The Significance of Symbiosis

Individuals of different species form persistent associations from which they all benefit. These relationships are symbioses. The core pur­ pose of this book is to assess the biological significance of symbioses and to investigate the processes by which symbioses are formed and persist in both evolutionary and ecological time. Symbioses are biologi­ cally important because they are widespread and dominate the biota of many habitats. I address this aspect of the biological significance of symbiosis later in this chapter. For the present, I suggest that any doubting readers should “look out of the window” and list every or­ ganism they can see. I can guarantee that most, probably all, organisms on the list are a product of symbiosis. The prevalence of symbioses is not, however, the only reason why symbioses should be important to biologists. An additional reason is that symbiosis challenges two widely accepted tenets of biology: the universality of descent with modifica­ tion in evolution, and the primacy of antagonism in interactions among organisms. I will start by explaining these challenges.