Biodiversity and health
Human health in any given environment depends on the diversity of organisms that the environment supports. At a recent conference in Galway, evidence was presented to suggest that development that damages biodiversity could have adverse effects on human health by encouraging the spread of diseases. Carlos Corvallan of the WHO argued that it would not be possible to meet the UN Millennium development goals (on reducing child poverty and fighting major global killer diseases) without reducing the rate of destruction of the ecosystem.(New Scientist, 3 Sept 2005, p10)
The health of an ecosystem can usually be indicated by the variety of life forms that it supports. "Biodiversity" refers to the variety of forms of life. The term is a contraction of biological diversity.(Definition on biodiversity from Stanford University) Because of the interdependence of life forms, the more life forms can survive the better it is for the health of each species.
This is partly because an ecosystem which supports many varied organisms is more resilient in its response to environmental change. As a practical example, a farm that only produces one crop will be ruined if that crop is struck by a specific disease. This was the case in Ireland, in the 1840s, at the time of the potato famine. A spread of potato blight led to widespread starvation when most Irish family farms relied on the potato as their staple crop. The boll weevil in 1930s Southern USA destroyed cotton production, with disastrous effects on the rural economy. Organic farmers are well aware that a smallholding with a variety of crops will not suffer the soil degradation and vulnerability to pest and diseases that can result from monoculture.
However, the ecologists' arguments for biodiversity have often been treated as relating to the aesthetics of the planetary environment. Biodiversity may be seen as something of a luxury - fine for National Parks, but an obstacle to development.
At a recent conference in Galway, Ireland, according to the report by Linda Geddes, in New Scientist of September 5, 2005, several scientists argued that there is growing evidence that biodiversity has a direct impact on human health.
Studies of Kenyan lakes, carried out by Kristensen, showed that, in the areas of Lake Victoria with the most human activity, the diversity of the aquatic snail populations was reduced. The snails that thrived were those carrying bilharzia - a disease with a severe impact on human populations. In Lake Nyasa, pollution and overfishing had also encouraged an explosion in the population of the bilharzia-carrying snails and a reduction in the number of snail species that do not carry disease. The effects on the health of the people who live in these areas is to spread a disease that weakens whole populations, with effects including blindness and death.
Further evidence from Western Australia, presented to the conference by Jardine, showed that the effects of intensive land clearance - soil becoming waterlogged and subject to high levels of salinisation - had encouraged the growth of a specific salt-tolerant species of mosquito, which carries the deadly Ross River disease. The impact of this has not translated into adverse effects on human health but has the future potential to do so.
The conference papers therefore support a view that development that reduces the diversity of natural organisms in an area may encourage the spread of the most aggressive species, by wiping out the natural constraints on their expansion. When these species carry diseases that affect human health, diseases that were previously relatively uncommon or limited in their impact may threaten large numbers of people.
Some useful links on biodiversity:
National Biodiversity Network (UK)
The Convention on Biological Diversity
Natural History Museum world map on biodiversity
Biodiversity and human health
Biodiversity and human health - papers from a 1996 conference