A number of international conservation donors support efforts to encourage conservation indirectly by subsidizing commercial activities. Such plans beg two questions. First, if commercial ventures are expected to be profitable, why is external financing necessary for their initiation? Second, if commercial ventures are not expected to be profitable, could not greater incentives for conservation be generated by making direct payments? We examine these questions in detail. While we find that the practical impediments to instituting a direct payment programme may be substantial, the practical impediments to instituting any effective conservation programme may be substantial. On balance, there is a strong case to be made for greater experimentation with direct payment schemes than heretofore.

Economic models for assessing costs of greenhouse gas abatement can be classified as macroeconomic (top-down) models or micro (bottom-up) models. As yet little attention has been focused on the modelling of developing countries. This paper proposes a methodology for integrating the two approaches and illustrates it with the example of India. The results show that a carbon tax would have limited effectiveness in controlling carbon emissions. Investing carbon tax revenues in carbon-abating technologies can give substantial carbon savings. The costs of carbon abatement using the integrated model are higher than those predicted by other global models with India as a sub-region.

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.

The sustainability of natural resource use is influenced by population pressure, but this exercises a much less critical impact than the overall policy framework. In Colombia, various agricultural and other policies whose effect is to constrain the poor's access to land encourage environmental degradation. A case is made in favour of the new land reform process that Colombia is launching.

The search for sustainability indicators should be guided by a theory of sustainable development (SD). In this paper we investigate two such theoretical frameworks and the indicators that they suggest. Indicators associated with weak sustainability are characterized by aggregative indicators such as green national income. We conclude, however, that a more promising offshoot of green accounting is measures of genuine savings (i.e. savings adjusted for loss of assets). To achieve SD, genuine savings rates must not be persistently negative. Strong sustainability indicators accord a more central role to the conservation of critical natural assets within the broader goal of prudently managing a nation's portfolio of assets over time. We discuss two approaches—carrying capacity and resilience—and conclude that, while measures of resilience are potentially attractive, more research is required regarding the resilience–SD link. However, an important conclusion that we can make is that, even in an economy operating under a strong sustainability regime, genuine savings are still key indicators of SD and are complementary to measures of changes in stocks of critical natural assets.

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.