DOI: 10.1126/science.1140734 , 1347 (2007); 317Science et al.Joan B. Silk,Social Components of Fitness in Primate GroupsThis copy is for your personal, non-commercial use only.. clicking herecolleagues, clients, or customers by , you can order high-quality copies for yourIf you wish to distribute this article to others. herefollowing the guidelines can be obtained byPermission to republish or repurpose articles or portions of articles (this information is current as of March 18, 2010 ):The following resources related to this article are available online at www.sciencemag.org http://www.sciencemag.org/cgi/content/full/317/5843/1347version of this article at: including high-resolution figures, can be found in the onlineUpdated information and services,found at: can berelated to this articleA list of selected additional articles on the Science Web sites http://www.sciencemag.org/cgi/content/full/317/5843/1347#related-content http://www.sciencemag.org/cgi/content/full/317/5843/1347#otherarticles, 7 of which can be accessed for free: cites 40 articlesThis article 3 article(s) on the ISI Web of Science. cited byThis article has been http://www.sciencemag.org/cgi/content/full/317/5843/1347#otherarticles 10 articles hosted by HighWire Press; see: cited byThis article has been http://www.sciencemag.org/cgi/collection/evolutionEvolution : subject collectionsThis article appears in the following registered trademark of AAAS. is aScience2007 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on March 18, 2010 www.sciencemag.orgDownloaded fromfitness (i.e., at the end of its lifetime) thanpursuing more individualistic strategies.What Microneurobiology Has to Tell UsThere has, of course, been growing interest inrecent years in some of the neurobiologicalcorrelates of social bonding. Particular interesthas focused the role of oxytocin (and its maleequivalent, vasopressin) in pairbonded species(40), but other neuropeptides have also beenidentified as playing an important role in so-cial bonding [e.g., endorphins (41)]. In addition,a parallel interest has been developing in the roleof several specific neuronal assemblages, includ-ing mirror neurons (42) and so-called spindlecells in the anterior cingulate cortex (43), as wellas in specific genes such as GLUD2 [a retro-gene, derived from glutamate dehydrogenase,which is responsible for clearing the by-productsof neuron activity (44)] and the abnormal spindle-like microcephaly-associated (ASPM) gene andmicrocephalin, which are implicated in braingrowth (45).Each of these has been seen by their respectiveprotagonists as the holy grail for understandingboth social cognition generally, and, in particular ,for explaining the differences between humans,apes, and monkeys (43, 46). There is no questionthat these are individually important and noveldiscoveries, and they undoubtedly all play arole in the nature of sociality. However, there isa great deal more to how and why humans aredifferent from other apes, or why apes are dif-ferent from monkeys. We will need better studiesof cognition and behavior to answer these ques-tions. More important, perhaps, is one key point:Species differences in a handful of very smallneuronal components do not explain the apparentneed for massive species differences in total brainsize. Most of these studies fall into the sametrap as the developmental explanations f or brainsize did in the 1 980s: They mistake mechanisticconstraints for evolutionary function. It is un-clear why this point continues to be ignored, butwe will still have a lot of explaining to do aboutvolumetric differences in brains.References and Notes1. L. C. Aiello, P. Wheeler, Curr. Anthrop. 36, 199 (1995).2. J. A. Kaufman, Curr. Anthropol. 44, 705 (2003).3. H. J. Jerison, Evolution of the Brain and Intelligence(Academic Press, London, 1973).4. E. Armstrong, Science 220, 1302 (1983).5. P. H. Harvey, T. H. Clutton-Brock, Evolution Int. J.Org. Evolution 39, 559 (1985).6. R. D. Martin, Nature 293, 57 (1981).7. M. A. Hofman, Q. Rev. 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