In chapter 2's entry he covers some of the ground I did in one of my earlier posts - about how Darwin views the definition of species. I particularly noted his comment:
Here's some advice for anyone agonizing over creating a perfect, all-encompassing species concept: chill out. Pretty much any biological category you care to think of has fuzzy boundaries. Genomics is making the concept of the gene more problematic. Colonial, clonal and modular organisms, such as slime moulds, aspen, and the vast underground mycelia of some fungi, make the concept of the individual tricky to pin down. The giant mimivirus blurs the line between viruses and cellular life. There's been a long debate over whether viruses themselves should be classed as living things. And it's proved impossible to come up with a list of properties that unambiguously define life.I shall post, asking for comments on thoughts about the utility of the terms...will at least enlighten me!
This does not mean that terms such as species, gene, individual or life are useless. In many or most cases it'll be obvious whether the thing or group of things you're looking at belongs in a particular category or not.