I stumbled on this word while looking for something else. The definition given
in this book review is much wider than the one give in my dictionary:

In this exciting work on the cutting edge of
scientific knowledge, Henry Gee, Chief Science
Writer at Nature, tells the story of a recent
revolution in palaeontology. For the first time, all
of us can share in the wonder of a deceptively
simple idea known as cladistics, the science of
comparison. The cladistics revolution is
transforming almost everything we know about the
science of life in Deep Time--the billions of years
in which life has evolved on this planet. It provides
insights and solutions to questions about ourselves
ordinarily considered beyond the realm of science.

it's taxonomic jargon; you could define it as the Taxonomic science of comparison via ancestral lineages.

Dear tsuwm: The writer makes it sound as though he means the whole
science of life, not just lineages.

In my view, the book-reviewer quoted tends to hype. As far as I remember (I used to subscribe to Nature), cladistics is a tool used to trace the history of living things from fossils fragmented in time and space. It is subject to just as much controversy as other fields of science.

as though he means the whole science of life

I don't think so. The cladistics revolution would just be a natural outgrowth of the advances in genetic sciences that allow us to make connections between different species in more ways and with greater accuracy than in the past. These advances have allowed us to greatly increase our understanding of the the way life forms have evolved.

Well, to me it sounds like the statistical measurement of how much clothing the population is wearing ...