Heterochrony: the Evolution of Development

Heterochrony can be defined as change to the timing or rate of development relative to the ancestor. Because organisms generally change in shape as well as increase in size during their development, any variation to the duration of growth or to the rate of growth of different parts of the organism can cause morphological changes in the descendant form. Heterochrony takes the form of both increased and decreased degrees of development, known as “peramorphosis” and “paedomorphosis,” respectively. These are the morphological consequences of the operation of processes that change the duration of the period of an individual’s growth, either starting or stopping it earlier or later than in the ancestor, or by extending or contracting the period of growth. Heterochrony operates both intra- and interspecifically and is the source of much intraspecific variation. It is often also the cause of sexual dimorphism. Selection of a sequence of species with a specific heterochronic trait can produce evolutionary trends in the form of pera- or paedomorphoclines. Many different life history traits arise from the operation of heterochronic processes, and these may sometimes be the targets of selection rather than morphological features themselves. It has been suggested that some significant steps in evolution, such as the evolution of vertebrates, were engendered by heterochrony. Human evolution was fuelled by heterochrony, with some traits, such as a large brain, being peramorphic, whereas others, such as reduced jaw size, are paedomorphic.     

Commodifying Development Experience: Deconstructing Development as Gift in the Development Blockbuster

This paper discusses the recent rise of popular ‘blockbuster’ books written by international development industry insiders and produced by commercial publishers. The paper explores a set of common stylistic devices found within this emerging genre. Though each book is different, a key trope is the story of an author's earlier professional life—the hard lessons and gritty insights that have supposedly emerged from it—that normally underpins each narrative. By living the challenges involved in development work at first hand, and by making mistakes and experiencing epiphanies along the way, these author-professionals want readers to know that they have found out the hard way that long-cherished beliefs about development now need to be questioned. Readers are invited to relive these lessons and epiphanies, and to think and act differently about development by upholding a highly pragmatic form of development professionalism. Combining elements of research monograph, self-help book and personal memoir, these development blockbuster books can be understood not only as commodities, but also as part of the development gift. The authors promise a gift of experience but, in reality, these books are mundane commodities enmeshed in capitalist exchange relations.     

Development: Hedgehog does the two-step

Hedgehog signalling establishes spatial correspondence between olfactory receptor neurons and their targets in the brain through a two-step mechanism.     

Development of the musculoskeletal system: meeting the neighbors

In March 2011, researchers met for the second Batsheva Seminar on Integrative Perspectives on the Development of the Musculoskeletal System. This meeting was a unique opportunity for researchers working on muscle, connective tissue, tendons, ligaments and bone to discuss the development of the musculoskeleton, recognizing that it is an integrated, functional system. The talks and discussions at this meeting highlighted that interactions between the different tissue components are crucial for musculoskeletal morphogenesis.     

Development: dissecting the dynamics of segment determination

A novel combination of high-resolution time-course expression data and computational modelling has provided a remarkably detailed picture of a key stage of Drosophila segment determination, highlighting the dynamic nature of this process.     

Growth and Development of the Banana Plant: 3. A. The Origin of the Inflorescence and the Development of the Flowers: B. The Structure and Development of the Fruit

In this paper, which is presented in two parts, the growth anddevelopment of the banana plant have been examined from thestandpoint of the origin of the inflorescence and the developmentof the flowers (Part A) and the structure and development ofthe fruit (Part B). First the main centres of growth in thesestructures are located and the manner of their development ispresented. Thereafter, attention is focused upon the salientevents which determine the alternative courses of developmentwith a view to designating the chemical and physiological stimulithat may be required.     

GABA Excitation during Development: the Nature of the Nurture

The lecture describes the role of GABA-mediated synaptic excitation during early ontogenesis.