Editorial

The general public has a limited understanding of the concept of biodiversity. Even the more informed regard it as a simple tally of all the plant and animal species. However, biodiversity is a systems concept that refers to the variation of life at different levels of organisation (Figure). It refers to the function of the species known as the "environmental engineers", which provide us with clean air and water, and fertile soils, as well as much of our food, shelter, medicines and industrial products.

The value of biodiversity to human health has been highlighted in a recent forum.⁵ The most obvious benefit is the large proportion of the pharmaceutical armamentarium that is derived from the natural world. Over 50% of commercially available drugs are based on bioactive compounds extracted (or patterned) from non-human species.⁶ Of the top 100 prescribed drugs in the United States, 55% are natural or semisynthetic, and these percentages are even greater for drugs used for respiratory, dermatological, gastrointestinal, gynaecological and infectious diseases.⁶ A recent example is taxol, first identified in yew trees (Taxus) of North America. It is one of the most promising drugs for the treatment of ovarian and breast cancer.⁷ Importantly, taxol has now been isolated from fungi associated symbiotically with the Wollemi pine, a living fossil discovered recently near Sydney.

Furthermore, it is not generally acknowledged how widespread the use of traditional medicines is in developing countries. It has been estimated that 80% of the world's population rely on plant-based medicines for their primary health care.⁸ The value of this ethnobiological knowledge is also recognised by pharmaceutical company researchers, who use this information source routinely in the acquisition phase of drug discovery. Of the 265000 species of flowering plants, it is estimated that less than half of 1% have been screened for their beneficial pharmaceutical properties.⁹

It has been argued that the loss of species will also result in loss of medical models which can increase our understanding of human physiology and disease.¹⁰ Numerous examples exist in species closely related to humans. However, examination of invertebrates is also yielding important models, such as a species of sea squirt (Molgula manhattensis) that develops stones in kidney-like organs. Study of this species has increased our understanding of how both uric acid and oxalate kidney stones form in humans.¹⁰

The consequences of such losses pale in comparison with the dire effects of the emergence and re-emergence of infectious diseases. In many cases these events are attributed to the erosion of biodiversity and human ecology. Any disturbance of ecosystems can result in loss of species diversity, a population explosion of competitive species, and host switching of pathogens from primary hosts to humans. For example, the emergence of hantavirus pulmonary syndrome in the south-western United States can be traced to an explosion in the population of deer mice,¹¹ the natural host of the virus, and the subsequent exposure of humans to the excreta of the mice. A similar population explosion of mice in agricultural areas in South Australia occurred in 1993, and, although no infectious diseases were associated with this outbreak, it serves as a warning.

The capacity of pathogenic microorganisms to switch hosts is well known. This, coupled with their high reproductive rate and mutation rate, increases their potential to cause serious illness and death in humans. For example, HIV has most likely switched hosts, possibly originating from a mutant simian immunodeficiency virus strain. The outbreak of infection caused by a morbillivirus in horses and humans in Brisbane in 1994,¹² resulting in fatalities in both species, is an Australian case that indicates that such switches can occur in any country.

Unfortunately, biodiversity loss occurs incrementally and is not apparent to most people. The extent of this loss is measured in terms of species extinction and destruction of habitats. Some scientists estimate that we are losing 100 species per day and that more than a quarter of all species may vanish within 50 years. This rate of loss would be at least 1000 times greater than modelled natural extinction rates. Some studies indicate that as many as 60000 plants could be extinct by the middle of next century.¹³ The disappearance of vertebrates continues unabated, with Australia having the worst mammal extinction record in the world.² But the most severe losses are occurring among the invertebrates, most of which are undescribed and yet play critical roles in ecological processes. The habitats of these species are being destroyed at an alarming rate. In the 20 countries with the greatest identified biodiversity, it is predicted that about a quarter of the remaining natural habitats will be cleared by the middle of the next century.¹⁴ Australia has an appalling record in this regard, and in the past decade has been identified as one of the worst land-clearing countries in the world.¹⁵

Aside from land clearance, the major threats to biodiversity are the impact of alien species, the indiscriminate harvesting of species, and the effects of pollution, urbanisation, and climate change. Fundamentally, living in an ecologically sustainable way is essential, and there is an urgent need for humans to accept that natural resources are limited and, once exploited, are unlikely to be repaired. There is a pressing need for an assessment of human population and consumption.¹⁶

Causation in science is empirically difficult to establish. None the less, the argument is persuasive that human population size, urbanisation and malnutrition in sections of the population enhance the emergence of diseases. Human health and well-being can be seen as indicators of the health of global biodiversity. The signs of a difficult future are gathering.

The conservation ethic advocated by biological scientists needs to be embraced by all sectors of the community. There is a unique opportunity for the healthcare sector to promote the principles of biodiversity, conservation and sustainable development.¹⁷ The obvious links between human health and biodiversity have not been exploited. It would be timely for major medical associations and members of the medical profession to be engaged in public debate on this issue and to support the need for an education program in schools, among doctors and for the general public.

Gerry Cassis
Centre for Biodiversity and Conservation Research
Australian Museum, Sydney, NSW
GerrycATamsg.austmus.gov.au

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2. Commonwealth of Australia. Australia, State of the Environment. An independent report presented to the Commonwealth Minister for the Environment by the State of the Environment Advisory Council. Melbourne: CSIRO Publishing, 1996.
3. Garret L. The coming plague. Newly emerging diseases in a world out of balance. London: Virago Press, 1994.
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7. Nicolaou KC, Guy RK, Potier P, et al. Taxoids: new weapons against cancer. Sci Am 1996; 274(6): 94-98.
8. Farnsworth NR, Akerele O, Bingel AS, et al. Medicinal plants in therapy. Bull World Health Organ 1985; 63: 965-981.
9. Cox PA. Biodiversity and human health conference. Session III: Biodiversity and traditional health systems. Washington, DC: Smithsonian Institution, 1995.
10. Chivian E. Global environmental degradation and biodiversity loss: implications for human health. In: Grifo F, Rosenthal J, editors. Biodiversity and human health. Washington DC: Island Press, 1997: 7-38.
11. Dobson A, Campbell MS, Bell J. Fatal synergisms: interactions between infectious diseases, human population growth, and loss of biodiversity. In: Grifo F, Rosenthal J, editors. Biodiversity and human health. Washington, DC: Island Press, 1997: 87-110.
12. Murray K, Selleck P, Hooper P, et al. A morbillivirus that caused fatal disease in horses and humans. Science 1995; 268: 94-97.
13. Farnsworth NR. Screening plants for new medicines. Wilson EO, Peters FM, editors. Biodiversity. Washington DC: National Academy Press, 1988: 83-97.
14. United Nations Environment Programme. Global environment outlook. Oxford: Oxford University Press, 1997.
15. Glanznig A. Native vegetation. Australia still in top ten land clearing country club. Life Lines: Bulletin of the Community Biodiversity Network, 1998; 4(2): 14.
16. Cohen JE. How many people can the Earth support? New York: WW Norton and Company, 1995.
17. Shearman D, Sauer-Thompson G. Green or gone. Health, ecology, plagues, greed and our future. Kent Town, South Australia: Wakefield Press, 1997.

Reprints: Dr Gerry Cassis, Centre for Biodiversity and Conservation Research, Australian Museum, 6 College Street, Sydney, NSW.

Photograph courtesy Land Information Services Division, Department of Primary Industries, Water and Environment, Hobart, Tasmania.

©MJA 1998
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