7.2 Nature conservation
The modern definition of nature derives from the development of the science of ecology and its application to conservation issues. There have been at least six developmental stages: formative, descriptive, quantitative, dynamic, interventionist and moralistic.   
Formative phase
Several people stand out as major influences on ecological thinking long before the field coalesced into a unified discipline. Charles Lyell, the father of geology, in his book Principles of Geology (1830) helped overturn Linnaean concepts of a static nature under strict divine rule. Lyell was among the first to understand that geological change occurred gradually over eons, that species dispersed actively around the world, and that competition was a driving force in evolution. Lyell was a major influence on Charles Darwin. In On the Origin of Species (1859), Darwin built upon Lyell and advanced natural selection as the primary mechanism of evolution.
Henry David Thoreau was contemporary with Darwin and one of the first naturalists to understand succession as a major pattern of change in ecosystems. Thoreau also was one of the first to glimpse the loss of species and habitat and its cultural ramifications at the onset of the Industrial Revolution. Another American, George Perkins Marsh, contributed a pioneering global account of humanity's role in reducing the capacity of Earth to support life in Man and Nature (1864).
Descriptive phase
Ecology in the early decades of the 20th century was a descriptive, holistic science. The key themes were the balance of nature and succession toward a stable, climax state. Plant ecologist Frederick Clements dominated the field with his idea of natural communities as interdependent superorganisms evolving collectively.
Quantitative phase
By the time A. G. Tansley coined the term "ecosystem" in 1935, Clements's views were falling from favor. Qualitative, descriptive ecology was being superseded by a more quantitative ecology of energy and nutrient flows, food chains, and trophic levels. Natural history was eclipsed by mathematical models.
Dynamic phase
In the 1940s, Raymond Lindeman developed important theories on energy flows in ecosystems and G. E. Hutchinson refined the concept of feedback and constructed some of the first mathematical models of populations. Later ecologists built on these fundamentals with Eugene Odum (ecosystem characteristics), Frank Bormann and Gene Likens (nutrient flows), and Robert MacArthur (population models) making key contributions.  Where in the past scientists (and environmentalists) characterised ecosystems as orderly and relatively balanced, these new  viewpoints emphasize systems as dynamic, changing at different space and time scales, and full of uncertainty. Nature is not always in "balance"; and changes are difficult, sometimes impossible, to predict.
No longer was the study of nature just about numbers of species or types of ecosystems. The new emphasis on non-equilibrium processes (especially natural disturbances such as fires and floods) resulted in a comprehensive definition of nature that includes not only the diversity of all life forms from genes to landscapes, but also the fundamental patterns and processes of that produce patterns in life forms over time and in space. 
Phase of intervention
Since the late 1970s, as knowledge of the growing influence of human economic development on natural patterns and processes has accumulated, the 'biodiversity crisis' emerged.  A new ecological world view appeared in which political and economic intervention is directed to support conservation management.  The management of biodiversity alongside world economic growth is at the heart of policies of sustainable development.
Phase of moral evaluation
Whether trees, or animals, ought to be preserved 'for their own sakes' wrote the social historian E.M. Trevelyan is an interesting question on which different opinions might be held. But the argument for the preservation of natural scenery and the wild life of English fauna and flora may be based on motives that regard the welfare of human beings alone, and it is those arguments alone that I wish here to put forward. To preserve the bird life of the country is required in the spiritual interests of the human race, more particularly of the English section of it, who find such joy in seeing and hearing birds'.
As Trevelyan implied, it was not for the sake of the creatures themselves, but for the sake of men, that birds and animals would be protected in sanctuaries and wild-life parks. In 1969 the United Nations and the International Union for the Conservation of Nature defined 'conservation' as 'the rational use of the environment to achieve the highest quality of living for mankind.'
But even in the early modern period there were some perhaps hypersensitive persons who were prepared to go further than this. For them it was increasingly difficult to accept the primacy of human needs when to do so involved inflicting pain on domestic animals or eliminating whole species of wild ones. In more recent times these difficulties have been widely perceived. Today there are writers of books who refer to the extermination of the wolf as a 'pogrom' or 'holocaust'; and the law journals carry articles on whether trees have rights.
The early modern period had thus generated feelings which would make it increasingly hard for men to come to terms with the uncompromising methods by which the dominance of their species had been secured. On the one hand they saw an incalculable increase in the comfort and physical well-being or welfare of human beings; on the other they perceived a ruthless exploitation of other forms of animate life.