We are biologically predisposed to provide for our offspring and may try to ensure that this provision continues after our death. However, our interactions with other members of society are wide-ranging and many people leave legacies to benefit the wider community.
All species alter their environment to some extent because they do not live in isolation from one another. The study of the interactions between plants, animals and their environment is known as ecology.
The relationships between plants and animals can be expressed as food chains and food webs. In both cases the primary producers are plants and they provide all the energy within the system (chain or web) by a process called photosynthesis. The systems can support fewer carnivores than herbivores because energy is lost from one trophic level to the next. This idea is shown diagrammatically as the pyramid of numbers. Because relationships within a food web are variable and complex we cannot accurately predict the effect of losing one species from the web.
Human activity has been responsible for some extinctions and other deleterious changes to habitats. These changes have not always been the result of thoughtless or selfish behaviour; often intentions were worthy but outcomes were not as predicted. The importance of genetic diversity is demonstrated here in relation to Dutch Elm disease. The need to retain genetic diversity in plants, used for food and medicine, is recognized in such initiatives as the Kew Millennium Seed Bank Appeal.
Pollution damages organisms, including ourselves. The link between air pollution and health is hard to quantify. It has to be extrapolated from epidemiological studies and is complicated because susceptibilities vary. Many pollutants are produced by industrial processes and it is expensive to reduce their emission into the environment. There are also difficulties in predicting the long-term effects on climate of airborne pollutants such as CFCs and carbon dioxide. These scientific uncertainties, together with the financial constraints, make it difficult to obtain international cooperation to reduce emissions. Not all pollutants are byproducts of industry; some, such as pesticides and certain plastics, were developed to improve the quality of life.