Hi Hossein:

This theory is part of a long history of looking at dynamics of inheritance, development, and intra-organism conflict. Two recent books with related material are Leo Buss's 1988 "The Evolution of Individuality" and Peter Godfrey-Smith's 2009 "Darwinian Populations and Natural Selection." Buss's book focuses on the topic; Godfrey-Smith's book looks at how germ/soma distinctions (amongst other factors) affect intra-organism competition and more generally how the germ/soma distinction affects the 'Darwinian' nature of systems.

There are likely many places to look to answer your question, but these topics come to mind as particularly relevant in contemporary evolutionary theory.

Hope this helps.

-David

p.s. James Griesemer also has several recent papers discussing the germ/soma distinction in the context of a contemporary understanding of development, inheritance, and reproduction.

To put it quite simply, I think, is because it the germ plasm that provides the continuity of information, not the somatic tissues. I think most other details of its importance to evolutionary biology can be tied down to this. Individuals don't evolve, populations/species evolve.

August Weismann developed this theory to distinguish between the effects of the environment (on somatic cells) and the absence of such actions on germ cells (germ plasm as it was then called). Weissman sought to counter Lamarck's assertion that acquired characteristics (eg through an animal's use/disuse of actions) could be passed on to subsequent generations. Lamarck presented the first full developed theory of evolutionary change through interaction with the environment leading to new species and increasing complexity. We now know that in their specifics both were wrong, but for different reasons. Lamarck lacked a mechanism through which such acquired characteristics could become heritable (not through activity but through exposure that changes the epigenome). Weissman because his 'study' of shortening tails of mice did not test the inheritance of a biologically important trait. Weissman was important in the development of the Modern Synthesis and evolutionary biology in general because of his emphasis on heritable units being contained in the germ plasm. This laid the groundwork for the science of genetics.