Myriapods (e.g., centipedes and millipedes) display a simple homonomous body plan relative to other arthropods. All members of the class are terrestrial, but they attained terrestriality independently of insects. Myriapoda is the only arthropod class not represented by a sequenced genome. We present an analysis of the genome of the centipede Strigamia maritima. It retains a compact genome that has undergone less gene loss and shuffling than previously sequenced arthropods, and many orthologues of genes conserved from the bilaterian ancestor that have been lost in insects. Our analysis locates many genes in conserved macro-synteny contexts, and many small-scale examples of gene clustering. We describe several examples where S. maritima shows different solutions from insects to similar problems. The insect olfactory receptor gene family is absent from S. maritima, and olfaction in air is likely effected by expansion of other receptor gene families. For some genes S. maritima has evolved paralogues to generate coding sequence diversity, where insects use alternate splicing. This is most striking for the Dscam gene, which in Drosophila generates more than 100,000 alternate splice forms, but in S. maritima is encoded by over 100 paralogues. We see an intriguing linkage between the absence of any known photosensory proteins in a blind organism and the additional absence of canonical circadian clock genes. The phylogenetic position of myriapods allows us to identify where in arthropod phylogeny several particular molecular mechanisms and traits emerged. For example, we conclude that juvenile hormone signalling evolved with the emergence of the exoskeleton in the arthropods and that RR-1 containing cuticle proteins evolved in the lineage leading to Mandibulata. We also identify when various gene expansions and losses occurred. The genome of S. maritima offers us a unique glimpse into the ancestral arthropod genome, while also displaying many adaptations to its specific life history.

Over the last twenty years, there has been rapid growth of a new approach to understanding the evolution of organismic form. This evolutionary developmental biology, or 'evo-devo', is focused on the developmental genetic machinery that lies behind embryological phenotypes, which were all that could be studied in the past. Are there any general concepts emerging from this new approach, and if so, how do they impact on the conceptual structure of traditional evolutionary biology? In providing answers to these questions, this review assesses whether evo-devo is merely filling in some missing details, or whether it will cause a large-scale change in our thinking about the evolutionary process.

What determines the direction of evolutionary change? This book provides a revolutionary answer to this question. Many biologists, from Darwin's day to our own, have been satisfied with the answer 'natural selection'. Professor Wallace Arthur is not. He takes the controversial view that biases in the ways that embryos can be altered are just as important as natural selection in determining the directions that evolution has taken, including the one that led to the origin of humans. This argument forms the core of the book. However, in addition, the book summarizes other important issues relating to how embryonic (and post-embryonic) development evolves. Written in an easy, conversational style, this is the first book for students and the general reader that provides an account of the exciting new field of Evolutionary Developmental Biology ('Evo-Devo' to its proponents).

The number of leg-bearing segments in centipedes varies extensively, between 15 and 191, and yet it is always odd. This suggests that segment generation in centipedes involves a stage with double segment periodicity and that evolutionary variation in segment number reflects the generation of these double segmental units. However, previous studies have revealed no trace of this. Here we report the expression of two genes, an odd-skipped related gene (odr1) and a caudal homolog, that serve as markers for early steps of segment formation in the geophilomorph centipede, Strigamia maritima. Dynamic expression of odr1 around the proctodaeum resolves into a series of concentric rings, revealing a pattern of double segment periodicity in overtly unsegmented tissue. Initially, the expression of the caudal homolog mirrors this double segment periodicity, but shortly before engrailed expression and overt segmentation, the intercalation of additional stripes generates a repeat with single segment periodicity. Our results provide the first clues about the causality of the unique and fascinating "all-odd" pattern of variation in centipede segment numbers and have implications for the evolution of the mechanisms of arthropod segmentation.

Over any period of evolutionary time, the prevailing ontogenetic trajectory within a lineage may either recur unchanged from generation to generation (stasis) or alter (developmental reprogramming). A key question about reprogramming is whether it exhibits intrinsic biases in favor of some sorts of change and against others, which may be referred to respectively as "drive" and "constraint." A simple logical argument suggests that both drive and constraint should be common, and conversely that cases of equiprobable modification in various phenotypic directions should be relatively rare. These proposals, that drive and constraint exist and that they are common, appear to be widely accepted, even among neo-Darwinians, who are sometimes portrayed as rejecting them. What is more controversial is that developmental drive (and constraint) can have a powerful influence on the direction of evolutionary change. It is argued that such an influence will occur, and indeed may be pervasive.