DOI: 10.1126/science.284.5420.1640 , 1640 (1999); 284 Science et al. T. H. Clutton-Brock, Selfish Sentinels in Cooperative Mammals This copy is for your personal, non-commercial use only. . clicking here colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others . here following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles (this information is current as of November 16, 2010 ): The following resources related to this article are available online at www.sciencemag.org http://www.sciencemag.org/cgi/content/full/284/5420/1640 version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/cgi/content/full/284/5420/1640#otherarticles , 1 of which can be accessed for free: cites 9 articles This article 117 article(s) on the ISI Web of Science. cited by This article has been http://www.sciencemag.org/cgi/content/full/284/5420/1640#otherarticles 21 articles hosted by HighWire Press; see: cited by This article has been http://www.sciencemag.org/cgi/collection/ecology Ecology : subject collections This article appears in the following registered trademark of AAAS. is a Science 1999 by the American Association for the Advancement of Science; all rights reserved. The title Copyright American 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 the Science on November 16, 2010 www.sciencemag.org Downloaded from