Mr Morton's thesis is that modern biology has become so focused on the movement of information, in the form of genes, that it has neglected the processes needed to move that information around: in essence, thermodynamics. People talk glibly of "using up" energy when in fact they are doing no such thing. What is actually used up is order. An energy flow drives the process, but it is disorder (or "entropy", to use the jargon) that changes, by increasing.
A highly ordered system such as a living thing thus needs an abundant supply of negative entropy (or unentropy, or call it what you will) to maintain its internal order. That negative entropy comes from the sun and is captured by photosynthesis, which uses light to split water molecules and combines the resulting hydrogen with carbon dioxide to form sugars. The sugars are a store of negative entropy that can be used elsewhere. The waste product, conveniently for the animals of Earth, is oxygen.
The book, then, is in part a refrain in praise of photosynthesis, the Earth's energy and order currency-exchange market. It is also an entertaining history of how the subject arrived where it is today...
I love the Economist.