Godfrey Hewitt was one of the founders of the new discipline of molecular ecology some 15 years ago. Since then, Godfrey has been a leading figure in the application of molecular markers to questions of phylogeography, hybridisation and speciation and, despite officially retiring in September 2005, he remains a key player with a high rate of published output. Godfrey has published more than 230 scientific contributions and has the rare honour of being on the ISI ‘Highly Cited Authors’ list.
Godfrey's major insight, in this latest phase of his career, was to see large-scale spatial patterns of genetic variation in Europe in the context of the continent's glacial history. Using information from a wide variety of sources, but especially the palaeoclimatic and palaeoecological records, he was able to make sense of current patterns of genetic diversity in terms of repeated cycles of range contraction and expansion. Southern refugia contain genetically diverse populations with long independent histories while northern European regions are genetically homogeneous, tracing their ancestry to the refugia: the pattern that Godfrey calls ‘southern richness and northern purity’. Expansion from refugia followed one of a small number of scenarios, typified by grasshoppers, hedgehogs and bears but each repeated across multiple taxa. Godfrey's synthetic papers on the phylogeographic history of Europe (Hewitt 1996, 1999, 2001) are the cornerstone of this field of research, with a combined total of more than 1000 citations.
Thinking about historical movements of populations, and about the markers used to follow them, led Godfrey and his collaborators to a variety of other important discoveries. For example, his group showed that rapid colonisation can generate local patchiness in the genetic structure of populations that can persist for long periods (Ibrahim et al. 1996). Their use of mitochondrial DNA sequence data led to the early realisation of the problem of nuclear insertions but also led them to consider the potential of these insertions as tools to dissect genomic processes (Bensasson et al. 2000).
Repeated cycles of range contraction and expansion along circumscribed routes help to explain not only the positions of hybrid zones, which form as a result of secondary contact between divergent populations from different refugia, but also the accumulation of many genetic transitions in the same narrow region. It was thinking about hybrid zones that originally brought Godfrey to phylogeographic questions. In the 1970s, he discovered a steep cline between two chromosomal races of Podisma pedestris in the Alpes Maritimes. Analysis of this cline led to the development, with Nick Barton, of a theory for the maintenance of ‘tension zones’ by a balance between gene flow and selection against hybrids. Their two major review papers, laying out this theory and surveying the range of zones then described (Barton and Hewitt 1985, 1989, attracting another 1000 citations), are the foundation on which modern hybrid zone research has been built. With the strong theoretical framework they provided, hybrid zones have become key natural laboratories for the study of barriers to gene exchange, and so speciation. Godfrey has exploited this potential with studies on another grasshopper hybrid zone, between subspecies of Chorthippus parallelus in the Pyrenees, where he has tackled post-contact modification by reinforcement and amelioration of hybrid sterility, for example.
Godfrey was born in Worcester in 1940 and attended the Worcester Cathedral King's School. He retains a strong affection for this part of England. He went to Birmingham for his first degree and started his career in cytogenetics there, working with Kenneth Mather, John Jinks and Bernard John for his PhD. He rapidly developed an interest in evolutionary questions and made his first important contributions with the analysis of B-chromosome polymorphism in the grasshopper Myrmeleotettix maculatus. These selfish genetic elements are maintained in populations by meiotic drive in females that is balanced by reproductive fitness costs in males (Hewitt 1973). Thirty years on, there are few, if any, better analyses of the interaction between levels of selection. After a short period at the University of California, Davis, Godfrey took up a lectureship at the University of East Anglia, Norwich, in 1966. UEA was then a very young institution with the innovative idea of single, broad biological sciences department: a structure that has suited Godfrey's synthetic approach ever since. He was promoted to Reader in 1975 and Professor in 1988.
It is not possible, in a few short paragraphs, to cover the full range of Godfrey's scientific output and its impact on molecular ecology. However, I cannot end without mentioning the exceptional contribution Godfrey has made to the evolutionary biology community. He has been, and continues to be an inspiration to literally hundreds of scientists: to those who have worked directly with him especially, but also to people who have simply met him at conferences or received his thoughtful and constructive reviews of their papers or grant proposals. Godfrey is unstintingly generous with his time and ideas, and in the support that he gives to young scientists interested in evolution. He has held numerous positions that reflect his standing and the affection felt for him worldwide. In particular, he was President of the European Society for Evolutionary Biology from 1999–2001.