Extreme environments affect the responses of organisms at many levels, from the structure of their proteins and membranes, to the ways in which they carry out their lives, their interactions with their environment and other organisms, and their life history, behaviour and evolution. While it would be an unhelpful truism to say that organisms are adapted to live in the places in which they live, there are some particular features of the biology of organisms in extreme environments. The extreme conditions which they face affect all aspects of their biology – theirs is an extreme biology which may give us some important insights into the nature of life in general. In this chapter, I will explore whether we can see any general patterns for life in extreme environments. But, first, let us revisit what we mean by an extreme organism.

WHAT IS EXTREME, REVISITED

In Chapter 1, I proposed a definition of extreme organisms by reference to the life boxes of organisms: the range of physical conditions under which they exist (the non-biological features of their ecological niche). I also proposed that we could recognise two groups of extreme organisms. Extremophiles have life boxes which are beyond the limits of those of the majority of organisms. Cryptobiotes have life boxes which are the same as, or substantially overlap, those of the majority of organisms, but, when the conditions of their environment deteriorate beyond those under which they can maintain their life processes (metabolism), rather than dying (as do most organisms), they cease metabolism and await the return of favourable conditions.