PERSPECTIVES ple grains or crystals with different crystallographic orientations that are separated by grain boundaries As a result of plastic deformation the original grains are subdivided into smaller grains separated by dislocation line defect networks Moreover commercial alloys always contain impurities that can form precipitates which are small particles with a different composition and crystal structure than the matrix Schmidt et al have determined the absolute crystallographic orientation position volume and shape of a recrystallizing grain in deformed aluminum Their work shows that the shape of a recrystallizing grain in aluminum is more or less spherical as it starts to grow in accordance with general belief but as it grows the grain progresses in different directions with different speeds and in a jerky fashion The mo bility of the grain boundary which is an important parameter in models is unambiguously determined and shown to be anisotropic The authors show that the jerky movement of the grain boundary reflects the inhomogeneous distribution of dislocations in the deformed aluminum matrix Knowledge about the density distribution and arrangement of the dislocation in the deformed matrix and their influence on the growth of an individual grain as measured by Schmidt et al is of utmost importance in understanding recrystallization phenomena The authors measured the recrystallization process in exceptional detail which is of great value for theoreticians because theory and experiment can now be compared at the elementary level of a single grain Characterizing microstructures in 4D opens great opportunities in other fields of materials science For example it should now be possible to study the underlying mechanisms of solidification solidstate phase transformations and precipitation of a wide range of materials As a result the 3DXRD technique will contribute to the development of materials with superior properties and optimal production routes References and Notes S Schmidt et al Science 305 229 2004 J P Hall Z Z Petch Can J Metallurgy 26 254 1954 D Larbalestier et al Nature 414 368 2001 R J Young P A Lovell Introduction to Polymers Chapman Hall London ed 2 1991 5 M V Kral M A Mangan G Spanos R O Rosenberg Mater Charact 45 17 2000 6 M Onink et al J Mater Sci 30 6223 1995 7 Supported by the Dutch Technology Foundation STW of the Netherlands Organization for Scientific Research NWO 1 2 3 4 GENOMICS The Chimpanzee Genome A Bittersweet Celebration Maynard V Olson and Ajit Varki hese are exciting times for those interested in human origins After almost a century of knowledge gleaned from the excavation of hominid bones in East Africa the draft sequence of the chimpanzee genome is now providing a flood of molecular data that may shed new light on human origins The challenge of integrating these molecular data with the fossil record and with behavioral studies of great apes was on full display during a recent symposium at the University of California San Diego 1 Most speakers discussed one of three principal sources of data a Japanese led analysis of chimp chromosome 22 2 a private sector initiative at Celera Genomics to sequence most of the exons of the chimp genome 3 and the National Human Genome Research Institute NHGRI funded project to produce a rough draft sequence of the whole chimp genome 4 Although the recent release of the draft sequence by the Washington University and MIT Broad Institute sequencing centers 4 was the primary im T petus for this symposium many other aspects of our closest evolutionary relative also were explored Yoshiyuki Sakaki RIKEN Genomics Sciences Center represented the Japaneseled effort Although this project analyzed only 1 of the chimpanzee genome it provides the first look at long range comparisons with the human genome based on complete high quality sequence The longrange organization of chimpanzee chromosome 22 is nearly identical to that of its human homolog chromosome 21 The level of single base pair substitutions between the two species is only 1 44 However there are tens of thousands of insertion deletion M V Olson is at the University of Washington Genome Center Departments of Medicine and Genome Sciences Seattle WA 98195 USA A Varki is at the Glycobiology Research and Training Center Departments of Medicine and Cellular and Molecular Medicine University of California at San Diego La Jolla CA 92093 USA E mail mvo u washington edu a1varki ucsd edu www sciencemag org SCIENCE VOL 305 variants including one 200 kbp human specific duplication Many sequence variations between the chimp and human lineages are attributable to differing activities of large numbers of retrotransposons Andy Clark Cornell University representing Celera s exon sequencing effort discussed chimp human comparisons of inferred protein sequences Interestingly proteins involved in amino acid catabolism showed a big positive selection signal in the human lineage whereas those involved in neural development did not This finding reminds us that diet and pathogens are dominant selective forces for all species Other genes undergoing rapid positive selection in the human lineage include those encoding proteins that are involved in hearing such as tectorin a structural innerear protein Evan Eichler Case Western Reserve University who based his analysis on the rough draft whole genome sequence emphasized the same point He reported major deletions in the chimpanzee genome totaling at least 8 Mbp which include a number of genes associated with immunity and inflammation Eichler also discussed the presence in the chimpanzee of many copies of a retroviral provirus that is absent from the human genome Its presence in chimpanzees bonobos gorillas and Old World monkeys but not humans orangutans and gibbons suggests multiple independent instances of horizontal transmission This serves as another 9 JULY 2004 191 PERSPECTIVES reminder that a dominant force shaping primate genomes has been the proliferation of mobile elements of various kinds Providing an overview of the roughdraft whole genome sequence Robert Waterston University of Washington discussed evidence for the possible rapid evolution of genes involved in host defense using protease genes as an example Discussing another aspect of primate interactions with the environment Svante Paabo Max Planck Institute Leipzig provided new data from his work on olfactory receptor genes 5 All great apes appear to have been steadily losing