What implications does Darwinism have for our attitude towards the environment? At first sight, it might look as though Darwinism is not friendly towards environmental concerns. Darwinism is often thought to paint a picture of ruthless competition between, as well as within, species. Moreover, Darwinism may be thought to encourage a view of the environment as something to be exploited for self-interested gain. The present paper proposes a more positive view. It will be argued that mutual benefit is just as central to evolution as is competition. This will be argued for partly drawing on the work of Lynn Margulis, who makes a case that many of the major transitions in evolution came about through the setting-up of symbiotic relationships, and that what we often think of as an ‘organism’ is in fact a collection of symbionts. Moreover, a proper understanding of evolution reveals the intimate connection between an organism and its environment. The organism is partially constituted by its environment, so that in radically altering the environment an organism is potentially damaging itself. Recent work in evolutionary developmental biology has revealed previously unsuspected deep structural similarities, as well as co-operation, across a wide spectrum of living things. Thus, it will be argued, there is an environment which has shaped, and been shaped by, terrestrial life as a whole. It will be concluded that, firstly, a view that sees our duties towards the environment as deriving from our duties towards other humans would lead to a strongly conservationist programme of action; and secondly, a view of the natural world as in a strong sense ‘ours’, where this means belonging to life as a whole, makes good sense in the light of evolutionary theory.