally, the primary feature driving the concern over the use of these drugs is that the evolution of resistance makes these ‘miracle’ drugs exhaustible. We can try to develop new and better antibiotics, but it is uncertain how successful we will be and how expensive they will be if we are successful.

Evolutionary biology is above all concerned with the way life on earth and its setting change over time. The problem posed by Daily and Ehrlich, of how humans, the myriads of organisms that humans carry around in their bodies and the stage on which they interact have been changing over time, may then be viewed as one of the concerns of this discipline.

Epidemiological environment (EE) could be denned as a set of conditions and processes, both physical and social, that influence the interaction between human beings and disease agents. The human epidemiological environment is shaped by various aspects of development and global change, viz. the influences of human population size, mobility, geographic distribution, urbanization, and nutrition status; modernization (macro-and microeconomic enterprise); loss of indigenous medicinal knowledge; microbial evolution of antibiotic resistance; land conversion and biodiversity loss; agricultural intensification; stratospheric ozone depletion; and climatic change (Daily and Ehrlich, 1995). Health status is affected greatly not only by economic development (e.g. by policies influencing per capita income and its distribution), but also through changes in EE.

The Daily and Ehrlich article presents, as expected, a detailed account of the myriad interrelationships between development, global change (notably population growth and global warming), environment and disease. It is a first-class exposition of what we know, and it would be invidious to raise a critical eyebrow about it. In this comment, I take a look at what we do not know—what we know we do not know, what we ought to know, and what we do not know we do not know. Hence it is a piece that reflects speculation supreme, albeit informed (and hopefully inspired) speculation.

In their article, Daily and Ehrlich have discussed a number of important recent trends associated with development and global change that appear to be reducing health security. Besides their immediate epidemiological implications, most issues raised in the paper have economic implications. However, from the point of view of the methodology of economics, despite the paper's being illuminating on the issues discussed, the immediate notable aspect is the lack of a model or framework with/within which those issues are being analysed. Indeed, it is very hard to think of a single framework which would be all-encompassing enough to be applicable to the analysis of all the issues raised in the paper. But I submit that these issues can be adequately addressed and analysed using the rather simplistic model of production and consumption,1 which is the core of all economic analysis. In what follows, I will pick only a few of the issues raised in the paper and put them within the context of this basic economic model, so as to examine their economic implications.

Our environment is complex, but it is understandable through rational investigation, and it is not to be feared. So wrote Titus Lucretius Carus of the nature of things some thirty human lifetimes ago—not so long, really. About species evolution Lucretius thought much, guessed well, and worried little. About microparasitic evolution he knew nothing. Would he have feared it? Should we fear it now?

William Nordhaus has gone further than any economist to date at building a dynamic integrated model of the world’s climate and economic systems, with some one-way linkages to agricultural systems and ecosystems. Managing the Commons is an admirably readable description of this effort which, in his words, ‘balances the costs of emissions controls in energy policies and other areas against the impacts to agriculture, coastlines, and ecosystem values’. In addition to a detailed description of the Dynamic Integrated Climate and the Economy (DICE) model and several scenarios produced by the model, the book includes large sections on sensitivity analysis of the model’s parameter uncertainty and an analysis of the value of information gained at various times in the future to the decision process.