Sex and Death: Evolution Undefined

Conceptually, evolution theory seems simple: 

Individual organisms vary in their various traits. Some are better adapted to survive in their environmental niche than others, because they possess (more and/or more highly) adaptive traits. Because the better adapted organisms succeed disproportionately in begetting offspring, the adaptive traits become more prevalent in the next generation. Over many generations, this process of filtering and concentrating the heritable traits of organisms has spawned diverse forms of life, with genes transferring traits from parents to offspring. 

I think I squeezed in all the relevant keywords.

This description works at an abstract level, but close up, the theory's fuzziness becomes apparent. What is a niche, anyway? Or an adaptation? Or a trait? Or an organism? Or a gene?

These questions make Kim Sterelny and Paul E. Griffiths’ Sex and Death a worthwhile read for anyone interested in probing the rigor of the received view. It turns out that researchers in the biological sciences have yet to settle on agreed-upon definitions of the above terms. Evolution theory is compromised by its own hazy vocabulary.

For example, do ecological niches exist independently of the organisms that fill them? Or are they defined by their occupants? Is average temperature sufficient to define a niche? Temperature and water salinity? Temperature, salinity, and the density of predators? “Niche” is, if not an essential, at least a supporting concept in evolution theory, but it amounts to a conceptual blur. Nobody can say what the necessary and sufficient conditions are to define a “niche.”